Help with Pfaff 346-H3 skipping stitches and rotating bobbin case

[Lucasn7]

Hi, recently i bought a Pfaff 345-3H (i’m not 100% sure but it looks like a double needle version of the Pfaff 335) and it worked fine. I’ve done a few projects with it and so far no problems. I did not do anything in particular for as far as i can remember but now both bobbins are rotating and skipping stitches(i guess there is not anything broken with one because both have the same issue). 

 

I’ll try to explain what is happening but please see video link below. The loop of thread around the bobbin gets stuck between the bobbin case and the thing that keeps the bobbin from rotating (i don’t know how this part is called). The thread loop stops and gets pulled trough with a click. It looks like that is causing the skipped stitches. Sometimes the whole bobbin case gets pulled with the threat and the case makes a full turn and gets tied up. According to the video in this thread  i found https://leatherworker.net/forum/topic/85248-please-help-thread-is-too-tight-when-pass-bobbin/ the bobbin case should not be rotating and the stoppy thing opens and closes in the right time to let the thread pass. 

 

I’m not very experienced with leather sewing machines but i searched a lot and could not find a solution. At this point i’m not even sure if the bobbin is supposed to be moving or not... Any ideas on what causes this and how to fix this? Forward thanks!

Video of the problem:

 

[Constabulary]

well first of all that yellow thingy is quite annoying and disturbing - don´t what it is and why you shoot the Video with it. Also, seems you have no needle plate / throat plate on the machine - the machine will not sew properly w/o a needle plate / throat plate.

Please post pictures of your machine so we can try to see if some other parts are missing.

 

 

Edited September 11, 2019 by Constabulary

[mikesc]

I don't know the machine..but..
Is the thread supposed to enter the needle eye at that angle, ( looking at those two pairs of holes up at the needle holder end of the needle bar , are you missing a thread guide just before the top of the needle there ? , ) I'd expect it ( the thread ) to be closer to the needle on the way down to the eye, so as to follow the long groove on the needle..maybe your thread path is off..which would make your top tension off..which in some machines will give a click, and pull hard on the hook and bobbin case..and make it skip occasional stitches. Might not be all the reason for your problem, but could be contributory. ..

Edited September 11, 2019 by mikesc

[Wizcrafts]

You are missing the throat plate that has notches to hold the bobbin cases in position!

Here is a download link for the pdf instructions manual.

Here is a parts manual for the Pfaff 346-H3.

[Lucasn7]

Quote

You are missing the throat plate that has notches to hold the bobbin cases in position!

Hi, thanks for pointing out that the bobbins are rotating because of the missing throat plate! Now i see, indeed there is a slot that matches the rotating part. Actually i was disassembling my machine because the left needle made a bit of a scraping noise and sometimes broke the upper thread. I removed the plate to see inside and indeed i saw the needle scraping the GIB. Also i can see small marks on the GIB where the needle touched. After this discovery i tried my machine (handcranked) again and then the above happend… 

For the scraping: i’ve tried different needles and only my thinner needles (size 80/12) do not scrape compared to the normal size i use. According to the manual size 130/21 should be okay. Any ideas for this? 

Also thanks for linking the instruction manual. i did not find that one online.
Regards!

Edited September 11, 2019 by Lucasn7
Added quote

[Lucasn7]

4 hours ago, Constabulary said:

well first of all that yellow thingy is quite annoying and disturbing - don´t what it is and why you shoot the Video with it. Also, seems you have no needle plate / throat plate on the machine - the machine will not sew properly w/o a needle plate / throat plate.

Please post pictures of your machine so we can try to see if some other parts are missing.

 

 

Indeed i saw the yellow thing when i uploaded the vid. It is tape in an attempt to make less marks on the leather, a temporary solution.. In a future project i'll investigate if i can buy a new pressor foot/ grind the teeth or CNC one myself..
Indeed i was missing my throat plate, thanks for pointing out. Furthermore the machine is working except from the scraping sound (see post above) but that is not because i'm missing parts. As far as i know i'm not missing any parts.

3 hours ago, mikesc said:

I don't know the machine..but..
Is the thread supposed to enter the needle eye at that angle, ( looking at those two pairs of holes up at the needle holder end of the needle bar , are you missing a thread guide just before the top of the needle there ? , ) I'd expect it ( the thread ) to be closer to the needle on the way down to the eye, so as to follow the long groove on the needle..maybe your thread path is off..which would make your top tension off..which in some machines will give a click, and pull hard on the hook and bobbin case..and make it skip occasional stitches. Might not be all the reason for your problem, but could be contributory. ..

I have a double needle machine so the second hole is for the second needle i did not install at the moment. For as far as i know it is a double needle version of the Pfaff 335 series and threads the same. 

Thanks for your replies!

[mikesc]

No.. :) I don't mean the second hole for the second needle..I mean that the needle holder area appears to be missing something like thread guide, which would guide the thread more parallel to the needle ( and thus it would sit in the long groove on the opposite side from the scarf )..When I'm done preparing and eating dinner, I'll download your image and re-upload it with a mark to indicate what I mean..I may well be wrong, but your thread path looks to be too far away from the needle until it reaches the eye of the needle..

[Lucasn7]

1 hour ago, mikesc said:

No.. I don't mean the second hole for the second needle..I mean that the needle holder area appears to be missing something like thread guide, which would guide the thread more parallel to the needle ( and thus it would sit in the long groove on the opposite side from the scarf )..When I'm done preparing and eating dinner, I'll download your image and re-upload it with a mark to indicate what I mean..I may well be wrong, but your thread path looks to be too far away from the needle until it reaches the eye of the needle..

Aah i see, well spotted. Indeed, in the video i was not using the thread guide. Normally do use it but when this problem that occurred the thread snapped a lot so i took a shortcut. See attachment.

 

[mikesc]

Yes..that is what I meant :) It looked like the thread guide was integral ( part of ) to that block,( those twin holes ) I'd already downloaded the screen cap from this page of your video to draw in what should be the thread path through that guide, thanks for saving me the trouble of drawing it :)

Check your thread path further up..in particular the "take up spring" ( check spring ) ..it may be keeping the thread too taut..that will make it "snap".. and make the bobbin and hook click and miss occasional stitches..as can the timing being very slightly retarded..But I'd check the take up spring first..with the thread going through the thread guide..having more than one variable "off" is not the best way to "troubleshoot".. :)

Edited September 11, 2019 by mikesc

[Wizcrafts]

3 hours ago, Lucasn7 said:

For the scraping: i’ve tried different needles and only my thinner needles (size 80/12) do not scrape compared to the normal size i use. According to the manual size 130/21 should be okay. Any ideas for this? 

You can move each hook drive laterally. There should be frames holding the hooks that can be moved by loosening big screws. There will also be a bendable deflector on each bobbin case that is supposed to push the needle ever so slightly out of harms way as the tip of the hook approaches it. If your hook tips have burrs, they need to come out and be buffed smooth again, or replaced.

[Lucasn7]

16 hours ago, mikesc said:

Check your thread path further up..in particular the "take up spring" ( check spring ) ..it may be keeping the thread too taut..that will make it "snap".. and make the bobbin and hook click and miss occasional stitches..as can the timing being very slightly retarded.

I threaded the machine according to the official user manual so that should not be causing any problems. 
The take up spring might be to taut because it is made (and adjusted) to be pulled by two threads at the same time for both needles. I've adjusted the spring and i'll keep experimenting. 

[Lucasn7]

15 hours ago, Wizcrafts said:

You can move each hook drive laterally. There should be frames holding the hooks that can be moved by loosening big screws. There will also be a bendable deflector on each bobbin case that is supposed to push the needle ever so slightly out of harms way as the tip of the hook approaches it. If your hook tips have burrs, they need to come out and be buffed smooth again, or replaced.

Indeed i've noticed the tracks and slots but never knew they were for moving the hook drives. When i look closely i can see that the left bobbin assembly (scraping one) is a bit closer to the feed dog than te right one (second image). I've unscrewed the big screws in the slots and also on a block on the bottom side that looks like it needs to be moved in order to make room. But still i cannot move the hook drive. Also i'm a bit afraid to mess up the timing when adjusting the driving gear by loosen and fasten it... Any thoughts?   
Regards!

[Wizcrafts]

If you can't, or won't move the left hook assembly, try prying our the deflector tab a little to push the needle away from the hook. Most lockstitch machines pull the thread and needle to the left as they sew, which explains why that needle makes more contact than its right counterpart. I would personally try to move the left hook a smidgen. The timing gear can be tweaked later.

[Lucasn7]

Hi it's been some time since i replied to this thread because i was busy and after that i've only used the right needle. At this moment i'm making a bag and need to use the left needle again because the workpiece can't fit onder the arm properly.. If i use the left needle the thread or needle breaks in a few stitches. 

On 9/12/2019 at 5:54 PM, Wizcrafts said:

, try prying our the deflector tab a little to push the needle away from the hook

How does this work? I cannot figure it out. Also the machine looks like the whole hook assembly can be moved? Forward thanks