Re: [CAD_CAM_EDM_DRO] How does one adjust Ballscrews on a Bridgeport

Stephen Wille Padnos wrote:

>I'm pretty sure the bearings went in the same way they came out. I'm
>not sure if they were correct when I got the machine though - it was used.
>
>
>
>>I have the Bridgeport manual here, and looked to refresh my memory of the
>>mechanism. (I don't have a real maintenance manual, but it does have an
>>illustrated parts breakdown of the leadscrew brackets. I don't see any
>>shims
>>in there.
>>
>>
>>
>Does the diagram look like this one:
>http://www.frugalmachinist.com/bp1jlongitudinalscrewinfo.gif ?
>

Yeah, that's the EXACT same drawing, with those "Norma Hoffman" bearings.

>It does look like the contact angle is "outward", though that seems
>backwars to me. If you push the screw left, then the right (inside)
>bearing "loosens", and the outer one should "tighten". But, it seems
>that you could just push the inner race out of the bearing, since you're
>pushing toward the wider side of the bearing. (I realize it would take
>a lot of force, but still...)
>
>

Yes, I think you are right. But, if the inner races are ground wider
than the outer, then
the handle nut just has to hold them together, and it is the clamping
force of the
retaining plate that sets the preload. But, that would make it come
apart the
OTHER way. Something doesn't make sense, here.

>
>
>> But, it is pretty clear that if you have the inner races
>>clamped hard
>>together, then they have simply hit each other, and not given any preload.
>>IE, the inner races should have a gap between them, transferring force from
>>the inner races to the outer races, and pushing them together. This is
>>obviously
>>not happening.
>>
>>
>>
>>

Well, I took my end bracket apart. The bearings ARE Norma Hoffman XF12,
as specified by Bridgeport. There are no shims, spacers or anything
else in there.
The bearings each have one face with a felt seal between two steel rings
that
holds it between grooves in the outer race. These do not appear to be
angular
contact bearings, but I would think they might be called deep groove
bearings.
I note that when placed as they were, with the Norma Hoffman labeled sides
facing toward each other, the inner races do NOT drag on each other. That
is a clue that there is some offset to the way the inner races are ground.
Miking the races, both outer races measured 0.607", but the inner races were
0.6025 and .604". I suspect the non-labeled face is not tightly
controlled, but
the labeled face controls the preload, and is ground to some critical value
in relation to the outer race. So, you might mike your races. If both
inner
and outer are the same, then these are not the correct bearings. You can
probably get it to work with a small spacer between the outer races to
accomplish the same preload. But, likely those bearings may not have a
deep enough groove, and may wear out.

Although it is not clear from the Bridgeport documents, I think the XF-12
may be a matched pair with the preload of the pair factory set.

Jon