Ron,
I shouldn't generalize, as it is possible to mag drill on a tower as you
are doing. But rigging my 60# mag drill on a tower with a custom
fixture and using Rota-Broach drills is not in most ham skills and
toolboxes. Maybe the fact my mags get heavier every year is another
factor ;) .
Grant KZ1W
On 7/28/2020 21:57, Ron WV4P wrote:
I hate to disagree with Grant but I'm making a plate out of 1/4" steel
to clamp to mast with 2 u bolts, pop mag drill on with a HSS Annular
cutter and smoking a cig as I send it through making a perfect hole. I
have worked way to hard in the past to drill oval holes.
Ron, WV4P
On Tue, Jul 28, 2020, 11:42 PM Grant Saviers <grants2@pacbell.net
<mailto:grants2@pacbell.net>> wrote:
I looked at the 71D picture at Array Solutions.?? Not impressed with the
bent up clamps.?? Grade 8 bolts can apply 2x the force of the stock
SS if
torqued to spec, the easiest thing to try.?? Torque the bolts with a
torque wrench, wait a day and re-torque.?? I've had SS bolts take an
initial stretch, a known property. One project I worked on required
torquing the grade 9 bolts 3 times and temperature cycling the joint in
between.?? Quite amazing the change each cycle.
Or the 71D ears may bend around more.?? Measure the separation top and
bottom to check for that with what you have done so far.
A way to improve the existing bracket is bracing welded at least across
the top, say 5/16 thick x 3" with a V cutout.?? Even better if a second
one was cut to fit mid height and welded in.?? Or buy better one if it
exists.
The problem with pins is it is very difficult to get a round straight
thru hole of correct diameter in both parts by hand, especially on
alloy
steel tube.?? ??So the mast will still work back and forth, elongating
the
hole and wearing the bolt.?? The back and forth is hard on the rotator.
Your mast will still be "slipping slightly".
If the pin is your choice, I'd try a pilot point drill (Dewalt) of the
diameter that just fits the bracket hole.?? It has a center drill built
in and they are excellent quality steel. You might go thru with a
couple
of these. If they don't hack it a Co/M42 drill will have a good start
hole. You will need lots of thrust force and endurance and coolant.
Water in a spray bottle is better than oil, WD40 is easy and good
too, a
helper is necessary to have continuous application.?? The mast material
cert can tell you what you have and the possible hardness range is
greater than 2:1 Hrc. (there are 6 spec 4140 standards).?? Hand drilling
at the hardest level is doubtful.
A punch might provide a drill start on round alloy steel tube for maybe
a 1/16" drill but how would you get it centered??? It is possible to
step
up in a few steps to reduce the thrust needed but by hand it's unlikely
to preserve the position.
Drill from both sides, don't attempt to drill thru from one side.
There is no way you want to mess with a MagDrill (I own 2) on a tower
and there is nothing for the magnet to clamp to.
Good luck, be safe,
Grant KZ1W
On 7/28/2020 16:00, Les Brown wrote:
> I have 2 large Yagis attached to a 3 inch OD ?? inch wall
thickness Chromoly
> mast running down the tower to a ProSisTel PST-71D. On a windy
day, I hear
> creaking sounds from the tower. The mast is slipping slightly in
the rotator
> mast bracket. I???ve already tried to tighten the 6 bolts, but it
still slips.
> I don???t want to tighten them to the point where they might
snap. I???m
> thinking that what I need to do is to go up the tower, drill a
hole through
> the mast (the rotator mast bracket already has holes), and pin
the mast and
> bracket. I understand that it???s not easy drilling through
Chromoly pipe, so
> before I try this, I thought I would ask if any of you have any other
> suggestions.
>
> 73, Les VE3NNT
>
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