Interesting Schmetz Bit of Info

[bcurrier]

I came across the following on the Schmetz site ( www.schmetz.com ) regarding industrial leather sewing. Looks like the expectation generally, with industrial sewing, is not to suck the stitch up into the leather as with cloth:

When stitching tough and brittle materials, it is very difficult to interloope the needle thread and bobbin thread in the middle of the material on account of the inelasticity of the material. Therefore, the loop should always lie on the underside the material. This facilitaties stitching, but can lead to the bobbin thread of the finished product breaking more easily under elevated loads.

Garment industry:

• Stitch type 301:Lockstitch
  (Stitch type 304: Zigzag stitch)
  

Laether industry:

• Stitch type 301: Lockstitch
  (Stitch type 304: Zigzag stitch)
  

Bill

[Art]

Hi Bill,

I've seen this in the Campbell manual also, they never gave a why, but after thinking about it, it makes sense. When you are working with materials or applications that vary in thickness, keeping the lock low will allow for varying thicknesses of product without the bobbin showing through to the top.

Art

I came across the following on the Schmetz site ( www.schmetz.com ) regarding industrial leather sewing. Looks like the expectation generally, with industrial sewing, is not to suck the stitch up into the leather as with cloth:

When stitching tough and brittle materials, it is very difficult to interloope the needle thread and bobbin thread in the middle of the material on account of the inelasticity of the material. Therefore, the loop should always lie on the underside the material. This facilitaties stitching, but can lead to the bobbin thread of the finished product breaking more easily under elevated loads.

Garment industry:

Stitch type 301:Lockstitch
(Stitch type 304: Zigzag stitch)

Laether industry:

Stitch type 301: Lockstitch
(Stitch type 304: Zigzag stitch)

Bill

[bcurrier]

The part about the bobbin thread (or loop) lying ON the underside of the material is what caught my attention. Having the lock lower within the leather is fine, but if the loop is completely exposed on the underside you might as well use a chainstitch and save yourself the trouble of dealing with bobbins at all.

You do see some items with the exposed bobbin loops here and there. It looks pretty bad to my eye.

Bill

[JREIndustries]

I have never had a problem with the bobbin thread breaking under any normal load.

Could they be recommending this if you use a thinner bobbin thread?

And I agree, Bill. It looks bad to me also. If I stitch up a sheath and the loop is showing, I will restitch it or launch it!

Edited January 11, 2008 by JREIndustries

[Art]

Hi Bill,

That is disconcerting, however if you look at the diagram, there is some drawup involved. Maybe it's like those Chinese instruction manuals, something lost in translation.

Art

The part about the bobbin thread (or loop) lying ON the underside of the material is what caught my attention. Having the lock lower within the leather is fine, but if the loop is completely exposed on the underside you might as well use a chainstitch and save yourself the trouble of dealing with bobbins at all.

You do see some items with the exposed bobbin loops here and there. It looks pretty bad to my eye.

Bill

[jimsaddler]

This is actually a technique used for a lot of jobs where the Back (underside) is not exposed, ie Footballs and Pouches. I recall that a lot of Show type Backsaddles used the same method in the old days. I noted that this left a very neat topstitch when sewing Black Patent Lether at say 11 or 12 per inch. Just a fraction of Pull-up to sink the thread, usualy using a S twist Leather point needle on a Pearson #A1 or a Singer 45K25. The Back was covered by the Pannel so who was to know. The stitching sure impressed the Judges as I used the same technique on my top Harness in the 70's. Won every time!

As far as strength goes A New Zealand Company used a very heavy Braided Linen Bottom Thread and 8 cord Z twist as a top thread in The Union Lockstitch, to sew Competition Rugby Footballs. The Tension was screwed up very Tight, The Braid being stiff did not pull up at all. They lasted very well and were recognised as the strongest on the Market. Talk about Seam Stress, but they stood up to it. So don't write off the idea as there are times when you need it. By the way some of the Show Back Saddles I made in the mid 60's are still going fine, not a popped stitch to be seen.

[bcurrier]

Thanks for the perspective. I wasn't writing off the stitch itself - a lock is a lock is a lock - only the appearance when exposed. Now that you mention it, I have seen it on patent leather (and plastics).

Bill