When should I thread, when should I use a die?

wawoodman said:
For some reason, I was thinking that the die was a "sissy" way to go, and real men used the lathe.
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A real machinist will use what he's got, that fits the purpose needed and will do it the fastest, easiest most efficient way he has access to. In this case cutting the threads is the hard slow way, running a die over the part is all that is needed or called for in this case.
 
Some people will single point it to partial depth to make sure of the concentricity, then finish with a die.

It's only fair to state that flipping the die around presents the clearance ground into it the wrong way. There is a relief ground behind the cutting edges. I wouldn't count on cutting a very long section with it backwards.
 
If the application of the screws is really critical that they are threaded all the way up, you could (if you wanted to stuff your die), thread them as far as possible, then use a dremel or similar to grind a recess in your die to take the screw head, thus removing the tapered lead from the die. This would get you a lot closer.

cheers Phil
 
As an example of DMS's second suggestion, the adjusting screw on the left was made by drilling and tapping the hole after the head was made (not sure if it had been parted off yet) and setting in an 8-32 bolt with strong threadlocker.

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I have re-read this thread and I still don't get what I am missing. Please point it out to me.

Every thread I have ever been tasked to end at a shoulder has been terminated like these, Pump shafts, Baxter Bolts, every thing but plain ole form bolts in which the plain ole form nuts allow for the tapered threads at the end. I can not think of any item ever that required the threads to run 100% to the shoulder as that is pretty much impossible. Vis a vis 90° and 60° engineers typically avoid adding things like that to a design.

You may be able to kludge and make it work without the relief, but in most cases and this one (knurled thumb screws) there is no point. It'd be easier to cut the min diameter relief at the same time you cut the major OD after knurling.

Or what am I missing?

Steve

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swatson144 said:
I have re-read this thread and I still don't get what I am missing. Please point it out to me.

Every thread I have ever been tasked to end at a shoulder has been terminated like these, Pump shafts, Baxter Bolts, every thing but plain ole form bolts in which the plain ole form nuts allow for the tapered threads at the end. I can not think of any item ever that required the threads to run 100% to the shoulder as that is pretty much impossible. Vis a vis 90° and 60° engineers typically avoid adding things like that to a design.

You may be able to kludge and make it work without the relief, but in most cases and this one (knurled thumb screws) there is no point. It'd be easier to cut the min diameter relief at the same time you cut the major OD after knurling.

Or what am I missing?

Steve
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Steve,

I terminate my threads without an undercut simply because I like the look. My lathe has a quick lift tool slide so all I do is set a dial stop so I know when to lift the tool. It takes a little practice to do it under power, so it's that technique not for the novice (or the faint of heart) but the same thing can be accomplished by stopping the spindle and finishing the thread by hand. I don't have a very good pic of one that I've done, but you can sort of see it in the screw shown below.

An undercut is definitely the traditional way to terminate a thread, but sometimes it's more fun to stray from tradition. :cool:

Tom

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Tony Wells said:
Some people will single point it to partial depth to make sure of the concentricity, then finish with a die.

It's only fair to state that flipping the die around presents the clearance ground into it the wrong way. There is a relief ground behind the cutting edges. I wouldn't count on cutting a very long section with it backwards.
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I've not heard of that trick! That's a terrific idea. Thanks!

John
 
Sure there are lots of ways to skin a nauga. If you are dealing with a through hole and nut on back you can run a dye up to the shoulder and call her done. One could do the same threading into a hole with a little counterbore in the hole.

On rare occasion when I wanted a "body bound" fit I'd thread tight to the shoulder and countersink the hole to get the "bind" I wanted.

One could even undercut the shoulder and thread beyond along the axis to do the same thing.

It is certain though that you can only come within 30° of a 90° shoulder when cutting 60° threads.

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Even with the geometrics you either undercut or make some other compensation (possibly just live with it) for the partial threads at the end abutting the shoulder. They do get close since they are automatic and get you to right at 1/2 pitch out with proper setup.

I am wanting to point out that there is a more accepted way to thread to a shoulder than flipping dies (though sometimes it's the way) or finishing by hand. No wrong way as long as it works, meets your needs and is done safely.

Steve

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Note that I said BRASS when reversing the die. Brass cuts well with no cutting angle. I was making copies of some 19th.C. wood plane parts which were threaded all the way to the shoulders,so made mine the same. I do a lot of mechanical antique repair.
 
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