ball screw whip I have a large router that I am getting started on and have two x axis, 25mm ballscrews 108" long. What is the safest operating speed without encountering whip?
Not much IMO. Most large routers I've worked on keep the screw stationary and rotate the nut. Our 100 inch mills are supported on both ends, stretched and are about 3" dia screws. Even our 100" bed lathe has cast iron shoe supports that cam out of the way when the carriage moves by them.
Daniel, agreeing with underthetire, we do rotary nut with our designs and they are 1" diameter for our 96" X axis work envelop router systems. If you are going to be rotating the ball screw go here, Nook has a calculator that you can use as a rule of thumb.
Inch Ball Screw Calculators - Nook Industries, Inc. PowerTrac Ball Screws and Nuts
I come to 438 RPM using 104" (2,642mm) using dual bearing supports on both ends and 21.5mm root diameter.
Search in "the Google" this phrase... "ball screw critical speed calculator" to get some other readings.
If you want to consider rotary nut.....our site is blurrycustoms.com to see both our stepper and servo designs using rotary nut if you want some inspiration to go that direction.....it is the way to go.
Good luck.
Why do you need large diameter screws on these large machines with rotating nuts? I thought the diameter was mostly to beat whip on a std machine?Originally Posted by underthetire
You must have missed the word "mill".
Yes, I did! So the difference being that this is subject to very large tool forces, is that right?
And very large mass. Also helps with accuracy, your not as likely to wind up the screw, and the larger diameter with more mass helps with thermal growth. 25mm screw would be on the small side for most machining centers. Router shouldn't be any problem, your not putting a 1K part on and off. You only need to dial in for one weight load.
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