I spent a lot of time trying to find a good source for leather. Forget about calling leather suppliers, they think leather is worth more than gold. A good inexpensive source is Amazon or your nearby welding supplier where you can pick up a leather welding apron. Like this one: https://www.amazon.com/Safety-Shop-Protective-Blacksmith-Improvement/dp/B07NZVFDKD/ The aprons are roughly 1mm thick, can be cut with scissors, and make good piston seals with soft and flexible edges. One apron will make all the seals you need with plenty left over. The next thing you need to do is make the seal forming tools. Those are just a set dies. A small one can be made from some 1/2” PVC trim board, a piece of the pipe the seal is to fit, a threaded rod the same size as your piston rod, some nuts and flat washers You’ll need a forming disk (punch) that’s at least as thick as the raised lip at the edge of your finished seal, with a clearance between the pipe the same as your leather thickness. You need to be fairly accurate with the clearance, the leather needs to be compressed a little against the pipe wall. You can see I had to add a little diameter to the large punch with some blue masking tape. The large die set I made from a scrap piece of 2 x 8 treated lumber with a coat of poly. The pvc ring has a small radius sanded on the inner edge and the punch has one on the bottom edge. I used a 2mm radius on the small punch and a 6mm radius for the large one. You also need a way to push or pull the punch out of the seal. You’ll need an Exacto knife or sharp box knife for this next step. The leather should be cut the diameter of the cylinder it’s to fit + 2 times the height of the seal lip + about a 1/4” (6mm) extra. Before you begin cutting, punch or cut a hole in the center, the same size as the piston rod. Then center your outer diameter on that. Then you can cut your blank. To form the leather, soak it in hot tap water until it darkens all over on both sides. Rub the surface to remove all the tiny air bubbles that cling to it, then soak it some more. 10 minutes total will do. Push the wet leather onto the threaded rod followed by the punch disk, a flat washer and the hex nut. Tighten the nut snug enough to bottom the punch into the die and completely flatten the bottom of the leather. Take your knife and neatly trim the excess leather away while it’s still wet. Let each seal air dry for a day then pull the punch and carefully remove the leather. The next step is to melt your wax or paraffin by heating to F 200. That can take hours so be patient and allow plenty of time. Don’t go any hotter or you’ll cook the leather. Drop your seal into the hot wax for about 5 seconds, take it out until the wax ‘skins’ then put it back in until it turns a milk chocolate brown. That can take a minute or two but not longer. If the leather starts bubbling like a french fry in hot oil when you drop it in the wax, yank it out immediately or it will cook into a hard useless chunk of hide. After the seal cools, flex the raised edge between your fingers until it’s fairly flexible. You can see it turn a lighter brown as the wax coat fractures. That’s about all there is to it.
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Topic: Hydrostatic Displacement engine build (Read 660 times)
