Large Hole Drilling And Rotary Table Question

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Steve M

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Would classify myself as a moderately experienced beginner in the machine shop. Looking to make a jig to for threading barrels and the like. I need to make a 1" blind hole approx 1/2" deep to hold dies that would be secured by cap or set screws using my lathe. Right now I am using a 1/2"x28 die in a hand threading handle and using the tailstock to press the die itself against the item to be threaded. Was shown this by a more experienced machinist and it actually has worked fine for me. I'd like something a little more precise, though, to hold the die using something in the tailstock to align. I have tried cutting the threads using the lathe alone - works fine but the threading die is quicker.

Lathe is the usual import 12 x 36. Have 3 & 4 jaw chucks, Shars QCTP, HSS and carbide cutters, cheap 1/2" round boring bar set and head, more or less the usual stuff. Also have a Jet JDM-15 mill/drill, 6" rotary table, boring bar head, and various collects and end mills. Largest drills I have are Harbor Freight Silver and Deming that I believe go to 3/4". Not sure if they are any good but I do have a good drill sharpening setup.

Materials on hand are 1.5" 12L14 and some 3" aluminum round stock, alloy uncertain, plus brass in various diameters.

I also have a 4 jaw chuck for the rotary table but am uncertain how to attach. The table has 3/8" tee slots, and the back of the chuck (no backing plate) has four drilled, threaded holes that look to be 1/4" (6 mm?). I could easily cut the blind hole on the mill IF/WHEN I figure out how to mount the chuck on the rotary table. Thinking I need to make a backing plate of some sort for mounting the chuck.

I know that if I pondered this long enough I will come up with something but thought I'd ask the more experienced here how they would make the hole. Thanks in advance.

Steve
 
Your 1" x 1/2" hole would be simple enough to cut on the lathe. They make both tailstock die holders and mounting plates to put chucks on rotary tables.
 
Chuck up your 1 1/2 ledloy in your laythe, drill your 3/4 hole, the shoulder should be just a bit deeper than the thickness of the die. Put a boring bar in your tool post and bore it out, .010 or so at a time to the depth equal the thickness of the die.

Turn the piece around and turn it down to 1/2 or whatever will fit in your tailstock chuck. Drill and tap two holes in the sides of the die holder for set screws to secure the die, and BEHOLD you are done.

I'm about to do the same for a 5 - 40 die.
 
Steve M said:
Would classify myself as a moderately experienced beginner in the machine shop. Looking to make a jig to for threading barrels and the like. I need to make a 1" blind hole approx 1/2" deep to hold dies that would be secured by cap or set screws using my lathe. Right now I am using a 1/2"x28 die in a hand threading handle and using the tailstock to press the die itself against the item to be threaded. Was shown this by a more experienced machinist and it actually has worked fine for me. I'd like something a little more precise, though, to hold the die using something in the tailstock to align. I have tried cutting the threads using the lathe alone - works fine but the threading die is quicker.

Lathe is the usual import 12 x 36. Have 3 & 4 jaw chucks, Shars QCTP, HSS and carbide cutters, cheap 1/2" round boring bar set and head, more or less the usual stuff. Also have a Jet JDM-15 mill/drill, 6" rotary table, boring bar head, and various collects and end mills. Largest drills I have are Harbor Freight Silver and Deming that I believe go to 3/4". Not sure if they are any good but I do have a good drill sharpening setup.

Materials on hand are 1.5" 12L14 and some 3" aluminum round stock, alloy uncertain, plus brass in various diameters.

I also have a 4 jaw chuck for the rotary table but am uncertain how to attach. The table has 3/8" tee slots, and the back of the chuck (no backing plate) has four drilled, threaded holes that look to be 1/4" (6 mm?). I could easily cut the blind hole on the mill IF/WHEN I figure out how to mount the chuck on the rotary table. Thinking I need to make a backing plate of some sort for mounting the chuck.

I know that if I pondered this long enough I will come up with something but thought I'd ask the more experienced here how they would make the hole. Thanks in advance.

Steve
Click to expand...

You can purchase die holders for your tailstock. MSC has some with straight shanks. If you want to roll your own, it shouldn't be too difficult. Bore a hole deep enough to accept the threads you want to cut and use a boring bar to finish the hole to your 1" diameter. You will probably want to start with a piece of 1-1/2" or more round stock.
The four jaw chuck is most easily mounted with a backing plate. Make the plate a larger diameter than the chuck so you can clamp it to your rotary table with the Tee slots and Tee nuts. The back of the backing plate can be a simple flat surface and you can indicate it into concentricity on you RT. Rather than using external clamps, I would mill oversized slots and use bolts to hold the plate.
 
Thanks for the info. Never knew rotating tailstock die holders were so readily available. Planning to go ahead and make my own anyway.

The issue with the rotary table and 4 jaw chuck is that they are both 6" and would probably need something like a lathe backing plate, a fat spacer, and a RT mounting plate. Think I will look at getting a 4" chuck to mount. Both are loaners to me but will buy RT at some point just the same.

Steve
 
There are plans online for die holders that slide so you don't have to loosen your tailstock.

I have used your method of using the tailstock to keep my die aligned.
 
I bought a couple of inexpensive die holders and found some problems. The ones that I purchased are held in a tailstock drill chuck and are very short. There is a likelihood of misalignment from the combination of errors contributed by the tailstock, the drill chuck , the die holder and the die itself. Often the die holder isn't long enough to clear the carriage when threading close to the headstock (the tailstock hits the rear of the carriage).

Below is a die holder that I made up in an afternoon. The body is a scrap piece of pipe with stock welded to both ends. One end has been bored to accommodate both hex dies and 1 inch round dies.

Three socket head screws are arranged around the perimeter for securing the dies. The opposite end has been taper turned to MT-2 to fit the tailstock on the 8 x 18 Emco for which it was made. A slot was milled in the pipe near the head to help clear chips if necessary.

After all of the diameters were turned concentric, a hole was cross-drilled for a rod that rests on the edge of the lathe ways to prevent rotating when threading. The sequence of lathe operations was as follows:
  • The head of the die holder was turned and bored with the remainder of the tool inside the spindle.
  • After turning the tool around and indicating the head in a 4-jaw, the end was then carefully center drilled after indicating and tapping it into position with a soft-faced hammer
  • The MT-2 taper was cut on the end with the compound which had been previously adjusted to a known good dead center taper
Note that the length is quite long for two reasons. The first is so that the die holder can clear (pass over) the carriage when threading close to the headstock. The second reason is to provide for a slight amount of misalignment - the same reason that reamers have very long shanks.

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Why not learn to single point the threads on your lathe. It isn't that hard heck I learned . You will get much beter threads.
 
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