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[TowerTalk] Welding Chrome Moly

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Subject: [TowerTalk] Welding Chrome Moly
From: (Steve Bookout)
Date: Wed, 02 Jul 1997 09:36:34 -0400
Bill Coleman AA4LR wrote:
> On 7/1/97 21:22, Kenneth Mathews at wrote:
> >I have read the postings on drilling Chrome moly and wonder if anyone
> >has thought about having a bead of weld put down both sides of the
> >mast that will go into the rotor mount and help keep it from twisting in
> >the mount due to the torque.  Does anyone have knowledge of how
> >to and what type of welding to use of this type of material.
> Just so happens....
> 4130 chromemoly steel has been an aircraft building material since
> shortly after the Wright brothers perfected their all wood and wire
> designs. Typical tubing sizes are around 3/8 to 1 inch and a wall
> thickness from 25 to 150 thousands. Not the typical tubing you find for
> tower masts, but the same metal.
> Oxy-Acetyline torches are the classic method of welding, although
> production lines (eg Piper aircraft of the 40's and 50's) typically use
> TIG (Tungsten Inert Gas). Either method would work in your case.
> Good quality welding rod suitable for 4130 is typically used, however,
> many of the racing planes from the 30's used whatever they could scrounge
> (read steal) up.
> Welding thin-wall 4130 tubing takes a fair amount of skill, but you are
> talking about running a simple bead down a thick-wall mast, which isn't
> as critical. In short, anyone familiar with a welding rig should be able
> to do this for you.
> --
> One problem I can see with this idea is that the bead may be poorly
> positioned in the rotator clamp and actually reduce the contact area.
> If clamp slippage is a real problem, perhaps you might consider some kind
> of torque dampener?
> Bill Coleman, AA4LR, PP-ASEL        Mail:
> Quote: "Not in a thousand years will man ever fly!"
>             -- Wilbur Wright, 1901
Finally, something where I can add my two cents worth!

Besides the obvious problems associated with the skill and knowledge of
welding, heat treatable alloys present another problem.  I think this is
really the big one when it comes to chrome moly.
Unless the cooling of the welded area is controlled, somewhat, there is 
a good chance the area will be come brittle.  
As a general rule, if you suddenly cool a piece of heat treatable steel,
the faster it cools, the harder, but more brittle it becomes.  It needs
to be 'drawn' back to some intermediate temperature.
Realize, that a big hunk of tubing will rapidly draw the heat away from
the area welded, possibly causing it to cool too quickly, making it
brittle.  Use a oxy-actelyne torch to keep the area hot, while slowly
letting it cool down.  Use the torch to heat the surrounding area so it
can all cool more gradually.  
In auto racing, safety cages, if not annealed or tempered correctly, can
bust at the weld area, just like they were ceramic.  This is not good.

The intent was generalities, not to get into metallurgy.

It is not a difficult thing to do or work with, but you just need to be
aware of it.

73 de Steve, NJ4F

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