Shaft Whip

[thielert]

I did a search for any discussions related to shaft whip and came up with little.

What max RPM can one reasonably spin a 5’ 1/2" ACME threaded rod without developing any shaft whip or resonance?

Does anyone out there use screw drive on a larger (4’x8’) table? Shaft whip problems? What RPM?

Tim T

[balsaman]

For half inch it's around 500 rpm at 30" long (from experience). I am guessing a bunch less for 5".

[Bloy2004]

I don't know the answer to your question, but as an alternative(if there is one), set up the drive in the middle of the screw, turning the nut/nuts instead of the rod.

[turmite]

I don't know about the 1/2" but Mariss from Gecko did a calc for me on my 1.125" X 48" at the fastest rapid I wanted, 300ipm, and he told me I would need 1500 rpm and the screw would whip so bad it would be useless. Maybe between the two sizes given here at by balsaman you can get close.

turmite

[ger21]

This will give you the information you need.

http://www.nookind.com/pdf/powerac1.pdf

Read it all, there is a lot of information in there. The speed chart is page 11.

Gerry

[balsaman]

I currently run my 3/4" acme at 720 rpm for 120" per minute, down from 150" per minute because my motors can handle the speed but the rods whip to much for me. It's smoother at 720 than at 900 rpm. My longest screw is 48" long.

One way to get around this problem is to get 1 pitch screws and gear it way down. Then you only need 100 rpm to go 100" per minute. Rack and pinion or belt drives are also an option, but it's hard to get the backlash out of the gearbox you need for those systems.

Eric

[thielert]

Thanks for the info everyone. I was afraid you were going to say exactly what you have.

I imagine the efficiency of 1 pitch screws is a lot lower than a higher pitch. Maybe I'll investigate ball screws a bit more.

I have been designing for belt drive, but don't want to go down a path without considering all possible routes.

I have seen the photos of the Axxus belt 4’x8’ table. Does anyone know of any other examples?

Tim T

[yukonho]

I was going to tension my 36" threaded rod shaft. Will that not help a bunch?
co

[chuckknigh]

There's another possibility that you're not considering. The lead screw only has a problem with whip, if it's turning!

Keep it still!

I saw mention of a design on CCED, which basically turned the nut, rather than the screw. Of course, keeping backlash down was a concern, since there's a rotating mechanical linkage between the nut and the stepper, but the general tone on the list was that it was a workable solution.

You should be able to get away with a MUCH smaller screw, using a system like this.

-- Chuck Knight

[avsfan733]

I would think that a lot of the whip would depend on how well the shaft is suppored..or am I mitaken?

[HuFlungDung]

Originally posted by yukonho I was going to tension my 36" threaded rod shaft. Will that not help a bunch? co

I would think that yes, tensioning the screw would help a lot. This will require a sturdy frame and real thrust bearings, though, because the preload will be quite high to actually create significant tension.

[balsaman]

Originally posted by avsfan733 I would think that a lot of the whip would depend on how well the shaft is suppored..or am I mitaken?

You can only support it at the ends. Therin lies the problem.

Eric