Something Wrong, What Do You Think?

[alexitbe]

I have a Pfaff 38-6, which is basically a slower runing version of a 138. It is a very old version of the 38, I think before the War.

When I go forwards, the tension is fine but when I reverse the upper thread tension is too little.

I have timed the feed dogs to the setting it should be for the 138, which is stationary at 4mm above minimum needle height.

When I got it, the feed dogs were stationary at about 2mm above the minimum needle height. Might this be the problem?

TOPSIDE- forwards (right line) and reverse (left line)

UNDERSIDE - forward (left line) and reverse (right line)

What do you guys think?

Cheers

Alex

Edited January 10, 2016 by alexitbe

[shoepatcher]

Alexitbe,

Obviously, when it goes in reverse, the tension is much tighter in the bobbin area which would indicate that the top tension is being released. I would check the take up spring and also make sure the tension discs for whatever reason are not being pushed and released to start. I would also look at the thread coming out of the bobbin case when in reverse to make sure something is not tightening that tension. I believe the problem is in the top tension somewhere and that would be the take up spring.

glenn

[Cobra Steve]

Alex, I agree with Glenn. It seems that the top tension is the problem. Try tightening the top tension a half turn at a time and test.

[alexitbe]

Hi Glenn and Steve,

Thanks for the help.

At what point in the needle cycle should the take-up spring move down? I have no idea. I can compare if it is at a different point in the needle up-and-down cycle for forward and reverse. However, I don't know the ideal point that this should happen.

I have tried steadily increasing the upper tension, whilst in reverse, and it is very strong now, yet it is still getting pulled down by the lower thread. Whilst running the sewing machine forward, it is easy to balance the thread tension and it is also a very light presure that does this. Surely there should not be so stark a difference in required tension for forward and back?

Lastly, if I manage to get the upper tension correct for reverse, surely it will then be too strong for forwards direction and pull the lower thread up?

Cheers
Alex

Edited January 12, 2016 by alexitbe

[Uwe]

In a properly adjusted machine the bobbin tension should not change significantly when switching from forward to reverse. You should not have to adjust thread tension when switching direction. Adjusting the top tension may only fix the symptom and not the root cause.

It's all relative when it comes to thread tension. Either the bobbin tension gets tighter (or binds?) or the top tension gets loose for some reason. I suspect the trouble originates in the bobbin/hook area.

The bobbin tension may appear to be tight in reverse for various reasons. Perhaps the thread struggles to wrap around the bobbin, or the bobbin case opener doesn't quite work as well in reverse (or not at all), perhaps a loose screw causes some thread passageway to open or close slightly when changing direction. I'd tilt the machine back and closely observe what's happening underneath as you make a few hand-turned stitches both forward and reverse. I little close-up video with a decent phone camera is worth about 15 postings, in my experience.

I'm just guessing at some of these things, I don't have the machine in front of me.

As for the take-up spring, the rule I read somewhere is that the spring should rest on the adjustable support and no longer pull on the thread the moment the eye of the needle enters the material. I'm not sure if this is a general rule or if it was a machine specific one.

Check the basics, too. Properly threaded? Bobbin spin direction OK? Top thread release works when lifting the presser feet? Needle/thread size a good match? Needle-to-hook timing good?

Edited January 12, 2016 by Uwe

[Uwe]

Since you asked what I think, let me also say that I think descriptive topic titles are helpful. Something like "Thread tension problems in reverse on a Pfaff 38-6" contains considerably more relevant information and gets the right people involved.

Before I get lectured on free speech and start another topic derailment, let me point out that of course everybody has constitutional/god-given/human right to start a topic with whatever they choose to say and nobody can make them use descriptive topic titles if they don't feel like it.

[alexitbe]

HI Uwe,

Thanks for the sewing advice.... I will take a careful look tonight, when at home.

I tried to change the title, but the edit function is no longer available. You are right, its not very descriptive...

Cheers

Alex

[Gregg From Keystone Sewing]

Always learning something new here, never heard of a 38-6, but have seen many 138- machines. And I thought the 138 was really old! The 38-6 will be around as long as any machine if it's anything like the 138s.

[alexitbe]

Hi Gregg,

Well the 38-6 is the prequel to the 138-6. It runs at a much lower speed than the 138-6, I think about 800...

I think mine was made before the war

Cheers

Alex

[alexitbe]

Ok..... I have done a few things....I

I cleaned the hook area with kerosene, it did not look like it had been cleaned for a long time and there was plenty of fluff...

I then cleaned the upper thread tension gizmo. There was a washer behind the two tension discs acting as a spacer, that on closer inspection was more like a minature pully. So I put it between the two disc for the thread to sit in. The discs now seperate a little when the presser foot is lifted whilst it didn't before. I think I would like a little more, its leass than a mm. I am not sure this made any difference to the stitch.

Lastly, I changed the needle bar height. I set the stitch width to max 4.5 mm. Turned the wheel until the hook was just behind the needle. THe needle eye was almost level with the hook, so I droppped it a little.

I know get good stitching back and forth for the straight stitch. The presure does not change depending on direction. This is really good progress for me, since I can happily start making stuff now.

However, I still get a change of upper thread tension for the zizag on reverse...I think the zigzag is better though... I must look more closely tmrw.

Thanks for all the help.

Alex