Compound Gear for Kenmore Sewing Machine Stitch Selector

[RobinHood]

Was doing some maintenance on my coveralls (patching holes) when the sewing machine stitch selector failed. This is a 1994 vintage machine, made in Taiwan. And yes, I have to repair it because it is the boss’s machine… (or buy her a new one).

After disassembly of the sewing machine, I found this:

It is actually three pieces - two injection moulded plastic gear halves and the steel hub.

A view from the obverse and a side view.

This compound gear (spur gear together with a bevel gear) was injection moulded as a unit and then pressed onto the steel hub. The hub has knurl marks for better grip. The reason the gear failed was because of a manufacturing defect. You can clearly see the voids on the left hand side of the two halves.

Some measuring and calculating revealed that they are 32 DP gears. I happen to have 6 of the set of 8 32 DP involute cutters (two are missing; one of them being the 26T to 34T one).

I am going to make the gear from two parts: a 20T spur gear pressed onto the hub extension of the 27T bevel gear (this is the cutter that is missing - I’ll use the 25T cutter I have and call it good). The whole thing will then be pressed & locktighted onto the OE steel hub. Going to use aluminum for the material. I will have to make some arbours to hold the individual parts for machining.

Pictures to come once I get to making the gear(s)…

 

[DPittman]

I look forward to seeing the project. I'm sure you will do a fantastic job. The only thing that surprises me is that the gears are DP and not metric module.

 

[RobinHood]

They could well be the Module equivalent of DP 32. The OD of the 20T spur gear measures about 0.690 with the dial callipers. 32 DP with 20T calculated comes out to 0.688. I call that close enough.

This gear does not turn constantly. It is only used when selecting one of the 32 available stitch forms on the machine. There is a profile drum with a follower arm that determines the pattern. The gear just changes the position of the follower arm.

 

[phaxtris]

oh this looks tough

just food for thought, by making it from aluminum you might be moving the failure point from that gear to maybe something more difficult to repair

 

[deleted_user]

Was doing some maintenance on my coveralls (patching holes) when the sewing machine stitch selector failed. This is a 1994 vintage machine, made in Taiwan. And yes, I have to repair it because it is the boss’s machine… (or buy her a new one).

After disassembly of the sewing machine, I found this:
View attachment 21288
It is actually three pieces - two injection moulded plastic gear halves and the steel hub.

A view from the obverse and a side view.
View attachment 21285

View attachment 21289

This compound gear (spur gear together with a bevel gear) was injection moulded as a unit and then pressed onto the steel hub. The hub has knurl marks for better grip. The reason the gear failed was because of a manufacturing defect. You can clearly see the voids on the left hand side of the two halves.

View attachment 21286

Some measuring and calculating revealed that they are 32 DP gears. I happen to have 6 of the set of 8 32 DP involute cutters (two are missing; one of them being the 26T to 34T one).

View attachment 21287

View attachment 21290

I am going to make the gear from two parts: a 20T spur gear pressed onto the hub extension of the 27T bevel gear (this is the cutter that is missing - I’ll use the 25T cutter I have and call it good). The whole thing will then be pressed & locktighted onto the OE steel hub. Going to use aluminum for the material. I will have to make some arbours to hold the individual parts for machining.

Pictures to come once I get to making the gear(s)…

I like that you can sew.

It is a skill everyone should have. I have a pfaff 360 all mechanical all metal cams and gears, so no breaky...

 

[RobinHood]

just food for thought, by making it from aluminum you might be moving the failure point from that gear to maybe something more difficult to repair

I thought about that as well. I do have some Delrin I could make it out of. The problem with that is how to bond the two gear to each other. Acetal is a tough material to bond. Not much of anything bonds it well reliably that I am aware of.

Aluminum avoids that problem.

If the machine lasts another 28 years after the repair, we should be very happy.

 

[RobinHood]

I like that you can sew.

We had to learn the basics in school as part of home economics. Girls got to go to the shop for both woodworking and metal working basics.

 

[DPittman]

I like that you can sew.

It is a skill everyone should have. I have a pfaff 360 all mechanical all metal cams and gears, so no breaky...

Ha ha now I know I'm among friends that won't laugh at me....I too sew my coveralls and work jeans. My wife doesn't seem to care to do that too much.
I'm at the mother in laws right now and I was just admiring one of her old sewing machines that is all metal and it too is a Pfaff. Apparently that was a good name but I certainly had never heard of it.
Even the old basic sewing machines are pretty cool pieces of mechanization.

 

[Chicken lights]

We had to learn the basics in school as part of home economics. Girls got to go to the shop for both woodworking and metal working basics.

Sewing, much less tailoring, is a dying art I feel. I wouldn’t mind knowing more about sewing but it’s a skill not often needed

Books mention darning socks and nobody does that today, I’d be curious how many years ago this was common

 

[RobinHood]

This was in 70s and early 80s in Europe.

 

[PeterT]

I can't quite tell by the pictures, do you think the set screw pressure is acting to push the hub open & split the assembly? Does this gear engage another plastic gear? Aluminum should be fine I imagine. Metal on plastic is quite common on many RC heli/car applications, application specific of course. The plastic runs smooth & quiet that's for sure. Yes Delrin & UHMW & nylon can be a bugger to bond & not without its machining challenges in certain modes.

 

[RobinHood]

I don’t think so. The two set screws are in the thickest part of the hub (12 mm OD). The ID is a very good sliding fit on a steel shaft. Not much pressure required to lock the gear assembly to the shaft.

Both the bevel and the spur gear engage on other plastic gears.

The only time the gears actually move is during the stitch selection process. If one selects straight stitch, for example, it will remain in that position until that type of stitch is no longer needed - could be a very long time…

 

[deleted_user]

We had to learn the basics in school as part of home economics. Girls got to go to the shop for both woodworking and metal working basics.

Exactly the same at my high school, but my mom had already taught us to cook, sew and do macramé.

I sew fairly often too...

 

[deleted_user]

Ha ha now I know I'm among friends that won't laugh at me....I too sew my coveralls and work jeans. My wife doesn't seem to care to do that too much.
I'm at the mother in laws right now and I was just admiring one of her old sewing machines that is all metal and it too is a Pfaff. Apparently that was a good name but I certainly had never heard of it.
Even the old basic sewing machines are pretty cool pieces of mechanization.

Pfaff is an awesome old stock brand. I almost bought a leather working business, as part of the negotiations I worked there for a month and got to use some serious sewing machines... most were pfaffs. I used the opportunity to make a new dodger for my father in law's sail boat.

I really want to buy one with a walking foot to do more leatherworking, but I am stuck hand stitching or doing very light work on my 360.

I have a modern pfaff as well.

 

[deleted_user]

when you can sew you can make nice hats...

 

[DavidR8]

Could that be 3D printed more easily?

 

[Tom O]

Sewing, much less tailoring, is a dying art I feel. I wouldn’t mind knowing more about sewing but it’s a skill not often needed

Books mention darning socks and nobody does that today, I’d be curious how many years ago this was common

Dad use to darn his socks using a lightbulb in the 60’s.

 

[deleted_user]

Dad use to darn his socks using a lightbulb in the 60’s.

Brilliant.

I darn my very well worn levis when they wear a hole in the ass... because you have to save the most comfortable pairs of jeans... but I have a special function on my sewing machine..

 

[6.5 Fan]

I need to dig out my late wife's sewing machine and install new zippers in 2 pair of coveralls. A couple of local ladies do this work but i can buy new coveralls cheaper than what they charge for a zipper install. Can't be that hard.......
For the gears i think aluminum is the way to go.

 

[Dusty]

I need to dig out my late wife's sewing machine and install new zippers in 2 pair of coveralls. A couple of local ladies do this work but i can buy new coveralls cheaper than what they charge for a zipper install. Can't be that hard.......
For the gears i think aluminum is the way to go.

@6.5 Fan, you might consider using Velcro what is usually called hook and pile for a closure.

Might be easier and cheaper to install rather than replacing zippers, just a thought.