Breaking strength of a row of stitches

[chrisash]

Often wondered about how much strength is required to break a row of say 69 thread, as I assume the strength would not be just one stitch but spread over a few stitches each to a lesser amount.

So whilst 69 bonded nylon has a breaking strain in the region of 11 pounds, what force would it take to break say a one inch length of stitches (ignoring the material and tensions etc)

[kgg]

3 hours ago, chrisash said:

So whilst 69 bonded nylon has a breaking strain in the region of 11 pounds, what force would it take to break say a one inch length of stitches (ignoring the material and tensions etc)

From the information I have see I think it would be be based on the number of stitches per inch. The formula would be the number of stitches per inch X the breaking strength of the thread X the thread loop factor:

Example would be:

stitches per inch: 5

V69 breaking strength equal: 11 lb

thread loop factor for 301 stitch (lockstitch) type: 1.5  and thread loop factor for 401 (chainstitch) type: 1.7

Lockstitch Seam strength = 5 X 11 x 1.5 = 82.5 lbs.

Chainstitch  Seam strength = 5 X 11 x 1.7 = 93.5 lbs.

The reason a chainstitch seam has more strength for the same thread size with the same seam length but there will be about twice the amount of thread used.

kgg

[Gunnarsson]

This agrees with kgg, if I remember the content right.
https://www.sailrite.com/How-to-Sew-Webbing-Loops

[chrisash]

So 8 stitch per inch would have a staggering 132 lbs = 60 kilo, boy does that put things into perspective

Does it still apply if the pressure is at one end of the row, which would maybe be the normal pressure point on many items

Toledo gives the 11lb breaking strain for bonded 69, what sort of variance do you think there is for other makes of bonded 69

[Wizcrafts]

9 minutes ago, chrisash said:

Toledo gives the 11lb breaking strain for bonded 69, what sort of variance do you think there is for other makes of bonded 69

It varies more with other base materials. Bonded polyester has a lower breaking strength and Nomex is almost half as strong. I do a lot of sewing with Nomex and nylon, but only a little with polyester. I find it much easier to cut through Nomex, or cotton/linen, than nylon or polyester. When I do have to cut something off, I go inline with a seam ripper (up to b92).

The strongest seams I have sewn were on an old Singer 28 stitch bar tacker, using b69 thread. The entire item would dissolve before those sewn items would come off!

[kgg]

1 hour ago, chrisash said:

Toledo gives the 11lb breaking strain for bonded 69, what sort of variance do you think there is for other makes of bonded 69

I would say that all the brand name threads are probably within a certain tolerance of one another. The cheaper quality no name brands who knows.

56 minutes ago, Wizcrafts said:

The strongest seams I have sewn were on an old Singer 28 stitch bar tacker, using b69 thread. The entire item would dissolve before those sewn items would come off!

The strength would probably be in the far north of a 1000 pounds.

kgg

[bj139]

Kevlar has twice the thread strength of nylon or polyester for an equivalent size.  I used V92 Kevlar to sew my tree saddle since I didn't want to fall out of a tree.  With all the stitches in it I calculated the main seam would break at around 13,000 pounds.  Cutting it with scissors is surprisingly difficult.  Now I know why it is used in bulletproof vests.