[TowerTalk] [BULK] - Re: Cushcraft A3 center insulator

Steve Katz stevek at jmr.com
Thu Aug 31 18:46:12 EDT 2006

Guys, I've used PVC for this same application (A3-A4 and similar beams DE
center ins).

In one case, in a pinch, I bought a solid block of PVC from a local plastics
supplier (cost about $5), gave them a drawing of what I needed.  They put it
into a multi-axle CNC machining center and about ten minutes later I had a
custom made PVC center insulator for $25.  Took them more time to clamp the
block into a fixture than it did for the actual machining.

A lot of plastics shops can do this.  PVC is really strong, not bad for the
application.  This was the "black" stuff, UV tolerance seems pretty good --
the beam's been up for years with no sign of deterioration.


-----Original Message-----
From: K8RI on TowerTalk [mailto:K8RI-on-TowerTalk at tm.net]
Sent: Thursday, August 31, 2006 3:50 PM
To: towertalk at contesting.com
Subject: [BULK] - Re: [TowerTalk] Cushcraft A3 center insulator

> >
>>I had a new one kicking around in my garage, and finally
>>threw it out, I think.  But if I still have it, it's in the same
>>storage tub as my rotor and coaxes.  I'll check.  You can have
>>it for postage. Wl msg you privately, in 24 hours, if so.
>>But...why not just order what you need from Cushcraft?  Crash parts
>>for these things aren't all that expensive, and then you know you have
>>the right stuff.  Reinventing the wheel usually isn't a productive
>>jimjarvis at ieee.org
> Just got my Inquirey back from Cushcraft, this is why.
> The fiberglass insulator fo the Driven El. on A3S is 122096, and is $34.70
> Its a 10 in. piece of fibreglass for heavens sake.

The earlier ones were phenolic. I have an ATB-34 out in the shop that just 
uses a phenolic tube about 8 or 10" long. The elements fit into it. It is 
drilled and tapped, 1/4-20.  They use a SS round head screw plus a double 
nut to hold the crip on connector that goes to one side of the coax or the 
other. The insulator is held to the boom using an Aluminum plate  and a pair

of U-bolts.

To make one of these would only take drilling out a phenolic rod of the 
proper size.  The same could be done with a fiberglass rod of a large enough

diameter. I used the phrase "only take". It'd only take a lathe to do it the

easiest way and keeping things centered. OTOH the resin in fiberglass is 
sensitive to UV light and will not last near as long as those old phenolic 

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com (Use return address from home page)

> Scotty W7PSK
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