Leather cup stitching problem!

[toxo]

1 hour ago, Frodo said:

You have 2 parts. The outside piece of leather and the inside piece of leather

4" circles circumference is 12.56"

so the back side of the outter piece is 12.56"

the front side of the inner piece is 12.56"

that's is assuming your bottom is fitting inside the top 

That is how I figured this jewelry box

i used my sewing machine with out thread to make the holes in both pieces  

glued the plug inside the outter piece  using bits of wire to align holes  while glue set up

then sewed it,  using an awl when needed 

 

Well done Frodo. That's similar to how I do some bags.

[Frodo]

There are 2 other ways I use to make a cup

turn that plug in the picture over.  See it from the outside 
 

and the other is to bend the cup side out at the bottom on a 90 degrees, then sew to a flat piece ,  this comes in handy if making a stein that needs a bigger bottom for stability

[dikman]

I'm guessing that Toxo is talking about making it like a toeplug in a holster, which is usually done by marking out the holes on the outer piece, scribing a guide line on the plug, gluing the plug in and then using an awl to punch the hole so it comes out on the guide line. The spacing on the plug is determined by where you punch the awl through. I think this is what chuck is talking about.

His method of drawing out the two circles is probably the only accurate way of doing it, if a little time consuming, but there's no margin for error if it doesn't line up exactly when you assemble it.

[TomE]

The math is analogous to the question in the post below - how to calculate the allowance for padding a collar - with the additional consideration of hole spacing that is proportional to the 2 circumferences.  That said, it will be a small difference and difficult to accurately mark on the 2 pieces. I'd use an awl.

 

 

[toxo]

I didn't give any thought to it initially. just punched the body and the bottom with the same punch and started thinking about it near the end when I had this bubble that I knew wasn't gonna go away. Chucks drawing is an easy way to see it. I still don't know if it would be better to lose a stitch or use a wider spacing for the bigger circumference.

[TomE]

7 hours ago, toxo said:

I didn't give any thought to it initially. just punched the body and the bottom with the same punch and started thinking about it near the end when I had this bubble that I knew wasn't gonna go away. Chucks drawing is an easy way to see it. I still don't know if it would be better to lose a stitch or use a wider spacing for the bigger circumference.

The diagram is easy to see but it's not easy to calculate stitch spacing from the angles shown.  I think it's easier to calculate the inner and outer circumferences then convert the spacing of the outer piece to that for the inner piece as the ratio of circumferences.  My point is you will end up with something like 6 and 5.5 stitches per inch for the 2 pieces and I don't know how to accurately mark 2 spacings with a small difference.  Won't have to do this with an awl.  Skipping a hole doesn't fix the spacing.

[toxo]

49 minutes ago, TomE said:

The diagram is easy to see but it's not easy to calculate stitch spacing from the angles shown.  I think it's easier to calculate the inner and outer circumferences then convert the spacing of the outer piece to that for the inner piece as the ratio of circumferences.  My point is you will end up with something like 6 and 5.5 stitches per inch for the 2 pieces and I don't know how to accurately mark 2 spacings with a small difference.  Won't have to do this with an awl.  Skipping a hole doesn't fix the spacing.

OK here is what I was trying to do in the first place. As I've said, I don't think skipping stitches is the proper way to go even if this guy get's away with it. Another consideration is whether you're going with hole punches, chisels or awls. I got into trouble because I used punches which can be problematical unless you happen to have the corresponding set of punches with the wider spacing for the bigger circumference so unlikely to be the way to go especially if you want the 45 degree holes. I did see something a long while back where someone (might have been Leodis?) where he made a wooden 45 degree gadget so you could chamfer the edges and use punches but I digress, anyway, I'm loving this conversation and I'm trying to keep up even though my hair stands on end when I see a scientific calculator but I love that every day is a school day.

TWO New Stitches to Elevate your Leathercraft! (youtube.com)

 

[chuck123wapati]

38 minutes ago, toxo said:

 I'm loving this conversation and I'm trying to keep up even though my hair stands on end when I see a scientific calculator but I love that every day is a school day.

TWO New Stitches to Elevate your Leathercraft! (youtube.com)

 

I fought this problem to the death on moccasin toes last month. you cant just glue up and sew those with an awl at least I couldn't figure out how to. 

 

1 hour ago, TomE said:

The diagram is easy to see but it's not easy to calculate stitch spacing from the angles shown.  I think it's easier to calculate the inner and outer circumferences then convert the spacing of the outer piece to that for the inner piece as the ratio of circumferences.  My point is you will end up with something like 6 and 5.5 stitches per inch for the 2 pieces and I don't know how to accurately mark 2 spacings with a small difference.  Won't have to do this with an awl.  Skipping a hole doesn't fix the spacing.

yup you can mark the holes on the outside piece then draw the same diagram to find the inner hole spacing measure it and you have the answer pretty close. 

On 2 mil leather it would be a very small difference on a miter joint type. That's why I didn't draw the thing to actual proportions, probably should have. 

[toxo]

Not really germane to this problem but my cup is cone shaped which brought up a whole nother set of shapes which I hadn't thought of.

I think everyone who calls themselves a leather crafter should make a conical leather cup/mug/jug.

I do think that provided you get both sets of holes lined up, it's easier to run an awl through both punched holes on the 45. Wouldn't be watertight of course but not needed in my case.

[chuck123wapati]

1 hour ago, toxo said:

OK here is what I was trying to do in the first place. As I've said, I don't think skipping stitches is the proper way to go even if this guy get's away with it. Another consideration is whether you're going with hole punches, chisels or awls. I got into trouble because I used punches which can be problematical unless you happen to have the corresponding set of punches with the wider spacing for the bigger circumference so unlikely to be the way to go especially if you want the 45 degree holes. I did see something a long while back where someone (might have been Leodis?) where he made a wooden 45 degree gadget so you could chamfer the edges and use punches but I digress, anyway, I'm loving this conversation and I'm trying to keep up even though my hair stands on end when I see a scientific calculator but I love that every day is a school day.

TWO New Stitches to Elevate your Leathercraft! (youtube.com)

 

i watched the video and you can sew that up in minutes with an awl with nothing but a stitch marker around the outside piece.  Even the video maker is making this way to hard. Make a form so you don't have to hold the thing and sew. I just had a thought for an accurate coozie form fill a can with plaster of paris or maybe even that expanding crack filler foam crap and insert a couple of pins, dowels or some such that you can clamp in your stitching pony. simply slide the sewn outer piece over it then you can easily glue the bottom in and start sewing.

Step away from your calculator very slowly and have a beer instead. remember people made this stuff before rulers were even invented.