chart for rod diameter for threading?
This question may seem very elementary to many here, but I've been trying to find some kind of chart that will tell me what the starting diameter of a rod should be for threading with any given size die. For example, I learned the hard way that a 1/4-20 die really struggled when I tried to thread a full 1/4 " diameter rod with it. Apparently, the starting diameter needed to be smaller. Any tips as to where I can find a chart that might cover this for the popular size threads? ( 6-32, 8-32, etc...)
The starting dia. for any thread is the nominal size of the thread. You put a chamfer (lead) on the end to start. Cutting a thread free hand is not easy and requires some experience.
The main thing to do is keep your threading die at 90 deg. to your work. Also look at the die from each side. One side will have a longer starting chamfer. That is where you start.
Practice! But is is best to have lathe, vertical mill or a drill press to help you get started.
Good luck and use cutting oil.
If you look at Machinery's Handbook, you'll see that the major diameter tolerance allows the diameter to be a little smaller than nominal. For average work, making the outside diameter about .005" smaller than nominal works well. This reduces the torque required to turn the die.
In addition to the advice already offered, if your die is adjustable, make sure it is fully open when you make your first pass. You can close it up a bit and take a finishing pass afterwards.
I think I'd also add, as an amateur, that the quality of the die makes a lot of difference, and yet it's not generally obvious (to me) from looking at it. I've collected a lot of dies over the years and they really are very variable. I've got dies with reputable names on them which I wouldn't trust to put a thread an a piece of brass, and one particular 5/8" die nut which puts a beatiful thread on a piece of (reasonably) hard steel at full diameter.
So, what's the secret from the Professionals?
Using a thread cutting lathe. Or a Geometric threading head (never used one myself)
Originally Posted by AlanBeckett
I've also been guilty of starting a thread in the lathe, and doing a "finish pass" with a die (for 1 or 2 pieces).
Send the parts out and have them rolled?
There are also threading dies and re-threading dies. I think this is or once was indicated by the shape, round or hex. Make sure you have the right one. My experiences with modern dies have been less than wonderful. Single point or a die head ($$) is way better.