Odd ball thread

So I've one that's a little off-the-wall LoL

I want to make a new spindle clamping knob for a very common imported spin indexer.

The thread is 12 mm 1.75, but the hole in the casting makes the knob very loose, a very sloppy fit.

I'm sure I can bore the hole and re-thread for the next larger size, but that's getting fairly big.

My off-the-wall thought is either thread milling or single point threading on the lathe, but starting with stock that is a bit larger than 12 mm.

Just wondering if anyone has ever tried this approach?

Terry

Or maybe just use a HeliCoil o bring it on size. Even make it 1/2-20 with a HeliCoil.

Hee Hee......just wind some thin plastic sheeting around the screw and it tightens up magically........only joking but it will work.

It sounds like you have a 12mm screw in a 1/2" threaded hole and the threads are being forced to accommodate .........12mm is smaller than 12.72, which is half an inch, so it goes in but sloppily.

Test the hole size carefully with a 1/2" bolt NC, NF, BSW or BSF.....you might be able to re-tap the hole clean up to the 1/2" size if you get a near enough pitch match solution and the threads are a bit mangled.

Apparently they (the Chinese) have difficulty in working with Imperial thread sizes as I recently ordered a 1/4" NPT tap and received a 1/4" BSP tap.....1/4" NPT threads are 18 tpi and 1/4" BSP threads are 19 tpi
Ian.

The thread in the spin indexer is definitely 12 mm 1.75, not 1/2' or anything like that. The threaded part of the knob is fine, the thread is accurate and on size for 12mm, it's just the hole in the castings that's poorly done.

I'm sure I could bore and re-thread, or even a heliCoil, as mentioned, I'm was just playing around with oddball solutions in my head.

I finished my current project today, so I'm going to try the over-sized shaft thing tomorrow. I'll let you know if it pans out.
Thanks
Terry

Quote:

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Originally Posted by MFchief

The thread in the spin indexer is definitely 12 mm 1.75, not 1/2' or anything like that. The threaded part of the knob is fine, the thread is accurate and on size for 12mm, it's just the hole in the castings that's poorly done.

I'm sure I could bore and re-thread, or even a heliCoil, as mentioned, I'm was just playing around with oddball solutions in my head.

I finished my current project today, so I'm going to try the over-sized shaft thing tomorrow. I'll let you know if it pans out.
Thanks
Terry

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I ran into this scenario yesterday in one of my tool holders, needed a 5.5 mm hex key ha! I tried the sae set as well and nothing fit except the 5mm and it was really sloppy........

So, I was able to play around with this today, and I achieved what I was going for.

Measuring the major diameter of the external thread on the original knob came to 11.73 mm. I turned a piece of stock (brass) to 11.89 mm on the lathe then thread milled it at 1.75 pitch and it fit fine in the casting, much less play.

I'd like to tell you this is what I did, but in reality, I sneaked up on it. I started at 12.1 mm, then worked my way down to the 11.89 mm to get a good fit.

But the principle worked fine, obviously not a technique you would like to use in many situations. Standard sized fasteners are much to be preferred.

Terry