Redesigning the X-Axis slides
After I installed the new motors and was seeing how much performance compared to the Genicom stepper motors I salvaged from some old printers, I noticed that I had some jittering and jumping from the gantry at a speed of 29 i.p.m. The problem after a closer inspection was that all four bearings were not making contact on one side. At a higher speed, the gantry would rock and cause it to jitter at the top.
The problem was I didn't have enough room to adjust the pipe. It would run up against the bore of the front and back plate before I could get it adjusted into position. I could open these bores up but then would have to bore out the pipe adjusters as well. Then I started wondering if there was deflection in the pipe in the middle. I don't know how much the gantry weighs but it is pretty heavy. Well, I fought with it until I was thoroughly frustrated and decided I would look at something different. So it was off to the Internet and see if I could find something different.
I spent a ton of time on BuildYourCNC.com watching Patrick put together his machine, and watch all the videos of him putting together his v1.3 machine. Well his site offers the nc files free, so I downloaded them to take a look. They were a little problematic for me for a couple of reason. If my machine was running correct, it wasn't big enough to cut some of the parts, and if it were big enough, EMC2 seemed to choke on the g-code in the files. I din't really want to build his machine, I just wanted to use the I-Beam slide that he was using.
I set out to reverse engineer the nc files back to a CAD drawing so I could get some measurements. I used a G-code to Cad converter and LibreCAD to create the drawings. It was a good learning exercise for LibreCAD anyway. Armed with the knowledge I gleaned from his work I set out to build some slides for my now Frankensteined JGRO machine. If you are interested in the drawings for what I done, let me know and I will either post them to the site, or email them to you. They were drawn up using LibreCAD. LibreCAD is free CAD software that will run on Windows and Linux. (Not sure about Mac).
Here is a side view of the finished X-Axis slide. The I-Beam construction resists horizontal and vertical deflection. I did lose an inch and a half of travel on the x-axis because of the plates that bolt to the front and back plates, but I am no longer using the bottom support on the machine either.
This is a shot of the X-Axis slide from another angle. Here you can see the box that wraps around the I-beam and bolts to the gantry. The nice thing about this is that you have support for the weight of the gantry and the thrust from the cutting tool plunging into the material. Not to mention that the slide is much smoother than the black pipe I was using before on the original design.
Some final thoughts.
With the machine back together I set back to see how fast it would run before losing steps. I can rapid up to 32.5 inches per minute with no problems. Not as good as I had hoped but still better than what I used to get. My lead screws are 3/8" 16TPI rod. I suspect I would do a little better with 1/2" 13TPI rod or 1/2" 10 Acme rod. But that is an upgrade for another day. I want to get back to cutting, after all, I still have those plaques to make. My poor wife probably thinks I have forgotten about them.
If I do more to the machine, it will probably be build a new gantry and Z-Axis assembly using the I-Beam method of Patrick's. I will move the gantry sides to the outside of the box slides rather than the inside to get a few more inches of Y-Axis travel.
Thanks for visiting. I appreciate it. If you have questions or thought or even constructive criticism, please feel free to email me. :-) Happy cutting!