[TowerTalk] Noob question re: Thrust Bearings

[Grant Saviers]

Art,

In reverse order

1. Natural colors for many plastics aren't UV resistant unless specified 
as such when a "sunscreen" chemical was added.  Black is a safe bet 
since carbon black is the colorant and the material is opaque.

RE chemical resistance, here is the McMaster spec sheet 
https://www.mcmaster.com/4296a164  UHMW is pretty tough stuff.  I've 
also used blue nylon for element clamps and it works well, no UV problems.

2. Commercial hot dip galvanizing should be around a max 0.007" 
thickness.  I machine the diameter 0.030" oversize and lightly file off 
any Zn droplets in the mast contact area.

3. Drilling UHMW has to be done with definite precautions since the 
material is gummy.  A stock twist drill will grab into it and since it 
is so slippery grab it out of most any vise.  Twist drill tips need 
stoned with a small flat (dubbing) to prevent that.  Easy to do and also 
needed for drilling most plastics, brass, or bronze.
https://www.practicalmachinist.com/vb/general/dubbing-drill-bits-183967/

An advantage of using a stack of thinner materials (maybe up to 1") is 
the hole can be made with a standard hole saw.  Drill a three 1/2" holes 
just inside the final diameter so chips have some place to evacuate from 
the hole saw slot. A very slow RPM is needed.  I have a milling machines 
and lathes so they make it easy, drill a pilot hole and bore to diameter 
or I can CNC it.  Most any garage lathe can do the job or a hour at a 
job shop.  Another choice might be a router with a plastic routing 
cutter and a plywood guide, but I have not done that.  TAP and other 
plastic suppliers with CNC routers might do it.

Have fun! Be safe.

Grant KZ1W



On 5/10/2020 05:54, Art Greenberg wrote:
>> My choice is a UV resistant UHMW radial top bearings for low cost, no
>> maintenance, long life, and low friction.  A 6x6x4" thick block ($47) is
>> what I made for the 3" mast radial bearing with 500# loading.  In
>> perfect condition after 6 years.
> 
> Grant,
> 
> I'm curious about this. Some questions:
> 
> - How did you drill the hole for the mast?
> 
> - How much oversize? I imagine its not very critical, is that true?
> 
> - Is any particular color better with respect to UV and other environmental exposures?
> 
> Thanks, and 73.
>