[j3dprints]

I've noticed the z-axis on my mill moves the head significantly when I tighten the z axis locks. The head moves so that it 'leans back' and straightens up. It leans forward normally without tightening the z axis locks. I would think this should not be an issue. Is there any way to correct it? I want to go down the cnc route soon and this doesnt seem acceptable.

[awerby]

Most people, when converting a mill like that to CNC, remove the whole quill/rack mechanism and replace it with something else, like a screw. As you noticed, it's too sloppy to drive positively with a motor.

[j3dprints]

Sorry, do you mean replace it with linear rails? I edited my post, what I meant was the head nods backwards when you tighten the z locks, and forwards when you loosen them.
I am guessing one or more of these is required:
- scraping the gibs
- scraping the dovetails
- replacing all with linear ways
- adding a counterweight

Thanks to all for any advice.

[ninefinger]

I don't believe that scraping the ways will produce any benefit. If your head moves with the Z locks then the gibs aren't tight enough. The problem is that if you tighten the gib so that there is no nod with the head in the middle of the column its usually to tight to travel to the top or bottom where the column is closed and better supported. The root of the problem is the weight of the head causes the open channel of the column to pinch in.The fix?

• Checking the gibs for proper fit and correcting any bend can help by reducing spring in the gibs. (probably not the issue)
• Linear ways is one option that has been done successfully. (time and $$)
• Taking some of the weight off (i.e. via counter weight or gas strut) helps somewhat as well and is a much cheaper / quicker job.
• Address the column pinching in by reinforcing the column externally (I want to try this on my mill)

I think a combination of counter weight and reinforcement might be good enough to make the mill work a whole lot better.

Mike