What Size For Threading?

[4GSR]

AR,

You didn't mention how long the thread is going to be, the portion that you are turning down. If over 1" in length, center drill the end and run a live center especially if you use a grade 2 bolt! One problem trying to thread on a small part like that in a collet, it could slip. If running 5C or bigger collet, probably be ok. If your using a 3C collet, it'll slip on you while threading. ER collet, I don't know. Putting two nuts, tighten together and chucking on the two nuts as Tom mention works. That's how I do it.

 

[rgray]

Since you're just turning down the end and not single point threading, I'd probably turn it between centers. You could put paper or thin cardboard on the threads while holding it in the dog.

I usually use brass shim stock under the dog screw. .020 is usually heavy enough.
Turning that between centers would make it come out real nice and accurate, but would cramp the work space and be a little tricky.
Having a die holder for the tailstock would help and you would not need to single point thread at all. Hold with collet and thread from tailstock die holder.

 

[AR. Hillbilly]

The 5/16" threads need to be near 1" long. It has to screw in to a lever and have a jamb nut. Once set it should never need to be adjusted. How could I hold a die in the tail stock? So far All I have is a dead center and drill chuck. I don't have a lot of tooling yet. I'm just getting started and my work is very busy right now. I soon hope to be able to get to some serious learning. How hard is a grade 5 or grade 2 bolt to turn and thread? As someone mentioned above I'd like to use stainless for this project.

 

[Ulma Doctor]

to hold a die in the headstock,
you'd build a simple attachment to put into a drill chuck or turn the tailstock taper present on your machine and put the holder onto it.
if you have round dies, most likely they are 13/16" in diameter but do come in larger sizes for larger fasteners.
if you have hex dies they are normally 1" hex, the holder will be a little more difficult to make but still completely doable
grade 2 cuts like butter.
grade 5 is tougher but still machines ok- use a dark cutting oil or anchor lube for better results, the new threads appearance may appear a little grainy- take relatively light cuts
you'll want to use anchor lube for stainless if you go down that road, it's the cat's meow!
when you machine stainless , use relative low speed for a relatively deep cut.
i like carbide for stainless, but HSS will cut it
i just yesterday rethreaded some 316ss studs that were operator damaged, from 16mm 1.0 to 1/2"-13 tpi to keep a processing machine machine running.
during threading i'll take .010" cuts (per side) and 60-80 rpm spindle speed

 

[Ed ke6bnl]

An excellent choice is to subtract the thread lead from the major diameter, this will get you close, if you have reason to make a very accurate thread buy a thread gauge or measure over wires, this is unpleasant in many ways however.

What is the thread lead? Thanks

 

[Wreck™Wreck]

What is the thread lead? Thanks

Thread lead is the distance that a thread advances per revolution , for instance 17 threads per inch has a lead of 1/17 or .0588 lead for a single start.
A metric thread such as M8 1 has a lead of one millimeter per revolution for a single start, The lead is important.

I suspect that a discussion about multiple start threads will not help.

 

[kd4gij]

Just don't mic a 5/16 bolt from the big box stores.

 

[Wreck™Wreck]

For most threads, go with nominal OD, 5/16 or .3125" with a minus tolerance of about .005". This should be good for most of us.
In industry, we have calculations and machinery's hand book that give you more information.

You get it turn down to .312/.308", I would single point the thread to near depth, about .034". Then chase the rest of the thread with a die.
BTW: actual thread OD is .311/.302" I always go about .001-.003" big (.314/.312) and at the end of threading, I dress up the thread with file to remove burrs and a little emery. By the time I do that, the OD always wind up around .310".

Why would you set up a lathe to turn a thread large then finish it with a die? If already set up why not finish it in the lathe.

 

[benmychree]

Why would you set up a lathe to turn a thread large then finish it with a die? If already set up why not finish it in the lathe.

Because it is easier for an amateur to get a fairly accurate size on his thread; the reason to rough out the thread with a single point tool is to get an accurate and non wobbly start for the thread, as it seems that using a die from the start usually ends up wobbly, even when using a guided holder. I have Geometric automatic dies and do not have the problem, but sometimes I have only one small thread such as AH describes, and I do exactly as suggested, single point it oversize, and finish with a button die, this procedure is best for small sizes of threads.

 

[4GSR]

I made that statement in the support of an amateur as benny said. I've long since graduated from using dies to finish threads with. Occasionally, I will grab a die to chase a thread if needed or even the check a fit when I don't want to use a thread mic, too. Kind of hard to break old habits!