The Complete Online Guide to Knifemaking, BOLSTERS
The Complete Online Guide to Knifemaking BOLSTERS
Bolsters can enhance many knife designs. They can be as elaborate or as simple as the designer wishes. Brass is commonly used and is available in convenient 1⁄4 x 1-inch bar stock. Bolster holes should be pre-drilled through the knife blank prior to heat treating. Two pieces of the brass are then cut to length. Clamp one piece to the knife blank and carefully mark the location holes by partially drilling through each of the pre-drilled bolster holes in the blank. The object is not to drill all the way through the 1⁄4-inch brass but just deep enough to mark the location of each hole on the bolster. Now, take both bolster halves and place them into a drill press vise. The piece with the hole location marks should be on top. We commonly use 1/8-inch pins for our bolsters. Take a #30 drill bit (.1285 for clearance hole) and with a drill press carefully drill through both bolsters while they are clamped together. If done correctly, the stock square side edges of each brass bolster will be perfectly aligned by the vise and the holes square to the drill press table. Next, test the assembly of the bolsters on the blade with pins. The unglued assembly can be placed into a bench vise. Excess material can be ground off the bolsters with an angle grinder and flap sanding wheel or the 2x72 grinder. Do not grind down to finished dimensions. At this time you are just removing bulk and leaving the final grinding until after the bolsters are secured in place. Both bolsters can be removed from the knife blank and then clamped back together with pins in place for alignment. The front edge of the bolsters can now be rounded or carved as desired. After this front edge is carved to shape, usually with a contact wheel on a belt grinder the front edge should also be sanded with fine grit and polished. It's much easier to polish this edge before its mounted to the knife. Now, rough up the bottom surface of each bolster with sandpaper. This is the side that will be in contact with the knife. It’s recommended to peen brass bolster pins in place. Although not mandatory, peened pins do make for a stronger mechanical bond. If you are going to peen the pins take a tapered reamer and ream each hole from the outside in. You want to end up with the larger side of the taper facing out and the smaller end of each hole taper facing the blade. This way once the pin swells from the hammer peening it will fill the tapered space and wedge the bolster in place. After the pin holes are reamed, clean all surfaces with alcohol to degrease them and add a little two-part epoxy to the blank and contact sides of the bolster. Both can be assembled now with brass pins. Leave the pins a little long and clamp the bolsters together. Take a careful look at the front and back edge of the bolster and clean up any epoxy that gets squeezed out onto the blade. A paper towel and an alcohol wipe works well for this. Both sides of each pin can be hammered. It's better to lightly tap each pin then turn the blade over and start again on the other side. Keep hammering and rotating until the pins are completely smashed flat and the void created from the tapered ream filled. If the pins are peened correctly once the bolsters are sanded and polished, you should hardly be able to see the pins at all. Note that at no time did we ever grind the back edge of the bolsters. The straight square back edge is the factory edge of the 1/4 x 1 brass rod. This is important because now as long as the scale material is cut square, we will get a perfect fit between the scales and bolsters.
If a disc grinder with adjustable work table is available, the back edge of the bolster can be ground flat or at a 45-degree angle to create dovetail bolsters. Disc grinders have sandpaper mounted directly to a flat plate. They are ideal for grinding nice flat surfaces. When creating dovetail bolsters the scale material also has to be ground with a matching angle.
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