Re: ball screws

PTENGIN@... wrote:

> Les,
> Thanks for the reply. I know about the wave washer. My CNC FB-2 mill has
> them on all three axis. The preload nut was turned until the washer was
> virtually flat. Not recommended. I would love to buy some THK's or NSK's but
> you know how much they cost. When you ordered your screws, what specifics
> did you order to get the preload you need? What type of seal do they come
> with or did you order them as options? What lead did you get? I noticed they
> have 1/5" pitch in 25 mm screws also. I know a high end CNC can use mm or
> inch screws either way but it is easier for my stuff to go 1/5". I look
> through the NSK or THK catalog, even the Nook catalog is filled with classes
> and preload specs- nobody really mentions a "typical" application.
>

Peter,

Mine are 5mm lead which is 5.08 turns/in.

Hiwin can make inch series and special preloads , etc. but the lead time is 12
weeks.
I just took stock items at the warehouse. I believe they have labyrinth seals so
should be
covered up.

5% of maximum dynamic load is a typical preload for ball bearings and ball
screws. It is
also referred to as a light preload. I don't have the technical data in front of
me but I think it
is several hundred pounds for the 25mm screw. I think this is about right for our
applications.
I also used the light preload specification for the universal flush ground
angular contact bearings
in the end blocks. There is a very small gap in the inner races of the duplex
pair that closes when the locknut is tightened to provide the light preload. This
is called the DB or back to back configuration.
Buckling and torque displacement would limit the usefulness of more unless the
screw was
very short.

The reps that have visited me from THK, etc. have said not to squash the preload
spring completely
as you said. The short term or "drunken thread" errors could result in very high
preload values.

I have been working on an update to my web site. I will be sure to include
closeup pictures of the
ballscrews.

--
Leslie M.Watts
Illinois Tool Works
Corporate Advanced Technology group
(847) 657-4559
http://www.netcom.com/~leswatts/leswp.html