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Thread and bobbin tension - offset to 1 side

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Old March 17th, 2019, 10:19 PM   #1 (permalink)
Kalkake Kalkake is offline
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Default Thread and bobbin tension - offset to 1 side

Just bought a new to us tajima tehx-c1501. Got some new needles, thread and getting it all setup. We are new to embroidery, so bare with us.
Using the tension gauge upper tension is 120-130 using polyneon 40. When running the maderia tension test the back bobbin is offset to one side. I think if it was centered the tension looks good, but open to opinions from experienced users.

Could this be hook timing?

Thanks
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Old March 18th, 2019, 08:50 AM   #2 (permalink)
Robert Young Robert Young is offline
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Default Re: Thread and bobbin tension - offset to 1 side

sorry, to me if the front side looks good... go with it! your bobbin lines are pretty straight otherwise just not centered.
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Old March 18th, 2019, 03:24 PM   #3 (permalink)
ltpemb ltpemb is offline
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Default Re: Thread and bobbin tension - offset to 1 side

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Originally Posted by Robert Young View Post
sorry, to me if the front side looks good... go with it! your bobbin lines are pretty straight otherwise just not centered.
Actually if you get strait even but offset lines like that more often then not when you go to do smaller details/text you end up having bobbin show on top.

I have run into and solved for this problem before. Usually its a timing issue of being too Early for optimal loop off the needle catching.

The loop that is formed between the needle down position and the hook point position has an optimal catch point where the forces/physics involved creates the least amount of instantaneous tension on the top thread.
Generally its when the loop is fully formed at its largest before the needle starts pulling the thread loop back out/up where the needle no longer manipulating the thread.
That is when you want the hook to make contact with the thread as it hands off the point of tension from the needle to the hook.

If the hook makes contact early you get a weird jolt in the top tension that pulls a small bit of excess thread gets pulled into the material. Because the release time of the rotary hook and the timing of the thread take up happen at the same time as pantograph movement you get directionally biased stitch tensions because the release always happens on the left side of the of a counter clock-ways rotating rotary hook, you end up with a looser top tension going one way because the slack in the thread tension you get a looser side, and a tighter tension going the otherway because instead of the take up lever being what pulls and forms the bottom stitch the pantograph movement is what forms the bottom stitch after the take up lever has fully pulled up the remaining slack... (Thats what I think happens at least I need an ultra high speed camera to confirm the hypothosis)
But in practice changing the rotary hook timing solves the issue (and allows you to lower tensions to reduce puckering issues.)

Whenever I buy up a used machine I always go through lots of testing and adjustments and fine tune the machine far beyond the original from the factory adjustments or even what a technician would adjust for.
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Old March 19th, 2019, 09:03 PM   #4 (permalink)
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Default Re: Thread and bobbin tension - offset to 1 side

ltpemb

cool! I wish I had your knowledge! I just do not know how to do said adjustments.
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Old March 20th, 2019, 11:06 PM   #5 (permalink)
Kalkake Kalkake is offline
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Default Re: Thread and bobbin tension - offset to 1 side

Little update.

Hirsch tech said to make sure the locating bar on the front of the hook was centered. I verified tonight it is centered. Just to test I pushed it all the way to the left and ran a test, then again to the right to run a test. There is no change to the bobbin placement.

I then played with bobbin and upper tensions. Tighten loosen etc etc. Again no change.

Going to call the tech back again tomorrow and get timing specs and procedure. Looks like this one is set at 197 deg. I will see if that is in spec or not.

Any other suggestions?
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Old March 21st, 2019, 10:55 AM   #6 (permalink)
Kalkake Kalkake is offline
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Default Re: Thread and bobbin tension - offset to 1 side

Talked to the tech, machine should be at 200 deg. I am going to retime it tonight and verify the hook is not bent or damaged in any way and see what happens.
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Old March 22nd, 2019, 01:23 PM   #7 (permalink)
ltpemb ltpemb is offline
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Default Re: Thread and bobbin tension - offset to 1 side

Timed to early lol yep.

My machines are all weird and somewhat poorly built/have design flaws so ive come up with my own diagnostic and testing procedures to dial them into a quality producing machine to dial the machine and each head into its own timing. (I can out produce new machine quality in some cases)

4-head #1
Head #1. 201.5 on needle 5
Head #2. 203 on needle 8
Head #3. 203 on needle 1
Head #4. 203 on needle 7 or 8

4-head #2
All heads 203 on different needles.

4-head #3
All heads at 204 on different needles.
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