Need advice for cutting #12-20 threads

mwebster51 said:
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.
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I see, then yeah, as the others suggested & like you are doing, beveling the ends is pretty much all you can do I guess. Bezel them more if needed, like a longer taper. Make your rods longer to account for this so you can grind/cut off that longer bevel. And cutting fluid is your friend.

Curious, how are you holding the rod & die, pretty securely?

Gotta make friends with a hobby machinist! That's what I did before I got into this hobby, but the best I could do was a friend of a machinist. :D

Too bad you weren't closer, I'd help you out. But sounds like this is not a one time thing?
 
Yeah I am about 3+ hrs above you, thanks. As far as holding the rod and die. The rod is in a metal vise, and the die in a die stock. To start the cut, I am holding the die down as hard as I can while keeping is as square as I can. Can one do things like cut this type of thread or turn a rod down to 0.216 on a less expensive "hobby lathe"? Or is that impractical. Like trying to do good accurate efficient woodworking on a recently made Sears woodworking machine?
 
mwebster51 said:
Yeah I am about 3+ hrs above you, thanks. As far as holding the rod and die. The rod is in a metal vise, and the die in a die stock. To start the cut, I am holding the die down as hard as I can while keeping is as square as I can. Can one do things like cut this type of thread or turn a rod down to 0.216 on a less expensive "hobby lathe"? Or is that impractical. Like trying to do good accurate efficient woodworking on a recently made Sears woodworking machine?
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Yep, I'm familiar with where Arroyo Grande is. My buddies and I go out to Pismo (Oceano dunes) once a year to "play", well it's been almost 3 since we last went.

Yes hobby lathes are very well capable. Some of them like the Chinese 7x that are very popular may need some work to get them working well but there are many resources online to help with all that as well as the mebers here. Or if you spend a bit more money & get something nice like a Sheline you'll have loads of fun.

But as far as turning down a 6" long rod down to .216 can get tricky because of the length & small diameter. There's things that you will need. I won't get into the details as it's irrelevant right now but it can be done.

I'm not familiar with wood lathes. Does the head stock have a through hole? Just thinking if you might possibly be able to use your wood lathe. Mount the rod in a chuck. Die on the tailstock. Use the tailstock to help put pressure on the die to get started. Would also keep the die square.
 
Starting a die straight is tricky even with a lathe. Since you only need a few studs maybe you could mail the original stud to a hobbyist friend who could make up a few blanks by single pointing the threads to about 3/4s of the depth. Then you could use an adjustable die to finish the threads yourself to get the fit you want.
 
I have occasionally put a slight taper on the very end of a rod to help get a die started. All that takes is a bench grinder if you're careful.

As far as turning down a larger rod, it may be that only the threaded section needs to be reduced and a larger diameter is acceptable for the rest of the rod?
 
I’d use a quality hss die and brass stock. Use a lot of tapping lube. I know you are restoring the plane, and the original might be steel but I seriously doubt anyone would look down on a brass threaded rod. Brass is more expensive than the original steel and always looks great in my opinion.
I see you don’t have a lathe but I’m sure if you found a local machine shop.... they wouldn’t charge much at all if you showed up with a few 1’ length 1/4” brass rods and asked them to turn the rods down to .188.
12-20 is really an odd ball which has pretty much been replaced by 1/4”-20.
Brass is a joy to machine.
If you were in my area...I’d do that for you in an instant and wouldn’t charge you anything to turn down a few 1/4” brass rods to .188”
FWIW.... I suggested a few 1’ sections because it’s just easier to turn down than a long length of brass rod. For a long length.... I’d have to rig my follower rest on my lathe. For your needs... I’m guessing 3 one foot rods would last you a while..
 
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To help start threads straight when using a die, I will turn down a short portion to slightly over the root diameter to act as a guide for the die, when the thread is finished, I cut off the turned down section. Dave's suggestion of starting with the 1/4"-20 die is a good alternative.
 
I live pretty close to you - in Los Osos, so maybe I can help.

We could pretty easily take your 0.2188" stock down to 0.216" on the ends -- leaving the middle untouched, as FanMan suggests, then thread the ends using a tailstock die holder. My holder can accommodate 1" hex dies and 1-1/2" round split dies.

If need be, we could also turn the whole 6" down to 0.216" - it would just be a bit more work. I have a follower rest and a tool post grinder - plus we could lean on Will for his ideas on successfully doing that. :)

We could also see how 1018 mild steel might work. As has been said, it would be a bit easier to machine than 01. We could also explore single point threading in lieu of using the die.

Let me know if you're interested in coming over and giving it a whirl.

Bill
 
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If you have a drill press, and the appropriate die holder, you could use it to guide and hold tension on the die to ease starting your thread. Mike
 
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