View Full Version : Newbie needs help with thread cutting
05-19-2001, 12:07 PM
Please forgive if this inquiry sounds elementary, but I am new to metalworking and I am puzzled by some of the more basic skills. In particular, I have been having difficulty using a die to cut threads (6-32) on the end of a brass rod.
I turn the rod to the diameter specified on my tap and die chart and mount the die and get after it. I follow the technique of turning the die a full turn and the backing off a 1/2 turn. The result is a rod with threads, but only in the loosest sense of the word. They are wallowed out and a nut fits very loosely on the rod. I believe I have two problems. 1) starting the die exactly perpendicular to the work, and 2) turning the die so that it does not tip from side to side as it rotates.
Can someone give me some tips to overcoming these difficulties, or describe a jig that may help, or list a book that I might reference. I know this is MACH-101 and again I apologize if it is too rudimentary, but any help would be appreciated. One must walk before they can fly.
05-19-2001, 07:20 PM
What type and brand of dies are you using?
The first die & tap set (cheap import) I bought was made of carbon steel and meant for touching up existing threads, rather than making new ones. Gave me no end of trouble until I started buying good quality dies. The better ones, for my purposes anyway, are split with a set screw to allow you to adjust the thread fit.
Mike Henry in Batavia, IL
05-19-2001, 08:30 PM
Mike's right, the best dies are the ones that have a split and a set screw for adjusting. If you have this type it could be set too tight. You can try setting it by using a new 6-32 screw, close the die until you have a slight drag on the screw. You can also try using your tailstock to keep the die perpendicular when you first start the thread. Make sure you're using the correct side of the die to start your thread, the side with the chamfer. Good luck, I hope
this helps. J. Belanger
05-19-2001, 08:51 PM
Never apologise for trying to learn something new. I am glad that you and many others are trying.
Ditto on getting a GOOD die! The cheap ones are really awful. For brass, especially, you need a good, SHARP die to get the best threads.
Also think about making yourself a tailstock die holder. I made one out of a piece of aluminum 2" dia. x about 4" long. drill a 1/2" hole down the middle, machine a 13/16" dia. counterbore in one end, a 1" counterbore in the other end, so 13/16" and 1' dies fit loosely, drill/tap for a setscrew at each end to hold the die.
Round off the sharp corners, do a light knurl on the outside for gripping.
To use, put about a 5" length of drill rod in your tailstock chuck, slide the die holder (with die inserted onto it. Start up your lathe in slowest backgear with the work in the chuck, grab on, and slide the die along the drill rod and onto the work. You can cut up to about a 1/4-20 thread just holding the die holder by hand.
And you don't need to reverse the die. Just keep going. There is plenty of chip clearance in a die, unlike with a tap.
Harry J. Dolan
05-22-2001, 10:00 AM
Just a couple of suggestions. (1) Try putting a little 60 deg. champer on the end of the rod, just a little deeper than the thread you are cutting. (2) If you do not have a tail stock die holder, you can use a tail stock drill chuck to assist you. Retrack the tail stock chuck jaws back into the coller, this gives you a flat face perpendicular to the work you have in the lathe. Bring the tail stock, with the drill chuck installed, up and just touch the back of the die or die holder. Keeping just a little pressure on the back of the die or die holder will keep the die straight as you turn it by hand.
05-27-2001, 01:55 AM
Ditto on the cheap tools. If it isn't made in the good ol' US of A, I don't buy it. Costs more, but you get what you pay for. Also, I smear Crisco on my taps and dies before I start cutting. Things go smoother and threads come out better with less chance of tap breakage.