First off -- if the die is otherwise free to rotate in the
tailstock ram, and the handle is long enough to contact the bed ways,
add a layer of something like Delrin (acetal) or perhaps Nylon to keep
the swinging handle from dinging the ways.
Are you planning to cut threads under power, or to manually turn
the die holder? If the latter, slip fit will make it easier to shift
the handle from one hole to the next to enable you to swing it, shift
handle, and swing again.
Only reason to make them threaded instead of slip fit would be
if they were shorter than the reach to the bed, and you were going to
put in two or three of them to allow you to switch your hands from one
to the next.
Or -- if you are planning to cut under power, and the handle is
planned to rest against the bed (properly covered with a non-dinging
Personally, if you are going to cut under power, I would make
the holder capable of sliding towards the headstock a short distance,
and a pin locking the holder against rotation until you pull forward a
short distance -- thus making it like a releasing tap holder for a
turret lathe. (For dies, the turret lathe would use something like the
Geometric die head -- sort of like a 4-jaw chuck with the jaws being the
chasers to cut the threads. When the holder is pulled a short distance
towards the headstock (once the turret reaches its stop) the chasers all
pop out releasing the threading cutters from the threads in the
workpiece, allowing the workpiece to keep rotating while the die head is
BTW It *should* be possible to mount such a Geometric die head in a
boring bar holder for a quick-change toolpost. If you position
it truly on center, you can feed it by hand using the carriage
handwheel -- and with a bed stop you can cut equal length
threads on multiple workpieces. (Or -- you could feed using the
threading feeds and release the half-nuts before you reach the
end of the threads -- once you have a few threads, it will self
feed. I've never tried this, because I do have the bed turret
to use with my Geometric heads.
It has been made, and used now. Simple construction. Pin and sleeve. Set
Screw to hold die. Slip in tommy bar. Four holes for tommy bar to maximize
ability to work it. The business end was simply ID turned to 1" and some
slop was left (.01" apx) between the pin (.75/.76) and the sleeve. I really
wanted an MT taper on the back, but I just am not good enough to cut that
smooth, and then harden it and get it all just right. So instead I just
turned the fixed end to 1/2" and clamped into my taper mounted drill chuck.
Still not totally happy with that (it works, but, but takes up a lot of the
total working room of a small lathe) I thought about maybe putting it into a
1/2" MT tool holder. Of course that requires I turn it perfectly or accept
even more slop in my sleeve. I thought about a collet holder, but then that
drives up the cost. Then finally it came to me, and will allow me to use my
die handle tool on any taper machine easily. There are MT1, 2, & 3 tapers
with a 1/2 20 end for a threaded drill chuck all over the place for about
$5.. Problem solved. No real precision machining required, and pretty
consistent overall tool center even on a cheap lathe. Drill and tap the
back end to 1/2-20.
Now that I have done one of these and come up with a cheap near universal
solution I don't see why those selling them in the states are so expensive.
And of course I learned that it would have been better to make it out of
1144 for a better looking finish instead of the scrap (mostly 1018) I had
laying around. Small pieces of 1144 are not much different in price than
small pieces of 1018, but I had the 1018 on the shelf.
This is a similar item to what I went with. About the same price. I stuck
with the 1/2-20 because I can also get MT1 and MT3 with 1/2 20 from the same
source. In the future I'll be able to swap the taper quickly and use my die
holder on a larger lathe if I ever get one. My 8.5 by 18 also has an MT2
taper so for now just one does the trick.
Not to change the subject but in many cases, a person can buy chinese
tooling items for less than he can buy the raw material.
This appears to fall under the "law of unintended consequences"...while
placing duties on import steel in order to protect domestic production
seems at first to be good policy...
--if you don't also place duties on the finished product(s), then the
steel industry AND it's customers BOTH end up going down in flames.
This does appear to be the case. I had several projects in
mind and just the material cost/cut charges for the big
pieces, omitting my labor and the small pieces, e.g. screws,
nuts, washers, bearings, etc. was more than the finished
project delivered to my house would cost.
One problem is that I don't know how much of a domestic
commodity steel (or aluminum) industry we have left. Not
everyone can afford or needs HY150 when 11L44 will do.
Why do you need to harden it? Dead centers (solid ones used in
the tailstock) are hardened for good reason. The old meaning of "live
centers" (solid centers which fit in the headstock spindle and rotate
with the spindle) are normally dead soft -- so you can true them after
inserting immediately prior to use.
For a *single* machine -- make it a slip-fit over the tailstock
ram. About as short as you can get. (You probably would need to start
with a large diameter stock.
For moving between multiple machines, the screw-in (or for that
mater, Jacobs taper) drill chuck arbors are a good approach. (I would
consider the Jacobs arbors to be closer to true. :-)
[ ... ]
And you could probably get an even better finish with 12L14 --
which I love to turn. :-)