Here is a write-up for a process I demonstrated at the SBA:
Forged and Hot Fitted Knife Bolsters/Guards
It is a curse to be an impatient bladesmith. There are so many little processes in knifemaking that give a whole new meaning to tedium. One such process has been emphasized more and more in modern times, and that is guard fitting. The main purpose of bolsters and guards is to act as a surface for the handle material to rest against, giving the handle material extra support. Another function is to protect your hand from accidentally slipping onto the blade.. The accuracy of a guard fit has become an important part of bladesmithing because it makes the knife look neater overall, and having a tight seal around the blade keeps dirt and debris from getting in and causing rust. Using solder or JB Weld to close the gap is a good method, but not always the cleanest looking. It is best to get the fit as close as possible.
The usual way to make a guard that fits a knife is to drill a series of holes that are slightly undersized, then file out the rest of the way until the guard fits. I have done that plenty of times, and the first time is just as tedious and hand-cramping as the last. Another way is to mill an oversize slot most of the way through and the last bit is filed and fitted. I made it my mission to find a way to fit a guard so that I would never have to touch a needle file again. Punching and drifting in the blacksmithing realm is preferred over drilling because you have less loss of material, and on top of that you can make the shape of the hole as complex as the punch. I have figured out a simple way to create a precision fit with thick stock without intense filing.
The process begins with making a punch. This process is all about the punch. You can forge it out of spring steel, or any other high alloy steel you like. You need a punch that matches the width of the tang, but it needs to be thicker than the tang by a small amount. It needs to be slightly tapered to release the punch. For knives with plunge lines or a ricasso, a rectangular punch with rounded corners works well. For knives like puukko and historical seax knives that do not have a plunge line, you will need to make a triangular punch. This is because the shoulder at the spine is full thickness, and the shoulder at the edge is almost ground down to an edge.
It is crucial to make sure that the tang of the blade is tapered. Most of my guards are hot drifted onto the shoulders of the blade, so I make the thickest part of the blade just past the shoulders. If the tang is not tapered, the guard fit will only be as close as the thickest part of the tang. All the corners of the tang should be chamfered, too.
For metals that are easily worked hot like steel or copper, I like to punch a hole through hot. For metals that are trickier like brass or aluminum, I drill holes that remove most of the material that is in the way of the punch, then I drive the punch right through to break away the “web” between the holes.
Now at this point, the guard can slide up all the way to the shoulders, and there is still a considerable gap on each side. We can remedy this situation by inserting the punch almost all the way through the bolster, leaving about a 1/8” or smaller gap. This leaves an area of the guard that is not supported by the punch, so with the punch in, focus hammer blows at a slight angle over the unsupported area so that it deforms, and hammer evenly on both sides. I have found that it is harder to deform the areas closer to the shoulders, so focus hammer blows there, preferably with the round side of a rounding hammer.
The face of the bolster should be smaller but not completely closed, and the punch should keep the rest of the bolster oversized to the tang. The face of the bolster can be ground down or left at its rough finish state if that’s the look you’re going for. At this point, you could break out the files and fit your guard, but I don’t have time for that.
Instead, I like to make the tapered tang do all the work. With the face of the guard slightly undersized, the very end of the tang can fit in, and I can hot or cold drift the bolster onto the knife. I do this with aluminum vise inserts and a piece of pipe used as a monkey tool. I set up the knife tang up in the vise with the aluminum inserts, leaving the shoulders higher than the jaws because it will get pushed down no matter how tight you make the vise. In the case of steel or stainless, I heat up the bolster to bright yellow, transfer to the knife, making sure it is in the right orientation, slide the monkey tool on, and get to hammering. In the first heat, I drift up to the shoulders, and in the second heat I drift onto the shoulders to make an impression in the bolster. For more malleable materials it can be done in one go. When hot fitting, getting the blade too hot is always a concern. I usually hot fit my guards before heat treating, but I have noticed that the temper colors don’t extend too far, probably because the aluminum acts as a heat sink. I could feasibly get the knife heat treated and finish ground, then hot fit the knife and be done with it. The aluminum will leave a couple marks, but no intense refinishing needed.
When it comes to finishing these the order of processes can be rather tricky. If the knife is rough ground when the bolster is fitted, there will be gaps when it is finish ground. These gaps can be closed by squeezing in a vise with the knife in it, or in extreme cases re-inserting the punch, closing the gap further, and then refitting. Sometimes the guard is hard to fit back on the knife, so padding the vise jaws
and the back of the bolster with leather will keep it from marring. There are also tools that allow you to slowly press fit the guard that use threads and nuts, much like a vise in reverse, and it doesn’t touch the blade at all. There are still a lot of things I have not tried out with this process, and I’m looking forward to seeing how others modify this process.