[TowerTalk] center insulator material

[Grant Saviers]

I've been using black UHMW for mast radial bearings - cheap, slippery, 
good insulator, and UV resistant (just inspected after 4 years).  Not as 
strong as delrin or glass filled, but should work fine for your center 
insulators.

One BIG caution using home shop tools - soft plastics (also brass) will 
grab a standard twist drill flutes and pull it out of most any vise. 
That makes for a whirling finger/hand slicer.  It is important to stone 
the sharp drill point cutting edges flat for about 0.020 - 0.030" for 
drills bigger than 3/16" diameter or so.  Sometimes called dubbing the 
drill point, see

https://www.bing.com/videos/search?q=drilling+brass&docid=608050047239851308&mid=00A1314A97BD2D20C1D800A1314A97BD2D20C1D8&view=detail&FORM=VIRE

https://handycrowd.com/drilling-brass-the-easy-and-safe-way/

Grant KZ1W

On 2/8/2020 10:47, jimlux wrote:
> On 2/8/20 8:57 AM, charlie carroll wrote:
>> I need some help selecting some type of material to build some custom 
>> center insulators.  I have what approaches zero experience in this area.
>>
>> The insulators will be used to support near vertical dipoles for 
>> 160-meters.  The antennas will be installed in the Caribbean and will 
>> need high resistance to UV and salt water.  I also want to install an 
>> SO-239 and home made common-mode choke on the insulator.  It would be 
>> preferable that I be able to fabricate the final shape with common 
>> home workshop tools and not have to rely on a machine shop.  The 
>> insulators won't be under a lot of tension because of their 
>> orientation, but low weight material would be preferred.  The 
>> insulators may be subject to some winds containing sand particles.
>>
>> I'm looking for some help selecting some appropriate material (UHMW, 
>> Ultem, UV augmented HDPE, ...) that I can investigate further.
>>
> 
> Most any UV resistant plastic would work. The shape is almost 
> immaterial, you can get flat bar stock, drill holes, and be done.
> 
> http://www.sdplastics.com/ultravioletresistance.html has a bunch of info.
> 
> I've used Acetal Copolymer (aka Delrin) with UV inhibitors. There's 
> decades of experience with it. Ultem is very good (we use it on 
> spacecraft), but probably costs more than what you want.
> 
> Looking at the McMaster Carr catalog, i see they they have a VHMW 
> Polyethylene which is weather resistant.  I'm not sure that I'd use PE 
> though.
> 
> 
> Speaking of machine shops - you might look at one of the prototyping 
> companies like First Cut Protolabs: 
> https://www.protolabs.com/services/cnc-machining/ - there's a fair 
> number of these places around, and they typically stock all the useful 
> materials, and will turn it around in a few days.
> 
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