Gas Fired Crucible Furnace
The Gas Fired Crucible Furnace
I have decided that I want a gas fired crucible furnace for my general melting needs. I have decided I will go with David Gingery's project called, "Building a Gas Fired Crucible Furnace". I will detail my experience here for those of you that might want to try a similar project. My reasoning for this particular design was that I like the side approach to the crucible and the ease of which it looks like it is constructed. Information on this book can be found in the resource section and can be ordered through Lindsay Books.
I am excited about doing this project for another reason. My fiancee has a son named Jason who thinks he is cut out to be a mad scientist. Hmmmm .... We will see. I told him he had to be my Igor first and then we will determine if he is mad scientist material. He has decided to help me build this furnace and promises to stick through with it until the end. (Good or Bad) hehehehehe :-)
Remember, as with most other pages on this site, you can click the image to get a larger version of the picture.
Building the furnace forms.
The furnace body is constructed with forms made of sheet metal. It should be noted that with the exception of the inside collapsible form all the metal used in the body is plain black sheet metal. This is necessary because it is possible that the skin temperature can reach high enough temperatures to vaporize any galvanized coatings on the sheet metal which can lead to health issues. - Jason and I set out to making the furnace forms!
The first order of business was to make the inside form. This form is a simple sheet metal cylinder wrapped around some plywood forms. This form determines the inside diameter of the furnace. This form will be used to form the inside of the central body as well as the inside of the lower unit of the furnace that holds the burner and crucible.
Next I built the burner inlet form. This form holds the burner in place and will be installed in such a way that it is tangent to the inside form. This was an interesting part of the project for me as I have never done any layout on sheet metal to make anything more complicated than a cylinder. Laying out a pattern for the tangent intersection turned out to be a fairly simple and was an enjoyable process.
Next I built the central body form. This was a fairly simple process. The challenge for me was brazing the bolt to the reinforcement plates that are attached to the body. These bolts are used as lifting lugs on the furnace.
Next came the bottom form. This form will hold the burner and the crucible. The only challenge to me was cutting the circular bottom of the form. This turned out to be a simple task with the help of my jig saw and a metal cutting blade. I used the same saw on the burner inlet hole located on the side of the form.
Next, Jason and I started on the top form. We have it cut out and the holes drilled but we are not quite done with it. We decided that was enough for one days work. Hmmmmm ... No blood yet, a little sweat and few tears. He may just have the makings of a mad scientist. It is still early yet and there is the blood and tears part that eventually comes to be. We will see, but so far I have to give Igor (Jason) an A+ for effort. He stuck through most of the metal form making madness.
·I finally picked up the stuff to blend a homemade refractory for the furnace. It looks to be a promising night and we may find some time to mix it up!
Blending and mixing the Furnace Refractory
Jason and I decided it was indeed a good night to do some mad scientist work. I decided to go with a homemade refractory blend, mostly because I could get most of the material somewhat locally, or at least a couple of towns over from mine. The original recipe that Gingery gave in his book was fire clay, sand, grog and borax. The only difference in my blend was that I wanted to try to use perlite instead of the grog. In my thinking, it will still help prevent the shrinkage and also at the same time provide a bit more of an insulating value than that of the grog. I guess only time will tell.
We decided that since we had nearly 200 pounds of material to mix up we would help our cause a little by layering it all in a wheel barrow. Clay ... Sand ... Perlite ... Clay ... Sand ... Perlite ... etc. After we layered all of the material we started mixing. At first I was a little worried. The perlite would just seem to roll on top and never distribute itself within the mix. After what we thought was a good texture and color we added the borax to the mix until it was thoroughly blended. Still it seemed that the perlite was coming to the top and staying there. I was hoping the addition of some water would help. We added water in two batches and mixed until our arms gave out. Once we put the water in and started mixing the perlite seemed to blend with the other material better. We added just enough water so that when you grabbed a handful and squeezed it up, it held its shape and broke cleanly, very much like casting sand. We covered our hard work with some plastic and will let it age until this weekend. This will allow the clay to really absorb the water, or at least according to ol' Dave Gingery. Again, Jason was a trooper. He hung out and helped mix the material until we were done. I think he just might make a mad scientists yet. A little more hard work ... and the blood and tears part, but hey, one thing at a time. Here you see Igor (Jason) mixing the magic heat holding brew. Do you think he looks like he is hard at it?
Tomorrow, I am hoping to finish up the top form and cut the vent hole in the bottom form to finish it up. If time permits, we will cut some circular forms from plywood to keep our metal cylinders round while we ram them up this coming weekend. Come back soon and look for updates.
Today Jason and I finished the main furnace forms. The bottom form only needed the vent hole cut in the bottom.
The top form was a little more fun. We had to bend the angle iron to fit the curvature of the lid. We gave a good quality mad scientist laugh and grabbed the torch fired it up and heated the pieces of angle iron until they turned red. Next we grabbed a piece of round stock, supported the outer edge with a piece of pipe and gave the angle a couple of good hard whacks with the hammer using the piece of round stock to form our bend. Not exactly perfect, but we got the job done. Here is a picture of the completed lid form. Hopefully tomorrow we can start ramming the forms full of refractory and give them a good cooking! }:-)
Jason and I did not get as much done as we had hoped. After a grueling night at Karate and a late dinner, we did not end up starting work until after 9 p.m. tonight. But we did get a little refractory rammed.
Ramming up the forms with refractory
The first form we started with was the middle form. It was by far the easiest as it has no tubes or wires to ram around. This went along pretty smoothly but did take a while to get it rammed full and tight. I am pleased to see that the perlite did after the addition of water to the mix finally did manage to get distributed throughout pretty evenly. Pictured here is the middle section rammed full of refractory mix with the inner form still inserted in it. Next we started on the bottom form. We have about two inches of the two and one half inch layer in the bottom. By now it is 10:45 and we decided we had better quit for the night. We covered the forms with some plastic so to help prevent the surface from drying too quick. Tomorrow we hope to finish the bottom and top forms and get to fire them. Unfortunate though, rain is in the forecast. We will have to wait and see what it looks like tomorrow. Again, I have to give Igor another A+ for the day. You know, I think he may be serious about being a mad scientist. He keeps telling me that he wants to see it fired up and melting metal. The truth is, so do I! Till next time happy melting!
After a long meeting in Nashville, TN I am finally back home and am looking forward to ramming the rest of the forms. I called for Igor to join me and we set off to work.
Last night we stopped with the bottom form being almost filled to the burner tube hole. When we finished ramming the bottom layer in tight we placed our inside form with burner tube attached. We continued to ram the refractory as tight as we could get it until we were level with the top of the form. As you could guess, the project was going way too smoothly and good ol' Murphy stopped in for a visit. I realized that when I put the inside form back together, I didn't realize but I put the screws in from the outside rather than from the inside. This really on posed a problem for the bottom most screw in the form. I tried to cut it with a pair of diagonals, but to no avail. Finally, we managed to get the form out without too much damage to the inside wall. Here you see the bottom form rammed full of refractory.
Next we started ramming the lid with refractory. This job was not too bad, we only had to watch for the wires that we inserted to reinforce the refractory. The plans called fro 16 gauge but all I had was 20 gauge. I hope they will hold out, they were a little on the light side. One thing I would like to point out is that I used a hammer and a block of wood to pack the refractory. Now whether or not this is approved practice I have no clue, but the refractory is very hard packed in all the forms. Here you see the lid for on its side rammed full of refractory. If you look close at the images you will see the white specks distributed throughout. That is the Perlite. It did with a little work mixing it up, distribute very nicely throughout the mix.
Firing The Forms!
Now that we had all the forms rammed full of refractory, we set out to fire them. Here you see the bottom and Middle for with a charcoal fire built into them. Gingery instructs the reader to cook the forms for two hours apiece and then cover them with a piece of sheet metal and let them simmer. He said that they should be brought up to red heat. Now whether or not they actually made it to red heat I do not know, but this little nagging sensation in me said that they were not hot enough. But that was OK, I figured when I got them all cooked, I would assemble the furnace and really get a hot fire going into it. I didn't have another piece of sheet metal to fire the lid, so I figure I will do that tomorrow if the weather holds out. They say rain is on its way, but so far tonight it is clear and the sky is filled with stars. Rather nice to look at after a hard day of furnace building.
Well it's about 10 a.m. and looks good outside. I think we will finish firing the furnace parts while our luck holds out.
I uncovered the bottom and middle forms this morning. I was surprised to find as many hot coals in the forms that I did, and they were still really hot. I raked these coals onto a piece of sheet metal and saved them for the lid. Next I set the lid on a piece of plywood and set my retainer ring on top. Next I dumped the remaining coals on the lid and added some more charcoal to it. I gave it a little starting fluid and took the torch to it to light it up. Next I gave it a little forced air to help it get hot and let it cook for the next two hours. After the allotted time was up I raked the coals back onto my sheet metal and turned the lid over to repeat the process, giving it another two hours to cook on the other side. Here you see the top cooking. (If you are wondering, the pipe you see was set under the retaining ring to allows some are to get to the fire.)
With the lid finished cooking, I thought I would set the furnace on top of a few fire bricks and assemble it. With the bottom and Middle parts in place, I took the remaining coals from the lid and dumped them into the furnace. Next I filled it to the brim with charcoal, gave it a good dose of starting fluid and lit it off. Once the charcoal on top was starting to burn, I started giving a little air in the burner inlet hole. I blocked the remaining portion of the hole off with a couple of sticks. When the charcoal was blazing nicely, I cut the air and put the top on. Then I turned the air back on. It has been a while since I have had a furnace fired up, but seeing the 18 inch flame shooting out of the top vent hole gave me a rush. I cannot wait till this bad boy is done and ready to use. I may have to get me an ingot melt out of it before I am finished with it. Once the furnace was really cranked up and burning hard I stuck my thermocouple in to get a reading. 1750 degrees F. (Yeah, she is heating up just fine! I let it burn with the air on for the next 25 minutes. Finally, I removed the air and covered the top vent and burner inlet tub to let it soak. But before I closed the top hole I took a little peak inside, YEP, it was a nice bright orange! I think that will get her cooked. We will have to see later today how the lining held out.
OK ... OK ... OK ... Patience is not my strong point and I just could not wait. I yelled for Igor to come play and loaded my crucible up with a small piston and some old sprues and gates. I just had to melt something. After the crucible was loaded and put in the furnace I packed some charcoal around the sides and kicked on the air. Five minutes had passed and the stuff was already starting to melt. Once it was melted well, I loaded more into the crucible which made it about half full. Ten minutes later it was ready, a half crucible full of beautiful molten aluminum ready to be skimmed and poured. Here is a picture of the six tasty cupcakes we got for our 15 minutes of work. Now, should I think that was a great melt time??? No, not really because the furnace was already hot and has had a fire in it for a couple of hours after I brought it up to over 1700 degrees F. But, the crucible and metal was cold when I started. If I had started from a cold furnace as well I would have expected it to take five or ten minutes longer. I can't wait to get to the point I have it set up on it's framework and fired up with forced gas. I may have to put together a Oliver upwind burner and try a propane melt. You can find details on Oliver's burner by going to Backyard Metalcasting. (Opens in a new window)
The results are in ... after the baking and firing, it looks like the furnace lining has held up reasonably well. Aside from a few small radial cracks and some chipped edges the lining seems to be in great shape. Although it does seem light, but I am guessing that would be due to the fact that the refractory is made up of 1/3 Perlite and reduces its weight slightly. Anyway, only long term will tell and a couple of really *** HOT *** heats. If it survives that, then I will continue to use the mix, otherwise I will have to look for a better home brew or have to scrape up the money for the commercial cast-able stuff.
The building of the body proved to be an enjoyable experience. Although I did run into a couple of snags. Both of which were brought on by me and not Ginery's plans. The other problem that I had aside from putting the screws in the center form from the outside rather than the inside was the sheet metal I used. The sheet metal that I had was too small to make the rings in one consecutive length, so I decided to pop rivet two pieces together to get pieces long enough to make the forms. I don't know if I measured incorrectly or what, but my ring that made up the bottom form came out a little small. I went ahead and used it as the only functionality I lost was aesthetics. Well, if you ever seen my work area, you would know that pretty to look at does not fall in the definition of my space!
Next, Jason and I will start on the frame that holds the furnace. This is mostly made up of angle and a bunch of little welds. The bad part is I don't have a welder but have a couple of friends that do. If I can persuade them to weld it up for me, I will be in great shape. Hopefully it won't take long and they can find the time, otherwise it may be a little while before I get another update to this project online. Be sure to check back occasionally to see what is happening. Until then, HAPPY CASTING!
·Well we have taken a couple of days off the project, but tonight I hope to get some of the metal cut for the frame.
Building the Frame.
Well, I tried something stupid. I bought a metal cutting blade for my compound miter saw and thought I could use it to cut the metal. It sort of worked except there is a plastic piece on the saw that the blade passes through when you cut. The metal would heat up enough to melt it. Oh well, I would try something else.
I used a jig saw with a metal cutting blade and cut out the parts for the main frame, legs and rails along with the rail support. I got back late tonight from a road trip so didn't spend a lot of time on it. I am hoping tomorrow that I can get a friend of mine to weld it up for me. If he has time I will post a picture of it's progress, Otherwise, I will continue to cut the pieces of metal I need to build the framework.
Today was a pretty productive day as far as the furnace project goes. Tony King, a friend of mine, was kind enough to weld up for me the parts of the frame that I had cut out. Here you see a picture of the welded base frame. I am waiting on pipe from my local Gas company, once I have it, I can get more of the framework welded up. But in the mean time I did get more parts cut. Tonight I finished the lift tube supports, the foot lever for lifting the lid and the two lift brackets that hold the furnace body and the lift wheels. I am hoping that tomorrow, I will get my pipe and get some more of the parts cut out. I may start working on the burner / blower assembly. Check back, Igor and I will keep you posted. Speaking of Igor (poor sap) he got a small cut last night on a piece of sheet metal. So far he has got the sweat and blood part. I wonder if he will experience the tears before this project if finished. Stay tuned and see what happens with Igor. Will he have the Right Stuff (or lack of) to be a mad scientist? Only time will tell!
It has been a while since I have updated the Gas furnace project. My last writing I indicated that I was waiting on pipe from my local gas company. Since then I have received the pipe. I have the pipe sections cut for the guide tube, lid lifting mechanism, and body lifting tube. I also finished cutting out all the parts for the foot pedal and pivot. Next I cut the parts out for the lifting arms. These arms connect to the furnace body and the lift linkages. I owe a big THANKS to Danny Brown for welding them up for me. Thanks Danny!
In other news, I bought a small 110V wire fed welder. I thought I would like to learn a little welding and do some of the stuff for myself. Now for a little funny story. After I assembled the welder (Connected the cables and put the spool of wire in.) I grabbed a piece of scrap angle and tried to run my first bead. Well, I may have lasted a whole fifteen seconds before I run the tip into the work and fused the end closed. Hmmmm.... At this rate of learning, I figured I better buy a bucket full of tips. The problem as it was turned out to be that I did not have the tension on the wire feed set tight enough and the wire would slip between the rollers and not feed consistently. With that problem solved and a couple of packages of tips, I was back in business. Now, I am no welder by any stretch of the imagination, but I am slowly getting the hang of it. My first beads were splattery looking and incomplete. They are getting better though. It took me a little bit to figure out not to watch the arc, but instead, watch the puddle that was forming up behind it. My first welding job was to weld a disk on top of the lid lifting mechanism (aka 1" black pipe) so that when the pedal is pressed the lifting rod (1/2" black pipe) pushes against this disk and in turn lifts the lid. After a couple of spot welds to hold it on, I run a bead around it. Not pretty but it did grind up and clean up pretty good.
Next I cut the pieces out to make the lift handle. and pivots for it that connect to the main frame. We are nearing completion of the furnace frame. All that is left to make are the offset links. These links connect from the lift handle to the lifting arms. I hope to get these cut out and assembled tonight if time permits. When I finish these I will attach a picture of the completed frame assembly.
Well today I was lucky enough to find a motor to run the fan with. My friend Larry Trailor had an old one laying about. It is a quarter horse that runs at 1050 RPM with a half inch shaft. I will have to sit and figure out the pulley ratio to get to the 3450 RPM that the fan s supposed to run.
Tonight I finished the lift linkages and assembled the last of the frame. I learned a couple of things. When I made the linkages, I made them too short. I misread the plans, as the measurement was from the short side of the linkage and not the long. I ended up with them being about a half inch or so too short. Rather than making new ones I moved the connecting points on the lift handle towards the uprights by 3/4" to allow the bottom of the linkage to clear the lifting arms. Now, I suspect that either this error threw the thing off or I mis-measured somewhere else along the line because when I worked the lift lever and brought it all the way to the top, the lever did not quite reach the breaking point of being over center. It was really close but no cigar. To fix the problem, I ground two grooves in the top bracket about 3/8" deep to allow the lifting linkage to extend a little more. The result was the lifting handle now breaks past the center line of the frame and allows it to stay there without the addition of a locking mechanism. Here you see Igor holding the handle of the frame in what would be the closed position. (The middle section of the furnace resting on the bottom section of the furnace.)
Another little lesson I learned was that I could not use 1/4" bolts with two nuts to make a pivot point. The more I would work the frame, the more some of the bolts would tighten down and make it seize up. I tried this because I could not find any 1/4" hammer set rivets. I guess I will have to locate some or try something different. I am open to ideas if anyone wants to share. Oh yeah, Those UGLY welds, well I suppose I have to take credit for those. I need to get more practice! :-) Here you see the frame opened up fully. In this position the middle and top section of the furnace will be lifted up to allow side access to the crucible. A practice that I hope will be a little safer than pulling the crucible from the top of the furnace.
Next, I need to make better pivots on the framework and attach the furnace to the frame. When I get it all worked out I will follow up here. Come back occasionally and look for updates!
I managed to find some cold set hammer rivets at the local farmers COOP. The problem with them was that they were too small diameter, being 3/16" rather than the 1/4" that I needed. Needless to say, I went a different route. I took cardboard and cut small washers and placed them between on the bolts that I used as pivot points. The idea was that I could snug these down a little, put a couple of tack welds on the nut and then the paper washer would burn out leaving enough space to allow the part to pivot like it needed to do. This worked very well for me so tonight I fixed all the pivot points and attached the furnace to the framework. Here you see the completed furnace attached to the frame. If you look close you will see that there is some alignment problems with the furnace. The inside is lined up perfectly, which it really what matters. The poor alignment of the outside is my fault. The cylinders I made to create the furnace forms are slightly different diameters and they are not perfectly round. At any rate the frame and furnace seem to work together so I should be able to use this beast.
In this image you see Igor depressing the foot pedal and swinging the lid to the side. When I attached the lid supports that run from the top of the lift to the sides of the lids I had a little problem. The supports had to be bent to fit both the pipe and the side of the lid. The vise and my new 4 pound hammer persuaded it to exactly where I wanted it to go, or at least close enough for government work!
In this image Igor is in the process of lifting the furnace body. (I guess he felt like we should have an action photo on the web page. :-) ) As you can see the lift assembly lifts the entire furnace body up and allows access to the side of the crucible. The lifting lever swings above the furnace and past its center line. This allows the arm to stay in place without the need for any latching mechanism. Now the lever and linkage all seem to work together pretty smoothly, but it has a tendency to want to tilt the whole works backward away from the lift arm. This could lead to a
This concludes the frame portion of the furnace. Next is to build the fan and framework to mount the fan and motor to. Hopefully, I can work on some of this over the weekend. I am not sure if I will have time or not, but check back occasionally to see where Igor and I are at on the project. Happy Metal Casting!
It has been almost two weeks since Igor and I have updated the web page. We figured we better tell you something before you thought we quit on the project.
catastrophic event. I will continue to oil and work the linkage to see if it gets any better, but my fix to this will be to add a piece of angle iron to the front leg so the operator can step on it while lifting the furnace. This will prevent the frame and furnace from tilting back.
Most of my free time has been taken up but we have managed to get some more done on the furnace. Here you see the arbor. This will be used on the fan and driven with a motor. I found this arbor at a True Value hardware store on my way to Celina, Tennessee to a hospital I take care of. It cost about $18.00 US. It is threaded on both ends (One left hand and one right hand. It came with the pillow block bearings, 2 set screw collars and 2" / 2 1/2" pulley.
Here you see the motor we have found for the project. Another big thank you goes out to Tony King who happened to have one laying around. This motor is a little different from most that I have seen. It is a 1075 RPM variable Horse power. I have no clue why one would be variable horse power but it can be wired to 1/4 horse, 1/2 horse and 3/4 horse. I don't think the fan will be very demanding on the motor so I will start out at the 1/4 horse setting just to save a little on the electricity it will use while it runs.
The fan housing is put together using a form a little smaller than the volutes that were made for the housing. Gingery suggest using 3/8" or 1/2" plywood for this form. Two are made and wood placed between them to make the total thickness 2". I had no small plywood on hand so I made the from 3/4" plywood. Hopefully it will work out just the same.
Tonight I hope to get a little more done on the project. Life is kind of busy so you never know. The next thing Igor and I will do is assemble the fan housing, then start on the stand that will hold the motor and fan. Be sure to check back occasionally and see where we are at.
We had a good night of furnace building last night. and even a little extra time to update the page. Igor and I are starting to get excited about the project. We are nearing completion.
Here you see the finished fan housing. Bending the outside edge around the form was not too bad of a job, but it did require constant adjustments of the flanges on the outside to stretch the metal. I drilled the holes on my little drill press and it went together fairly smoothly. It did turn out a little lopsided, but I think it will work fine anyway. One thing to note, the form I made was with 3/4" plywood. I like to never got the thing out from the fan housing. I broke the edges of the form in a few places trying to get it out and distorted the fan housing a little in the process. I think that is why the housing is a little skewed. I would suggest, if your going to do this project that you use thinner plywood than I did for the form.
Here you see the frame assembly all welded together. There really is not much to say about this part of the project other than my welding skill is slowly getting better. I still have a long way to go though to have really great welds. But I think I got good penetration even though a few of them are rather ugly. But then again, holding them up next to Igor, they don't look so bad.
Here you see the fan housing mounted to the frame as well as the fan blade attached to the arbor. This is only hand tight at the moment, I need to mount the motor yet and figure out the size of belt I will need to drive this bad boy. It is starting to look like a fan though isn't it?
In this image you see the back side of the fan housing and the arbor that is attached to it. The only problem I had with the mounting of the arbor was alignment. If I did not tighten the bolts down slowly and evenly the arbor seemed to bind up a little bit. I guess self aligning bearings would be a better choice, but the bearings that came with my arbor are bronze bushings. Oh well, I have it together and it seems to spin fairly easy. I guess some time running would wear the bores of the bushings enough to free them up some.
Next comes mounting the motor and building the cover that varies the air flow through the fan. The motor I have does not have any mounts so I will need to figure a way of mounting the thing to the frame. I also need to find a pulley large enough to get the fan speed up to the 3400 plus RPM that it is supposed to turn. I cannot wait to fire the fan up. If it is anything like the Gingery video you can watch on Lindsay Books website, it should sound like a jet engine! :-) Keep coming back and checking out the project, I think it won't be much longer and we will be getting our first melt from this furnace. After that I will have the ability to melt metal quickly and cleanly and open up doors to even more projects. This metal working business has turned out to be a fun hobby. I just hope I can keep up with the learning curve!
Well, what can I say. I have not worked on this project in ages. To bring you up to speed, here is how things played out for me. The fan that I built was so far out of balance that it was totally unusable. When I started the fan, it would vibrate so bad that sparks would shoot out from it. I knew that was not going to work. I had no desire to kill myself with flying debris that I just quit. I wanted to step back from it and take a break and get over my self induced frustration. Then, as life has it's funny way of happening, I got busy and left it alone. For the next several months I didn't work on anything except my Glen-L 10 sailboat. But that is another story. Well that was how it worked out for me till this weekend. I looked at the thing and decided, if I was going to get anything else done, I had to have a furnace, so I set out to finish the project up.
Building Another Fan Rotor.
The parts for the first fan were cut out by hand with a Jig Saw. Well my hand is none too steady so needless to say, the parts were something less than perfect. There were small variances in the vanes and the backplate was not exactly a perfect circle. So when I decided to make a new one, I wanted to make sure the parts were as close to perfect as I could manage to get them.
The Circle Cutting Jig.
The first course of action would be to make a new back plate for the fan rotor. And as luck would have it, I found a circle cutting jig for a table saw on Brian Boorman's website. You can see it by going here. Brian's circle jig was intended to cut circles from wood. I figured that the same principle would work with a piece of sheet metal. Instead of using a regular saw blade, I wanted to use a metal cutting blade. But as luck would have it, the arbor on my table saw was too small for the blade. I ended up using a masonry blade. I hoped that it would be good enough to cut a piece of sheet metal. (Now using a masonry blade in your table saw may be a really dangerous practice. If you elect to go that route, you do so at your own risk!) Well, to make a long story short, the ending circle turned out better than I cold have hoped. It was much better than the original one I cut by hand.
The Fan Rotor Vanes
To cut the vanes, I decided that I would let the machine do the work for me as well. I clamped a piece of wood to the table of my worn out band saw and used it as a rip fence. When all the parts were cut to dimension, I cut another piece of wood on a 45° angle to use as a sort of make shift protractor. I pushed the parts into the band saw using this wood to cut the 45° bevel you see on the vanes. Finally I filed off the small ridge left from cutting them with the band saw and stacked them together. They turned out to be pretty close to all being the same size. Next, I clamped them all together and filed the stack together to make sure that they were as near the same size as I could get them.
Assembling the Fan Rotor
I assembled the fan as per the instructions in the book. After it was complete I took a couple of measurements from the old blade to the new one. The new blade gave good measurements everywhere I measure, where the old one was a sixteenth off here and there and a thirty-second off here and there. Over all I felt pretty good about this new fan!
To put my work to a test, I mounted the new fan on the arbor and and turned it on. WOW, no noise except the jet engine sound from the fan and a whole lot of air blowing around. I thought it was a success. Next I put the cover on the fan and fired it up again, I cannot explain just how much air this thing puts out! The only problem now was that it was noisy. Not fan blowing noise but some sort of vibration that sounded as if it were coming from the fan housing. I grabbed the housing and still the vibration. Hmmm... I didn't know if it was the fan rotor or something else. I grabbed the book and re-read the part that covered the fan construction. Then I seen it. Gingery tells us to put a fiber thrust washer on either side of the outer pillow block bearing. I turned on the fan, and pushed against the arbor and the noise disappeared. OK, I guess I need some thrust washers. I don't know where to get them so for now made a pair from some PC board material I had laying around. They help a whole lot but there is still a little noise, but nothing like it was. Maybe real thrust washers will take care of it. We will see.
Back To Building.
Now that I am past that hurdle, I can progress with the furnace. Next comes a sheet metal box that covers the air inlet on the fan and has a damper door, its job is to control the amount of air the fan puts out by restricting the amount of air allowed to the inlet of the fan. I hope to get the done this week if time permits. Come back and check on progress occasionally. You never know, you may come back and actually find that I have done something new! Thanks for your patience folks! :-)
Now that I had a fan that seems like it will work out, I set out to build the inlet duct work. The duct that you see here is a simple box that will get riveted to the front on the fan housing over the inlet. The hole that you see here will get a flap type valve that will control the amount of air the fan will put out. The duct also helps prevent someone from accidentally getting their fingers in the way of the spinning fan rotor.
Here you see the air flow valve. It is a simple disk with a couple of tabs to allow it to be attached to the inlet duct and provide a place where you can get a finger on it to position it where you want it.
Here are a couple of pictures of the completed assembly attached to to back part of the housing and ready for a test! That took a while. I hope the test go as smooth as the building and assembly of these parts!
Testing the System
With all the housing and duct work in place, I powered the fan up with the damper door all the way open. Things sounded good at first, then as the fan gained speed there it was again, this awful rattling noise. By the time the fan reached top speed (in a matter of a few seconds) the noise would drive you nuts. I pushed on the mandrel with the end of a screwdriver to see if the noise was being generated there and no luck, there was not even a little change in the noise level. Next I closed the air valve and the noise got worse. The good news is that it does control the amount of air coming from the outlet very nicely. With the valve closed, only a small amount of air was blown from the outlet of the fan. Now, before I feel safe using this contraption, I want to figure out what is causing the vibration. My only real guess it that the fan is out of balance and as it increases in speed the rotor vibrates more causing all the noise.
After some thought on the thing, I decided to get out my Gingery book on building centrifugal fans. I am going to attempt to build the balance beam and balance the fan rotor. The only problem I see with this though is the fan does not have a collar of any type to fasten the fan to a piece of round stock to use on the device to balance it. So I am trying to decide if I want to add a collar to the rotor or use two set screw colors with the set screws opposing each other to balance it. Well I have plenty of time to think about it as I have to dig up the stuff to make the balance beams and find some set screw collars to boot. Finally, to make matters a little worse, the old motor I used to power the fan has decided to get hot and start smoking. I don't know if I am over driving it or what but it needs to be replaced. This may be a blessing in disguise since I know neither the horse power rating of the old motor nor the actual R.P.M. rating of it. So, in the mean time if you are following this saga and have some suggestions, I would love to hear from you, otherwise, I guess I will have to tell you again to check back occasionally and look for the next installment. Happy Casting!
I have a few ideas to try out on my fan before I set out to balance it. If these ideas do not work then I suppose I will permanently attach a hub to the fan disk. This way when I balance it, it is balanced as a unit and not thrown off by removing the hub from the fan rotor.
IDEA 1: The first thing I decided to do was to replace the motor that drives the fan. Fortunately, a friend of mine gave me a brand new motor still in the box. This motor is rated at 1/3 H.P. at 1725 R.P.M. and is reversible. The only drawback was that it did not match my existing holes to mount it. Before mounting the motor, I had to find what pulley ratio I would need to make the fan turn at the targeted speed of 3450 R.P.M. Now I really do not know why Dave Gingery chose this speed as I don't really recall him discussing that topic in the furnace building book. Now on the other hand, he does talk a lot about this sort of stuff in his centrifugal fan book. Dave tells us that the following formula can be used to find the motor pulley size when you know, (a) The mandrel pulley size, (b) The motor speed and (c) the speed at which you want the mandrel to turn and therefore the speed of the fan. This formula is given below.
(Mandrel Speed) x (Mandrel Pulley) / (Motor RPM) = (Motor Pulley Size)
Using the above formula for the pulleys I had on had on hand yielded the following. My mandrel came with a 2" and a 2.5" cone pulley, and these were the smallest I have. So putting the 2" pulley located on the mandrel gave me the following result. Keep in mind that the running size of an 'A' pulley is 1/4" smaller that its outside diameter.
3450 x 1.75 / 1725 = 3.5
And using the 2.5" mandrel pulley yields the following:
3450 x 2.25 / 1725 = 4.5
So my choices were to run either a 3.75" pulley or a 4.75" pulley. I had neither, but I did have a 5" pulley. So if I use the larger pulley the speed of the fan will be slightly faster. Rearranging the formula would tell me just how much.
(Motor RPM) x (Motor Pulley Size) / (Mandrel Pulley) = (Mandrel Speed)
Plugging my numbers into this equation gave me the following results:
1725 x 4.75 / 2.25 = 3641.7
or roughly 3642 R.P.M. which turns out to be about 192 R.P.M. faster than it was called for. I figure that since the air inlet is controlled I should be OK in terms of the amount of air that it can and will put out. The only other question is driving the fan faster than it is supposed to, especially if it is not well balanced.
Armed with the knowledge of what side pulleys I would need to use, I set out drilling new holes in the frame to mount the motor. This was soon finished and with the motor mounted and the belt tightened up, I gave it a test drive. Good so far, just drive train noise, but then again, I didn't expect anything more from it at this point. One thing I did notice was that it was somewhat quieter than the old motor was under the same conditions.
IDEA 2: Now that the drive train was back in working order, I decided that some rubber spacers between the fan housing and the motor frame would help reduce some of the noise. Fortunately, I had some cured flat pieces of RTV from where I made a mold that did not quite work out. What I ended up with were three rectangular pieces of cured RTV that measured 1" x 1/2" x about 3/16" thick. I drilled holes through these and replaced the nuts that were used as spacers with these rubber pads. Which brings me to idea number three!
IDEA 3: When I was attaching the fan housing back to the frame I noticed that on one side of the mandrel there was plenty of clearance but on the other side it was a little tight. Not touching but I wanted to give it a little room to breathe. So I took off the housing and filed the hole for the mandrel to open it up a little.
IDEA 4: While I had the fan housing off, I noticed that the strip of metal that forms the width of the fan had some gaps here and there and generally was not seated well onto the center strip. So I removed the strip to take a closer look. What I noticed was where I drilled the holes for the sheet metal screws was a lip on the underside of the hole. This lip is formed when the drill bit passes through the sheet metal. I took the time to file down these little ridges around each hole on the fan housing. When I was happy that the holes were good and flat, I took an chisel and flattened down the lip of the strip of metal that forms the center of the fan housing. I put it back together and noted that the whole thing went together much tighter with no gaps at the seams. This I thought would help with air leaks and maybe some of the vibration noise. With the motor side of the housing and center stop reassembled, I attached it back to the frame. And then went ahead to file down the ridges on the fan housing that goes on the air duct side.
I threw the switch and gave it another test run before putting the fan rotor back on the mandrel. Great, no noise except for the drive train and just a little vibration coming from the fan housing. At this point I would have felt pretty good so far, but I had been this far before. It would not be until I had the fan rotor mounted back on the mandrel that I would know if any of this would help. I next installed the fan rotor and then gave it another go. Two things happened. One I noticed that there was some vibration, but as soon as I touched the fan housing it quit. Good I thought, maybe it is the housing and when I put the front on it will be rigid enough not to vibrate. The second thing I noticed was that the fan turned quite a bit slower than it did with the old motor. Well, the truth be known, I didn't have a clue how fast the other motor was, but if it was a 1725 R.P.M. motor with a 5" pulley driving a 2" mandrel pulley the calculated speed would have been over 4650 R.P.M. exceeding the 3450 R.P.M. target by more than 1200 R.P.M. Hmmmmmm ... I wondered if it was just high speed vibration from an out of balance fan and loose parts.
Next came the moment of truth, I assembled the rest of the fan housing, opened the inlet flapper valve all the way open and started the thing up. WOW ... Just fan noise, no vibration and the drive train noise was not too loud either. So I started to close the inlet flap to see how it affected the system. Nothing at all, just fan noise and no vibration and with the flap closed all the way, just a trickle of air escaping from the outlet. FINALLY, I think I have reached a point where I can continue with the project! :-D
Where to from here?
There isn't much left to do to finish this project up and have a working furnace. All that is left is to build the burner tube, make some plinths and glaze the furnace. I need to scrounge up the stuff to finish the burner tube. I need to find some 2" exhaust pipe and a machinery washer or something like that. I need to look in the book. The plate to attach the tube and the 1/2" pipe nipple I already have. I also have the stuff to make plinths and glaze the furnace. By the way, while collecting the material for the glaze (6 very tasty miller light bottles) I want you to know that I didn't work on projects while prepping the raw materials. <GRIN>
Well, so far so good huh? I hope you come back and check out the next installment! Check back occasionally to see what has changed. Hopefully, time will permit me to locate the stuff I need to finish up. Happy Metal Casting!
I have managed to find all of the parts for the burner and have started the construction process. To start, after cutting my exhaust pipe to length I measured in from the end about 1 7/16" and punched a mark to drill a 5/8" hole. Next I pushed in the machinery bushing that serves as an orifice to create a vacuum at the gas inlet. Next I tried to braze this in place, but I could not seem to get a good joint. The bushing was taking the brass really well, but it seemed like I was not getting the pipe hot enough to get the brazing wire to flow onto it. So I thought I would move on and come back to it. Next I clamped my half of a 1/2" coupling over the hole I drilled into the exhaust pipe. I figured that I would just weld it on with my wire welder. I run about a 1/2" of bead on the coupling and pipe and burned a hole in it. Sheesh, I was not thinking, I was last welding on some 1/8" angle iron and had the welder too hot. I turned it down and finished the weld job. Now, I have to be totally honest. My welding skills are nothing to brag about and I managed to burn a second hole in the works by the time I was done. I ground the weld a little to clean it up and decided that I would just braze the holes closed. Well this time the brazing went pretty good. I had filled the holes and went ahead an tinned the rest of the joint. I figured I could use the extra practice. The first go with the machinery bushing, I think I was just not using enough gas. But while I was practicing I my oxygen tank went empty. (Just as a note I was using MAP & OXYGEN to braze. My setup has very little tanks and I normally use it to melt silver to cast with.) Well, not to be discouraged, I figured I would get the rest of the stuff ready and then ask a friend of mine braze it up for me.
My setup will be using Propane to fuel the furnace. So I had to create an orifice for this gas to go through. I measured the I.D. of the 1/2" pipe nipple and seen that it was very close to 5/8". (That just seems too weird to me, 1/2" pipe with a 5/8" inside diameter. The folks that created this must have used a different ruler than I did.) I took a piece of 5/8" cold rolled round stock and cut a piece off of it about 1/2" long. Next I took this piece of cold rolled and ground the sharp edges off and marked a rough center, then drilled the orifice into it. Next I drove this into the pipe nipple and set it aside so that it can be brazed in. (Just as a note, I had to drive the plug into the pipe nipple and I don't think it could be blown out by the pressure of the propane, but as a safety factor it will get brazed up anyway.)
Finally all that was left to do was to fabricate the plate that attached the burner tube to the fan housing. For this, I cut the plate to fit the exhaust of the fan housing. Next I clamped it into position and drilled the holes to connect it to the housing. Then marked the top of the plate so that it would fit back on the fan when the plate is brazed to the burner tube. By that point I was wondering how to cut a 1 7/8" hole in the center and have a reasonably good hole, and how the plate could be held onto the pipe so that it would not shift out of position. A few minutes of contemplating gave me a solution. First I found the center of the plate and gave it a light fine punch mark. Next I set my dividers to a 15/16" spread and scribed the 1 7/8" circle onto the plate. Then I reset the dividers to 13/16" and scribed a concentric circle inside the 1 7/8" circle. Finally, I set the dividers to a 1/4" and made tick marks all around the inside circle. At every mark, I put a punch mark then took the plate to the drill press. I step drilled each hole to 1/4" then took a chisel and cut the little sliver of metal that was left between each hole. Originally, I was going to file the hole to the outer circle, but decided that I would take some pliers and bend the little spiked tabs up at the edge of the outer circle. What I was left with was a plate the could be pressed into the end of the exhaust pipe with enough friction to hold it into place. This way it can be brazed on without any worry of it moving and the little tabs will not interfere with the operation of the burner and cannot be seen from the outside of the burner tube.
With a little luck the burner tube should all be brazed together and ready to use tomorrow night. I will snap a couple of pictures and put them here so you can see them. Well, we are getting really close to trying it out now. Only thing left to do is make some plinths and give the furnace a good firing before glazing it. The bad news is that there is rain in the forecast where I live this weekend. Go figure. Well, until next time, Happy Casting!
The burner tube is all brazed up and ready to go and I must admit I am getting excited. Below are a few photos of the burner tube. Also, more from an accident than on purpose, the photos from here on out will be a little larger than the ones above. After looking at it I decided I liked the larger photos a little more. I hope that if time permits, I can replace the smaller ones above with larger images too.
In this image, you see into the entrance end of the burner. If you look close you can see the little tabs that were left on the plate to keep it in position on the pipe. A little harder to tell is that about an inch inside the pipe you see the machinery bushing. Brazing this in turned out to be a tough job. My friend Tony said that the brass acted as though it did not want to stick to the inside of the pipe.
Here is a picture of the gas inlet coupling that has been attached to the side of the exhaust pipe. If you look closely, you can see the hole drilled into the side of the pipe and on the left side of that hole you can just see the edge of the machinery bushing inside.
This photo has the pipe nipple screwed into the coupling on the side of the burner tube. Like I mentioned earlier, I am setting mine up to burn propane, but if I wanted to burn natural gas, I would only need to replace this plugged nipple with one that was not.
Well, next I will need to attach this to the fan and it is all ready to go with exception of some plinths and glazing. I hope the weather holds out to let me play with it some this weekend. I will take a few shots of the whole thing assembled and put them up next. I also hope to get some video footage of the thing in action as well. Keep checking back, I will get this done sooner or later. Happy Metal Casting! :-)
Well the moment of truth has arrived. Will this contraption work or better yet, will it work well enough to use???· I hooked the new burner to the fan and took it outside to test. I was getting excited about the project now, thinking of what would I cast first and stuff like that. Well I started the fan with the flap completely closed. Now keep in mind that the fan still blows some amount of air fro the inlet even with the inlet valve closed all the way. I am guessing that this is due to air leaks throughout the system. Next I started opening the gas regulator releasing propane into the burner while I held my MAP torch at the outlet end of the burner. I kept increasing the gas until it would light and stay lit. To make a long story short, I had the gas fully cranked open with the regulator. What was observed was a flame of about 5 or 6 feet in length that started about 4 or five inches from the end of the burner tube. The flame was a nice blue color with a tinge of yellow in it. I figured it did not burn correct because I had no flare on the end of the burner.
Next I decided that I would install the burner in the furnace and give it a go. Besides, I wanted to get the furnace good and hot before I glazed it. More to make sure that it did not have trapped moisture from sitting in the garage so long than anything. The picture above was taken tonight after it had run for about ten minutes. Lighting the furnace was pretty straight forward. I lifted the body section up and turned on the fan. Next I opened the gas until I it would ignite and stay lit. At which time I lowered the furnace body. After lowering the body, I gave it just a little more gas and then started opening the air inlet flap valve. I opened this valve all the way allowing as much air into the system as was possible. The fire was still yellow / orange in color. So next I started giving it more gas. In retrospect, I suppose this is where I went wrong. I think the yellow flame is formed when there is not enough oxygen in the system. The flame should have been blue. I have questions posted on the Internet groups Hobbicast and Gingery Machines to see if someone can guide me in getting the flame and burner setting correct on this setup.
I let the furnace run like this for about ten minutes. I figured I may as well dry any moisture that it may have absorbed. Then I noticed it. There was something dripping from the burner inlet tube on the furnace body. Something was wrong, so I shot the picture above and shut it down. Next, I will try to post some updates on the burner and furnace condition.
In this image you can see how the lower portion of the burner tube melted away. Suggestions that have been given to me for this happening is that the flame was burning inside the tube. I suppose this is because there was not enough air to push it down the tube to clear the end. Given that the flame was yellow, the mix was starved of oxygen. The next go will be done with far less fuel being injected into the burner tube.
This is another view of the burner tube. This help give a better idea of the area it melted. One thing I find confusing is, if the flame was burning inside the tube causing it to melt, why did only the lower half melt away and leave the upper half intact?
This picture shows the inlet of the furnace body. It is here that the burner tube was inserted. The burner tube was pushed into this hole deep enough to bring the end of the burner tube within about 3/8" of the I.D. of the furnace. If you notice, this part is still good shape. Notice that inside this inlet you can see bits of melted steel from the burner tube and if you look below on the ground you can see where the melted burner tube was dripping on the ground.
I have been given a number of suggestions to try from the casting related yahoo groups. First though, I suppose I should build a new burner tube. I am also thinking of cutting it off behind the damaged area and adding some sort of extension to it until I get the bugs worked out. Then when I have figured out how to use it, build a new burner to replace the temporary setup. :-) Well, I guess it is back to the drawing board! Check back, sooner or later I will get a melt from this furnace! Until then, Happy Metal Casting!