Cowboy cb4500 thread snagging on bobbin case

[michaelcbarr]

Hi all - I have a strange issue with the cb4500 which I don't think has been there before but I may just be going mad :D

 

The top thread is being picked up fine by the hook, but when it slides over the bobbin case to form the knot, it seems to snag on the little hole right at the bottom of the bobbin carrier and then snaps back up when the tension is increased at the end of the stroke. I don't think this is correct as it makes a loud snapping noise and I cant remember that happening before. It is still making stitches but seems to be putting a large strain on the thread and the rest of the assembly so I'm concerned.

 

I took the whole bobbin shuttle and race assembly out to clean it, oil it and reinstall. I also gently sanded the case to remove micro burrs around the hole. This seems to have helped a little bit but it is still snapping very loudly!

 

Link to video

 

I tried to compress the video to add directly to the post but can't get it small enough so apologies for the external link.

 

Mb

 

[CowboyBob]

@michaelcbarr So what size & type of thread is this?

[michaelcbarr]

Hey @CowboyBob, thanks for your reply. Currently using 277 top and bottom with a 200 needle. Tried a 250 needle but seems to be the same issue.

I'm making leather knife sheaths so this is stitching through 3 layers of 9/10 oz leather - so perhaps 12-15mm thick.

I have tried 2 layers and one layer but very similar issues. 

I have tried adjusting too and bottom tensions, and rethreading top and bottom thread in case there were snags somewhere along the path.

Mb

[Northmount]

7 hours ago, michaelcbarr said:

I tried to compress the video to add directly to the post but can't get it small enough so apologies for the external link.

Yes, can't make them fit here, so use YouTube or other video sharing site.  Best we can do for videos.

[shoepatcher]

It's catching on part of the hook.  Looks like the end of the tensions spring.  I would take off one you determine exactly what part and rind and buff that part out so noting to catch on.  I had one do this on another machine years ago.  I ground it down ever so slightly and buffed it out.  It corrected the problem.  Shit happens!

glenn

[Wizcrafts]

Oftentimes, when the top thread is snapping going around the shuttle it's because the timing is retarded. Or, it can be from excessive thread tension and too long of a throw on the check spring. A shorter throw gives some slack on top that may let the thread go around the shuttle without snapping.

[michaelcbarr]

Thanks all - i will have another look at tensions then I'll check if the timing has been thrown out. @Wizcrafts is the check spring throw something that can be adjusted on a cb4500 and of so, then how?

Mb

[Wizcrafts]

6 hours ago, michaelcbarr said:

@Wizcrafts is the check spring throw something that can be adjusted on a cb4500 and of so, then how?

Absolutely! Look at the lower tension disks. There is a spring wrapped around the inside of the bottom roller disk. It has a loop that sticks out to the right and a stopper bracket under it. The stopper bracket has a screw securing it to the faceplate. If you loosen the screw you can move the bracket up or down to control the travel of the check spring.

The spring that coils around the bottom roller disk is tensioned by rotating it one way or the other. It is locked down by a nut on the back of the housing it mounts to. Loosen the nut and turn the shaft with a screwdriver blade until you get the desired amount of spring tension to properly control the slack in the top thread as the take-up lever moves down from TDC. It should be preset for #277 thread by the dealer who set it up. That setting is also valid from #207/T210, but may be a little too strong for #138 thread and maybe a little weak for #346 thread. It is definitely too strong if you try to sew with #92 thread and needs backed off.

[michaelcbarr]

Thanks @Wizcrafts - I'll see what I can break over the weekend :D

Mb

[CowboyBob]

You might try decreasing the travel of the check spring(raise the bracket up) & like Wiz said the timing could be alittle slow causing it to drag.

[michaelcbarr]

Thanks @CowboyBob - I have tried some minor tension adjustments which haven't been successful. 

Next is the check spring, then the timing.

Mb