Tool Caliper with broken screw

[Susquatch]

Is using a threading die out of the question?

No, it's a very reasonable way to do it. The problem with that option is that I'd have to go with standard SAE thread profile. If I have to do that, I might as well just get threaded bar and a nut from MC. Which I still might do. I'm not sure how much benefit there is in the Acme thread profile but it is not zero. To rebuild it to factory, an Acme thread is required. To do that, I'd have to single point. Albeit still with a slight thread pitch mismatch.

 

[ChazzC]

From the latest post to the H-M thread:

 

[Susquatch]

From the latest post to the H-M thread:

$122US. That's $200 Cdn. Not happening Charlie!

More and more I'm leaning toward just buying a piece of 2-56 threaded rod and a ball nut from McMaster-Carr. It's not a perfect original repair, but it is more than adequate for my needs.

Even that is not without issues. I'd still have to drill it for the pin.....

 

[PeterT]

To rebuild it to factory, an Acme thread is required

Ah, that detail was mentioned & I forgot. OK that changes things

 

[Megar arc 5040dd]

Cut your self a gear and then you don't need to modify the nut and then it is as original as it can be. Everyone knows it's not a real project unless it requires at least 1 other sub project first.

 

[Susquatch]

Cut your self a gear and then you don't need to modify the nut and then it is as original as it can be. Everyone knows it's not a real project unless it requires at least 1 other sub project first.

That's very true. But it's more than a gear (or two). It's also a micro travelling steady.

But ya, I always seem to need to make tools for my tools and sometimes tools for my tools for my tools! It would be ridiculous if it were not so enjoyable.

 

[ChazzC]

$122US. That's $200 Cdn. Not happening Charlie!

It’s not a real project if you don’t buy at least one tool that costs 5x the cost of replacing the original item.

Even that is not without issues. I'd still have to drill it for the pin.....

There you go: you need to make a small shaft cross-drilling fixture, complete with hardened drill bushings.

 

[kstrauss]

Or m2x0.4 https://www.amazon.ca/HiPicco-M2-250mm-Threaded-Stainless/dp/B0C94XWC6M/ (0.0787x63.5 tpi)

 

[FatherWes]

Hmm
The bearing tips on the follow rest look familiar..
I have some used roller tappets. They look remarkably similar to those bearing tips…
I might have to dig them out and do some measuring.

 

[Susquatch]

But isn’t cool watching him single pointing 2-56 in CRS on what looks like a 14” lathe?

Yes, VERY COOL! I was flabbergasted! His first shot was pretty much what I expected. Not easy to thread a noodle......

But his micro follower clobbered that pesky little issue.

I like this concept: saves remaking the entire follower. If it were me, I’d use the bearing mount to attach the individual “backers.”

The bearing axles are pressed in pins. I didn't know that till I had a better look. Quite frankly, I think I'll add another item on my project list to make that a Stub threaded axle so I can change the bearing or insert a custom end ala this project. I'll call that item "Follow Rest Threaded Axle" or something similar. I'll also add a micro follow rest.

Setting that pesky little issue aside, I agree it's a better plan. Just need to make the Bearing axle replaceable first.

Joe used Linen Phenolic because the threads will cut into it without tending to transfer material into the threads (and he likes using this material ).

I'm thinking some kind of plastic would do the same. Maybe nylon or ABS.

But if you don’t use the original TPI you’ll need to modify the nut; if you’re going to do that you may as well up-size the diameter to make it easier to cut.

Can't increase the screw diameter. Won't go through the existing caliper legs which are already thin enough.

I was thinking I could rethread the existing nut from 60 to 56. That would jam over the length of the nut. But, if I drill out half the nut so it's just a tube, the remaining portion of threads might not jam.

Hey: you were the one who (foolishly? unnecessarily?) asked for opinions!

Not complaining Charlie. I like debate, discussion, and hearing other opinions. None of us is perfect and I really do treasure other opinions and input!

 

[Downwindtracker2]

There is graphite impregnated phenolic (sp) board . I use some on my Callander Foundry Beaver wood bandsaw blade guides.

 

[Susquatch]

There is graphite impregnated phenolic (sp) board .

Worth looking into. I just need a small plug. Maybe 3/8 diameter by 1/2 long.

 

[kstrauss]

There must be a cheaper source but...

https://www.amazon.ca/Olson-Saw-CB50055BL-12mm-Accessory/dp/B000H69ULC/

 

[Downwindtracker2]

I got mine from a Canadian source, I think it was B&D., I think . If you go on Canadian Woodworking, they might even advertise there. If not, just ask.

 

[ChazzC]

And from another corner:

https://www.hobby-machinist.com/thr...lds-smallest-hand-made-electric-motor.116647/

 

[Susquatch]

And from another corner:

I've seen Nano motors made at the molecular level. The motor in your link would look like mount everest by comparison. They are not hand made though. Both are WAAAY beyond my skill set.

Thanks Charlie!

 

[Ishmael]

Just saw this.

Don't know if you've solved your problem yet, but I have lots of these if you want some...

 

[Susquatch]

Don't know if you've solved your problem yet, but I have lots of these if you want some...

Your post is timely. I just wrapped it up today.

I bought a 2-56 tap, threaded SS Rods and 2 ball nuts from MC. My thought was to drill the rod for the pin and tap the existing nut for the thread after drilling it out a bit (recessing it) so the re-thread has less length to accommodate the difference.

I flattened the end of the rod to make it easier to drill (may have made it worse), center punched it, and then tried to drill it. NFW.

Yes, I have a cheapo sensitive drill chuck and yes I was using my mill and yes I had the part clamped and supported below the drill.

Then I happened to be talking to @Dabbler on the phone about another matter. When we were done I asked about the caliper. He said that his experience with small stainless parts is that they work harden just looking at them. He suggested annealing and then after talking to John Neilson added the need for stainless cutting oil. He also wished me luck with a very sarcastic tone.

He was right to be sarcastic. It didn't work. Could well be my inability to anneal such a small part properly. Or maybe it's instant rehardening on drill contact.

I also tried a tiny diamond dental burr. At first I didn't think it was working. Then my good eye (good compared to my left eye, but poor by any other standards) spotted what looked like dust. So I kept at it for another 6 days..... (actually more like 6 minutes) Success!

Just have to cut off the excess, decide what to do with the ball screw, install the ball stop and polish up the parts.

 

[Tom O]

Nice did you consider rounding the nose of the nut to fit better against the caliper leg?

 

[ChazzC]

Nice did you consider rounding the nose of the nut to fit better against the caliper leg?

Mine (https://canadianhobbymetalworkers.com/threads/caliper-with-broken-screw.13739/post-182738) and @140mower ’s (https://canadianhobbymetalworkers.com/threads/caliper-with-broken-screw.13739/post-182865) have a little round nose conical washer between the nut and the leg - which has a mating dimple. This was probably lost by the original owner when the screw broke.