New Machine Build- Need advice with Z axis design

[isvflorin]

Hi guys,

could use some advice regarding the Z axis design. The determining parts of the design are the 420mm hiwin hgh15, the motor&spindle assembly and of course - wanting as much travel as I can get -hopefully 170mm

I've drawn some sketches for both versions -up/down.
My main concern is rigidity and weight of Z, basic options are - 1 having the motor(stepper+screw) side on the moving up/down part versus -2 -having the motor(stepper+screw) on the gantry side. The sketches are quite crude and for the moment disregard the screw assembly.

Please let me know what you think , and what would be best for rigidity/runout. Or if there are better options for the parts I have.

Thanks,
Florin

[johnmac]

From the many pictures of DIY machines I looked at before building mine, most people mount the motor and screw to the gantry half of the Z.

Try to keep the distance from the rails to the spindle as short as possible. It will help reduce the possibility of flexing (less leverage).

I have seen some designs that use springs to counter balance the weight of the router. Taken one step farther, if the spring(s) are just strong enough to pick the router up, the stepper will push it down, rather than pick it up.

Doing so can help cancel any backlash in the screw, as the nut will always be pushing the Z down. Just don't over-do it with the spring tension.

John

[isvflorin]

Thanks for the input John.
That would be my preferance too -keeping the stepper and screw on the gantry side, however I noticed that if the stepper and screw are on the spindle side the assembly will be stiffer when the z is fully up.

Florin

[johnmac]

Just remember, you need the stifness when the Z is down. That's when your cutting.

John