[TowerTalk] Cutting Large Holes in Aluminum
K7GCO@aol.com
K7GCO@aol.com
Tue, 26 Jun 2001 17:36:38 EDT
In a message dated 6/25/01 11:26:26 PM Pacific Daylight Time, writes:
<< I have aluminum rectangular blocks (4"x4"x1") that I need to cut a 3"
diameter hole in (using them instead of muffler clamps). I tried a bi-metal
hole saw and also a circle cutter with not much success since I need to make
about blocks altogether. I have a metal lathe that I can bore the finish
diameter on but I would like to get a big chunk of the material out of the
way (to save some time). I have also thought of using a smaller drill bit
(1/2") and drilling a series of holes around the diameter and may do this
but there seems like there has to be a better (less labor intensive) way.
Thanks
Mike W9RE
>>
Mike: If you drill multiple holes and then start to bore the hole it will be
a bangedy bangedy jarring job and can even break boring bars. It's hard on
the lathe bearings also. If you use a carbide tipped boring bar (and a
higher HP motor if needed), you can tear off thicker strips of aluminum to
the point where the even steel chips would be coming off blue and smoking.
It will do this very well in aluminum but any bumping will break the carbide
tips. The aluminum can be hogged out of there really fast. Even with normal
boring bars this is a short job as it is. The clean up time would take
longer. I've been there and done that.
When I built the mounts for my 10M 7 element beam I also had all kinds cheap
aluminum tubing from Boeing Surplus and did all kinds of fancy lathe and mill
work. The beam had all kind of mechanical and electrical concepts not seen
on commercial beams. I solded the joints with a great flee market aluminum
solder, had a special DE, a unique mast to boom mount and it had 40 dB
F/B/Side This was done under the concept that with all that cheap aluminum,
I could make an "inexpensive beam". Nothing would be further from the truth
but it did work great. It took about 6 months of spare time using an
expensive lathe and mill and supporting tools. That beam cost me a fortune
and I said "I'd never do that again if something close was available." That
big stack of cheap aluminum I've accumulated held in special racks over the
years has ended up costing me a very big chunk of money and time.
If someone wants to give you a beam or tower--hang up or run as fast as you
can the other way. You will have to pick it up, store it until it can be
cleaned up thoroughly and properly before installation. It will cost you
more than it's worth. Any special pieces missing will be hard to find and
costly. I'm yagi'd out and am switching to mostly quads for new challenges.
I just purchased 2-2 element and a 5 element 6M Raibeams. It would have been
very costly to duplicate. I assembled all 3 in an hour and had them up 1
hour later. It's "absolutely the least expensive beam I ever bought and
there isn't a thing I can do to improve it." It ruined my whole day. With
all the money you save by buying a good beam you can go out and buy a new
rig. You can't build a yagi as cheap as you can buy one. More on the
Raibeam "Butt Kickers" later.
There was a article in QEX on building a 5 band yagi that would have cost
several thousand dollars to make--if you could get the aluminum in small
quatities. The article was by a SM2 using "Metric Tubing" which isn't even
available in the US as far as I know. It was a design using 3 elements on
each band one in front of the other using about .25 WL of boom each. It has
about a 70' boom and that had to be some boom with bracing.sidewards also.
Only the medium Prop Pitch Motor could handle it along with a big heavy tower
with lots of guys, big headaches, initial and regular crane costs and wasn't
really of DX antenna which was infered .
You would have to put it in Eznec and determine the length of a US tubing
diameter to replace the metric diameters. A single 12' length of small
quantity purchase can cost $100. I shutter to think what the boom would cost
or weigh. It had 5 separate DE's and coaxes and all requiring adjustment
perhaps with a crane to get to each one. A tipping boom would be needed
otherwise. Even I wouldn't have all this aluminum. You would need a lathe
and a mill for the hardware, a computor and know how to use Eznec.
The moral of this story is:
"A 5 band quad on a taperd boom of 8' spacing and No Stray
RF costing less than $500 would probably out preform
it and you could sleep on windy nights.
There was another 20M beam some antenna software had in it as a sample that
had about 50 telescopng joints requring 50 SS hose clamps. Inaddition to the
50 telescoping joints and all that extra weight and excessive cost, it had
100 more SS to aluminum joints (one on each side of the clamp)(150 total).
This kind of design nonsense still goes on.
A quad has ZERO telescoping joints and "NO Electrical Deterioration" with all
soldred joints. Quads with the right spreaders are a great antenna to build
or buy if the DE's aren't all tied together and copper wire is supplied that
doesn't stretch. It totally destroys the potential pattern.
If you have any desire to build a yagi I'd forget it unless you have a lot of
time and money. The only technical knowledge you need to buy one other than
the one that fits your needs is to create the money to buy it. You will get
over it. Buy one. I may build a few more. Don't do as I do--do as I say!
I'm still working on new yagi designs and there it's justfied. K7GCO
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