[TowerTalk] Mast slippage

[Ron WV4P]

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 at 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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