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I am (partially) disassembling an old sewing machine to clean it up.

While removing the bobbin winder, I found this thing that has a screwdriver slot, but it isn't a screw.

This is the part:

enter image description here

It came out of here:

enter image description here

enter image description here

It is actually held in place by a set screw. The hole for the set screw can be seen just to the left of where the axle goes into the sewing machine housing.

The axle is completely round - no flat side.

The set screw is screwed into the housing and only presses on the axle to hold it. There is no hole in the axle for the set screw.

  • Why does this axle have a screwdriver slot?
  • Is there a general name for this kind of thing?

Yes, it is "the bobbin winder axle." The machine has several axles installed this way, though. That makes me think that this is some kind of hundred year old standard method for installing axles.

I don't know why it is there or what its original intended purpose was, but without that screwdriver slot I'd have never gotten the bobbin winder off of the machine.

With the screwdriver slot, I could squirt WD40 in through the set screw hole then work the axle round and round to scrape decades of dried oil off of the axle until it was clean enough to pull out.

enter image description here

To clarify:

The left arrow is pointing at a speck of dirt. The right arrow is pointing at the screwdriver slot in the axle.

The speck of dirt caused some confusion. The axle is round and smooth. It has no flat side or hole for the set screw.

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4 Answers 4

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"...but without that screwdriver slot I'd have never gotten the bobbin winder off of the machine."

It sounds like you've answered your own question here - these machines were designed to be easy to maintain, they had to be, for use in an industrial setting.

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  • $\begingroup$ If the axle hadn't been "glued" in place with decades of dried oil, I could have removed the set screw and pulled the axle out using the bobbin winder as a grip. The slot helped me, but I'm having a hard time imagining that the manufacturer planned decades ahead and included the effects of decades of "oil but never clean the machine." Maybe they really did plan it that way. I'm just not seeing it. $\endgroup$
    – JRE
    Commented Jul 31, 2021 at 21:08
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    $\begingroup$ Well, they probably designed for industrial use and repair. If there is a similar screw on machine, then machining process would produce similar blanks, with a portion being tapped. $\endgroup$
    – StainlessSteelRat
    Commented Jul 31, 2021 at 22:06
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When you this part was assembled, how would you align the two holes for the set screw without something to mark the rotational position of the post, and something to turn it accurately? The screwdriver slot has both functions.

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  • $\begingroup$ There isn't a flat side or a hole in the axle. It is completely round and smooth. $\endgroup$
    – JRE
    Commented Jul 31, 2021 at 20:11
  • $\begingroup$ You said it was fixed by a set screw. Is there really nothing to locate the position of the screw on the axle? That doesn't make much sense as a design. $\endgroup$
    – alephzero
    Commented Jul 31, 2021 at 20:52
  • $\begingroup$ There's nothing at all to locate the set screw. The screw screws into the housing. You can rotate the axle (and the screwdriver slot) to any angle you like and tighten the set screw - it'll hold tight, no problem. $\endgroup$
    – JRE
    Commented Jul 31, 2021 at 20:58
  • $\begingroup$ @JRE Isn't that exactly the way I've guessed? Aren't you using a screwdriver to rotate the pin? $\endgroup$
    – r13
    Commented Jul 31, 2021 at 21:08
  • $\begingroup$ I used a screwdriver to rotate the axle to work it free of the crud. There's nothing anywhere on it that needs to be lined up, though. The axle is just a smooth, round rod with a head at one end. $\endgroup$
    – JRE
    Commented Jul 31, 2021 at 21:11
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Because some had threads. I guess those fell on the floor before they got to the threading die were used for shafts.

enter image description here

In response to a comment, they used to form the head and shaft first, then cut the threads on a lathe one by one using the head as a driver. Master screw on right. Blank to be threaded on left. They are connected by the doughnut thingie. The shaft was turned down on a lathe from rod the size of the head.

enter image description here

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  • $\begingroup$ That's not how parts are produced $\endgroup$
    – Carl Witthoft
    Commented Aug 2, 2021 at 12:27
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    $\begingroup$ It used to be . $\endgroup$
    – Phil Sweet
    Commented Aug 2, 2021 at 20:44
  • $\begingroup$ Yep. Couldn't always form threads. $\endgroup$
    – DKNguyen
    Commented Aug 2, 2021 at 21:26
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Looking at the mechanism, it appears that the slot allows rotation of the axle so that the operator can compensate for uneven wear.

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