Date: Tue, 14 Sep 2010 19:58:43 -0400
From: "Roger (K8RI)" <K8RI-on-TowerTalk@tm.net>
Subject: Re: [TowerTalk] Skyhawk
On 9/14/2010 6:17 PM, ac9s@mchsi.com wrote:
> I am a little behind, but I thought I would offer my Skyhawk observations. I
> had one for a few years - worked very well, but the boom broke in an ice
> storm. I have a 3el Steppir on the ground now for electrical repairs and am
> considering either a TH7 or Skyhawk in the near future. If I do the Skyhawk
> again I am going to put a DX Engineering Boom Truss on it.
## The DX eng version uses a 3/16; thick, wrap around, cast AL irrigation
type clamp.....and also a mating SS lag bolt and nylock..for the assy that
goes around the boom. DX eng has them in only 2 boom sizes..2" and
also 3" .
I used the exact same boom truss assy years ago..and still have it. [ both 2"
and 3"]. Back in the late 70's... the local supplier of irrigation pipe also
had these mating cast AL wrap around clamps. Back then, they only came with
plated carriage bolts, not SS. There is 2 x square holes in the wrap around
clamp flanges.....to take the square nut that's built into every carriage bolt.
The assy is simply slid over the 2"/3" boom, and tightened, once
positioned. A thimble is slid over the SS carriage bolt 1st of course...and
5/32 " or 3/16" galvanized / SS winch cable used along with nicropress
crimps..or cable clamps. If cable clamps used... the saddle bears on the
long end of the cable [ live end]..and not the short end] . I use nicropress
crimps at both the boom end..and also the mast end..then nothing is going to
fail / rust. I have had cable clamps that have rusted ..eventually.
## These wrap around cast AL clamps are ideal for a boom truss. They stick
like glue with barely any tightening..since they have globs of surface area.
I have given up on U bolts / muffler clamps etc..for the boom truss. U bolts
and muffler clamps have virtually zero contact [ no surface area at all] and
just crush booms.
## The DX eng assy to terminate the truss onto the mast is slick. The plate
they have designed, has an offset built into it... such that the actual truss
line itself is dead center in the boom..and not off to one side. The off
set plate attach's to the mast with a PAIR of 2" DX eng saddle clamps..which
are SS..and have 5/16" threads. The pair of mating saddles are SOLID
AL..and textured..the same as the typ dx eng saddle clamps. All you add is
either a pair of turnbuckles, eye bolts or what ever you want. Their pair
of clamps will no way ever slip on the mast. And the solid, wide, thick AL
wrap around clamps for the 2/3" boom will never slide, nor rust,etc. I
have never had a problem since I cooked up the idea back in 1976. They had bins
of em back then..and as soon as I saw them, I grabbed a few... for truss line
work.
## Interesting enough..when I was in the local Home depot a week ago, they had
bins of SS carriage bolts..and had the correct size for AL wrap around
clamps. The bolts on mine are rusted, so will be replaced. There is no need
to drill holes through the boom either. That all got started when folks had
trbl with muffler clamps slipping on the boom, and truss lines going slack.
Later... Jim VE7RF
A boom truss is one of the easiest things you can make. Two saddle
clamps (plain U-bolts will work) to fit the boom and one to fit the
mast. 4 eye bolts (two for the boom and two for the mast) three
relatively shot pieces of Aluminum angle (2 to fit the boom and one to
fit the mast), and a cable to use for the truss. I used Phillystran but
wire rope would work as well. I do not trust aluminum tube used in this
application.
The two pieces of angle for the boom only need be long enough to
securely fit the U-bolt that goes around the boom. The center of the
angle is drilled to take the eye bolt. The angle that goes on the mast
needs to stick out far enough so the two eye bolts will line up with the
boom.
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