Fixing hairline crack in buttplate?

[Hemo]

This question is similar to the recent post on repairing a mis-drilled hole in a buttplate. I was just finishing inletting an investment cast brass buttplate onto a stock blank when I noticed a short hairline crack in the upper inner angle of the left side of the buttplate where it lies against the wood. The crack is about 1/4 inch long, oriented vertically, and doesn't appear to affect the overall structural strength of the buttplate. I undoubtedly created this by rapping a little too hard on the plate while applying transfer color during inletting. What to do now? I could attempt to braze a tiny bit of brass onto this site, but that risks melting a big hole in the casting, or warping it. I could run a little solder into it, which would leave a tiny silver-colored line in the yellow brass, which might or might not be visible. Any ideas?

Hemo (Gregg)

[Acer Saccharum]

Peen the area on either side of the crack to close it up, then file over the area til smooth, then finish your gun.


Brazing will require so much heat, it will change the shape of the BP. Good luck getting low temp solder to flow into an old crack. I'm recommending to minimize it by peening and move on.

[Jim Kibler]

In the process of pounding out butt plates to stretch them or change their shape, I've occasionally caused a crack to form.  If this happens I use silver braze to fix it.  I much prefer this over soft solder.  With good flux, the braze will fill the crack very well.  Might be an option for you.

Jim

[Hemo]

Thanks for your suggestions. Jim, when you say silver braze, are you referring to an alloy of silver and brass? I looked up some silver braze products on the internet and it looks like the melting temperature is about 1200+ degrees. Can this be done with propane, or without melting the investment casting? Is there a product you like?

Thanks,

Gregg

[Jim Kibler]

Silver braze.  Not the hobbyist silver solder stuff.  Stuff that melts around above 1000 F.  About any good brand will work fine.

[WadePatton]

I never see the % mentioned but that is how we specify our silver solder when making socketed (lugged) bicycles frames.

56% is the stuff for fine cracks- Harris white flux, or try borax (I've never used borax, so can't make specific rec. on that)  56% silver wicks like crazy, but not good for fillet.  45% or so makes fat little fillets but won't flow as thin as the 56.  Propane will work. 

Flux must be brought up to temp slowly, but will readily take the heat once warmed.  Blackened flux is burnt and heck to remove.  Watch the flux. Glassy flux is perfect temp to add filler.  UN-burned flux will soak off in water.  Always de-flux.  Flux the back side too. 

Sunglasses are plenty shade, no need for goggles or shields.  Dripping flux is hot.   

[P.W.Berkuta]

Hemo, If you are interested in obtaining a rod or two of silver braze I have some that I will sell. I have 1/16" X 18" fluxed EutecRod & 3/32" X 18" fluxed EutecRod- melts about 1150 deg and flows about 1225 deg. Depending on the thickness of your work the 1/16" rod will work OK with the propane hardware torch but the thicker rod would do better with two propane torches or Mapp gas or a hotter heat source. This stuff goes for $832 per pound at the moment - not cheap stuff. I like the 1/16" plain rod and add the flux as I need it. I will also be advertising this stuff on the "for sale board" soon.

QTY 1-- 1/16" X 18" fluxed EutecRod = $20.00
QTY 1-- 3/32" X 18" fluxed EutecRod = $30.00

[Dave B]

I have seen a technique used to assemble Jaeger but plates of two pieces. They used what look like little bow ties of brass. Maybe they used an extrusion  through a draw plate to make them but the one I saw had two of hem holding the return that was chiseled to the plate that was not. They were soldered with some kind of silver braze to complete the joint. not far off from what it is you need done.

[flehto]

I've repaired cracks w/ what I call hi-temp silver solder and a white flux paste. It comes in 1/16 dia wire and .005 sheet. Depending on the job, both of these forms have done a good job. The sheets are for attaching carbide inserts into what  then becomes a lathe tool bit, but is handy for many jobs where a thin joint is needed.

The color of the silver solder isn't a perfect match to yellow brass, but is close enough so that it doesn't  "stand out". Have done some attaching butt jobs on both brass and steel and the joints were very strong. This type of silver solder melts approx. at. 1000-1100 degrees. .....Fred




  

[Hemo]

Thanks to all for your input. I ordered a small quantity of silver braze and flux online--I'll test it out on a bit of the casting sprue and see how it goes.

Gregg

[Mark Elliott]

I use brass colored silver solder that I purchase from Rio Grande to repair brass.   

[jerrywh]

 If the butt plate is sound otherwise as you say and peening doesn't do the trick I would put a brass inlay in the crack and extend it past the and of the crack.   This is a lot easier than brazing and is simple to do. Acer can tell you how. I am too busy now to do a tutorial on it.  If it cracks later you can braze it with silvaloy 45.   It melts at about 1200° and is brass colored. Elliott knows.  
  If you put the inlay across the crack at right angle it will help hold the plate from cracking anymore. Annealed sheet brass will work.

[Dphariss]

I use brass colored silver solder that I purchase from Rio Grande to repair brass.   

Ditto..
Fastest, easiest, best fix.
Would not bother with anything else.

Dan

[E.vonAschwege]

Thanks to all for your input. I ordered a small quantity of silver braze and flux online--I'll test it out on a bit of the casting sprue and see how it goes.

Gregg

If you've never used it before, remember that the braze will melt before it "flows".  If you can, heat the part from below or from the side, bringing the plate up to the point where the chunks of braze will flow into the crack.  With brazing, the quicker you can bring the piece up to heat the better.  I've used this method many times to repair cracks, mis-drilled holes, voids, etc.  It's incredibly useful, far more than soft solder IMO.  Good luck!
-Eric