G0704/g0759 Counterweight

[ttt]

Please take a look a the G0704 manual from Grizzly, page 47, exploded view. It's pretty clear that the head "hangs" on the Z-axis acme screw, on a single thrust bearing. The acme lead screw is held in with two locking nuts on the top only. There no nut holding it in place in the upward direction. If you counter balance the head with the same weight as the head there is a chance that the lead screw or bearing might just jump out of the retainer hole in the top plate. With enough force only of course and only so far as the two ring gears crashing into each other. You will certainly get at least some movement though.

I did convert my G0759 to a CNC/manual combo with ball screws. Since I use the mill mostly in manual mode the ball screw has the downside that unless I lock the Z-axis it gives way too easily; even with the stepper motor somewhat restricting the movement. So right now I am trying to figure the right counter weight to avoid this. Which also depends on how much weight I did add to the head. But I will certainly try to keep it well under the weight of the head itself.

 

[RJSakowski]

Tom, I always lock down the Z for all milling so it not like it is going to move around at that point. Is there some other reason to have down pressure on the screw?

Jim

Actually, I would think that you wanted upward force if anything as the cutting force from drilling or end milling will be pushing up. With a downward pressure, if you set your tool offset with zero force applied and the weight, now slight, is pushing down, when you start to machine, whatever lash you have will take effect. If you take a final pass of a few thousandths, there will be only a slight cutting force and the tool will cut deeper.

When you have 65 lbs of downward force, it is sufficient to bias the drive so you won't notice this effect but not so with only a few lbs. of force.

When I set my tool offset on the Tormach, I always make my final motion in the down direction for the same reason, to take up any lash, much like setting the cross feed on a lathe.