31-15/31-20

[DonInReno]

Back in my 20’s as a lowly Forest Service seasonal firefighter in the middle of Wyoming, the smoke jumpers in Missoula (who manufactured their parachutes and packs in the off season) had a “commercial sewing machine” in the list of inter-governmental surplus so I filled out the form and a month later it showed up table, needles, thread and all.  Honestly I don’t know if it was a 31-15 or 31-20, but it sewed 138 weight thread well and by the end of the summer all the guys on the crew learned to sew. There’s a soft spot for the machine and when a nearby repair shop was essentially giving this 31-20 away I picked it up.   It was made in the 1920’s and is obviously a past factory machine with an inventory badge and at least one repaint.  It was well used for sure and surprisingly well maintained by someone who took the time to not bugger up a single screw slot or let schmoo build up anywhere.  It looks like it was last taken out of service decades ago when a needle broke or bent and rounded off the replacement non-singer hook a bit.  

I’ve heard the wives tale repeated numerous times online that the 31-20 bobbin is larger than the 31-15 ... it’s actually a slightly smaller bobbin and case, and the shuttle sits in the same size hole as the 31-15 (I’m assuming that’s to allow clearance for thicker thread in the 31-20 since the same bobbin/shuttle combination was also used in the 31-22 which was labeled as a heavy thread model). As far as I can tell from early manuals these three parts are the main difference between the 15 and 20  (not counting presser feet/feed dog/needle plate part numbers).

All my flat bed machines share the same table so a few adjustments were made to the cutout and it gets its own belt since the hand wheel pulley is so tiny.  I’m looking forward to the bobbins and case showing up to see if what’s left of the resharpened hook will be long enough. It will be a good starter machine for someone, especially if it sews 138 well.

What has worked to adjust the needle/hook gap? It’s as non-adjustable as hook timing? Seems a paper shim between the bed and shuttle carrier ring is the place to start? With a new needle it wouldn’t hurt to close the hook gap .005”

[Ken Nelson]

I have owned both 31-20 and 31-15 and the 31-20's I have had  do have a larger bobbin case and bobbin than the 31-15 have.  I have upgraded 2 31-15 to the bigger bobbin case and bobbin by changing out the whole shuttle assembly.  Not a hard job.

[DonInReno]

Hmm... yep I stand corrected - I figured the fatter bobbin on the 31-15 would easily hold more thread even though the diameter is slightly less.  The 19131 bobbin has .003 cubic inches more volume - less than  2% so I’m guessing nobody could tell the difference.

31-15 uses a bobbin #2996.   .460” x .800” .175 cubic inches

31-20 uses a bobbin, #19131  .360 x .910” .178 cubic inches

[Ken Nelson]

I thought I would post a picture of the Singer 31-20 I have in my shop.  I don't really know why I keep it as I rarely use it these days.  A few years ago, I was using it quite a bit with a roller foot on it sewing designs in padded seats on saddles and some of my college boy buddies' girlfriends were using it to make boot top purses.  It has 4 or 5 original feet and the original treadle stand is kind of net.  Note the original pittman on it.

The post office dropped it on the way to deliver it and broke a vital piece of casting off of the bottom and I had a friend of mine, who is a machinist repair it and you have to look close to see it and it has worked good for 10 years with no issues on the repair.  I have another one of these treadle stands that does not  have a top and has a smaller wheel on it and a  metal pittman that is not original but it would be good if someone wanted an off grid stand for any standard size industrial sewing machine.

I put this machine in a power stand with a servo motor when I use it.  pulls a remarkable stitch with 92 on top and will do a good job with smaller sizes of course.  I have used 138 in it just to see if it would do it and it does but I don't sew with 138 in it.  That is what my chap machine is for.

Edited July 29, 2018 by Ken Nelson

[dikman]

There's something very classy about those old treadle stands. I restored one once, but sold it because a.) I realised I wasn't going to use it much and b.) I didn't really have the room to keep it.

[DonInReno]

That stand does look nice with the machine.  

[Ken Nelson]

Too bad I have never mastered operating a treadle sewing machine.  I have no use for either of these stands but they are COOL.

[DonInReno]

In the past I’ve suggested a machine like this, even used this exact machine as an example, to someone interested in the cheapest way humanly possible to sew 138 weight thread.  

I didn’t want to wrap up any more $$ in this machine than absolutely nessessary so the bobbins, bobbin holder and roller foot were ordered and shipped from China - they estimated delivery in 4-5 weeks which is about right.  At half price of similar cheap parts shipped from a US location it’s simply amazing that there’s any margin left for the seller.  The bobbin cases came in a two pack, which is good because one had a snag that made it useless until I feel motivated to take it apart and modify the catch.  The bobbins are nicely machined and could easily be confused for others costing  5x as much.  The roller feet are interesting - crude in some respects, but with nicely machined wheels.  At first it looked like the body that attaches to the presser foot bar was injection molded powdered steel, but it’s just a steel looking finish on an aluminum part.  Still, for something like $5 each they are fun to play with without breaking the bank.

Keeping in mind I had no idea how it sewed before being shelved and the hook is less than perfect with a point that’s been filed down just to the point of being sharp and recontured, it’s a little bit of a crapshoot as to what’s going to happen when the needle is first threaded.

With 138 nylon top and bottom and a #23 fabric needle it sews canvas quite well.  I sewed 8 layers (1/4” compressed) of Carhartt canvas straight, hard right, hard left, all without a skipped stitch so the hook is doing pretty good.   While a roller foot is a small improvement, it’s still worlds away from a good triple feed machine.

 

[Rockoboy]

I have a renewed respect for my 31-20. Its been so long since I even powered it up, but this thread has motivated ... reminded me that I should use it more often.

[DonInReno]

On 8/26/2018 at 5:45 AM, Rockoboy said:

I have a renewed respect for my 31-20. Its been so long since I even powered it up, but this thread has motivated ... reminded me that I should use it more often.

It amazes me that this rather simple design is so old and has touched so many people over the years.