The Home Machinist!

Ok then, I need some more help here. I accepted your evidence that the die holder pictured was the way to go. THEN reality happened.
I pulled 9 round dies out of my inventory and measured them to be sure I knew where I was headed. Excluding the #2-56 small dies and including those from #6-32 to 1/2-20 all made by ACE, (not the hardware store), the ODs and thicknesses were not consistent. The ODs varied from .990 to .997, the thicknesses varied from .307 to .375. Some had 2 circumferential anti-rotation divots and some 1. The location of the divots was not consistent on all dies and even from one divot to the diametrically opposite one (if there was one).
So how does the die holder in question hold the die(s) concentric if the ODs vary, and how does it hold the faces of the die(s) perpendicular to the axis of the screw if the divots are not evenly spaced from a face?
Sorry I am asking such elementary questions but I must be missing something very obvious to others. I would have expected that the die holder would clamp the dies firmly against the face of the holder so that its thread axis was co-incident, or at least parallel with the intended screw axis. If it doesn't, one might as well hold the die with water-pump pliers.

--earlgo

If you have several different divot patterns, I suppose you could drill multiple hole sets to match them, but it would be confusing to find the correct ones!

Steve

The die should rest on a shoulder, which guarantees perpendicularity.
As far as concentricity is concerned, you can explore the idea of three screws in the body, @ 120° intervals, not just one. Provide clearance, which is a requirement anyway, so the die can be adjusted. By adjusting the three screws, which need NOT bear on a groove, aside from one of them, to prevent rotation of the die, you can center the die to your satisfaction.

My choice when holding the die is for the screw to engage the split in the die, not one of the grooves. Doesn't matter where the screw is located from the edge, it will engage the die so long as it's within the die cavity.

Harold

Thanks, Harold, for the information.
Unfortunately some dies, like the 9 I have, are not split or adjustable, so there is no split to use as an anti-rotation device. Furthermore, it seems that unless the 3 radial screws are judiciously placed, the screw in the die slot would tend to open the die under heavy torque load. I'm thinking 3/8 die here, not the below #10s. And I know that the anti-rotation screw would not be cinched down tight.

I am thinking that the die needs to be pulled back against the face of the die holder with some headed screws, or a screw and washer. Set screws, in my experience, tend to twist whatever they are pushing on. I guess the dies I have can have a shallow slot ground into the circumference in lieu of the split.

Undoubtedly I am making way too much of this issue. But that is what I was trained to do so that there was no rebuild required.
Details, details.

--earlgo.

I confess, I've no experience with large dies, nor with dies without a split. I've always relied on die heads for such threads, and often even the small number sizes.

Where I began using a die, like we're discussing, was when I had to make small custom screws with long lengths of threads. By single pointing the thread (using a center that would later be removed from the finished part), I'd rough the thread, then take it to size with a die. That was the only way to eliminate deflection, so I'd achieve a uniform pitch diameter. The light finish pass (with the die) had a tendency to yield a rather nice thread, even the form, as I used ground dies. I expect that you'd not achieve the same success with the dies you've mentioned, but I could be wrong.

Harold

Harold, you wrote, "...I'd rough the thread, then take it to size with a die."
This is what I do typically, even with short threads, but it is a bit of a chore with no QC box (5 min gear change), so I am trying to get a better way for a short screw. Incidentally, I have found that if one turns a short stub the diameter that the die will just slide over before the 'to-be-threaded' part, the die will locate better.
I'll post a pic of the die holder if/when I get it done. (The lawn is calling, dang it.)
--earlgo

earlgo wrote:The lawn is calling, dang it

I fought the lawn and the lawn won.

Steve

earlgo wrote:Harold, you wrote, "...I'd rough the thread, then take it to size with a die."
This is what I do typically, even with short threads, but it is a bit of a chore with no QC box (5 min gear change), so I am trying to get a better way for a short screw.

My sympathy. I have a quick change on my Graziano (capable of both metric and imperial), as well as change gears, for capabilities beyond those which can be quickly selected by levers. I've had to make gear changes several times, for specific pitches that can not be readily dialed, and it's a real time sink. The only benefit, beyond the one of being able to achieve my goal, is that the gears that get removed and reinstalled get a good cleaning.

Incidentally, I have found that if one turns a short stub the diameter that the die will just slide over before the 'to-be-threaded' part, the die will locate better.

Yep! Orients the die much better, and offers a good opportunity for the die to engage. Always a good idea if a die must be used, assuming it's possible.

I'll post a pic of the die holder if/when I get it done. (The lawn is calling, dang it.)

A good idea, so others will benefit.
Luck with the lawn. So much nicer than shoveling snow!

Harold

I have done power tapping by leafing the tailstock unclamped and pushing it by hand until the tap starts. For running a die, I made up a holder that slides on a dowel in the tailstock. It is similar to those shown in the pictures except that I added a cross hole for a tommy bar.

Fwiw Earlgo George Thomas showed a die holder in one of his books. It adds to the work but he made it to fit his largest dies then machined adapters that fit the die holder and went down in size to hold the smaller die sizes. Visualise a short length of machined all over heavy wall pipe and that's about what they looked like. He used set screws located to match the dimples in the dies. And added more dimples to the OD of the adapters that fit the die holders set screws.But he also had a very well equipped shop and left the smaller dies in those adapters so he always had a set of dies ready to go for his die holder. The die holder had an internal shoulder the large dies located on and the adapters did the same so they were always held square to the lathes C/L.

pete: Hadn't thought of an adapter for each die and a 'universal' holder. Good idea.

--earlgo

I just received the tailstock die/tap holder set from:

http://www.neilsniche.com/lathe-tailsto ... older.html

Precision made and will serve my purposes perfectly.
I recommend this set for those not inclined to make their own.
~RN