Forward & Reverse Tension

[Bosbus]

Hi

I recently bought a Techsew 3800 and thus far am rather disappointed. (2 weeks in)

While Mike is trying to help me via email, the one question I do not seem to get an answer on is if it is normal to have different tensions for forward and reverse? I am not talking about going back over previous stitching, but when I for reasons of access need to work first in one direction & then in the other, I get significantly different tensions for forward & reverse with the reverse bottom being looser than when I stitch forward. (Using 415 and 250. gets closer using 270 at the bottom, but the different sizes does not work well with the design I have in mind

Is this normal? If it is normal, what would be the reason for this?

Advice?

Thanks :-)

[Wizcrafts]

The best I can do is offer some suggestions. Try them and hopefully, one will solve your tension differences.

1. Reverse the direction of the bobbin in the bobbin case. Readjust the tension on the bobbin spring, if necessary, for the best knot position.
2. If this changes nothing, try increasing the bobbin tension. Increase the top tension to match. Sometimes tighter top and bottom tensions will overcome variations in the knots and bottom thread.
3. Sewing in reverse means that the hook arrives sooner above the eye of the needle than for the same stitch length in forward. If your timing is just barely adequate, the loop may be drawn around the bobbin case and shuttle at a different tension than in forward. Retarding the timing a few degrees might help if this is the case. The hook to eye of needle timing should be set with the stitch lever at zero, between forward and reverse. This gives the best compromise. Set the needlebar a little lower to give more travel on the upstroke. However, you can overdo this and make matters worse. Sometimes you have to set the needle bar to its designated position, then adjust the hook to meet it in the middle of the scarf at so many degrees on the upstroke. Consult your adjustments section of your owner's manual.
4. The throw of the check spring affects the loop. It should keep the top thread under tension until the needle just meets the top of the feed dog, or passes the top of the throat plate slot if no feed dog is used. It must let go and give the top thread some slack before the needle reaches BDC and begins its upstroke. Otherwise, the loop will be dissolved on the upstroke. The bigger the loop, the easier it is to pull it around the bobbin case and tension and the less likely it is to skip stitches.

[Bosbus]

Thank Wiz!!

At last I understand why there could be difference in the first place!

The options under 1 & 2 I have tried

I will try point 4 first as my fiddling with the spring limiter was random/trial&error so far as I did not know what to look for and your info in 4 will enable me to check that one fairly easily.

For point 3 I will have to go back & double check, but I do not recall any tech spec info in the manual to inform on the degrees proposed for the hook/scarf meet. I do however think that your description will enable me to get wiser with a bit of careful play. Must say on paper & not in front of the cylinder head the detail in 3 sounds intimidating, but so was my slide rule back in the days so I trust with patience I should get the hang of this too.

Thanks for the logical explanation, it really helps a lot to know what to look for! Judging by your photo and your explanation, I will venture to say with safety that you proved again that there is no replacement for experience ! All I now need to do is prove the adage re old dogs and new tricks wrong on my side! :-)

[catskin]

Wiz is the expert no question. But here is something I have had happen, some times under some conditions sewing in reverse and then forward the foot puts more pressure on the thread at different times and affects the amount that the take up arm is able to pull back up. This could depend on if the foot is grooved on the bottom or not or if the groove is small for the thread size. Disclaimer: I do not own a machine of that model, this is just general observation.

[Bosbus]

Thanks Catskin

Any advice is always welcome. I do not think its only that as it does so even when I do not sew over previous stitches and the top foot does not have grooves at the bottom, but hey! I dont know yet, so I will try everything :-)

I hope to get time over the weekend to experiment and will revert thereafter.

[catskin]

To explain better the grooves I am talking about are not ones across to feed the material (although they to could do it)

but the one that is length wise that is supposed to clear the thread to allow it to pull up. If you look on the bottom of the foot it will be one groove in line with the needle hole or slot. Having this one would make it less likely to hold the thread back.

[Wizcrafts]

Catskin;

The O.P. owns a Techsew 3800, which is the Canadian equivalent of the US Cowboy CB3200. These are 441 type triple feed machines, with modern harness presser foot sets (also used in the biggest 441 stitchers). There is no metal behind the inside foot on the outside feet; just open space. The bottom of the inside foot is either totally flat, or could have a tang protruding to push down the stitches (depending on the manufacturer of the foot). These feet are radically different from standard type 111 walking foot sets.

Edited March 19, 2015 by Wizcrafts

[Cobra Steve]

Hey Wiz, hope all is well. There is some good advice here, but if you still can't get the tensions balanced, try reading the "Maintenance Tips on the 441 style machines". You will find this info in the Leather Sewing Machine section in the Forums. It is the first one that is "Pinned". Read the section about re-calibrating your tensions.

[Bosbus]

Thank you very much Steve! Will do