Peening bolsters - How to keep them from pulling away from the tang?

M

Maelstrom78

Joined
Sep 21, 2013
Messages
1,574
Just took off a brass bolster right before the point of locking in a bad peening job. I usually peen scales before the epoxy cures and haven't had a problem with micarta.

A previous stainless steel bolster went fine. This time the bolsters kept pulling away from the tang. How do you guys avoid that? Thanks!
 
Make sure you surfaces are as flat as possible, taper your holes(away from the blade), and pien lightly....
 
I did taper with a 2 degree reamer. I suspect that I had the pins too long though. Might that cause a problem?

I was rushing though, that likely didn't help. Thanks h20oni though. I thought maybe people clamped, or let the epoxy cure first or something.
 
If you peen too hard, you will bend the bolster up around the edges.
 
In the future, always countersink the holes through the tang. That gives any metal that gets upset (thickened by hammering) in that area a place to go. Works for me.
 
Maelstrom, I had this problem a couple of times and I solved it by using some very small vise grip pliers (maybe 4 inches long that I got from Harbor freight...very cheaply made but they work) on the top and bottom of the bolsters holding them tight to the blade until I got the pins smacked enough to draw the bolsters down to the blade. Yes , they pop off frequently but a minute worth of repositioning and hitting the pins again works for me every time. If the pins are too long then I hit one side to make the other side stick out more and use a Dremel fiberglass reinforced cutting wheel to cut a 1/16th or an 1/8 " off the pin and go back to smacking them with your ball peen hammer. And as previously mentioned by elementfe chamfer you knife tang holes before mounting. I always drill my tang holes with an oversize drill so the pins go through the tang with no resistance. ( Don't drill oversize holes in the bolsters though) Use a #30 drill for 1/8th inch tang holes, a # 21 drill for 5/32 holes, and #12 drill for 3/16 pins. I also use a letter F drill for drilling tang holes for scales that are held by 1/4 pins. You may need to do all these things to get tight fitting bolsters. Works for me. Larry
 
The problem is almost always caused by the pins being the same size as the hole in the tang. They need to be a snug fit on the bolsters, but should have some slop through the tang.

Why the bolsters rise up is;
As you peen the pins, they are compressed down their length between the hammer and the anvil. This causes them to swell in diameter. This is the desired effect at the chamfered hole on the bolsters, but not what you want at the tang. If the fit is tight at the tang as well as the bolster, the pin will try and squish out in the minute gap between the two. This is a very powerful force, akin to hydraulic pressure. Even firm clamping may not be enough to prevent the bolsters from raising up a little. As most makers have learned. no amount of hammer bashing will make it go down flat again.

The solution is to have a place for that expansion to go. Drill the tang hole with at least 5% extra room. For a .1250" pin that would be a .131" hole. This will eliminate the raised bolsters.
Also, gentle peening to expand only the ends of the pins, not hard pounding, will greatly reduce the chance of a lifted bolster.
 
OK I've got carbide bits I'll use to chamfer the tang holes a bit, will keep the pin length sticking out 2x diameter of the pins on a side and peen gently.

I think I was trying to bash it too hard as well to try to get the pins to blend into the bolster material. I believe I read that cleanliness of the materials is more important maybe than smashing the pins.
 
Last edited:
If chamfering the holes make sure you chamfer both the tang and the inner bolster holes.
The amount of pin sticking out needs to be approx. 1/2 to 1 diameter. Cut the pin the knife thickness with the bolsters plus two diameters for a pretty simple method of figuring length. That will place about one diameter on each side. As I get the pin flared evenly on both sides, I file it down to just above the surface and do the final peening. A few file strokes cleans it up nicely.
 
I never thought to chamfer the inside of the bolsters as well but it makes perfect sense now that Stacy said it. Thanks for the advice.
 
Last edited:
You must log in or register to reply here.
Back
Top