At 03:32 PM 9/28/2005, Mark . wrote:
><< G'day, I wonder if anyone can point me in the direction of a supplier
>for fibre glass rod suitable for bridging the centre of a split driven
>element. The element I am assembling is the heavy duty 20m unit from the
>ARRL antenna Handbook and it will need to be 7/8 inch diameter to fit within
>the 1 inch O.D. tube tripler. I'm only looking for approximately 12 inches.
> DX Engineering only list a component for 3/4 inch O.D. tube. Regards, Mike
>VP8NO >>
>
>Mike,
>
>My favorite one-stop shop, McMaster Carr, only lists 0.75 and 1" dia.
>fiberglass rod. You can buy 1" and have it machined for exact slip fit, or:
>
>Look at G-10 Garolite rod, available in 7/8" OD and sold by the foot. I've
>never used it, but the specs seem well suited for the job. According to
>McMaster's info page, it's a glass cloth laminate, impregnated, epoxy filled
>composite commonly used for electrical applications (good insulator), and
>the tensile strength is an impressive 38,000 psi. Low water absorption and
>flame resistant.
>
>Looks like it's difficult to machine (requires diamond or carbide tools).
>
>Good luck.
I've used it, and many other similar products. The problem with machining
is that it's made of glass fibers, which are harder than steel, and so,
cause your steel cutting tools to go dull instantly. (just like drilling or
cutting fiberglass or glass-epoxy circuit boards) Interestingly, though,
regular old aluminum oxide sandpaper works quite well (alumina being harder
than glass). Carbide works too. Coarse grit, lots of water to carry away
the dust, chuck it up in the lathe and have at it.
If you have to cut it to length...A dremel tool and carbide cutting wheels
works well, although tedious. Or, get one of those carbide hacksaw
blades. Diamond hacksaw blades aren't all that expensive.. about $40 or so
(5 or 6 years ago).. it's not like they're gem quality diamonds on there..
just looks like fine black sand.
If you're a brave man.. you can use an abrasive cutoff wheel.. but I've
found that the polyester or epoxy just melts and gums up the wheel.
If you know someone with a tile saw, they have a diamond blade, and the
water feed, and can zip right through the fiberglass bar in short order.
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