Bouncing stitch length levers

[northliftbelts]

Hello! 

I've been scouring the google, this forum, everywhere, to try to solve my issue of a bouncing stitch length lever on my adler 69 and pfaff 93. As the feet pull the material, my stitch length lever bounces upwards and shortens the stitch. I've been through the entire adler 69 service manual, and for the life of me cannot find a resolution. Would love some help! Thanks so much in advance. 

[Wizcrafts]

I used to have a Juki LU-563 that had a bouncing stitch lever. The faster I sewed, the shorter the stitches became. I had to replace the spring that held it in position. Many years ago. Look at the inside of the lever and see if there is a spring that's maybe stretched out, or missing, or loose.

[northliftbelts]

Hello Wiz, 

It does have a spring but seems like it has a good amount of tension on it.

I remember I had a similar issue on my 441 clone, which just required me to tighten a screw inside the lever chamber. I cannot find a corresponding screw in the 69.

There is also some forward/backward play in the feed dog, which at times results in my needle missing the needle hole anteriorly, and breaking/bending. The manual goes over that positioning, but nothing specifically about this play, which to me seems excessive.

 

Thanks for the response!

[Uwe]

Here’s my two cents worth:

1: You need need find out why there is play in the feed dog. Something must be loose, worn, or incorrectly adjusted. It may just be the screw that holds the feed dog itself.

2: The bouncing lever may be due to the feed mechanism touching something it shouldn’t. When certain mechanical linkage movements are restricted by hitting something solid, the mechanism either stops hard (ok-ish), or it keeps moving a wee bit and bends (bad), or moves a lot and breaks (bad), or it keeps moving and something else in the linkage moves out of the way to compensate (ok). That lever moving may be the mechanism compensating for lack of movement elsewhere. Feed mechanisms vary greatly between machine designs. I believe the 69 design generates horizontal feed motion from an eccentric on the main shaft.  

If the feed mechanism touches something even just lightly, it will still greatly increase pressure and wear on the linkage and that may lead to worn/loose linkages that may cause play in feed dog movement.

 

Edited January 12, 2023 by Uwe

[northliftbelts]

Uwe, 

 

Thank you so much for the reply. I found the culprit for the feed dog play - it was a new bolt that came with a binding attachment system. It was not large enough to fit into the hole that moves the feed dogs (See pic). I swapped it for the old screw and the longitudinal feed dog play has reduced from 0.5mm to around 0.1 or 0.2, barely noticeable and a huge improvement.

 

 

Regarding the lever bouncing - I'm still at a loss. Your thoughts make a lot of sense - something is rubbing up on something else and the lever's play is the weakest link that allows for a mechanical compensation. The machine stitches very well now, and the bouncing happens the most at the longest stitch lengths. There is an audible click coming from the rear right of the machine on every stitch however, and it coincides with a little jump of the lever. It seems to happen near the middle-end of each stroke cycle, before the needle leaves the material. 

 

Do you have a technical manual for this thing? The service manual just doesn't go into this at all, but I have found some older, far more technical manuals for this machine, they are just hiding behind paywalls to shady websites it seems.

[shoepatcher]

The feed cam on the top shaft may be out just a little bit.  Lets see if I can remember??   Nothing in the mechanics manual for the 69 class that I can see.

Put machine at 0 stitches.  Run the machine slow.    If it the reverse lever moves even a little, the feed cam is off\ and has to be recalibrated.

glenn

Edited January 12, 2023 by shoepatcher

[Quade]

My Juki had the bouncing stitch length problem. 

It turned out the feed dogs were contacting the top plate on one end of the travel and that was enough to make it bounce the lever. I was able to tell by taking the screws out on the plate over the feed dogs then manually advancing the machine. At part of the cycle I could see the plate being pushed up.  That's where the dogs contacted the plate.  Adjusting the feed dog position and re-centering it made this problem go away. 

On my Juki, it wouldn't bounce on short stitch lengths but would bounce more, the longer the stitch length. That's because with short stitch lengths, the feed dog travel was also short so it didn't contact the top plate. 

Edited January 13, 2023 by Quade
Added details.

[northliftbelts]

On 1/13/2023 at 8:11 AM, Quade said:

My Juki had the bouncing stitch length problem. 

It turned out the feed dogs were contacting the top plate on one end of the travel and that was enough to make it bounce the lever. I was able to tell by taking the screws out on the plate over the feed dogs then manually advancing the machine. At part of the cycle I could see the plate being pushed up.  That's where the dogs contacted the plate.  Adjusting the feed dog position and re-centering it made this problem go away. 

On my Juki, it wouldn't bounce on short stitch lengths but would bounce more, the longer the stitch length. That's because with short stitch lengths, the feed dog travel was also short so it didn't contact the top plate. 

Quade, 

I have went through the entire service manual, done every step in that book - the feed dogs are lying perfectly in the feed plate. Im glad you figure it out though! It did get me thinking, maybe theres some spacing issue between the needle and presser feet. 

[northliftbelts]

On 1/12/2023 at 5:10 PM, shoepatcher said:

The feed cam on the top shaft may be out just a little bit.  Lets see if I can remember??   Nothing in the mechanics manual for the 69 class that I can see.

Put machine at 0 stitches.  Run the machine slow.    If it the reverse lever moves even a little, the feed cam is off\ and has to be recalibrated.

glenn

I did adjust the feed cam I believe, I'll check your process to see if it bounces at 0 stitches. The whole machine now sounds like it is just working really hard. i can't get a nice slow speed on it, even with my servo. Takes a lot of power to overcome this feeling of tension in the machine, and by the time it does, its stitch speed is quite fast and pulls my work out of my fingers. 

Strange! THank you for your thoughts. 

[Quade]

Quote

the feed dogs are lying perfectly in the feed plate. 

If you set your stitch length to the minimum does it still bounce? 

Quote

The whole machine now sounds like it is just working really hard.

What servo are you using? My servo had a built in brake that made it near impossible to manual turn the cranks unless I was pressing on the pedal some. I removed the brake. I have my machine speed reduced so even the fastest speed isn't that fast. 

 If you take the belt off, can you feel it binding when you manually cycle it?  If yes, I might experiment by maybe disconnecting the upper from the lower section of the machine and see if the upper still binds. 

Edited January 15, 2023 by Quade