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lampy · Veteran Member

I have made a few leather piston seals over the years and this is the process I use.
I found a ready supply of leather at the local Farm and Home store, they probably have these at the big box hardware stores also. They are good quality and the leather is just the right thickness, about 1/8 inch. I can get three or four seals from this $10 tape measure holster.

I turn my seal form (mold) out of aluminum, I turn the recess to match the OD of the seal I need. For the size of the plug that forms the inside of the seal I subtract twice the thickness of the leather from the OD. It doesn't need to be exact, the leather is very forgiving. It just needs to be close. You don't have to have a lathe to make a form, a good chunk of wood a spade or forstner bit for a flat bottom hole and the right sized socket from your tool box will work.

I cut a piece of leather large enough for the seal, soften it up in some warm water. once it is nice and pliable I add some neatsfoot compound or Mink oil to the leather.

Posistion the leather (rough side out) between the two halves of the form and press them together with a C clamp.

Trim some of the excess leather away and use a flat tip screw driver to force the leather down along edges of the form. I found doing this gives a more flat bottom to the seal, other wise it comes out with a round bottom. Like this...

Mine don't come out perfectly formed and do have rounded bottoms but once it is installed and shot a few times it will take on the shape of the compression tube and have nice square corners.

Once I have pressed the sides down and forced as much leather into the form as I can, I trim the leather flush with the top of the form. I let it sit over night (with the C clamp holding the form tight) to give the leather a chance to dry out so it will hold its shape when it's removed from the form.

My form has a hole drilled in the center and I use this to drill a hole through the seal for mounting. If you are using a wood form there should be a dimple centered on the seal from the pilot on the drill bit.
With the seal mounted on the piston and just before I insert it into the compression tube I add more Neatsfoot compound to the seal.

Easy peazy Lemon squeezy Smile

you have a new leather seal.

Slavia · Moderator

Thanks, lampy. That was great.

twalter · Veteran Member

How do you stop that leather seal from peeling back?

Also, how much would you charge to make a seal press for others? Wink

lampy · Veteran Member

I'm not sure what you mean by peeling back?
I only build stuff for my self, any machine shop should be able to build what you need.

twalter · Veteran Member

lampy · Veteran Member

There isn't enough room between the piston and the compression chamber for the seal to peel back. The pressure pushes the seal outward against compression chamber making it seal better.