Book - Chapter 2 - Tools

A Spin Casting Centrifuge by Gary Overman


This spin casting centrifuge designed and built by Gary Overman would be a great addition to any shop.  This unit is capable of casting wax, resin and other mediums.  We are grateful to Gary for submitting it here to be added to the tools section of the book.  You can click the image to see a larger sized image.

Arm 1Here is the Arm Assembly for the centrifuge. At the far left is the counterweight which is held in place with a large bolt and security nut. In the center is the slipring assembly which is bolted in place with 4 bolts through the flange.The slipring is constructed from common pipe fittings and bronze bushings are expoxied in place. The red hose provides a vacuum ling from the slip ring to the vacuum box at far right, which is just a plywood box that has been sealed with polyurethane. The box is bolted to the 5" alum channel arm and is constructed to sit tight in the channel. The box has thick rubber hinges on the left hand side, and Velcro latches on the right. A rubber seal allows the vacuum to pull the lid down very tightly and securely. Should the vacuum be broken and the lid loosened, centrifugal force is pulling against the rubber hinges and the lid remains closed with the simple aid of the Velcro. In other words, all forces are working to keep lid closed, rather than trying to open it. The drive pulley can just be seen on backside.

Arm 2This is a photo showing hinge end of vacuum "chamber" and camera hungry Binky attempting to get into the shot as always. Now you know why I had to rebuild the shroud to be Binky-proof.

Arm 3This photo shows the Velcro end of the vacuum box.

Assembly 1This photo shows the backside of the centrifuge without shroud or controls.In the foreground is the vacuum pump and filter.The pump,from salvage at about $60,is a gast dry rotary vane 4 CFM pump. It only achieves about 22"hg vac in this configuration at this altitude, but with about 350 RPM of centrifugal force behind the spin , it is MORE than sufficient to produce perfect castings.

The PVC "egg" at far right protects electrical connections. At far left sits the blue DC permanent magnet motor. It is a 90VDC 1/3 HP I bought from salvage for about $70.

The red hose connects the pump to PVC line which runs to the front of the machine and to a valve which allows operator to control vacuum in and out of box. Note that the Pulley is bolted to the 5" alum channel arm, and the whole of the arm assembly and pulley spins on a stationery shaft which is bolted to the steel angles which run midway of the horizontal plane of the frame(visible where the red hose meets the white PVC). This principle is easy to understand in use but difficult to describe on paper.

Assembly 2This is a view into the assembly from the top backside of centrifuge. It has a better view of the pulley. It also more clearly shows how the stationery shaft is bolted to the frame. I used 2 u-bolts for redundancy safety sake, though I imply none as you are totally on your own when it come to safety.

Assembly 3Opposing view to assembly 2

Assembly 4From front of machine. At top left is the vacuum valve. Center shows slipring detail.

Assembly 5Close-up of slipring. Please note the use of a shaft stop collar that sits against bronze bushing. Not visible is a rubber o-ring that is covered in lithium grease and compressed between the stop collar and the bronze bushing.

Assembly 6Another view from the front of the machine.

Assembly 7Yellow box is a multi function box that a friend with electronics experience threw together for me. It is an AC to DC converter that has a relatively simple circuit inside that converts but does not regulate or filter current. A rheostat is used that purpose and since this is hooked up after the rheostat, the meter on the yellow box allows me to see the adjusted DC current that is leaving the combination (rheostat and yellowbox converter) of the two.

The box also has a cross-wired double-throw switch that allows me to reverse the direction of spin on the motor as well as turn off power to the motor should I elect to do so at this connection. It is fused for protection. Power flows from the yellow box ( now reduced for speed control ) to the pushbutton switch mounted in the white PVC fittings. Connection is simple jackscrew posts.

Assembly 8Here is the on-off switch to the motor mounted in a spring activated paddle. Spring pushes paddle off switch into an off position until weight of hand is placed on paddle. At that point, switch in PVC is turned on and motor begins spinning centrifuge. PVC switch can easily be removed for "remote" use since cord is 10 feet long.

Assembly 9Here are all the controls used to operate the centrifuge.

Far left is simple homemade paddle ( as hand or foot ) switch that toggles vacuum pump on and off. Center is a 10 amp rheostat that limits ac voltage into ac-dc converter. This controls speed of DC motor. Far right is yellow-boxed AC-DC that is desribed in another photo.

This will explain why I use my centrifuge in the vertical position.I let gravity be my guide to control the start of the casting process, and then apply centrifugal force to overcome gravity and then use vacuum to avoid air bubbles. Here's where it all comes together.

Assembly 10This photo shows half of RTV mold prepared for use in vacuum centrifuge. The figure is of Jack Daniel whose famous still is 12 miles from my house. The mold has the typical lock and key features. Please note the air vent in the bottom left corner to allow vacuum to purge casting chamber ahead of the casting material as it enters the mold chamber when cast out of the copper pipe.

What is unique is how the wax ( or whatever you're casting) is held out of the mold until the centrifuge does its job. The copper pipe and cap holds the melted wax away from the casting chamber ( Jack ) until the centrifugal force spins the wax from the copper into the RTV where it quickly solidifies. The copper is hot the RTV is not and with vacuum and centrifugal force it is all done in just 2 minutes!

Assembly 11This photo is spun upside to make it more understandable to the human brain process. Again , remember casting material is kept away from chamber until centrifuge says otherwise.

Assembly 12Another shot.

Assembly 13Closed mold assembly. This is how the mold looks as it is removed from the centrifuge with Jack in the "down" position and sprue up top.

Assembly 14This is the basic slipring assy. It's a simple pipe fittings with oilite bronze bushings epoxied in place on both ends.

Assembly 15Backside view of slipring.

Assembly 16The pulley is approx 6" and has the center turned out of it for clearance. The exact diameter is not important since the unit is speed controlled.

Assembly 17View of Pulley and slip ring assy. Later bolt direction was reversed to make assembly easier. Binky wants in every shot and forced me to do the right thing and build a proper shroud.

Assembly 18Here's the pulley slipring mounted in the machine.

Assembly 19Here's a view of the completed slipring assembly. Please note the use of a shaft stop collar . Also note the rubber o-ring that is covered in lithium grease and compressed between the stop collar and the bronze bushing. The shaft and o'ring's are dissassemblied every 3 month or so and recoated with lithium grease. Because the unit is low RMP and only run for about 30 seconds at a time, wear and heat has not been an issue. I've used it hundreds of times and there has been so sign of wear or decrease in performance.

The red hose provides a vacuum line from the slip ring to the vacuum box at far left, which is just a plywood box that has been sealed with polyurethane. The box is bolted to the 5" alum channel arm and is constructed to sit tight in the channel. The box has thick rubber hinges on the left hand side, and velco latches on the right. A rubber seal allows the vacuum to pull the lid down very tightly and securely. Should the vacuum be broken and the lid loosened, centrifugal force is pulling against the rubber hinges and the lid remains closed with the simple aid of the velco. In other words, all forces are working to keep lid closed, rather than trying to open it. The drive pulley can just be seen on backside.

Assembly 20This photo shows how the frame can be laid on side to use the centrifuge horizontally like a merry-go-round rather than vertically like a ferris wheel if desired. But since my preferred molding method utilizes gravity to kept the wax out of the mold until centrifugal force is applied, the vertical orientation works best.

Assembly 21Here's the frame as I assembled and use it. The frame is 3" square 1/4" thick steel tube and weighs in at about 200 lbs. It's mounted on a wheeled platform with casters that are rated at about 250lbs ea. 2 casters swivel and 2 do not.

They are oriented so that the unit do not roll left to right as displayed in this photo. This is the ensure that if the unit is off-balance, it won't walk off on its own. In other words, the line of force is left-to-right and the wheels will only roll front to back.

Assembly 22Angled shot of vertical frame.

Assembly 23Side view of frame.

Assembly 24Assembly 25Here's photos of the finished unit with shroud and controls:

Assembly 26Assembly 27Assembly 28I was going to cast a wax as a demo for the website , but wax doesn't show up well in photographs due to its translucency. Instead I mixed up some quick set epoxy with some colorant and cast it into the mold. I cut the sprue off while the epoxy was still soft and removed minor flash around hat with my fingernail. Other than that, this is straight from the mold. Wax because it is much more fluid casts even easier!

The plans and photos for this project were done by Gary Overman

Variable heat gun by Gary Overman


I got an email from a fellow caster the other day with his plans for a one touch, variable heat controlled hot air gun with permission to put it on the site. When I looked it over, it didn't take a rocket scientist to discover that this was indeed a nice project and one that others would like to make and use. I am posting some of what Gary had to say about the project below.

I sculpt wax miniatures for casting in bronze. Electric wax pens are very limiting in terms of tool tips. Alcohol lamps take the temper right out of tools, are dangerous, and take a delicate touch to heat the tool to just the right temp.

A hot air gun can be controlled very precisely, activated by the touch of a hand ( while holding the tool) and cut off automatically, rather than create heat the whole time you're working ( un-like other heat sources).

Here's the photo-plan to make just such a tool for around $50. One might be able to use a cheaper hair-drier or hot air gun, but I used a very thin embossing gun which kept the overall footprint of the unit down to a very small size.

The plans for the project are shown below. You can click the image below and a larger version of the image will open up in a new window.ยท You can save and print this larger version. Gary has done a great job of illustrating them. If you are in the need of a one touch, variable heat source, then this project may be for you. Thanks Gary! :-)

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Vacuum Caster & Debubbler


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The Wax Injector © Alan Lewis


How to make a Wax Injector for lost wax casting.

To safeguard yourselves please follow these instructions carefully. A wax injector can be dangerous if not constructed and used correctly. These instructions are given freely and must only be used by those who are competent to undertake this work in a safe and proper manner. No responsibility will be accepted by the designer for accidents caused during manufacture or use of this injector.

Finished Wax Injector

You will require a 5 to 6 inch by 3 inch wide brass or copper tube, silver solder a cover on both ends a thicker one or double up for the base to retain the heat. Ideally the tube and top plate should be 1/8th inch thick with the base plate being ¼ inch thick approximately.

You will require a 5 to 6 inch by 3 inch wide brass or copper tube, silver solder a cover on both ends a thicker one or double up for the base to retain the heat. Ideally the tube and top plate should be 1/8th inch thick with the base plate being ¼ inch thick approximately.

Drill a 3/4 inch hole in the top and silver solder a one inch brass internally threaded connector over the hole and in this connector fit a brass blanking cap with a rubber seal supplied by a plumbing store. This will serve as a supply point for the wax pellets and also a place where air pressure can be applied.

Drill the blanking cap to take a metal tire valve and fit the valve into the end cap. DO NOT BE TEMPTED TO PRESSURIZE THE VESSEL AT THIS STAGE. Next drill two holes either side of the central filler cap to take, on one side, a pressure gauge with its connector and on the other side a pressure relief valve with its connector. All connector can be obtained from a plumber’s supply or DIY store.

Although I made my own pressure relief valve, I would recommend buying a professionally made one for peace of mind. You will need a valve, which relieves pressure at 30 psi. Silver solder the pressure gauge connector and the connector for the relief valve into the top of the tank do not connect the relief valve or the pressure gauge just yet.

Next, drill a hole in the side of the tank at the front, one inch from the bottom to take a connector for the injector nozzle. This needs to be silver soldered in place. If you can purchase a commercially produced injector valve do so, but if you cannot I have included a sketch of the type I made for my own injector. A lathe will be required to do this work. As an update, it was found that an "O" ring works better than a tap washer to seal the injector delivery valve. Also, by placing the spring on the outside, it allows room to fit a metal sealing cone between injector valve and tank body, giving better sealing possibilities.

To heat the wax I’ve used a domestic hotplate with a thermostatic control. The thermostatic control is important to prevent overheating of the wax. Placing the injector tank in the center of the hotplate helps prevent the wax solidifying in the injector nozzle.

Some way of measuring the wax temperature is required and I chose a digital clock/thermometer for this purpose. The type I bought had a wire with a sensor at the end, which allowed for the measurement of outdoor temperatures. These can be bought from a car accessory shop and I paid five pounds for mine. The range will need to measure as far as 80 degrees C. To use the temperature sensor you must first attach it with large nylon cable ties placed around the injector body so that the sensor is near the nozzle and in direct contact with the outside surface of the injector tank.

To secure the injector tank during use, I obtained a plumbers flange which fitted around the tank and then screwed it via a threaded bar securely to a wall. You will find these are standard plumbers fittings including the threaded bar. You should now be ready to fit and seal all components such as end cap with tire valve, air pressure gauge, relief valve and injector valve.

To test the tank for leaks I used a tire foot pump and pumped in air to a pressure of 5 psi. Then using a soapy water solution, I tested all joints for leaks and resealed as required using PTFE tape. When satisfied release the pressure and reapply air pressure to the injector tank taking it to 30psi (the relief valve setting)

I would recommend taking the tank to a tire-fitting center and asking them to do this for you in their safety cage. Once this has been completed and you are sure the relief valve has operated correctly you are ready to melt some wax and use the injector.

Firstly unscrew the end filler cap with tire valve and fill 3/4 full with wax beads leave the top off and turn on the hotplate until the wax starts to melt, which takes around 15 minutes. When fully melted reduce to about half the temperature just to keep the wax molten. It will be obvious that by leaving the filler cap off you will be able to see the point at which the wax has melted. You will need to experiment with these setting to get the melt and simmer temperature correct. DO NOT OVERHEAT THE WAX. I have found that simmer temperature was about half the melt temperature.

Now you can screw the filler cap on tightly and re-seal. Using the tire foot pump inflate the injector tank to about 10 (ten psi) and maintain a wax temperature of around 65 degrees C. (sixty five degrees C) at this point you should be ready for injecting. It may be necessary to vary temperature and pressure under different conditions and best results will be found with practice.

If available a compressor can be used to pressurize the injector but only when there is a pressure delivery regulator and water trap fitted.

Using a foot pump will produce about three or four waxes before having to pump A Wax Injector.again, which is usually about two strokes.

Please follow these instruction carefully - they are for your safety.


Click on any of the thumbnails below to see a full size version of the image and a description.

Injector Nozzle SketchInternally sprung injector valvePlumbing Parts Used To Make Injector ValveInjector valve with modified externally springWaxes made with injector.

 

Contact Details
Alan Lewis
The Watch & Jewellery Workshop
1 New Street. Neath. W.Glamorgan.
S. Wales. SA11 1RT
Tel: + 44 01639 644410

Chapter 2 - Tools


As with any type of profession or hobby there are a number of tools involved that will make your job easier. This chapter is dedicated to those tools that will make your job of creating masters, molds and casting easier. It will be by no means all inclusive but it is intended to get you a feeling of what is needed and what you may have at your disposal.

Rather than listing tools you can buy or need, the primary goal of this chapter will be to deliver to you plans or examples of how to make tools. You may either navigate by the menu on the left or click any of the links below.


Wax Injector - By Alan Lewis
Vacuum Caster and De-Bubbler - By
Variable output, one touch Heat Gun - By Gary Overman
A Spin Casting Centrifuge - By Gary Overman
A Ron Reil Type Burner - By Gary Overman
A Tumble Mixer for Dry Components - By Gary Overman
A Poor Man's Engraver Ball - By Gary Overman
A Wax Warmer - By Gary Overman
A Homemade Sand Muller - By George Vontorn