Help on Singer 153 stripped hook saddle screw hole?

[rlevine]

I've been looking for a small cylinder arm machine for bag work and found a Singer 153W102 (needle feed ) in ok shape for not too much money. It was badly set up by a prior owner, but I did not find too many surprises as I took it apart. However... I just discovered that one of the hook saddle screw holes in the casting is stripped.

Dealing with threaded casting holes is new to me. Can anyone suggest first aid techniques? The screws are healthy, they measure 13/64-32-ish, and the slot in the hook saddle is 7/32" wide.

Thanks!

Rick

Edited June 2, 2023 by rlevine

[nylonRigging]

Screw that holds the saddle stripped ? man that sucks,
probably need to drill and tap new thread for machine Screw just slightly larger in size. The threads are stripped-out, so that leads me to believe ?..that the metal area is not that hard of temper in the Cast . So tapping new threads should be doable .
I have drilled and taped some screws in Head and Beds of machines, and I find that most cast heads when tapping thread. The cuttings from Tap cuttings are kind of loose dust because Cast is soft .
also.. you might have to just hand File the slot Diam. just a little if  the it needs to be slightly wider to make slide movement with new size, but that would be easy to do.
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Or.. you might drill and Tap for a machine thread size Heli-coil thread insert . Then use a ' similar  ' Diam.Size screw, as the factory size . I have heli-coil threads on other metal repairs, and they are pretty good hold strength.
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[nylonRigging]

One other thing popped into my head this morning about your stripped thread problem . ( If Possible ? )
My 3rd suggestion is simple and direct fix . if the clearance is there on underside of the stripped-out screw hole ? , I saying if area bottom-side of the hole is clear of interference with any other mechanics of operation.

This may sound like true garage macgiver'ing .. but sometimes the simplest direct method may not be the one of proper aesthetics, beauty and craftsmanship . But sometimes .." You got to do, What you got to Do". . the old machine keeps sewing, and you keep using it for some more years.
And that would be just simply doing a nice straight clean pass-threw cut with a bit, just to clean cut-out the fouled threads, and then using a small machine bolt with keeping nut on the bottom side . maybe with use a trim small button-head/Allen drive machine bolt or...?
.

Edited June 2, 2023 by nylonRigging

[kgg]

20 hours ago, rlevine said:

The screws are healthy, they measure 13/64-32-ish

If you decide to re-drill and re-tap the hole be aware that Singer was notorious for using their own thread pattern on screws. Be prepared to drill and tap for a standard thread pattern and use a readily available screw with either metric or imperial threads in the correct length or as @nylonRigging use a nut and bolt.

kgg

[Quade]

There's not much meat to work with so a threaded insert like a helicoil or time-sert probably won't work. You have to drill quite oversize for them to make room for the body of the insert. 

  I'd go the next bigger size up and tap it. Either SAE or metric, whichever lets you remove the least amount of metal. 

As Kgg mentioned, singer uses crazy non-standard thread pitches. 

 

[rlevine]

Thanks for the great ideas! I hadn't seen time-serts before; looks like they have smaller inserts than I remember from using helicoils. They're a bit spendy for this problem, but interesting. 

In this case, it wasn't as bad as I feared. The hole is deeper than the screw, and singer used a fairly thick washer under the bolt head. Removing the washer allowed threads to catch and hold. I could do the same thing by thinning the ear on the saddle, but once I realized there were healthy threads beyond the end of the screw, losing the washer was the easiest fix.

[Quade]

Quote

 I hadn't seen time-serts before; looks like they have smaller inserts than I remember from using helicoils.

Helicoils are fine if you have a part that doesn't get taken apart often or ever. They can unscrew with the bolt.   I primarily use time-serts for anything that has to be taking about more than once. The inserts can be removed and replaced of they're damaged. There's a tool that comes with the kit that both expands the threads and wedges the insert into the hole. That's why they don't back out. 

I use them in aluminum quite often. 

I used one to repair an arm on my Singer 211. 

Edited June 4, 2023 by Quade

[rlevine]

On 6/4/2023 at 11:43 AM, Quade said:

Helicoils are fine if you have a part that doesn't get taken apart often or ever. They can unscrew with the bolt.   I primarily use time-serts for anything that has to be taking about more than once. The inserts can be removed and replaced of they're damaged. There's a tool that comes with the kit that both expands the threads and wedges the insert into the hole. That's why they don't back out. 

Thanks for the pointers; that's useful info. Now I just need a project that will justify the tool set cost!

Rick 

[DonInReno]

If down the road those last few threads give way I’d vote for a helicoil in size 10-32. The only helicoil inserts I’ve ever seen that came out weren’t installed correctly or the bolt corroded - helicoils are by far the most common method used to restore threads.

The 10-32 is only .015” or so smaller than 13/64, but because they are the same thread count it wouldn’t be impossible to reduce the factory screw thread to fit the helicoil hole so it looks right.  Many Singer screws are pretty hard, so I’ll bet that just trying to run the screw through a 10-32 die would chip the die teeth and/or make a mess of the threads.  However, a thread file could be used to carefully reduce the size enough that a die could then even out the threads and reduce it the last few bits.  If you chuck the screw in a low speed drill that’s clamped to a table and run it in reverse, it’s not to difficult to hold the file as it travels down the threads.  For one screw it is probably just as easy to use a small triangle file if the edges are sharp enough to get down into the bottom of the thread.   You only have to take off .005” or so - much more important to be careful than fast.

A good quality die would help a lot - avoid the hex shaped ones at Home Depot or Lowes.   While at Home Depot, in the plumbing section where they will rethread a pipe while you wait, dip a few qtips in their bad smelling cutting oil - this is really good cutting high pressure oil to use with the die, just clean it off everything or the smell will linger for a year.   Every time I run a die down a semi hard high strength bolt I’ll use an adjustable die and do it in three passes, but each time I’m cringing hoping the teeth don’t break.   
 

[rlevine]

Thanks @DonInReno! Great suggestions, and good feedback on helicoils. You opened up a new rabbit hole for me; adjustable dies. I've never used one, didn't know they existed. Split rounds, two-piece rectangular ones like Little Giant. Fun!

Amen to the nastiness of cutting oil. When I moved into my current shop, the prior owner left some in a jar. The jar was out of sight under a bench, tipped over, and had a verrry slooow leak, a drop or two a day into some cardboard. Took me months to figure out where the stench was coming from!

Rick