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[TedP]

I’m not sure what the correct terminology is for what I am describing, but I had a question about using common seams in vinyl. This would be where you have a simple stitched seam attaching 2 or more pieces of vinyl ( or leather) together.

So, if I take 4 pieces of vinyl of 4” width ( let’s say different colors) and sew them together with 1/2” seam allowance, technically I would end up with 4 pieces with 3” exposure equaling 12” ( ignoring the 1/2” extra on each end).

In reality, once the newly sewn piece is laid out it will not be 12”, but more like 11.5”, because of the 90 degree bend of the vinyl at each seam.

Of course, I could stretch the piece to get to the theoretical 12” of width, but that tends to expose the threads between the individual pieces to an undesirable extent.

Is there some sort of norm or guidance in allowing a little bit of extra dimension in each piece to be sewn so that the results end up being at the desired dimension (12” in this case)?

What I have done in my current efforts on vinyl seat skins where I am sewing 6 pieces together is to add 1/8” of dimension to a few of the pieces, so that the resulting sewn piece is closer to the desired/intended dimension and does not need to be stretched as much.

Hopefully, I have explained my issue/question well enough. Just wondering if there are standard practices in allowing for the dimension lost at each seam (albeit a small loss that adds up).

[John Long]

You are way over thinking this. What you are describing applies in working sheet metal but is irrelevant with upholstery. You need for your work to be stretched somewhat. If it is not tight it will look loose and sloppy and will quickly get looser with use. If you think about it, no one ever tells you to add to your pattern when you use sew foam. (scrim).

John

[TedP]

The main reason I asked is that on my boat seat re-upholster project (in the Marine forum). After sewing the 6 pieces of the main portion of the skin together, I was about 3/4” short when matching it up to the end panels. So, I had to stretch the main portion by the 3/4” so the main piece would line up with the end pieces. Stretching the main piece that much seemed like a lot.

I figured on needing to stretch the main piece somewhat, but not that much.

[Cody]

Say your total length is 36” and in 6 sections like you mentioned. Your cut length of the pieces should total 42” in total if you’re using .5” S.A. Giving you an extra inch per piece. Once sewn together your panel will be 37” long in total, factoring the .5” S.A. On each end for whatever you are sewing it to. If you factor an extra inch per section and sew it up, and it’s too short, your sewing more than .5” at the seams.