Pfaff Metal Thread Type?

[dikman]

My Pfaff 335 needs one ot two bits replaced, but I'm blowed if I can figure out the metal thread system used. Being a European machine I assumed it would be metric, but while I have a large assortment of metric screws, nuts and bolts (and a few taps and dies) I've had a devil of a time trying to match the threads used.

Anyone know for sure what they use?

[Cascabel]

Not sure regarding Pfaff machines, but Singer uses their own proprietary threads, which are non-standard. You may be dealing with a similar situation with your Pfaff. I have custom made screws for singer machines on my lathe, so you may want to try to find somebody in your area with a screw-cutting lathe to make what you need if you cannot order from a Pfaff distributor. Don't try to force a standard screw to work, as you can damage the threaded holes beyond repair.

[Constabulary]

what particular screws are you looking for?

[Uwe]

Perhaps this chart helps:

Specifications of historical Thread Standards for sewing machines.

I found the chart referenced on an external discussion forum for the practical machinist.

A part number is always useful when trying to figure out particulars - can you find the screw you're talking about in a parts diagram for the Pfaff 335?

I've used AAASEW.com in the past to research and occasionally order oddball parts and screws. They have a "screws page" that I've used to find things by part number using my browser's find function. Some screws have sizes listed and the 9/64-40 and 11/64-40 sizes seem to pop up more than others.

Edited November 26, 2015 by Uwe

[dikman]

Thanks guys. I've already run into the issue with Singer, so I bought a couple of cheap machines and gutted them for parts.

There are two bits I'm looking to fix at the moment on the Pfaff (it's an old model, btw, not the one in the parts list that Uwe provided), one is the screw on the top that adjusts the presser foot tension, the other relates to the edge binder - one of the brass "nuts" is missing, and while I can easily turn a new one I can't match the thread size of the existing bolt! A 3/16" Whitworth actually almost fits the top adjustment screw, it screws in ok (with no forcing) and does work, but I can feel that it's not quite a perfect fit.

Judging by that chart, Uwe, it appears that there is significantly more variation in screw threads than I realised! (My life was somewhat simpler before I got into sewing machines - I usually needed either Whitworth, very occasionally a BA thread, metric - reasonably standard size/pitch - and, in the case of old firearms, the US system of sizing. Now I'm faced with all manner of weird thread sizes. ).

Edited November 27, 2015 by dikman

[Uwe]

I've not seen a parts manuals for the old casting Pfaff 335's. However, the head portion should be mostly identical to the Pfaff 545 for which there are parts manuals available , but they use multiple foot pressure schemes.

If you can see the bolt part, you can always go old school and simply measure the diameter with a caliper and count out threads/distance to figure out pitch and find a suitable match. Most tap/die sets also have little thread pitch gauges that are useful to determine pitch.

If that fails, a photo with an arrow will go a long way towards mobilizing the resident detectives.

[dikman]

I've figured out the two thread sizes - the edge binder nut is an M4 x 0.7 pitch and the pressor tension is M5 x 1.0. I have a lot of (assorted) metric bolts used in various electronic/communications assemblies/racks/panels etc, and not one of them has that particular combination of size and pitch. It appears that, at least in that particular industry, they are not "standard" sizes (e.g. M5 only comes in 0.8 pitch and I have to go to M6 to get 1.0 pitch).

My tap and die set covers M4 x 0.7, but not M5 x 1.0. At least I now know what I'm looking at.

[Uwe]

Sewing machine manufacturers happily mix fractional, metric, and specialty threads on the same machine.

There are also a few places where the metric and fractional systems line up confusingly close. In my threading adventures I've noticed that, depending on tolerances and material, an M5-0.8 is interchangeable with a #10-32 bolt/nut. The #10 bolt diameter is just under 5mm, as are my M5 bolts; and fractional 32/inch thread pitch is 25.4mm/32=.7935mm. A #10-32 bolt often fits nicely into M5-0.8 nut, but a M5-0.8 bolt does not necessarily fit onto a #10-32 threaded hole.

I found this out some time ago taking my (assumed made-in-germany metric) mystery bolt to the hardware store to get more, test fitting it nicely into the M5 thread on the test board - yay! So I happily buy a bunch of M5 bolts and when I got home it wouldn't fit into the threaded hole the mystery bolt came from - ugh.

Your shouldn't-really-exist M5-1.0 thread looks suspiciously close to a #10-24 on the spec sheet (just under 5mm diameter and 24/inch fractional thread pitch is 25.4mm/24=1.05mm)

A short nut with five or so threads is more forgiving than a deeply threaded hole in a machine.

Edited November 28, 2015 by Uwe

[jimmy eng]

I ran into the same issue with my 335 I recently bought and needed the stitch length lever replaced (the machine went through the van window whilst moving it when I turned a corner!). I have an older model 335 and no repairer I contacted had a contact to get the part, the rod bent and snapped in half, so I got an Engineering business to make the part. The thread and rod was in between standard sizes so they had to make it from scratch. Cost me AU$170 including GST.

I haven't used this type of machine before so I was wondering where I could source the thread and needles (I bought it on Gumtree). I have one spool of poly thread that happened to suit it (bought from the op shop!).

[Trox]

I have to ask the same question as Constabulary asked before, what screws are you looking for? When it comes to adjustments screw like the thread tension and stitch lever adjustment they are special screws with fine threads. It got to be like that when it's for adjustments. Old Pfaff spare parts might be hand made in Germany if they are obsolete, that's expensive. Some are still avaiable.

Tor