CB4500 reverse stitch bottom loops

[Uwe]

There may not be a "qualified" Cowboy dealer in all of South Africa, since the original dealer/agent didn't really set things up correctly to begin with, according to the original post. Sometimes taking the machine in for service is just not an option. Well over 99% of all people do not live within driving distance of a qualified Cowboy dealer.

I'd say certain hook + race combinations just don't work well together. Mixing and matching parts between OEM (Juki) and aftermarket copies (Cowboy and others) does not always yield desired result. If an aftermarket copy is a truly faithful copy of the original, then the OEM parts should work. Some manufacturers make subtle design or manufacturing changes (on purpose or accidentally) that go unnoticed but result in poor parts interchangeability.

I have a feeling the issue of thread getting pulled into the race during reverse has, among other things, to do with very subtle differences in the curves and slopes of the shuttle hook tip itself, and also the shape of the right edge of the race and backing ring. Thread material, and how sticky/slippery it is may als affect this issue. If the thread does not want to slide back on the hook during reverse, it is more likely to get dragged into the race. A slight burr on the hook will have the same effect. Aggressive polishing of the hook tip may make things permanently worse. The opposing movement of hook and needle during forward stitches hides many imperfections and timing flaws. Sewing in reverse where both needle and hook move in the same direction, but at different speeds, is much less forgiving. 

I'm working through the hook timing instructions in the Juki TSC-441 engineering manual (Juki 441 Engineers Manual.pdf). It's not exactly intuitive and some steps don't compute in my head quite yet. Missing reference marks on the machine don't help, either. 

In the meantime, I made a video showing how my machine's race and shuttle hook fit together and how things come apart. Perhaps it will help others notice some differences, or confirm that theirs is the same as mine in the video.

 

[RockyAussie]

Excellent video as always Ewe. I found a video that I initially used to time mine and still had problems with missed stitches in reverse etc and when I followed the Juki guide as best I could it then went perfect. There was a large difference in the 2 different procedures as to where the hook ended up in relation to the needle height. The 25.9 height from the bottom of needle bar clamp and the throat plate seems a bit difficult (ha ha) but I rested a short ruler on the throat plate and got as close as I could see and now no problems. I believe that your hook is not going back as far as mine is Uwe and that may make the hook not fall back with gravity to open as easily at slow speed as is desirable. Logically a machine moving at some speed will make the hook throw back away more definitely as it reaches the end of its travel in either direction and is probably one of the reasons that miss stitches happen more when you are going slow. You'd think they would be able to work out some sort of alternating repulsing magnet to better force the opening on the hook. I should perhaps mention that I do not have any problems getting the reverse stitch lining up into the previous holes as it seems many do and I have not got any washers and so on to do this. Don't know why and if it develops I will have to find out I guess. Brian

[Zandeosaddles]

Thanks again to all for the very helpful replies. I am finding the engineers manual very helpful and Im re setting the machine according to manual. When I set the timing according to book. The needle height is not right. This makes me think the position of the needle bar relative to the drive shaft is off. The reference in the manual doesnt result in the hook to needle height relationship. Will also like to find the reference marks on the shaft of upper feed. Thanks Uwe for your inputs so far.

[Zandeosaddles]

Brian. Thanks for your input. It seems the distance between the needle bar and throat plate must be 29.5mm once needle has travelled up 5mm? I think we are getting close my shuttle friver touches the needle ever so slightly .

[Uwe]

2 hours ago, Zandeosaddles said:

It seems the distance between the needle bar and throat plate must be 29.5mm once needle has travelled up 5mm?

It may seem that way, but the manual states fairly clearly that the 25.9mm distance is the "Reference value of the lowest position of the needle bar stroke."

The shuttle driver is supposed to touch the needle slightly - that's what prevents the needle from getting deflected towards the hook (and getting hit by the hook.) The shuttle driver also acts the needle guard.

The Juki TSC-441 Engineer's manual can be confusing, especially if you read it on the computer one page at a time. The manual makes (slightly) more sense when viewed as two-page spreads, or printed as a booklet like this:

Now you have the target settings on the left, and directly opposite to the right you have instructions on how to change that particular setting.

Alas, the adjustment instructions for step 2. on the right side (middle of page 3) still confound me. But I'm determined to figure this out over the weekend. 

[RockyAussie]

5 hours ago, Zandeosaddles said:

Brian. Thanks for your input. It seems the distance between the needle bar and throat plate must be 29.5mm once needle has travelled up 5mm? I think we are getting close my shuttle friver touches the needle ever so slightly .

NO. That is wrong as Uwe has pointed out. The (25.9mm) is when the needle is at the absolute bottom. After that when the needle is raised up 5mm the hook tip should be lining up with the middle of the needle then. 2 different steps here . If the needle is in the bar fully and the needle bar is in its correct position the top of the needle eye to the hook tip should be 2.5mm apart as well. Hope that makes it easier. Regards Brian

[Zandeosaddles]

Thanks Brian. I get it now. As Uwe said, those manuals are rather vague. Uwe, my race does not offer the play or give which you show in your video with screws tight or loose. I will post my progress ad I go. Here in SA, technical service is poor at best. Thanks again.

[Zandeosaddles]

Ok. I found that the eccenteic cam at the back of the machine was not set properly ans the top feed cam next to it was not properly tightened. Now I have set it according to rhe juki engineers manual. Now I find needle bar height and hook timing is out. So I will set latter accordingly ans hope for the best. Please share whatever thoughts you have. I follow needle bar height point

[RockyAussie]

If possible please post some pictures of the parts you refer to and mention what adjustments you do .If you get all of it right it may help others and if you get it wrong we may see and pick up why. Regards Brian

[Zandeosaddles]

Thanks Brian. I will do. How do I shrink the size of the pictures.