Help, please. CNC Plasma Table DIY not quite right...

[HC B]

Hello, folks, I built a CNC Plasma table and it's got at least one problem.

I put it together and it ran but I found some small test parts were not correct even though I built my own drive reduction sets and knew they were identical. The X and Y axis are identical units, only the mount plates vary but the machine cut rectangles instead of squares and the circles it cuts are eye-shaped. After a lot of frustration I found the problem was that the belt-reduction pulley on the Y axis motor had blown one set screw (ripped out the edge of the threaded hole) and one had worked loose. I got my pulleys from McMaster and had to machine out the bore from 1/4" to 3/8" because I couldn't find a set of pulleys for the reduction I wanted in the shaft sizes I needed. I used a metal lathe to chuck up the pulley by grabbing the outside of the pulley in the chuck and bored the hole...only to find the outside diameter was not true to the original bore. Oops, the pulley kinds of wiggles when spun and in the process I reduced the amount of material the set screws passed through.

Can someone tell me a better place to get better materials/parts from? I need a 3:1 reduction with the drive pulley (3) fitting a 3/8" shaft and the driven pulley (1) fitting a 1/2" shaft.

If anyone is interested you can view a motion test video here:

YouTube - Plasma Table First Run.wmv
There's a link in the comments to a Photobucket album of pics of some of the details of the mechanics.

--HC

[WSS]

Can you over bore it to 1/2" (trued up of coarse) and broach it for a key and get a 1/2" x 3/8" bronze bushing or even a steel bush if you can find it and broach it the same and get a rectangle key to span the bushing?

WSS

[HC B]

Originally Posted by WSS Can you over bore it to 1/2" (trued up of coarse) and broach it for a key and get a 1/2" x 3/8" bronze bushing or even a steel bush if you can find it and broach it the same and get a rectangle key to span the bushing? WSS

Hello, WSS, thanks for the reply. I can not bore it to 1/2" as there is not sufficient material left to allow it (I got it pretty thin when I went to 3/8" from the original 1/4"). Thinking of what you've suggested I get an idea: I could bore the hole out to about 1/2" or exactly 1/2" and braze in a bushing like you suggested but that would leave me with ONLY the bushing as my attachment mechanism to the motor shaft (passing a couple of set screws to the shaft which does have a flat). However, I'm not sure I can get it any more true than it is now (which is not perfect). Since I found the circumference to be not true (by boring it in a lathe holding the outer edges) I must assume the manufacturer made the bore true to the face (if it was ever true). I'd have to have my drill press spot on and the piece clamped very securely to get a true bore. But as I think about it...that might work. Maybe not perfect...but better maybe. I'd need a bushing...I'll see what I can locate locally (small town...good luck to me).

Thanks again for the reply and thoughts.

--HC

[I Lean]

Have you tried looking at Stock Drive Components? They have a good selection of stuff, maybe one that will work for you? http://www.sdp-si.com

[HC B]

Originally Posted by I Lean Have you tried looking at Stock Drive Components? They have a good selection of stuff, maybe one that will work for you? Precision Mechanical Components Timing Belts Pulleys Spur Gears Couplings Bearings Sprockets Retaining Rings Brakes Helical Gears Clutches Universal Joints

Thanks, I Lean, I will look at their stuff this evening.

--HC

[flyinwilly]

try "econobelt" for pulleys and belts. I bought mine there and they are very good quality and much less than McMaster. The only problem is the pulleys above 40 tooth are only available in steel and the are very heavy.

I had the opposite problem that you had. I needed to reduce from 1/2 to 1/4 and the initial set of bushings that I made were slightly off center so I made a nice little sawtooth on cuts. A new set fixed that little problem.

Good Luck,


Willy

[najnielkp]

i cross drilled and drove in rollpins . have never had to worry about a set screw slipping and can still disassemble easily.