Coleman lantern and stove leather pump mold

This is the 15th (and final) version after a LOT of tweaks.  I got sick of paying way too much for the Coleman leather pump cups for my lanterns and stoves (if I was even able to find them).  The neoprene ones are horrible and always fail at the worst moment.  Leather pumps are also VASTLY superior in cold weather so if you do winter camping leather is your friend.

Tools required: 7mm leather hole punch, c-clamp or vise

Materials required: 0.5mm-1mm tooling leather, PETG

Print with at LEAST 6 walls and 100% infill.  You do NOT want any voids in the parts.  PETG is best as it allows some flex and doesn't seem to cause any issues with the wet leather (PLA often stains it or sticks to it).  You want solid chunks of plastic for this thing to work best.  Unless you are making many at once you will generally be fine with printing a single base.  Print off as many molds and dies as you need.

This design uses two parts to make the pump cup:  The mold and the die.  The base serves two functions: 1. To give you a stable base to use a 7mm hole punch without worrying about damaging the surface you are on (ie a countertop).  2. Flip it over and use the same punch in the same hole you just made to pop the pump cup and die out of the mold. 

The mold and base should last you a very, VERY, long time but you might find that the dies wear out after a few uses.  This little tool is designed to use 0.5-1mm tooling leather.  I've even used leather from an old coat.  The main thing is that you do NOT want to go any thicker than 1mm (VERY important as the cups will NOT fit in the lantern fount).  Cut the leather into a 35-40mm square and soak in water for a few hours (very important).  Once fully saturated pull and twist it a bit to loosen up the fibers and help soften the leather.  The leather needs to be flexible.  While still damp, but not dripping wet, center the leather on top of the mold and place the die on top of it over the indentation in the mold.  Now you need to press the die into the mold.  This will do two things: Stretch the leather slightly, form the shape.  Water WILL ooze out so have a towel handy.  This is expected.

You can press it in many ways but I find a c-clamp or bench vise to be easiest.  Typically I will start pressing the die into the mold using channel lock pliers and once it's in a good way I switch to the c-clamp (my preferred method).  This is where you need to be able to REALLY crank down on it SLOWLY to press the die in all the way.  It should fully bottom out but the top of the die should be very slightly proud of the surface of the mold (due to the thickness of the leather).  This is by design.  Do not press so hard that you start to bend the print though.  Once it bottoms out you're good.

Now, leave it with the clamp in place and let it dry for at least 8 hours (this is why I prefer c-clamps) as this will fully set the shape.  Leaving to dry for longer is better though.  Once dry use a sharp blade (I use #11 xacto blades) and trim off the excess leather flush with the top of the mold.  This is where the slight bit of height in the die comes in handy.  You can cut against the die to get a clean edge.  Be VERY CAREFUL when you cut!!!!!!!  You want to cut only the leather, not yourself. 

Once you have cut the extra leather away you need to punch the hole.  A 7mm leather punch is best but 8mm will work too.  The hole in the die is sized just a bit larger than 9mm to fit the punches I have on hand.  If needed, sharpen it first as this will give you a much cleaner hole.  Now get the base you printed off and turn it upside down so that the flat side is facing up.  Place the mold and die upside down on top of the base.  The hole in the bottom of the mold will be facing up.  Put the 7mm punch into the hole and tap with a hammer just enough to cut through the leather.  Don't go crazy here...it's just leather, not your high-school bully.  Once you have the hole punched out lift the mold off but don't turn it over.  Turn the base over and put the mold back inside it.  The die should be in the indent in the bottom of the base.  Now, use the same punch you used and gently tap it with a hammer again just enough to knock the die loose from the mold.  The pump cup may stick in the mold.  I usually use a toothpick or something similar to peel the edges away from the sides of the mold.  Don't use metal as you do not want to tear or mark up the surface of the leather.  That's where it forms the seal when you pump your lantern.

Leave the formed leather cup to dry for a few hours more before oiling and installing.  I usually will make 4 or 5 cups at a time and soak them overnight in neetsfoot oil.  You can also install directly on the pump rod and then soak in oil.  I just find that way a bit too slippery when installing.  The first time you insert the leather into the lantern fount it might be a bit of a tight fit but go slowly and use care.  I use the same toothpicks to carefully work the edges of the leather all the way into the pump tube and once it's in it should slide the rest of the way easily.  Add a drop or 2 of oil into the pump tube and move the pump up and down quickly 8-10 times, but do not cover the pump hole.  You aren't pumping the fount yet, just setting the leather in the tube.

Now you're done.  Pump that lantern or stove up and get out into the woods.