# Making a carbide threading tool



## cathead (Mar 20, 2021)

Yesterday a friend called me and asked about the possibility of silver soldering a part on a black powder rifle.  That prompted me to 
hone up my skills a little in case I end up having to do that job.  Anyhow, this morning in the shop I started with grinding a triangular tip
on a piece of tungsten carbide from my inventory of scrap carbide shown below.  It took an hour to grind an accurate 60 degree point as 
the carbide was a pretty rough piece.  I needed to mount the carbide on a suitable hunk of steel and ended up machining on the butt end of
a Kennametal threading tool.  I used my Henrob(Dillon) torch to silver solder on the insert using some Stay-Silv flux to wet the surface. 
Interestingly, the Stay-Silv was dried up and not readily reconstitutable but I have been using it that way for years so no big deal there.  
I applied a small piece of the dried flux and heated it with the torch until it melted and then proceeded to heat up the steel until the 
silver solder would coat the surface.  Then I added the carbide and got the carbide and steel up to about 1200 degrees and added a little
more silver solder to be sure there was enough on there to do the job.  A small bit of pressure on the carbide ensures that there is enough
silver solder applied as it begins to exude out at the edges.  It takes very little solder to do the job, I'd say about 1/2 inch of .032 solder will 
be sufficient.  After cooling the tool off, I did some relief grinding the the bench grinder.  Also, this morning I ground several other carbide
tools while I was at it along with several HSS threading cutters.  It seems stuff gets used to the point where lots of cutters need attention. 
Today was the day for that kind of work in the shop.


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## Shootymacshootface (Mar 20, 2021)

Very nice! This is something that I need to play with at some point. I have a small tray of carbide pieces meant just for this.


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## cathead (Mar 20, 2021)

My next project will be to fab up some carbide boring bars using my scrap carbides.  Old carbide table
saw blade carbides are handy as well for smaller stuff.


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## benmychree (Mar 20, 2021)

Commercial brazed on carbide tools use a silver solder shim to attach the carbide, it is made of a thin sheet of copper with silver bonded onto both sides, the copper provides a bit of cushion between the machined shank and the carbide part.  Both surfaces are degreased and coated with flux, the shim is set on the shank and the carbide is set on top, and if torch heated, it is heated principally from the bottom.  When the silver is seen to flow, the insert is pushed down  and the silver is allowed to solidify and the tool set aside to cool slowly.
The shop that I apprenticed in did quite a lot of this work with 1" square tools for facing large diameter line pipe, up to 1" wall thickness and 42" diameter.  After I left, they bought a induction heating machine to do the brazing, a much more satisfactory method of heating.


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## cathead (Mar 20, 2021)

You really do not need fancy induction heating and silver bonded copper to do good
work in a hobby shop.  As long as the flux whetting agent gets the silver solder to
bond to both surfaces, the joint will be satisfactory.  Both joining pieces need to 
be heated to above the melting temperature of the silver solder.


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## benmychree (Mar 20, 2021)

True enough, I just wanted folks to know how it is properly done in an industrial setting.


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