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- Jun 5, 2012
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This is my first post here. I used to do leatherwork as a hobby when I was younger, but just started again a couple months ago, and have been using vacuum molding this time around. I'm getting it dialed in enough that I thought I'd share. I'm primarily a knifemaker. Most of the sheaths I make are for my own knives, although I have done a couple commissions.
I don't claim to be an expert leatherworker, far from it. I think I do get reasonable results, and the customers seem very happy.
I've switched over almost exclusively to vacuum molding for my sheaths. Now that I have it dialed, the fit is amazing. The retention is good enough that in most cases I can hold the sheath upside down and shake it hard without the knife moving, yet the knife goes in and out smoothly and easily.
I also prefer vacuum molding because you don't have to fool with the leather very much, so it preserves the natural grain much better than hand molding IMO.
First I start by wrapping the knife in tape to protect it (this needs to be removed IMMEDIATELY after molding, or you may forget and have trouble brewing). I affix it to a few thicknesses of cardboard using the butyl rubber seen at bottom. This is also used to seal the vacuum bags.
Why cardboard? You want something stiff, but not too strong. Vacuum can apply a good deal of force, and if the knife was being molded on a piece of steel, for example, it's conceivable you could damage the knife. Plus, the knife sinks in a tiny bit, which adds some pre-load so it has a snug fit once the sheath is assembled.
I make spacers out of wood to make sure the mold allows clean entry/exit for the guard and blade. I also put a spacer under the blade so it has a bit of extra room (some of which will disappear).
Next I cut an appropriate sized piece of leather. This is not a good place to try and cut it close. You don't want the piece to be huge, either, as it will be harder for the leather to move.
I heat some water to almost boiling, then let it cool for a bit. You want the water to be nice and hot, but a good bit below boiling. Pre-soak the leather for a couple minutes before this in room temp water, to give it a head start.
You want to soak the leather in the not-boiling water until it starts to curl a bit and starts to have a soft, flexible, almost slimy feel to it. If you see the color change on the edges you were too hot, or too long. Pat dry with paper towels.
Sometimes it helps to curl the edges up, this gives you a better "corner" where the mold goes flat. You want to gently mold the leather to get it started. Don't go poking it with your fingers a bunch though.
After that, I apply a layer of soft foam to distribute the force of the vacuum bag, this prevents wrinkles and overmolded areas. I add a couple strips of tape on the edges to hold everything in place. You don't want the tape to go all the way across the foam, or else it won't stretch right.
This is what a very basic vacuum setup looks like. This is two Ziploc freezer bags taped together, using butyl to seal each end, and the hose. I'm using a basic refrigeration vacuum pump.
I taped a small piece of fabric over the hose end so it doesn't suck in the bag and rip it. It's okay to have some small leaks... you don't really need to pull a hard vacuum on this.
You can help it out a bit when first pulling the vacuum, holding the leather in place and pressing gently around the knife to help it mold better.
You want to leave the knife under vac until you feel that it doesn't have anywhere else to mold to, and you see the leather start to change color just a bit, this means it has started to evacuate the excess moisture. This shouldn't take forever, a few minutes, sometimes a bit longer.
If you're lucky, you'll get something like this (I still don't get it perfect every time). I normally like to use a couple layers of finer cardboard on top so not to get the lines as seen on this one, but they don't really hurt in the end.
Let dry until fully returned to original color.
secret trick: Using some gentle heat to accelerate the drying hardens the leather, which will help it keep the form of the knife, and keep good retention for longer. Just be careful. If you dry too fast you will make it brittle. super secret trick: If you use a heat gun on low to give the area around the guard a head start, it will be a bit harder there, which will help with retention of, um, retention.
Ok, so skipped a couple steps here, but nothing that probably needs to be shown. Basically I trimmed the molded piece about 1/2" around the whole edge, and dyed it black.
Then I cut another piece and dyed it black for the back piece, plus a thinner black leather liner piece that I skived down to zero taper and glued to the back.
Next I glued the pieces together with contact adhesive, and after the adhesive was fully dry, I trimmed with a knife.
The back.
The sander is my favorite way to trim and even the edges, but you have to get the hang of it to get a good result. Make sure to use proper grits and speeds, you don't want to burn the leather. You should get a nice clean look as in this photo.
After dying the edges. If you burn the leather when sanding, then you will get uneven dye absorption. This can be somewhat mitigated by using edge paint instead of dye.
Next I cut the stitch groove. This sheath is a bit oddball, as it is black with brown stitching, which normally does not show up well. Because of that, I waited to cut the stitch groove until after dying.
After rolling out with a stitch marker, I drill the holes using a 1/16" drill, which I find works perfect for standard waxed threads and 16ga needles. Some people prefer not to drill, but it seems to work well for me. It is a personal preference thing, if the piece is designed and constructed well, it doesn't seem to matter that much.
Hidden step: Sealing the leather, I used Satin-Shene. You can see that it darkened the stitch grooves a bit, which is a good thing in this case.
I taped the back piece/belt loop in place, it can be seen in the next photo.
I match drill the holes, using a needle to keep indexed when moving to each new set. Remove the tape ASAP. It's ok to use it real quick to hold something in place, but you definitely don't want to use it on finished leather.
Here I've started stitching the sheath. I use a saddle stitch. I fill in all of the areas that the back piece is not stitched. That allows it to be easily removable if necessary for change/replacement.
Here's what it looks like finished. The lighting is terrible, sorry. It looks much nicer in person. The brown stitching actually shows fairly well in natural lighting. As you can tell, I added a second row of stitching at the top, just in case.
You can see the stitching on the back of the belt piece, since I did it separately, I didn't have to run off the edges, so it is a cleaner look. The hole in the middle allows you to thread the sheath through a belt loop, so it doesn't slide around.
I don't claim to be an expert leatherworker, far from it. I think I do get reasonable results, and the customers seem very happy.
I've switched over almost exclusively to vacuum molding for my sheaths. Now that I have it dialed, the fit is amazing. The retention is good enough that in most cases I can hold the sheath upside down and shake it hard without the knife moving, yet the knife goes in and out smoothly and easily.
I also prefer vacuum molding because you don't have to fool with the leather very much, so it preserves the natural grain much better than hand molding IMO.
First I start by wrapping the knife in tape to protect it (this needs to be removed IMMEDIATELY after molding, or you may forget and have trouble brewing). I affix it to a few thicknesses of cardboard using the butyl rubber seen at bottom. This is also used to seal the vacuum bags.
Why cardboard? You want something stiff, but not too strong. Vacuum can apply a good deal of force, and if the knife was being molded on a piece of steel, for example, it's conceivable you could damage the knife. Plus, the knife sinks in a tiny bit, which adds some pre-load so it has a snug fit once the sheath is assembled.
I make spacers out of wood to make sure the mold allows clean entry/exit for the guard and blade. I also put a spacer under the blade so it has a bit of extra room (some of which will disappear).
Next I cut an appropriate sized piece of leather. This is not a good place to try and cut it close. You don't want the piece to be huge, either, as it will be harder for the leather to move.
I heat some water to almost boiling, then let it cool for a bit. You want the water to be nice and hot, but a good bit below boiling. Pre-soak the leather for a couple minutes before this in room temp water, to give it a head start.
You want to soak the leather in the not-boiling water until it starts to curl a bit and starts to have a soft, flexible, almost slimy feel to it. If you see the color change on the edges you were too hot, or too long. Pat dry with paper towels.
Sometimes it helps to curl the edges up, this gives you a better "corner" where the mold goes flat. You want to gently mold the leather to get it started. Don't go poking it with your fingers a bunch though.
After that, I apply a layer of soft foam to distribute the force of the vacuum bag, this prevents wrinkles and overmolded areas. I add a couple strips of tape on the edges to hold everything in place. You don't want the tape to go all the way across the foam, or else it won't stretch right.
This is what a very basic vacuum setup looks like. This is two Ziploc freezer bags taped together, using butyl to seal each end, and the hose. I'm using a basic refrigeration vacuum pump.
I taped a small piece of fabric over the hose end so it doesn't suck in the bag and rip it. It's okay to have some small leaks... you don't really need to pull a hard vacuum on this.
You can help it out a bit when first pulling the vacuum, holding the leather in place and pressing gently around the knife to help it mold better.
You want to leave the knife under vac until you feel that it doesn't have anywhere else to mold to, and you see the leather start to change color just a bit, this means it has started to evacuate the excess moisture. This shouldn't take forever, a few minutes, sometimes a bit longer.
If you're lucky, you'll get something like this (I still don't get it perfect every time). I normally like to use a couple layers of finer cardboard on top so not to get the lines as seen on this one, but they don't really hurt in the end.
Let dry until fully returned to original color.
secret trick: Using some gentle heat to accelerate the drying hardens the leather, which will help it keep the form of the knife, and keep good retention for longer. Just be careful. If you dry too fast you will make it brittle. super secret trick: If you use a heat gun on low to give the area around the guard a head start, it will be a bit harder there, which will help with retention of, um, retention.
Ok, so skipped a couple steps here, but nothing that probably needs to be shown. Basically I trimmed the molded piece about 1/2" around the whole edge, and dyed it black.
Then I cut another piece and dyed it black for the back piece, plus a thinner black leather liner piece that I skived down to zero taper and glued to the back.
Next I glued the pieces together with contact adhesive, and after the adhesive was fully dry, I trimmed with a knife.
The back.
The sander is my favorite way to trim and even the edges, but you have to get the hang of it to get a good result. Make sure to use proper grits and speeds, you don't want to burn the leather. You should get a nice clean look as in this photo.
After dying the edges. If you burn the leather when sanding, then you will get uneven dye absorption. This can be somewhat mitigated by using edge paint instead of dye.
Next I cut the stitch groove. This sheath is a bit oddball, as it is black with brown stitching, which normally does not show up well. Because of that, I waited to cut the stitch groove until after dying.
After rolling out with a stitch marker, I drill the holes using a 1/16" drill, which I find works perfect for standard waxed threads and 16ga needles. Some people prefer not to drill, but it seems to work well for me. It is a personal preference thing, if the piece is designed and constructed well, it doesn't seem to matter that much.
Hidden step: Sealing the leather, I used Satin-Shene. You can see that it darkened the stitch grooves a bit, which is a good thing in this case.
I taped the back piece/belt loop in place, it can be seen in the next photo.
I match drill the holes, using a needle to keep indexed when moving to each new set. Remove the tape ASAP. It's ok to use it real quick to hold something in place, but you definitely don't want to use it on finished leather.
Here I've started stitching the sheath. I use a saddle stitch. I fill in all of the areas that the back piece is not stitched. That allows it to be easily removable if necessary for change/replacement.
Here's what it looks like finished. The lighting is terrible, sorry. It looks much nicer in person. The brown stitching actually shows fairly well in natural lighting. As you can tell, I added a second row of stitching at the top, just in case.
You can see the stitching on the back of the belt piece, since I did it separately, I didn't have to run off the edges, so it is a cleaner look. The hole in the middle allows you to thread the sheath through a belt loop, so it doesn't slide around.
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