Relationship Between The Number Of Spi Of Iron Pricking, Thickness Of Leather And Linen Thread

[dado1965]

I send you some pictures of some objects I sewed using Vergez Blanchard # 9 (in these cases, a portmanteau) linen thread Cable 632 and the total thickness leather (2 layers) 2.4 mm to 2.6 mm. What I would ask is: is there a formula to determine the relationship between the number of spi of iron pricking, thickness of leather and linen thread diameter? For example, the seam having a thickness of 2.8 mm to 3.2 mm is preferable to use a mark No. 8 (8 spi) with wire 532, or a mark No. 9 (9spi) with wire 532 (it is preferable to increase the thickness of the wire or the distance between points?), and so to get up to a thickness of 3.2 mm to 3, 8 mm (maximum thickness that I sew some side cases) is better to use a wire 332 or 432 with a Claw No. 7 (7spi)?
While more points and higher and the strength and elasticity of the seam?

[TinkerTailor]

You need to shorten the list of interests in your profile, It makes all your messages pages long.

There is no rule for spi/thread size however there is a general guide that shorter stitches and smaller thread are for thinner and softer materials, For any given combination the range of spi and thread size is pretty wide, and open to interpretation due to style. There are limits, but within the safe range there usually are alot of options. See what others do, try things out, and see what you like. If you don't like it, change it up next time.

[9tpi]

When i hand sew (saddle stitch) I set up everything in such a manner as to "create a box" with the stitches.

What i mean by a box is if i am sewing 2 pieces of 4 oz ( 1.5mm x 2 =3mm) leather together then i will select a 3mm pricking iron. This will essentially create a 'box' as the the stitch will travel through the leather the same distance as is does across the leather. In theory anyway.This will maximise the strength of the stitch in all directions.

As for thread it's a little more subjective. my rule is 6-7 spi 332-432, 8-9spi 532-632 and higher than 10spi is 832.

Again this is just how I do it.

[YinTx]

Conversely, I did a fun experiment to compare different size threads in 7spi stitching spacing, and with different stitching tools (chisels, irons, different brands, different styles). You can see the results here:

http://leatherworker.net/forum/index.php?showtopic=64153&hl=

I hope it is somewhat enlightening.

YinTx

[DavidL]

8 SPI (532) I find is a good general length for anything.

7 (432) would be good for large bags.

9 -11 (532-632) for watches or wallets.

I think saddles are stitched with 10+ SPI on thick leather.

[johnv474]

When i hand sew (saddle stitch) I set up everything in such a manner as to "create a box" with the stitches.

This is a cool idea. Thanks.