Tool Caliper with broken screw

[Susquatch]

Just had a thought, @Susquatch can you make a new screw with a sleeve end (female) and fit it over the broken end of the screw? You might lose a little travel but you wouldn’t have to mess with getting the pivot end of the screw out of the leg.

You could join the sleeve to the old screw with one of the Loctite bushing retaining compounds. There certainly wouldn’t be much loading on the joint. You might be able to join the two halves of the existing screw with a bushing too. Maybe a nice shiny brass sleeve that shows that machinists can fix things elegantly.

The problem is that it's broken right at the middle of its travel. If I did this, I'd have to cut the remaining screw very short. Even the sleeve would have to be short and just at the very end. The new screw would have to be integral to the sleeve to yield enough thread. But it is a possibility. If I did that, I'd prolly just use steel epoxy.

 

[Susquatch]

If they were being very clever they could have drilled down the leg from the top then fitted a plug with a feature to retain the screw cross pin but again I don’t see any witness marks.

No, the pivot is the other way.

You have to appreciate the skill of “the old guys” who did this kind of work before all the modern technology came along!

Amen to that!

 

[Tecnico]

No, the pivot is the other way.

Looking closer at your photo I see now that it didn’t break at the end of the thread like I thought so you would have to shorten the stub and make another adapter screw to get more travel.

What I meant was the screw with it’s integral pivot pin would be slid into the slot in the leg then rotated 90*, then a forked retainer would be slid into the top of the leg to capture the pivot pin. Kind of hard to visualize without an image but doubtful that that they did something like that too.

D

 

[Dan Dubeau]

It should be pretty easy to approximate the position of a pivot pin. I'd take a small punch, and with the arm supported in a vee/bench block start tapping gently around the area and I'm almost 100% sure a peened in place pin will reveal itself. Should be straightforward from there.

 

[Dan Dubeau]

Ok, I just tried my advice above, and I'm now in the magic camp too......lol

There,s a good chance I didn't hit hard enough to dislodge a pin, but I really didn't want to go marking it up either. Just some very gentle tapping around the highest point of the cylinder, with enough force that I thought would have surely dislodged a peened pin even just slightly, but not enough to mark up the punch, but i got nothing.

There IS a very slight indentation around that area on my outside calipers though.....Witness from a pin? or box rash? Tapping there did nothing, same as the inside caliper. But then I don't really want to hit any harder. If the broken one were mine, I'd go for it. You're going to repair it with a pin most likely, so damaging that area from a punch isn't really a big deal. And It's already broken anyway.....To me, that really looks like a pin.

Looking down into the opening, there is almost certainly a cross pin in there providing the pivot, not a ball. Whether they drilled and peened it, or it's integral to the screw and they swaged it closed it the $10 question though.

 

[Susquatch]

There IS a very slight indentation around that area on my outside calipers though.....Witness from a pin? or box rash? Tapping there did nothing, same as the inside caliper.

I smacked the snott out of it. Nothing. Magic I tell ya! Magic!

My mind has been thinking its one of those push it in, turn 90 degrees and pull to catch an internal shelf. The tension would keep it in the shelf.

But it isn't pushing in and it isn't turning. Gotta be old time Craftsman Magic!

Looking closer at your photo I see now that it didn’t break at the end of the thread like I thought so you would have to shorten the stub and make another adapter screw to get more travel.

Here is what I have to work with for a sleeve. Doesn't leave much for anything.

No point in SMALL calipers that won't close small.

So I'm back in the camp that says drill it out from the back and install a ball nut. Maybe I can even find one to match the other one! Or maybe two new ones.

 

[Dan Dubeau]

There is a possibility that it's a pin, and it's been welded, then smoothed over.

 

[Susquatch]

There is a possibility that it's a pin, and it's been welded, then smoothed over.

Maybe. An amazing job if so.

Don't matter, I can't fix that the same way.

For now, I'm sticking to Magic!

 

[Dan Dubeau]

Abracadabra, Alakazam.....

 

[Susquatch]

Abracadabra, Alakazam.....

Well Dan. Turns out that you and a few others were right after all. You should have another look at the side opposite of where you tapped on it.

I couldn't see a thing. But I ran my finger ever so lightly across it, and I could feel an edge I could not see. I know for an absolute fact based on many experiences that can feel things I cannot see. That's another reason I like my lathe standard. My fingers can feel a few tenths.

Anyway, I could feel the edges of a pin I could not see, so I got a bit more aggressive with the punch and...... Magic!



The rest is easier. Just need to drive it out the rest of the way, find a long screw with the right thread, and make a hole in it for the pin!

This problem too was simple when solved!

 

[Dan Dubeau]

I'm still sticking with the magic theory. It never would have budged if I didn't do the chant.....

I didn't know Squatch's had such sensitive paws . I do agree with you on the feel thing. There is a surprising amount of precision tied up in sight and feel.

 

[Susquatch]

I'm still sticking with the magic theory. It never would have budged if I didn't do the chant.....

I didn't know Squatch's had such sensitive paws . I do agree with you on the feel thing. There is a surprising amount of precision tied up in sight and feel.

Ya, me too! I even looked with a big lighted magnifying glass and saw nothing.

Here is another surprise. They didn't flatten the end of the screw at all. They just drilled it!



I'll be flattening the new screw a wee bit. Hard to believe that tiny bit of metal holds. I'd have bet that the pin would break here instead of where it did!

I left the old pin there. I'll just drive it back after I find a screw.

 

[Dan Dubeau]

I wonder if they drilled that in place using a drill jig to position it in the slot. If I had to guess, based on how Starrett made a lot of things, that would be mine. A dedicated fixture, on a dedicated drill press. I doubt each piece was drilled first then assembled later, but I could be wrong. Often am.

 

[ChazzC]

Well Dan. Turns out that you and a few others were right after all.

Apology accepted

 

[Susquatch]

I wonder if they drilled that in place using a drill jig to position it in the slot. If I had to guess, based on how Starrett made a lot of things, that would be mine. A dedicated fixture, on a dedicated drill press. I doubt each piece was drilled first then assembled later, but I could be wrong. Often am.

Could be. Makes sense for an outfit like Starrett.

Holy shit. That Fkn thread is 78.5 thou x maybe 60 tpi. So probably an 80 thou #2 screw. Or perhaps a 2mm x 0.45 or or or.... Gunna need a better way to measure threads I can't see.

Clock makers? Any suggestions? My screw gauge is letting me down.

I suppose I could single point that but I'm not gunna. Just need to find a long screw whatever size that is!

 

[jorogi]

Could be. Makes sense for an outfit like Starrett.

Holy shit. That Fkn thread is 78.5 thou x maybe 60 tpi. So probably an 80 thou #2 screw. Or perhaps a 2mm x 0.45 or or or.... Gunna need a better way to measure threads I can't see.

Clock makers? Any suggestions? My screw gauge is letting me down.

I suppose I could single point that but I'm not gunna. Just need to find a long screw whatever size that is!

Aw just feel it !

 

[Susquatch]

Aw just feel it !

Ya, I deserved that. But I still have two words for you and they are not nice!

 

[Tomc938]

Could be. Makes sense for an outfit like Starrett.

Holy shit. That Fkn thread is 78.5 thou x maybe 60 tpi. So probably an 80 thou #2 screw. Or perhaps a 2mm x 0.45 or or or.... Gunna need a better way to measure threads I can't see.

Clock makers? Any suggestions? My screw gauge is letting me down.

I suppose I could single point that but I'm not gunna. Just need to find a long screw whatever size that is!

If you can't find the screw size, you could always go just a shade bigger, turn down the end where it goes into the leg and then tap the thumbscrew to match.

Original screw would be best.

 

[Susquatch]

If you can't find the screw size, you could always go just a shade bigger, turn down the end where it goes into the leg and then tap the thumbscrew to match.

Original screw would be best.

Good point Tom. All the holes are significantly bigger than the old screw.

Btw, when I stuck the old screw in the ultrasonic cleaner, the end ball fell off. No joy with the knurled nut yet.

 

[Tomc938]

Could be. Makes sense for an outfit like Starrett.

Holy shit. That Fkn thread is 78.5 thou x maybe 60 tpi. So probably an 80 thou #2 screw. Or perhaps a 2mm x 0.45 or or or.... Gunna need a better way to measure threads I can't see.

Clock makers? Any suggestions? My screw gauge is letting me down.

I suppose I could single point that but I'm not gunna. Just need to find a long screw whatever size that is!

Are you looking to buy a bolt? In person, or online?

If you have a good place you can go in person, take the thumbnut with you and try before you buy. If you have to order, order a bunch of sizes and use the one that fits. (shipping will likely be the largest portion of cost) If none of them fit, see my post above.