Tension Stitches

[CHT]

HI:

 

We recently purchased a Juki 1508.  Good machine.  We are building a variety of leather items using , mostly, veg tan.  Weights run from 11 ounce to 3 ounce.  The machine works well but, on occasion, we will get birds nest stitches on the bottom.  Pictures attached.  This happens, mostly, when we are sewing heavier things that go from heavy to a lighter part of the item.  Example, a binder we do puts two 11 ounces pieces together on the back and the stich line drops off from about 22 ounces to around 14 ounces.  We seem to see this when the depth of what we are sewing changes.

Would be grateful for any suggestions on how to address this.

Thank you

Chuck

[Ferg]

You might try adjusting your tension as close to being good on both instances. You are going to have a problem changing that much thickness in the same run. 

Actually, to correct it you may have to adjust the tension each time you begin the change in thickness.

It is a tension issue.

Ferg

[Northmount]

@CHT Moved your post to leather sewing machines.

Tom

 

[CHT]

Thank you Ferg, was afraid of that.  Interesting that after you have a couple of bad stitches it evens out.  So,, guess we will test since this is a regular thing we do and get some tension settings for the heavy and then the little less heavy and change them as the stitches move from one area to the next,

Best Regards

Chuck

 

[Wizcrafts]

Chuck, the stitches might lay better if you can lap skive the leading and trailing edges of the double leather that transitions to/from a single layer. This would give the machine a couple stitches to adjust to the different thicknesses. 

Another thing that may help set the stitches is to increase the foot pressure to press the layers together harder. Unfortunately, this will increase the foot marks and bubble through on the back side.

You can also try using one size larger needle. This will affect the top tension because it will be easier for the take-up lever to pull the knots up. This may be the easiest change you can test. Needle shape can also affect the stitch quality.

[CHT]

Thank you for that.  Looking at that item we make and the front piece that attaches to the back piece (spine) only has about .75 inch of attachment at the top and bottom.  So skiving that part is a good idea and will try that.  Would reduce the thickness quite a bit.  We like the design that we have there but is also an issue sewing it.  Would be a major hassle to have to change tension for about an inch on the top and bottom.

Question:  We are using ORGAN DPX17DIA size 20.  So would you think at 21 or 23 would work with 92 thread?  If needle size would do this is a much simpler solution.

Thank you again.

Chuck

 

[Wizcrafts]

5 hours ago, CHT said:

Question:  We are using ORGAN DPX17DIA size 20.  So would you think at 21 or 23 would work with 92 thread?  If needle size would do this is a much simpler solution.

Normally I would say no. I use #19 needles with #92 thread, or a #20 in difficult/dense materials. But, what have you got to lose by trying a #21 needle?

I think that a #22 needle will poke such a big hole it will look bad on top.

Another way to tame loose stitches is to tighten both sides so the thread is pulled tighter against the surfaces. In that case you would probably want to use an S point inline wedge needle that gives a submerged leading and trailing edge. That is a Schmetz design that is available for your machine in compatible System 134-35. They are pretty much the same length and shank as the 135x16/17 needles. I checked with Toledo Industrial Sewing Machines and he has those needles in stock in sizes 16, 18, 19, 21, 22 and 23. Unfortunately, he hasn't got any #20.

Those Organ needles you mentioned have a contradictory designation. System 135x17 is a round point cloth needle. Diamond points are usually leather needles and are System 135x16. But, who knows anymore? You could try some actual System 135x16 needles with different point shapes.

PS: if you tighten up both tensions you may also have to tweak the check spring travel and its position in the curved slot. Overly tight top thread tends to pull hard going around the bobbin basket and will make a snapping sound on the way out. The check spring position can feed a little more slack in the top thread to compensate for this, while still maintaining the required thread tension on the take-up stroke. Just keep that in mind.

[CHT]

Thank you, again.  That makes a lot of sense.  I know Bob and will give him a call and see what he says about what he has.  It is frustrating now that things are often not what they seem and we have to check and test everything.  That last point sounds like that may be a possible solution.  When this happens (almost always on this material going to less thick) we hear a sort of sound like the impact of the down stroke at bottom is hitting harder.  That seems to be correlated to the then messed up bottom stitches.  So we will also research that.  The machine is relatively new (got back in May or so) and does not seem to have many issues with lighter material.  Also notice that Schmetz seems to be preferred by many other leather workers.

Will get some Schmetz as soon as they open (if he is there today) or on Monday.

Appreciate the help.

[CHT]

Was at a show, first day back and Schmetz needles are here.  Will test this week.  Was wondering if the thread might also be an issue.  We are using Superior #92 bonded nylon,

 

Thank you again

Chuck

Edited July 21, 2020 by Wizcrafts
Corrected spelling of two words.

[Wizcrafts]

9 hours ago, CHT said:

Was wondering if the thread might also be an issue.  We are using Superior #92 bonded nylon,

I have some of their bonded nylon thread and it is fine.

[CHT]

Thank you.