Re: re:Final leadscrew design - (more ???)
Posted by
ballendo@y...
on 2000-10-27 15:34:06 UTC
Ron wrote:
If you are using face ground matched pair bearings in a fixed mount,
the nut torque serves only to hold the bearings in contact with each
other, where the "designed in" pre-load will then be in effect. So
you tighten the nut as you might any other bolted assy.
Using the shim washers with cheap bearings is the same.
In a rigid mount, the RELATIONSHIP of the distances BETWEEN the
inner races and outer races of the two bearings determines pre-
load/clearance. So as long as you are using TWO correctly sized(in
length) spacers(one between the inners', and one between the outers')
the torque(tightness) of the leadscrew nut will not affect the assy.,
as long as it is tightened enough to fully "seat" all the parts.
It is when we do LESS than a "real" rigid mount(by using only ONE
spacer, inner OR outer-or none) that the torque of the nut affects
clearance and preload. In which case adjustment is done in stages,
by "feel". (Jon E described this kind of mount early in this thread)
The import mill/drill spindles are an example of this. There is NO
spacer beween the 2 spindle bearings, only a big nut which adjusts
the distance between them(by "squeezing" them together, more or less)
Roland Friestad (of Cardinal Engineering, and a member of this list)
has done hundreds of CNC retro-fits to these mill/drills. He
recommends using temperature to tell you if the bearings
are "squished" too much. Adjust, run. Is it too HOT?? re-adjust, run
some more. And so on...
Hope this helps.
Ballendo
>What process allows you to determine the torque on the lead nut?Ron,
>This load must be related to the clearence between the bearings and
>preload, no? These details will be uninspectable on assembly, right?
If you are using face ground matched pair bearings in a fixed mount,
the nut torque serves only to hold the bearings in contact with each
other, where the "designed in" pre-load will then be in effect. So
you tighten the nut as you might any other bolted assy.
Using the shim washers with cheap bearings is the same.
In a rigid mount, the RELATIONSHIP of the distances BETWEEN the
inner races and outer races of the two bearings determines pre-
load/clearance. So as long as you are using TWO correctly sized(in
length) spacers(one between the inners', and one between the outers')
the torque(tightness) of the leadscrew nut will not affect the assy.,
as long as it is tightened enough to fully "seat" all the parts.
It is when we do LESS than a "real" rigid mount(by using only ONE
spacer, inner OR outer-or none) that the torque of the nut affects
clearance and preload. In which case adjustment is done in stages,
by "feel". (Jon E described this kind of mount early in this thread)
The import mill/drill spindles are an example of this. There is NO
spacer beween the 2 spindle bearings, only a big nut which adjusts
the distance between them(by "squeezing" them together, more or less)
Roland Friestad (of Cardinal Engineering, and a member of this list)
has done hundreds of CNC retro-fits to these mill/drills. He
recommends using temperature to tell you if the bearings
are "squished" too much. Adjust, run. Is it too HOT?? re-adjust, run
some more. And so on...
Hope this helps.
Ballendo