Pfaff 3334 Box Tack Knife Blade alignment

[Carlo]

I have a pfaff 3334 bar tack machine configured to do square cross pattern. My father bought it about 50 years ago and it still works very well.  I have cleaned it up, and found access to a photocopied service manual, but the illustrations are unusable.  

When the machine finishes the box-square and I depress the left pedal, it lifts the foot and cuts the needle thread but does not cut the bobbin thread.I have tried aligning the knife bar, but it doesn't seem to help, the bobbin thread still doesn't get cut.

Any help is appreciated.  I attached a picture of the blades.

[Constabulary]

I have an English instruction manual for the 3334 (but no machine). I can scan it but that may take some days. So here are some pictures with information which hopefully are helpful.

Edited September 5, 2016 by Constabulary

[gottaknow]

From looking at the first picture. If you thread your bobbin thread through the tip of the finger on the bobbin case, it will put your bobbin thread where the knife will cut it. Don't make any adjustments to your knife system since it's still cutting your needle thread until the bobbin is threaded. It will sew that way, but not cut.

Regards, Eric 

[Carlo]

Constabulary, thank you!!!  The scanned diagram is viewable, if you ever have spare time a scanned version would be tremendous help.  I have a xeroxed version of the manual and can read it, I just can't discern the images very well.  The scans you posted are Great, I am saving them with my PDF so that I have them in the future.

 

Gottknow, I will report back to you, I am not by the machine until later today, but I think that's what I'm not doing correctly.  My father and I were setting up the machine and being that it's new to me, I set it up like his other Pfaffs (145, 545, etc) and did not insert the thread through #3, the bobbin finger.  I went back to the pdf and was able to see what I was missing because of your comment.  Thank you!  

 

By the way, the animated illustrations show up well in the PDF xerox, it's the pictures like Constabulary posted that do not show up.

 

[Uwe]

By coincidence, I came across a Pfaff 3334 subclass booklet in my stash of manuals yesterday. It won't help with fixing the the thread cutting knifes, but it relates to the machine in question. I scanned it in and made a text searchable PDF. It's surprisingly hard to turn scanned booklet spreads into a normal sequence of PDF pages!

http://docs.uwe.net/Pfaff 3334 Subclass Patterns Reading.pdf (for reading online) 

http://docs.uwe.net/Pfaff 3334 Subclass Patterns booklet printing.pdf (For printing the booklet: print duplex on letter size paper, fold in half and staple)

Edited September 6, 2016 by Uwe

[Carlo]

Uwe, thanks for the documents.  Any additional documents are much appreciated.  I have the 3334-115C.  I didn't see it listed, but it does a box-cross.  I knew there were various models, but didn't know there were that many.  

GottaKnow, you were right about the thread going through the finger like the diagram shows above.  However, that still didn't fix the thread cutting problem.  

After reviewing the diagrams that Constabulary posted, and GottaKnow's comment, I ensured the proper knife bar alignment and I properly threading the bobbin. I even went as far as sharpening both sides of the knife.  It didn't help.  I manually ran the machine to get to the last stitch and found that the timing is a bit off.  Per the manual, the knife bar motion on the knife cam  is supposed to start at the highest point of the final stitch as it begins to descend.  The knife cam timing is off by about 1/4 of the stitch from the highest point to the bottom point.  Not sure I want to mess with the knife cam too much because the manual says there are deviations based on the subclasses and there are no steadfast rules. I ordered some new knives to make sure they are not too short from sharpening.  

[gottaknow]

The new knives are the correct next step. Whenever I trouble shoot a machine, I try and look at the most likely event that is causing the issue. First the threading, you did that, knife sharpening is subjective. I have a honing machine that I sharpen knives on. The stationary knife must be exactly parallel across it's width or your cutting will be hit and miss. Replace the knives with new ones, then address your knife timing. New mechanics will often make the mistake of changing the hardest thing before checking the threading and then the blades. It's keeping the diagnostics in order that will save many a headache. Good luck.

Regards, Eric