RE: [CAD_CAM_EDM_DRO] Re: Bearing question for ballscrew conversion

That sounds like a good price. What is the price and lead accuracy for the
screw stock?

Thanks,

Ward M.

wardmerk@... <mailto:wardmerk@...>



-----Original Message-----
From: Doug Harrison [mailto:prototype@...]
Sent: Monday, May 21, 2001 5:57 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: Bearing question for ballscrew
conversion

> To increase rigidity even further, a RIGID mount is used. This uses a
> spacer BETWEEN each pair of angular contact bearings. Shims are
> usually used for "fine tuning" this type of setup.
>
> A properly designed fixed-fixed (or rigid-fixed; or rigid-rigid)
> setup is NOT over-constrained.

I just perused the Rockford ballscrew catalog and came up with a nice chart.
RBS shows four arrangements and gives end fixity factors for determining
critical speed:

fixed-free = .36
simple-simple = 1.00
fixed-simple = 1.47
fixed-fixed = 2.23

The constant is in a first order term so you can see what a difference end
restraint can make.

I did the calcs on 10ft. screws and decided to rotate the nuts instead.

By the way, if you are looking for preloaded nuts you can't beat RBS for
price. They quoted $171 each for 1"X.250 lead, whereas Thomson quoted $950.
Both were single track. 5/8" was about $145 - not worth building your own
for that.

Doug


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