Problem peening bolster pins

Erin Burke

Erin Burke

KnifeMaker...ish
Joined
May 19, 2003
Messages
1,330
I am trying to peen some bolster pins on this afternoon and am running into some difficulty. I am peening 416ss bolsters to my knife using 416ss 1/8" pins. Holes in the bolsters are 1/8" and were tapered using a 2/0 taper reamer. I seated the bolsters with a thin layer of acraglas epoxy to provide some level of waterproofing. The pins were cut 1/8" longer than they needed to be and they were beveled slightly on the ends. So I put the bolsters w/ wet epoxy on the blade, inserted the pins so an equal length of pin sticks out both sides, and began peening with a small 8oz ball-peen hammer. Everything looks like it's working great until I notice that a gaps are forming between the bolsters and the blade. :confused: So I use some needle-nose pliers (wrapped in electrician's tapes so as not to damage the bolsters) to clamp the bolsters back tight against the blade. Again, everything looks good. However, as soon as I start peening again, the gaps appear between the bolsters and the blade again. I remember somebody saying that the holes through the blade should be chamfered (countersunk) slightly to avoid this very issue, and I did that. So what is going wrong? Has anyone else experienced this? This is my first set of peened bolsters, so there is very-likely something I am missing. Thanks in advance for any help.

Erin
 
I'm just guessing but it maybe that your holes in the blade and bolsters aren't drilled perfectly parallel to each other. Maybe the bolster hole is at a somewhat angle to the hole drilled in the blade. It maybe minute, but enough to cause you a headache.
Also how many pins? I started using 3 instead of 2 it helped put pressure in more spots on the bolster helping to really mate the blade and bolster tight.
 
Erin,
The problem is the epoxy you have between the bolsters and blade. When you hit , the epoxy is being forced out leaving a gap.
Either put the bolsters on without the exopy, or use a pin press that will provide smooth even pressure to set the pins.
Thanks,
Del
 
Once I get the pins started to swell, I go to a BIG hammer and whomp the hell outta the pins. Closes those gaps up real quick.
Leave out the accraglass, After you are finshed cleaning up the pins and bolsters, run some runny superglue around the perimeter of the blosters. What seeps in any crevises will act as a sealant. The rest just wipe off.
 
I had something like this happen once... This probably isn't a "pro" solution, but every time I saw a gap start to form, I took the knife to my arbor press and squished everything back together (sorry for the technical mumbo-jumbo). I probably did this four or five times before the pins took over. I've only done a handful of knives with bolsters, but that was the only time it happened.
 
The pins swell all the way down their length. If the holes through the tang are too close of a fit, the metal swells there and lifts the bolster up a bit. It takes a lot of pounding to correct, and sometimes never gets flush. Drill the tang holes at least 10% larger than the pins. This should eliminate the lifting problem.
If using a resin to seal the joint, I would recommend dry setting the bolsters, and using super thin CA after the pins are set. Flow it in from all sides, and let it wick in. let it sit for a day before clean-up and grinding.

Stacy
 
I use a vise-grip clamped on as close as possible to the pin and expect to do some sanding and polishing when done peening the pin.
 
I use birdog's method , a bigger hammer . Also , the countersink in the tang provides a place for the pin to swell internally without lifting the bolster .
 
Sounds like, per Stacy and Jack, that I should be oversizing my tang hole slightly and using a bit more cointersink to allow more room for the pins to expand without lifting the bolsters. Seems that almost everyone agrees that epoxy before peening was a bad idea. Quite a few responses to bash the hell out of the pins. Looks like I have some ideas for next time. Thanks all.

Erin
 
I use a very light hammer with a head weight of 2 oz for steel and 1.5 for brass. Lot's of light taps. I first create a "pyramid" shape with four sides and then do the top flat which rounds out the "pyramid". I use very expensive hammers made of hardended steel and a small anvil that weighs about 10 pounds. Pin steel does not even ding the faces of the hammers.
 
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Erin Burke said:
Sounds like, per Stacy and Jack, that I should be oversizing my tang hole slightly and using a bit more cointersink to allow more room for the pins to expand without lifting the bolsters. Seems that almost everyone agrees that epoxy before peening was a bad idea. Quite a few responses to bash the hell out of the pins. Looks like I have some ideas for next time. Thanks all.

Erin
Click to expand...

Erin , I use epoxy also and will continue to do so even though it is a little messier . I just like the added waterproofing and holding security . It is just me .
 
I just finished peening my first bolsters this morning, and I approached it with the following theory:

-Lighter hammer blows should swell the ends of the pins, while heavier blows should swell deeper into the pins. Therefore, I started with light blows, swelling the heads into the countersinks, which in turn (in my mind!) pulled the bolsters down to the tang. Once I had them snugged to the tang, then I increased the force of my blows thereby (hopefully!) swelling the pins the rest of the way.

I don't know if this was the correct way to approach it or if my theories are correct, but it seemed to work well and I had no problems with the bolsters lifting off the tang.
 
There's an old rule of thumb on how much pin should be left to peen. This is such an old rule of thumb I can't remember it its half the diameter of the pin or a third you want to stick out beyond the hole. Starting out with much more material than what you need can cause as many problems as not enough. I discovered after the first couple years of knife making not to do knives that required pins.
 
The heigth of the protruding pin is the diameter of the pin. IF using a common countersink, at a reasonable depth. The edges of the pin should be rounded to minimize cracking, and they should be annealed on the ends were you will be peening.
 
P J 234 said:
-Lighter hammer blows should swell the ends of the pins, while heavier blows should swell deeper into the pins. Therefore, I started with light blows, swelling the heads into the countersinks, which in turn (in my mind!) pulled the bolsters down to the tang. Once I had them snugged to the tang, then I increased the force of my blows thereby (hopefully!) swelling the pins the rest of the way.

I don't know if this was the correct way to approach it or if my theories are correct, but it seemed to work well and I had no problems with the bolsters lifting off the tang.
Click to expand...

This similar to the rivet setting method that I was taught by gentleman who used to repair/recreate historical armor for a museum. Though he talked about making glancing or angled blows to mushroom the head without widening the post and sharp, square blows to set the post (widen the shaft) without mushrooming the head .
 
Here is something that I posted a few years ago. It is not quite as detailed as it should be, but it may help.

Robert
 
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