How to ease when sewing leather on a 1341?

[friquant]

30 minutes ago, AlZilla said:

At 5:30 of this video, the lady is sewing those welted fingers with which you're struggling. 

How does she make the machine feed in reverse? She's got a knee lift for the presser foot, but both hands in the shot when she reverses.

[AlZilla]

8 minutes ago, friquant said:

How does she make the machine feed in reverse? She's got a knee lift for the presser foot, but both hands in the shot when she reverses.

l didn't notice that.  Probably telepathic.

[joetroba]

Yeah I have watch videos and they make it look so easy. I think the reverse is on the foot pedal.  You can get those where you push forward on the pedal to go forward and backward (or heel side) of the pedal to go in reverse.  
As far as stretch and mis formed due to use, I can agree there is probably some of that.  However, there are other pieces that are different lengths where I would say there is no way they distorted the amount that I am seeing. And there is one where the left edge is a slight S curve that the right edge is a regular curve.  And those have the most difference.  

I have created this out of EVA foam and glued canvas to the pieces so I could sew them.  They came out pretty decent considering the foam has so much stretch.  

I am going to attempt to explain this and I hope it makes sense.  If you take these pieces and you manipulate them in 3 dimensions and slowly keep the edges lined up, you can get them to start even and end even (even with a large difference in length).  Now the fun is getting that to work that way on the machine.  

As far as seam allowance, I get that (sort of).  Because the welting is only 3/16" wide and you are sewing in the middle of that width. And all those edges line up the, the seam allowance of sort of just 3/32".  Unless, I am completely thinking about that incorrectly. Tolerances are quite small.