1-1/8 x 3tpi ACME tap???

[LD1]

Can't seem to find a tap. Fairly certain the thread is acme. Don't know if I posted this a few years ago or not....but this project has been on back burner and I am back to tackling it again.

I have an old Columbian vise....5" jaws 8" opening. Here it is next to my Wilton bullet for scale.

The issue is the cast piece that is threaded is stripped. But the screw is good. I have kicked around the idea of making a new screw and matching threaded block....but if I could find a tap to cut 1-1/8" x 3 acme threads....I only have to remake the block.

The part is stamped 506-4 and can't seem to just source a new on either.

Anyone got any ideas on a tap before I resort to making both a new rod and block

 

[ultrarunner]

Years ago had special tap made for seat adjustment screw used in certain Early Fords.

It was expensive in 1980 but I could charge for the repair.

the quote for one was $65 but the quote for three was $90 so I bought 4 and sold one for $50…

 

[LD1]

Years ago had special tap made for seat adjustment screw used in certain Early Fords.

It was expensive in 1980 but I could charge for the repair.

the quote for one was $65 but the quote for three was $90 so I bought 4 and sold one for $50…

What is puzzling is I cannot even find a reference for 1-1/8 3tpi threads of any kind.

Usually you can find some info online for even old obsolete thread types and pitches. But. Coming up empty completely. For 1-1/8 acme....it seems 5 tpi is the common coarse thread.

I've measured and remeasured thinking I was overlooking something.

In all my years of wrenching, machining, etc....this is the ONLY thread I cannot find any info on.

Going through McMaster Carr, I can get a 3' stick of acme 1-1/8x5 thread rod and a coupling nut for about $70 for the pair.

Might do that and use the coupling nut to remake the anchor block

 

[TMGT]

Are you sure it is an ACME thread and not a square thread?
Either way McMaster usually doesn't have really odd stuff when it comes to machining, migh try some other sources.

Or as you already found, sometimes it's better to just switch to a more common size.

Sent from my SM-G715U1 using TractorByNet mobile app

 

[LD1]

Are you sure it is an ACME thread and not a square thread?
Either way McMaster usually doesn't have really odd stuff when it comes to machining, migh try some other sources.

Or as you already found, sometimes it's better to just switch to a more common size.

Sent from my SM-G715U1 using TractorByNet mobile app

Nope, I am not sure of anything other than it's 1-1/8" diameter and 3 threads per inch.

Can't find any types of threads that match that dimension let alone find a tap for it

 

[etpm]

Just remake the anchor block with the coupling nut. Especially since you need to make a new one anyway, no matter what thread is in it. It's pretty obvious that the original thread was a special. In my years of machining I have had many jobs that used non standard threads. Threads like .250-96 and .250-80. Those are some fine threads for such a large diameter. I have a drawer filled with special taps that I had made for me. Turning a 1 1/8-3 acme tap through steel or cast iron would be tough to do anyway. That's a big and coarse tap. You could also single point the thread. It wouldn't be that hard to do if a narrow tool was used. Just set the compound parallel to the ways on the lathe, thread out to the major diameter, and then start over but advance the tool a little bit. Do this a few times until the thread is the proper width. I have used this method before. It is slow but works. I have even done it in CNC lathes, but it is much faster that way.
Eric

 

[erikjohn67]

Edit

 

[jmc]

You could also single point the thread.
Eric

Is 3 TPI a common thread setting on lathes?

 

[ruffdog]

Without measuring the screw, we really don't know if it is an 29deg acme, a 29deg brown & sharp, or a modified acme etc. We would need root, crest, angle, and thread depth measurements.

 

[ruffdog]

A 3 TPI screw seems quite course for a vise of that type. Normally, 3 tpi would be like a carpenter's bench vise. I wonder if someone broke the original screw and fed in that 3 tpi one???? Something isn't right.

https://taytools.com/products/copy-of-2-1-2-drill-press-vise