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deloid

Knot Came To Top On 1/4 Run Of This Belt.

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Large belt with double run of stitching. !/4 came out with knot on top...don't know why yet. I removed this and tried various top tension settings to resew but the knot is always on top, I suspect due to the hole size/lack of leather resistance.

Cobra 4, using 138 thread and a23 leather cutting needle.

Any help with this? I don't want to saddle stitch this.

regards,

Dean

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post-9405-0-15745700-1404505860_thumb.jp

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When you resew using existing holes, you have to reduce the top tension a lot to keep the knot from rising to the top. I've had to do the same a few times.

Tom

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Did anything change tension-wise with the top or bottom thread? Hear any different sound when the bad stitches occurred?

Knots or the actual bottom thread showing on the top grain are either caused by sudden increase in top thread tension, or decrease in the bobbin thread. A properly balanced system places the knots in the middle of air.

What can cause these changes

  • Top thread getting caught under other windings on the spool
  • Top thread going under the spool on the stand
  • Top thread coiling over itself or a post, or tensioner, due to excessive twist and springiness
  • Top thread coiling back over the lower tension disk set and jamming
  • Bottom thread flipping out from under the bobbin case tension spring
  • Lint under the bobbin case tension spring
  • A starting thread stub catching on the bobbin case ejector spring
  • Too little pressure on the feet
  • Very soft area inside the leather
  • Too little combined thread tension
  • Bad thread

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Hi Tom,

I'm glad it can be done. I was starting to think that the knot needed material to be able to go halfway. My problem now is that in trying to correct it I have my pressor tension and upper thread tension all out of whack.

When you have done this in the past was it with the Cobra or similar? If so, do you recall how many turns you had to back off to get it right?

Thanks,

Dean

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Whiz,

I changed the thread color but I used the same thread (138) that has always worked well for me. I have always used Steve's (Cobra) recommended leather cutting needles and at his recommended size of 23.

There was a difference though. Even though I am meticulous about the threading route, as I was sewing at the highest speed there is some slack at the disc below the pretension disc (top), and the thread was looped and fraying on the spring/screw for this second disc with the felt pads. I corrected that but now I have messed with the pressor foot tension, the top disc tension and I can't get it to drop the knot even with the top tension almost unscrewed.

Problem #1 Don't know why all was thrown out of whack after the frayed string. There is no debris in the bobbin area.

Problem #2 I have lost my baseline for the different tensions. I didn't mess with the bobbin tension though.

Problem #4 When I was adjusting the top pre tension disc I didn't realize I was supposed to move the tension on the second felted roller disc. This one doesn't do anything I can see to the thread and other than functioning as a wrap around I don't understand the purpose of the felt and the tension spring.

Help would be greatly appreciated. My wife runs a leather business and I (and a friend) need to sew for her. The work orders are getting backed up.

Dean

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Hi Tom,

I'm glad it can be done. I was starting to think that the knot needed material to be able to go halfway. My problem now is that in trying to correct it I have my pressor tension and upper thread tension all out of whack.

When you have done this in the past was it with the Cobra or similar? If so, do you recall how many turns you had to back off to get it right?

Thanks,

Dean

Mine is a lighter machine, so the top thread path is quite different. But the principles should still hold.

Check to see if you have any bobbin tension by pulling on the bottom thread. Should feel some resistance, but not a lot. Check there is nothing holding the bobbin tension spring open. Check the direction the bobbin is inserted.

You might have to eliminate some wraps in your top thread path to get the tension low enough to let you re-sew the belt. (Or do it with a jiffy sewing awl instead of your machine. Then you can manually adjust the thread tensions to suit. Might be a faster fix than messing around with your machine.)

Since you haven't changed the bobbin tension, you should be able to get the top back to normal fairly easily by doing several test runs on scrap like you will be sewing, by increasing the top tension a bit at a time. Start with a new needle too, size you will be using, and the thread you will be using. You might increase a quarter turn at a time until you get close, then take smaller steps as needed.

The presser foot pressure just needs to be high enough to stop the leather lifting as the needle rises.

Good luck, Tom

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Deloid;

I believe that I have Grokked your problem. The Spice must flow and so must your thread. Your lower disks, as you surmised, do nothing serious to the tension on the thread, at 2 wraps of #138. But, I'll wager that the check spring was setup for #277 thread and is waaaay too tight for #138. In effect, that lower spring, if too tightly wound, will override the top tension disks. This is more evident when switching from a #277 or #346 setup to #138 or smaller thread. Happens to me too. When I have the machine balanced for heavy thread it is too tight on top even with the top tension almost unscrewed.

What to do

Find the 10mm wrench in your machine tool kit, or tool box. Locate the large (6mm?) metric Allen wrench that came with the machine, or one you buy at AutoZone. Proceed thusly:

  1. Remove the thread from the needle only
  2. Lower the presser feet if they were lifted.
  3. Rotate the hand wheel until both presser feet are all the way down and neither is lifted up (there is a happy place where this happens).
  4. Use the Allen wrench to loosen the bolt on the large arm behind the upper part of the rear of the head. This crank feeds the motion to lift the presser foot. The hex head bolt is visible from the top rear.
  5. Remove the C clip from the crank connection that feeds from the upper crank to a lower crank that goes into the head. The clip should be on the outside left on the crank arm.
  6. Pull the two piece double arm crank off the top and bottom pins
  7. Use your box or open end 10mm wrench to fish behind the head, inline with the shaft for the lower tension setup. Turn the locknut on the back of the head counterclockwise a bit to loosen it.
  8. Use a small screwdriver to rotate the split shaft whichever direction reduces the spring tension on the check spring. Leave enough tension for the spring to move all the way down after lifting it up, but not much more.
  9. Tighten the locknut to secure the check spring's lower action.
  10. Re-install the double crank onto the pins and install the c clip
  11. Tighten the hex bolt on the upper arm
  12. Thread the eye of the needle
  13. Make sure you have a straight path for the top thread. Don't wrap it around the upper post; just feed it through an eye in the post.
  14. Try the machine for knot placement.
  15. Report back here.

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Hi Whiz,

I was reluctantly prepared to dive in and follow your directions but Dave spent time with me and I had two issues

#1 Improper threading route. I can't believe I missed that but it was off.

#2 The bobbin required more tension.

The problem is fixed.

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