[TowerTalk] US Tower Crank-Up Tower Thrust Bearing

[Grant Saviers]

If it is truly a thrust bearing then it must have grub screws or a 
collar above with grub screws.  For the former the ID - OD mismatch 
could be large and still be ok.  For the latter you could get a collar 
machined with an 0.030" extension, but I would think that is overkill.

If it is a radial bearing then 1/16" really won't matter.  I machine 
plastic radial bearings with 0.030" clearance. I think that is the ID of 
the "2" inch tube on larger UST crankups.

While all masts are not equal, those of real DOM (drawn over mandrel) 
alloy (4130, A513, etc) are usually pretty round and very close on ID/OD 
diameters.  If you are using pipe then all bets are off re round and 
generous diameter tolerances. (plus not a good idea unless of a known 
quality source). (specs are published for both). Galvanizing adds a bit, 
on the order of 0.008 to 0.015" diameter plus some droplets etc to file off.

Grant KZ1W

On 7/28/2019 2:02 PM, Mac wrote:
> This measurement is near insignificant, it needs or should comport with 
> the mast size O.D. not all mast are equal in size by a long shot.
> 
> By its self is not enuff answer.?? The mast and thrust bearing are near 
> symbiotic in their relationship.
> 
> best:?? mac/mc?? w5mc
> 
> On 7/28/2019 1:06 PM, W3OA wrote:
>> A buddy and I are doing some work on a US Tower crank-up with an 
>> unknown history.?? He measured the inside diameter of the thrust 
>> bearing as 2 1/16 inches.?? Does this sound right or is it possible the 
>> bearing has been replaced with one that is not the same size as the 
>> original?
>>
>> 73 - Dick, W3OA
>>
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