Need advice for cutting #12-20 threads

[mwebster51]

I hadn't thought of that, that could definitely do it too! A die that isn't explicitly and correctly made for thread cutting (rather than thread repair) will be more difficult to use and will not cut as easily.

The die I am using is for cutting and not chasing so I think I am ok there... Thanks

 

[mwebster51]

A #12 thread has a Dmaj of 0.216 and the OD required for a class 3 thread is 0.2088 to 0.216"; for a class 2, OD is 0.2078 to 0.215". At best, a die will probably produce a class 2 fit unless you use a split button die, in which case you might get a class 3 if the OD is right. Basically, your best bet is to have your repair posts screw cut on a lathe if the fit is important to you.

A #12 thread has a Dmaj of 0.216 and the OD required for a class 3 thread is 0.2088 to 0.216"; for a class 2, OD is 0.2078 to 0.215". At best, a die will probably produce a class 2 fit unless you use a split button die, in which case you might get a class 3 if the OD is right. Basically, your best bet is to have your repair posts screw cut on a lathe if the fit is important to you.

When I cut the threads on the 0.212 rod the final fit is pretty good for what I am trying to do. As far as using a metal lathe, I don't have access to one, and for me to pay a machine shop to do it for me is not practical financially. Again I am a woodworker so I am not familiar with class 3 class 2 etc, ( I think I generally understand your point) The fit seems ok once I get the threads cut using the 0.212, it is just really hard to get the die engaged and into the cut. Thanks for your input

 

[forhire]

Does the part need to be tool steel? Hit an original with a file and see how hard it is. Most bolts are made of medium carbon steel like 1045. It can be heat treated and water or brine quenched.

 

[darkzero]

If I went to a softer steel rod, can you give me a name of a material that I can use to see what McMaster-Carr offers?

There are other grades of steel that will be easier to thread with a die but unfortunately they come in nominal sizes. 1/4" would be the closest so you would still need someone with a lathe (sounds like you don't have one?) to turn it down to size. I suspect that's how you wound up purchasing the O1 in the first place

I was going to suggest all thread but 12-20 is considered a specialty thread and probably not available. I assume you've already search for it. How long do the threaded posts need to be? Can you possibly find 12-20 screws that are long enough & just cut the heads off?

Another solution is to tap to 1/4-20. But being old planes I suspect you wouldn't want to do that, I wouldn't either.

 

[mwebster51]

I am not in the shop and will try the file tomorrow. I don't think the original posts are that hard. Maybe mild steel would be fine. I used the O1 thinking it was the best way to get the diameter of rod I needed. (again I am inexperienced when it comes to metal and machining) Being in the annealed state I thought it would be soft enough to cut the threads. But based on Erich's post I think I am understanding evening the annealed state it is still harder.

 

[darkzero]

The fit seems ok once I get the threads cut using the 0.212, it is just really hard to get the die engaged and into the cut. Thanks for your input

So once you get the die started, it then cuts the O1 fine? Issue is just getting the die started?

You mentioned you got the die from Victor Machinery. Just looked them up & they are split dies. So as suggested adjust the die to do less cutting (widen the die), then adjust back to proper depth & thread again. With out pitch dia measuring tools this may be tricky & you would have to test by fit.

Edit: doh, I should have read all the prev posts more carefully.

 

[mwebster51]

There are other grades of steel that will be easier to thread with a die but unfortunately they come in nominal sizes. 1/4" would be the closest so you would still need someone with a lathe (sounds like you don't have one?) to turn it down to size. I suspect that's how you wound up purchasing the O1 in the first place

I was going to suggest all thread but 12-20 is considered a specialty thread and probably not available. I assume you've already search for it. How long do the threaded posts need to be? Can you possibly find 12-20 screws that are long enough & just cut the heads off?

Another solution is to tap to 1/4-20. But being old planes I suspect you wouldn't want to do that, I wouldn't either.

As you noted these are "old planes" and I am trying to keep them as original as possible. The original posts are around 6" long. The threaded area is about 1/2-3/4" on each end. If I were just repairing these for my own use I would be more apt to use work-arounds, but I am selling to other woodworkers who like the old planes as original as possible.

 

[darkzero]

As you noted these are "old planes" and I am trying to keep them as original as possible. The original posts are around 6" long. The threaded area is about 1/2-3/4" on each end. If I were just repairing these for my own use I would be more apt to use work-arounds, but I am selling to other woodworkers who like the old planes as original as possible.

Ah I see, that's definitely out of the question then.

 

[mwebster51]

So once you get the die started, it then cuts the O1 fine? Issue is just getting the die started?

You mentioned you got the die from Victor Machinery. Just looked them up & they are split dies. So as suggested adjust the die do do less cutting, then adjust back to proper depth & thread again. With out pitch dia measuring tools this may be tricky & you would have to test by fit.

Yes it cuts "pretty well" once started, just a devil to start. I have tried to open the split die as much as possible which helps. Using the technique you are suggesting I can get the threads made, I am just looking for suggestions to make it easier. I am currently beveling the ends as best I can and that is the only way I can get the threads started.

 

[mwebster51]

Ah I see, that's definitely out of the question then.