CB4500 reverse stitch bottom loops

[Zandeosaddles]

Good day all. I am having a problem with my machine. It stitches fine forward, but in reverse it makes loops underneath. I have run through all the instructional videos on you tube. All the basic checks are done. When in reverse, the machine sounds as if the tension of the upper thread is too tight as opposed to sewing forward, yet it is the top thread that loops underneath in reverse. I would greatly appreciate it if someone would take up the challenge of running through all the settings with me esp the uncommon ones. My machine was never properly setup by the agents in south africa. I got a technician out to set it up. I recently re did the timing, feet balance threading, oiling race screw tension from videos, just to be sure. The thread is wound correctly on bobbin.  my email address is zandeo@gmail.com. thanks very much.

[CowboyBob]

Looping is almost always upper tension.Double check that you have the thread wrapped around the second tension 1&1/2x.

It's looping because the upper thread tension is too loose.

[Uwe]

I'd open the hook cover, turn a few stitches very slowly in reverse by hand and closely inspect what's happening as the thread gets wrapped around the hook. Your top thread may snag some place in reverse and pull more thread from the spool, which the take-up lever cannot pull tight anymore. A video snippet uploaded to Youtube is a great tool for remote debugging. 

Edited May 26, 2017 by Uwe

[Uwe]

So I was just trying this out on my Cowboy 4500, and, lo and behold, it does the exact same thing when I reverse at maximum stitch length! It sews just fine in both directions when I select a smaller stitch length, but at maximum stitch length in reverse, the thread loop snags momentarily between the shuttle and race, the take-up lever pulls more thread from the spool with a snapping sound in the upper thread path, and leaving a loop at the bottom.  I'm not sure yet why the thread snags or how to fix this, actually. I guess it's my turn to take a video snippet of my machine misbehaving and report back.

Edited May 26, 2017 by Uwe

[Uwe]

The fix was super easy!  Just point a camera at the machine and threaten it with public shaming in social media and it'll make perfect stitches in both directions at all stitch lengths! 

Edited May 26, 2017 by Uwe

[Hockeymender]

59 minutes ago, Uwe said:

The fix was super easy!  Just point a camera at the machine and threaten it with public shaming in social media and it'll make perfect stitches in both directions at all stitch lengths! 

So now you tell me.....after all those hours working and sweating over these misbehaving machines!!

[Uwe]

I finally got a few snippets of film catching the machine as the thread gets snagged. It's hard to see and even harder to film, but my machine actually manages to snag thread in two different ways. One is subtle and only causes somewhat loose stitches at the bottom, the other is a major snag and causes big loops of top thread on the underside.

The main problem is when the thread gets snagged between the shuttle and the race: 

 

The photo below shows four rows:

Top: forward

Second: reverse with big snag loops

Third and fourth rows are forward again with smaller stitch length followed by reverse with moderately loose bottom stitches.

 

I still don't know exactly what causes the snags or how to fix them. 

I put together a few video snippets showing how my machine catches the thread under certain circumstances. This is not some elaborate how-to-fix-it video, just documenting what can go wrong. 

 

 

[LumpenDoodle2]

Have you tried switching it on and off again?    Sorry, couldn't resist, that's my 'fallback' repair position'.    

Just out of interest though, is all this only happening at a specific point of the stitch cycle.   If reverse is chosen when the needle is slightly higher/lower, does it make it worse, or cure it.  

(I meant to use the word excasserbate, but neither me nor spellcheck could cope).

 

[gigi]

Just an opinion: Hook might be a little bit behind, timing-wise.

 

[Constabulary]

Is it probably the shuttle race spacer where the thread keeps hanging? Aren´t there different size shuttle race spacers out there? At least the 441 parts list shows a range of spacers in the listing.

Idea is when you add a thinner spacer (don´t know in what thickness they come)  the hook goes in a bit deeper and then there is a bit more clearance between "shuttle driver tip" and shuttle so the thread can easier pass through. Just a a wild guess guess

Or try thinner thread and check it it still does the same thing...

Have attached a 441 type parts list where the spacers are listed (#44 -#50)

part-441.pdf

Edited May 27, 2017 by Constabulary

[brmax]

Uwe

Hey thanks! for the video, it sure gives another perspective to look through. Besides i think to see that well the use of my hi-powr cheater glasses need found "again" As usual great work there

Floyd

[Zandeosaddles]

Wow!! you guys are awesome! Thanks so much for all the kind replies. I will work through each one carefully. I have a video up on my c ha on you tube. Search theus badenhorst and you will find it. Cb4500 reverse problem. Bob, thank you, I have played around with the tensions whichever way, problem persists. The theory about thread ctching on bobbin makes alot of sense but under close inspection there seems to be no snag that I can discern. see video. I will respond to other suggestions as I go through them. thanks again. This problem has been with us for 3 years. I have now taken up the challenge to sort it out. the reverse function on these machines is one of themost fabulous functions. have a great day all.

[Zandeosaddles]

Uwe, thanks so much, I believe this could be the issue here as well, I glad someone else has the same. It seemed everybody runs so smooth. Now the machiniacs must please help us with a fix... please.

 

Gigi, I have seen some improvement in the past with bonded thread, but I need to use all sorts of thread.

 

Constabulary, This is an option we may need other opinions on and maybe try out. Thanks!

 

[brmax]

Possibly in your test scenario ?

In the video on your channel i cannot see the top thread tensioner being used. And again maybe the testing or can you explain any tips with this setup. 

 

[LumpenDoodle2]

Again, out of curiosity, and probibly not pertaining to this problem, but.....

What would happen (if anything) to the timing of the machine, if the stitch length wasn't set properly when comparing the front stitch length to reverse stitch length.

As I said, just curious.........

[Zandeosaddles]

Hi brmax. The top thread tensioner just happens to be loose now as part of experimenting but stitches perfectly forward and adjusting it makes little difference to the problem in reverse.

Hi LumpenDoodle2. I don't know, but I set very carefully with stitch lever in forward on largest stitch setting. The machine stitches perfectly in the holes in reverse.

Hi Uwe. My thread does not seem to get caught where yours does. However:

In reverse the takeup lever picks up the thread tension spring sooner than it does in forward.

So it seems that a loop is left behind on every upstrokeof the take up lever. It feels lime something is catching the thread preventing the lever from pulling the thread in, however, I cannot see what it is when leather is in the machine.

 

 

[Zandeosaddles]

Gigi, just wondering, if hookwas a little behind, would that not affect forward stitch also?

[gigi]

I don't own this machine model, but I was just thinking there might be a 'play' between parts. How old is the machine? What was the stitch length lever position when you did the timing? I would try to set it in the middle when I do the timing to see if it solves the problem.

[mikesc]

I'd tend to be thinking along the same line as gigi, those loops ( and the fouling ) when sewing reverse at max stitch length, might be that the timing is just a gnat's smidgin retarded.

Edited May 27, 2017 by mikesc

[Uwe]

6 hours ago, Zandeosaddles said:

I have a video up on my c ha on you tube. Search theus badenhorst and you will find it.

You can copy and paste the web address of your video (in this case "https://www.youtube.com/watch?v=EDDnYJoJqH8" ) directly into a reply and it will be automatically embedded for easy access:

 

 

[Wizcrafts]

I don't usually have top thread loops on the bottom layer on my CB4500 when sewing in reverse. But, the bottom tension is sometimes reduced and I occasionally get skipped stitches going backwards. These are timing and check spring problems that I adjust for when they bother me enough. One should first set the timing to the default position. This is done with the stitch lever in the zero length position. When the needle passes BDC and has risen about 3/16", the hook should meet the center of the needle about 1/8 to 3/16 inch about the top of the eye. This is not a precise measurement. I find that different thread colors and sizes change the size of the loop. But, if you have a nice size loop at the zero stitch position, the forward and backward stitches should be good in both directions.

What could cause the hook to eye of needle timing to change?

Sometimes, despite having two hex head adjuster set screws on the needle bar clamp, the force of impacting tough leather can cause the bar to move up inside the clamp on the crank shaft that moves the needle bar up and down. This raising of the needle throws off the timing. When this happens you can simply zero the stitch lever, lower the needle until it passes BDC and moves up a few silly millimeters (3 to 4 mm for my South African and European friends) and the hook is in the middle of the needle. If the hook is too close to the eye, loosen the needle bar clamp screws and manually lower the needle until the hook is properly centered inside the thread loop, or about 3 to 4 mm above the eye. When you re-tighten those screws, make sure the actual needle clamp has not rotated out of position. Note, or photograph its original position as a reference.

The idea is to position the hook in the cutout (scarf) above the needle's eye where it has the best amount of top thread loop to pick off. There is a happy range of needle positions to do this. But, if the tip of the needle is too low, it will hit the bobbin case: = very bad. Too high and the hook will tend to miss the loop. Most dealers recommend lowering just the needle first to test for this vertical position problem. If lowering the needle improves the situation, then lower the needle bar. If not, you've saved the turning effort on a couple of screws that are usually set very tightly at the factory.

Advanced information!

The actual hook timing is adjusted with a large hex wrench inside the round access port cover on the right front of the machine body. There are probably YouTube videos showing how this is done. When I need to re-time my machine, I loosen the big bolt inside the access port, leaving it just tight enough that it turns with the hand wheel, but is turnable by finger pressure. I adjust the position of the hook by hand to meet the middle of the needle on the upstroke, centered in the thread loop, where it is giving me problems, then tighten the bolt down. This adjustment may only need to be tweaked a couple of degrees to make the machine stop snapping the thread or skipping stitches. Do this at your own risk!

Enter the check spring

The check spring must hold the top thread taut at least until the needle pierces the top layer. If it lets go too soon, the tip of the needle might split the thread before it penetrates the top layer, or on the way through the leather. There is a bottom stop that is movable to stop the spring's travel higher or lower.  It must stop moving down after the needle passes though the bottom layer, or there won't be enough loop for the hook to pick off. In between the extremes is a small amount of happy adjustment range that can cause the stitches to be looser or tighter.

Often overlooked is the tension of the check spring. There should just be enough tension to let the spring all the way move up on the upstroke and all the way down to the movable bottom stop on the downstroke - of the take-up lever.

A jumpy check spring may indicate poor or marginal timing, or pinching of the top thread as it goes around the hook. If there is insufficient clearance for the top thread to clear the exit side of the hook, it will bind and cause loops on the bottom, split thread, or other problems.

[Uwe]

I decided to get to the bottom of my machine's issues in reverse at max stitch length. I now know how it snags the thread and why it occasionally skips a stitch in reverse. Exactly how to fix the issue, I'm still not sure about. 

I made a needle feed throat plate from clear acrylic so I see could what was going on below. I made a video for the occasion and it might be of interest to folks with a Juki TSC-441 class machine, even if they are not experiencing any issues.

On my machine the thread snag is caused by the top thread loop getting pushed into the race channel by the hook. Using thicker thread may actually avoid this issue because the thick thread is less likely to squeeze into the tight gap between the shuttle and race channel. I'm using size 138 thread in the video. I may need to tighten up the race channel a little (not sure how/if that is even possible.)

The hook-to-needle timing on my machine looks spot-on to me. Alas the hook does not go back quite far enough to make reliable stitches in reverse at max stitch length. Perhaps retarding the hook a little bit may improve clearance between the needle/thread and the tip of the hook in reverse at max stitch length.  Sewing at higher speed may also help, actually, as the hook gets tossed back and forth and is more likely to rest against the shuttle drivers push point. My slow-motion hand turning in the video does not create much momentum to toss the shuttle to the limit stops.

 Here's the video for your entertainment:

 

Edited May 27, 2017 by Uwe

[Constabulary]

Acrylic needle plate - EXCELLENT IDEA - not only for Cowboy 4500

[LumpenDoodle2]

Agree, what a great diagnostic idea. 

[gigi]

9 hours ago, Uwe said:

Here's the video for your entertainment:

Thank you for releasing another great video for the community!  We've learned a lot about timing from your videos.