He might have been unlucky and bought under-par dies, but I suggest he measures the stock metal in several places and in more than one plane.

The alloy might be fine for the work, but slightly over-size or irregular, forcing the die to work as a stripping-tool rather than thread-cutter.

Skim the surface to a couple or thou or so under-size, to relieve the load on the die and remove any serious out-of-roundness. The tiny reduction in thread flank area, and flattened crest, will not affect its performance.

I assume he using the die opened for the first cut (it might not need a closed repeat); but it may also need more regular reversals to break and clear the swarf.

Sometimes I turn a little spigot on the end, of root diameter and a pitch or two long, using a slightly chamfered or radiused tool, to help the die start.

(I have occasionally seen this in full-size practice, neatly rounded off, projecting above the nut; but it does depend on the designed purpose and appearance.)

I've had a couple of dies where the dimples were poorly formed / located and would pull the die off-square even when used in a decent holder.

I had this very issue last winter, Jason suggested Volkel split dies and a rigorous attention to stock OD. I have had no further difficulty. I get them from Rotagrip or Shop4Fasteners in Sheffield. They are probably one of the most expensive ranges but since moving to exclusive use of their taps and dies my threading has become trouble free.

Regards

Martin

The problem with Tracy is they don't sell specific makes so you might get something nice from Tap & Die Co or you could just get Apex which is what RDG mostly sell

Nigel mentioned reversals. Is he doing the two steps forward one step back manual rotation of the chuck type of operation? Feel is very important for these small threads in soft material. If he is trying to cut the full thread under power then power back out without clearing chips then he will find it can strip threads very rapidly.

Martin C

Aha! Very likely the root of the problem!

He's probably letting the die hit the shoulder with enough force to at least distort the thread there, enough to start stripping the thread on the way back. Especially as Martin suggests, the die then has to fight its way along a thread choked with chips.

Using a die or tap under power needs great care in setting, slow speed and switching off well before the tool hits the limit. It is much safer to isolate the machine, disconnect or slacken the belt if possible (to make the next bit easier) and rotate the lathe by hand. By the spindle if the chuck is screwed on.

I do reverse the tool from a lengthy thread under power, but at low speed, and after brushing all the swarf off. Unless using a slotted die-holder in the tailstock I also gently help the tailstock back by hand so the new thread is not doing that all alone.

Quite often I do use a conventional die-holder but use the tailstock chuck or a bit of rod held in that, as a gentle pressure-pad to keep the die square to the work.

So to sum up from all:

Verify the work diameter and roundness, and faced with a small chamfer or step to help the die onto the bar.

Set the die correctly in an appropriate holder, with the grub-screw into the split and the others just engaging their dimples.

Ensure the die meets the work squarely

Take the cut slowly and gently, rotating the spindle by hand. Back off at intervals to brush off the chips.

Do not let hit the die ram the shoulder. Just ease it gently to the stop point.

Brush the work clean before running the die back off.

Cut brass dry but for other materials, use an appropriate lubricant.

Not necessarily comparable but I'll throw it out there for what it's worth: I bought a die from RDG a while back to fit the ML7 nose thread. The cutting edge of the die thread was 'smeared' to one side and took a fair bit of stoning to correct. I haven't bought from RDG since.

George

"RDG Dies" got excited until I realised I'd taken it in the wrong context

H

I liked that! They can be useful, sometimes – but I only use them if I am stuck and don’t want to wait for the item to be sent from China.🙂

FWIW

I only buy HSS Taps or Dies from Tracy or Tap and Die Company.

Problems?

One Tracy Dies was marked on the back instead ofn trhe front , another cracked. Both replaced without demur.

Tap and Die, again had one Die crack, replaced.FOC.

I set Dies, wherever possible, using a commercial bolt or setscrew as a gauge, before use. or open up and use the intended nut as a gauge for subsequent cuts, if needed.

Often cut under power, (Using the VFD "Jog" facility. or a Mandrel Handle for blind holes or shoulders ) dry for brass, lubricated for steel

HTH

Howard