[nquantum]

Plan to build CNC working area is 60cm x 90cm. Z distance is 10cm.
For robot, uav, drone, rov, small wood work.
Work with wood, acrylic, aluminium.
Plan for 10mm pitch. BK,BF support.

What should be ball screw dia size?
Any other comment is appreciate.

[joeavaerage]

Hi,
the diameter of the screw determines the stiffness/rigidity of it, obviously the larger the better from the point of view of strength.

A more subtle effective minimum diameter is the maximum rotational speed.

The most comprehensive deign guide I have seen on the subject comes from the NSK Precision Components catalogue:
http://www.nsk.com/common/data/ctrgPdf/e3162h.pdf

Section B-2-3

The important parameters are the max unsupported length, that is the max distance between the ball nut and either of the support units, and the nature
of the support units, ie fixed, floating etc.

[nquantum]

Thank for reply seem it more detail in those catalog. Will try to study it. Initially I plan to use 20mm diameter.

[joeavaerage]

Hi,
the design guide suggests that the max permissible speed for one fixed, one floating support and 900mm free length at 20mm diameter
is about 3000rpm. At 10mm pitch that is 30m/min rapids, that's pretty quick!

Craig

[nquantum]

Hi,
the design guide suggests that the max permissible speed for one fixed, one floating support and 900mm free length at 20mm diameter
is about 3000rpm. At 10mm pitch that is 30m/min rapids, that's pretty quick!

Craig

I capture to make sure I understand your. Start with 900mm free lenght then find the cut at 20mm diameter then down to fine permissible speed at fix-simple support. That is about 3000rpm. That correct?

[joeavaerage]

Hi,
yes, that how I read it also.

I would regard this as a maximum and your design and construction must be good to achieve it.

For instance if you have a significant misalignment between the motor and the ballscrew the flex coupler will exert a small cyclic force
as it flexes, once per revolution. That would be a vibration which could start the ballscrew whipping. Likewise any misalignment of the mounting
of the ballnut would cause a force which would promote whipping. In short any small error is construction could badly compromise the stability of the
screw in rotation.

Having said that....if your construction is good, and no doubt that's exactly what you'll be trying to do, and likely achieve in good degree, then I would
expect you to be able to spin 20mm screws at close to 3000rpm without whipping.

Craig

[nquantum]

Thank for verify my read. So base on that. if I use:
16mm I can have maximum of about 2500rpm , 25m/min
10mm I can have maximum of about 1000rpm , 10m/min

Aside from my construction good or not.
Then I think I can lower from 20mm dia to 16mm still good condition.
Am I miss something?