View Full Version : Just a small question

06-08-2010, 11:48 AM
Guys, I am just sorting out in my mind (and on the back of loads of envelopes) a few details for my mill build. There is nothing unusual in the design, an X-Y table and a Z.

On the Y I have the screw stationary with a moving nut, the X has a moving screw with a fixed nut.

The Z could do either. My question is which is the preferable method, fixed screw or moving screw??

:confused:Advantages and disadvantages of both options in words of less than 2 syllables PLEASE!!

John S
06-08-2010, 01:08 PM
Advantages of moving nut is there is less whip on the longer screws with them being fixed.
Disadvantages are more space needed, timing belt drive and larger bearings to support the nut.

X and Y will score more from moving nuts, the Z is better off fixed because of the space / bulk / weight problem.


06-08-2010, 01:17 PM
Do you mean rotating or moving nut?
I,d be interested to see the rotating nut set up! I always thougth is was a more complex design and Also adds extra weight to the set up as well.

If its just the moving nut then as John says it dosnt matter just look at how much load you are putting on it.

06-08-2010, 04:51 PM
rotating nut has less inertia so better efficiency for fast moving axis with big (length or dia) screws...

06-08-2010, 05:28 PM

I looked at the 'rotating nut' idea a while ago ... the vibes from the Gurus were mixed. It would appear to be the best way to go BUT the cost and added complexity of the drive system was prohibitive. If and it's a big IF, I ever get the chance I will look again. Maybe for the Surface Table build ...

I was/am leaning toward the fixed nut method ... the thinking is that the mass of the stepper and screw, being to the rear of the spindle may balance the load ...

Thanks for the input Guys,