Hi all-

I bought a COA mill in 2012 and have used it for light stuff here and there, and recently have started working with a partner making (a little) money with it. The problem is, i seem to have a backlash issue. The X axis is showing about 15 thou BL and the Y is at about 4, and for some reason, seems to increase and decrease with no apparent reason why. I tightened the machine's gibs until I thought it would bog the servos, I stoned the gibs flat, etc and it keeps coming and going. So, i decided to try and do a little research, and found that some folks use a spring washer between 2 captured ball nuts in order to take up whatever slack is in the screws. I dis some measurements (OD of lead to OD of lead is 0.783in, measured 5 leads per inch) and ordered myself up a couple of ballnuts I thought would match and a few bevelle washers from eBay, tore the mill down to the screws and tried to put the nuts on.

No dice.

The ball nuts go on as far as the non-ball barring leads cut into them, then bind to a dead stop where the BB start. I tried both sides of the ballscrew, put the ball nut on both ways and the same problem repeats with both barrings in both orientations and on both ends of both ballscrews.

So, I figured I would contact COA, and as can be seen in another thread on the company, nobody's home to answer questions.

Anybody here know what the hell the specs of the screws are? I was under the impression it was 3/4 RH thread 5 leads/inch. Am I wrong? Does anyone have any information or advice outside replacing the screws/ballnuts? I'm stuck, and need to get this resolved or I can't make accurate or repeatable parts...

Thanks in advance-

Farasien