Pfaff 34 - troubleshooting skipped stitches & wheel feed issues

[ElfLeather]

tl;dr - what's the order of troubleshooting for skipped stitches?

I posted a little while ago about that Pfaff 34-5AL I bought the other week, thank you to everyone that gave me info. I replaced the 3-phase clutch motor with a servo, gave the machine a cursory cleaning, oiled it, and crash-coursed my way through birdsnesting issues. Eventually figured out that the tension assembly wasn't seated right, it wasn't releasing right, and my threading was a little off. After fabbing a replacement tension release pin and reseating the tension assembly, a few minutes messing with the upper and lower tension and no more birdsnesting.

Now that the birdsnesting is resolved, I'm getting issues with skipped stitches and failure to feed properly. I don't know if these are related issues. I'm testing with pigmented goatskin and nappa lambskin with 70 tex polyester thread

The feed issues look like - I'll sew maybe 10 or 20 stitches, everything looks fine, then the leather just stops feeding. This system comes with a wheel feed mechanism, which I'm unfamiliar with.

The skipped stitches are a consistent problem, maybe every 5th stitch. Sometimes 2 or 3 in a row.

What are my options for troubleshooting look like for feed issues and skipped stitches?

 

[Constabulary]

reg. skipped stitches -  is the needle insert correctly with needle scarf toward hook tip? Maybe needle bar set a bit to high (check needle hook timing)? Hook tip probably a bit to far away from the needle?

If you are looking for timing values or an English manual look for the Singer 31-18, the machine is very similar and has wheel feed too. Not sure how similar the wheel feed mechanistic is but that's the best crossover reference I think. Needle hook timing values are the same.

EDIT:

I have this manual:

Singer 31-17,-18,-21 Instruction Manual.pdf

Edited October 31, 2024 by Constabulary

[ElfLeather]

On 10/31/2024 at 1:40 AM, Constabulary said:

reg. skipped stitches -  is the needle insert correctly with needle scarf toward hook tip? Maybe needle bar set a bit to high (check needle hook timing)? Hook tip probably a bit to far away from the needle?

If you are looking for timing values or an English manual look for the Singer 31-18, the machine is very similar and has wheel feed too. Not sure how similar the wheel feed mechanistic is but that's the best crossover reference I think. Needle hook timing values are the same.

EDIT:

I have this manual:

Singer 31-17,-18,-21 Instruction Manual.pdf 508.01 kB · 3 downloads

Thank you for this manual, it's helpful in getting a sense of what to adjust on this machine. The needle scarf is facing the center of the machine, the hook hooks through it, maybe 3/32" above the eye. It looks like the needle's eye is a pinch low, if anything, and it's set as high as the needle bar permits (I took off the needle lock and cleaned any possible debris from the needle bar). I'm pretty sure the hook is at or close to the right clearance from the needle (a paper's width)
 

 

 

 

The other thing - I'm having trouble buying a larger pulley. I've seen pulleys for sale with shaft bores of 3/4", 1/2", 5/8", or 15mm, but I measured the pulley on this machine and it's 11/16", or 17.5 mm, which I've found precisely zero of, for sewing machines or anything else really. Am I just going to have to get a 5/8" bore pulley and have it machined to open up the bore? Or does anyone sell a bushing to bring a 3/4" bore down to 11/16"

Edited November 2, 2024 by ElfLeather

[kgg]

7 hours ago, ElfLeather said:

and it's set as high as the needle bar permits

What needle system are you using, 34, 134, 134-35 ??? (reference: https://www.thethreadexchange.com/miva/merchant.mvc?Screen=CTGY&Category_Code=needle-systems-pfaff-8-to-143-U-12#Models_34_to_70). You could also try and raise the needle bar up.

 

7 hours ago, ElfLeather said:

The other thing

The simplest way would be to leave the existing pulley alone and install a speed reducer pulley.

kgg

[Wizcrafts]

On 10/31/2024 at 2:18 AM, ElfLeather said:

The skipped stitches are a consistent problem, maybe every 5th stitch. Sometimes 2 or 3 in a row. What are my options for troubleshooting skipped stitches?

From your photo, the hook timing is really close to spot on. But, it may be a tish too early for your material. Try backing off the hook a couple of degrees so it is just 1/8" above the eye as the needle ascends.

As for regularly skipped stitches, they can be caused if the leather lifts as the needle comes up. On a standard foot machine, there are toes on either side of the needle to hold down the material. On a roller foot machine there is only the edge of the roller holding down the work. If the edge of the roller is too far away from the needle the material can lift. This causes the loop to dissolve before the hook picks it off the eye of the needle. So, see if there is an adjustment screw on the top of the roller foot to move it closer to the needle.

If moving the roller doesn't solve the skipped stitches, try changing the settings and positions of the check spring assembly. Perhaps you need to have a little more slack in the top thread so the loop is bigger and last longer at pick-off time. Most check springs have a stopper on the shaft that sets when the spring stops moving down. It only needs to hold the top thread taut until the tip of the needle touches the top of the material being sewn. If there is a curved slot with a set screw on the check spring's disks, try moving it to the right or left. If the check spring action is too strong, it can pull the loop out as the take-up lever starts up. There's an adjustment on the shaft where it mounts to the body. If you loosen a screw that connects the assembly to the body, you can use a screwdriver in the split threaded stud to turn the unit to loosen or tighten the spring action. Tighten the screw after you are happy with the new setting. The spring must have enough force to rise and lower all the way down to its bottom stop bracket (which is also movable).

[ElfLeather]

On 11/2/2024 at 7:16 AM, kgg said:

What needle system are you using, 34, 134, 134-35 ??? (reference: https://www.thethreadexchange.com/miva/merchant.mvc?Screen=CTGY&Category_Code=needle-systems-pfaff-8-to-143-U-12#Models_34_to_70). You could also try and raise the needle bar up.

 

The simplest way would be to leave the existing pulley alone and install a speed reducer pulley.

kgg

It's a 34-5AL, and it's not one of the variants listed as an exception, so it's system 34 neeldes. I went back and forth but ended up getting system 34 needles, and it seems to be right. 

 

oof dropping another hundred-something dollars on a speed reducer. but that does seem the most straightforward way of resolving the speed issue.  I'll try it for a bit without and keep this option in my back pocket

 

On 11/2/2024 at 9:02 AM, Wizcrafts said:

From your photo, the hook timing is really close to spot on. But, it may be a tish too early for your material. Try backing off the hook a couple of degrees so it is just 1/8" above the eye as the needle ascends.

As for regularly skipped stitches, they can be caused if the leather lifts as the needle comes up. On a standard foot machine, there are toes on either side of the needle to hold down the material. On a roller foot machine there is only the edge of the roller holding down the work. If the edge of the roller is too far away from the needle the material can lift. This causes the loop to dissolve before the hook picks it off the eye of the needle. So, see if there is an adjustment screw on the top of the roller foot to move it closer to the needle.

If moving the roller doesn't solve the skipped stitches, try changing the settings and positions of the check spring assembly. Perhaps you need to have a little more slack in the top thread so the loop is bigger and last longer at pick-off time. Most check springs have a stopper on the shaft that sets when the spring stops moving down. It only needs to hold the top thread taut until the tip of the needle touches the top of the material being sewn. If there is a curved slot with a set screw on the check spring's disks, try moving it to the right or left. If the check spring action is too strong, it can pull the loop out as the take-up lever starts up. There's an adjustment on the shaft where it mounts to the body. If you loosen a screw that connects the assembly to the body, you can use a screwdriver in the split threaded stud to turn the unit to loosen or tighten the spring action. Tighten the screw after you are happy with the new setting. The spring must have enough force to rise and lower all the way down to its bottom stop bracket (which is also movable).

 

Thanks for all these suggestions. Before making any changes, I tried sewing some slightly stiffer pleather-y material and of course it sewed beautifully immediately. The "work is lifting during sewing" hypothesis is probably the right one. The lambskin is very soft, and I did see bunching and difficulty keeping the stitches even when I tried it. There's nothing holding down the right side of the stitch so maybe this is something to look into. 

if preventing the work from lifting doesn't resolve my issue, I'll look into the check spring and needle position/timing.

 

Thanks again everyone for helping me troubleshoot this machine, this is all really helpful.

 

 

[ElfLeather]

2nd edit: Is there any reason I shouldn't remove the stock pulley and handwheel and replace both with an 8" pulley, now that I've figure out how to remove it? Disregard the following post, unless you made the same mistake I made and mistook the goofy 17.5 mm "shaft" behind the handwheel for the actual driveshaft.

Unrelated question I'll put here, so as not to clutter up the front page - 

I can't figure out how to remove the handwheel from this machine. Looking at the parts catalog and the machine itself, all I can see that holds the handwheel to the shaft are 2 set screws. I removed both of them and dropped some oil into the holes, but even with a pulley puller, all I'm doing is damaging the screw head at the end of the shaft. Any recommendations? Anything obvious I'm missing?

edit: If you're wondering why I'm trying to remove the handwheel, I need the shaft length it's occupying for a larger pulley. I want to replace the 3" pulley with an 8" pulley, but the length through the bore is much much longer, more than an inch. I figure if I have an 8 inch pulley, it can do double duty as the handwheel.

Edited November 5, 2024 by ElfLeather

[Constabulary]

remove the slotted axial end screw from the top shaft first. The hand wheel is attached to the shaft with 2 set screws. Remove them and if the hand wheel is not gummed with old oil (happens) you should be able to pull it off the shaft. If it does not move use a rubber hammer or piece of wood + hammer or a gear puller. If you don´t dare leave it where it is and use a speed reducer instead.

Edited November 5, 2024 by Constabulary