[TowerTalk] drilling chrome-moly mast

[Jim Thomson]

Date: Tue, 28 Aug 2018 15:29:03 -0400
From: Warren Munro <wmunro1 at hawaii.rr.com>
To: towertalk at contesting.com
Subject: [TowerTalk] drilling chrome-moly mast

<All  
<This may have been mentioned before, but my machinist brother-in-law advises drilling starting with a quite small bit and then use new gradually larger bits as you step up in hole size. This will cut down on the annealing, and will help eliminate the "bite" at the <end of the final hole.

<73

<Warren    KH6WM

##  IMO,  trying to drill a .375 hole  into a  2.00  OD  X  .375 inch thick  heat treated  4130 chromolly mast.....  while up at the top of a tower would be a night mare.   And trying to free hand it with a hand drill ??   Good luck with that.
The original idea was to... pin the mast, so it wont slip.   IMO, it would be much easier and simpler to just use the correct  rotor clamp in the 1st place, like the K7LXC  or  K7NV units.  They dont slip period...end of problem..at least at the rotor
end of the mast.   Where the boom meets the mast... that assy is easily  done  with  2-3-4  of the  DXE  super mast clamps.  They come in 2 inch ID,  2.5  inch  ID..and also 3.0 inch ID.   I used the F12 concept, which uses 2 al plates, one is mounted to mast
using  several of the DXE  mast clamps.   The horizontal al plate is mounted to the boom with either  DXE  SS U bolts  +  solid  al saddles,  OR a pair of DXE  mast clamps.  Each al plate is  .375 inch thick.   Plates are mated  with 4 x .375 inch bolts. 
The  5th bolt is  typ  .5 inch.  I drill and tap the  5th hole into the  vert plate.   Vert plate is mounted to mast before hand.  Horz plate is mounted to boom.   Boom brought up and mated to vert plate simply by sliding hole  #5  over mating  stud  #5..
done deal.  Then align the boom, such that the  4 x remaining holes line up.  Stuff  4 x remaining bolts in..and u are done.   F12  called that assy the ..easy on mount.     I just took the same concept, and beefed it up a bunch.  And no, the vert plate
will not  spin on the mast, it cant.   Those  DXE  super mast clamps are things of wonder..with a massive a mount of clamping  force on each clamp.    80m rotary dipole gets a  8 x 14  vert al plate..and a 8 x 17 horz plate.  2 x DXE super mast clamps used on vert plate...and  6 x dxe ss u bolts with solid saddles used on Horz plate.  The 40m  assy gets a 8 x 17 vert plate..and a 8 x 14  horz plate.    40m  vert plate gets  4 x DXE super mast clamp..and horz plate gets  2 x DXE  super mast clamps.   Nothing can slip
on the mast, no need to pin the mast.  K7NV  small PP  with its 2 inch mast clamping assy.   All TQ balanced, so minimal tq required to rotate..and hold it in a wind. 

Jim   VE7RF