Union Special 51900 Alternate Presser Foot?

[Ogoki]

From what I can see on the Union Special site, there is only a parts manual for this series.  My experience with chainstitchers is limited to my Champion 77 and an old Puritan triple stitcher, both of which are single thread machines (if I recall the Puritan correctly), and different from these two-thread machines.  In any case, I am confident that with a manual and/or a bit of guidance, I can wrap my mind around this.   The "flagging" issue seems to be virtually non-existant when stitching a few layers of 15oz. denim (at the risk of getting the boot I must admit that this isn't being used for leatherwork), so I feel that I could ignore that variable with the right troubleshooting material, i.e. three flat layers of 15oz. denim.  The flagging occurs with thin materials, and it also skips when going over the seams, where I might have more like 12 layers of denim (I do use a height compensation tool to pin down the fabric by the needle, and walk the machine over the seams very slowly).  And, of course, when reducing the stitch length the machine becomes basically useless, which is the problem I would really like to solve.

Is there a proper service manual for any similar machine that might help me?  I also recently picked up a baby lock serger, which is a serger and a chainstitcher.  It doesn't loop properly either, so I think it is time to learn about chainstitching machines....

[gottaknow]

The specs you have to know are looper gauge, looper avoid, looper travel, and synchronization. Each Union Special machine in this general chainstitch class ( of which there are several hundred variations) , have specific values. Some do overlap for sure. I have a lot of US manuals, so I'll wade through them and see what turns up. If you know what the looper gauge and travel is, you at least have a starting point. The other issue is these machines are capable of being set with two needle classes. 128 and 108. The 108's are shorter. It's likely class 128 which requires a different looper avoid setting than  the 108's. So I guess I need to know which needles you're using first off.

Also, here's some general information. It covers the style of looper in your machine "across the line of feed loopers", it's pretty close to the beginning.

Regards, Eric

Loopers and hooks.pdf

Edited September 13, 2017 by gottaknow
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[Ogoki]

Thanks again!  I'll have a look through that pdf and see what I can find out about the looper.