RDG Dies

I have a friend on Messenger that I am helping to build a Stuart 10V.

He asks me what he should do if he is not sure. I reply back to the best of my ability and he gets on and does it.

he is not an engineer but his trade is as a Goldsmith so he is used to working with metal but not much machining.

He has a milling machine and C4 lathe from Ketan at Arc Euro Trade and is very happy with the quality and service he has had.

He has mucked up the odd part but is making great progress and the engine is well advanced.

“Our” next project will probably be a Stuart Victoria, the main thing governing this is the C4 is large enough to machine the flywheel comfortably.

So, to the first major problem he is having.

He purchased his taps and dies from RDG Tools.

he has tapped quite a few holes with no problems including the small ba sizes.

When he tried threading a 5/16” x 32 tpi bit of brass, the die removed most of the the thread. He is using a proper sliding tailstock die holder. He tried reversing the die in the holder and cut a fairly decent thread but the thread was crap at the back end and was ripped off.

RDG replaced the die and the same thing happened again.

I am wondering if two dies are likely to be faulty or if it is something he is doing?

I can’t think what would cause this. We have tried leaving the thread portion long which helps but sooner or later, the thread rips off.

I would add that the friend has used the die holder before to cut metric threads in stainless steel and titanium.

So, is it because it’s brass or is it the die?

To be fair, RDG is taking all of his taps and dies back and giving a full refund.

He is going to Tracy Tools at my suggestion.

I've had a couple of poor ME dies from RDG in the past, don't buy from them now.

Also checK if he is putting an imperial OD die into a metric holder

Why not bring him into the modern world with Metric Fine.

Suggest he dumps the oversize 2BA fixings and drops down to at least 3BA with 4BA heads or M4 with small hex again as they are oversize.

Watch which drawings and errata sheet he uses some have the wrong length conrod ctrs and the bearing blocks above engine ctr height of 5/8". Piston rod assembly also wrong on the errata sheets

Edited By JasonB on 09/08/2023 09:52:18

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.)

Is the die holder the correct size for the die, metric and imperial can be different outside diameters, when using a sliding die holder with a slightly undersize die in the holder the screws holding the die will push the die off center in the tailstock which will result in the die stripping the thread or a very poor undersized thread.

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.

Hi Nigel, component machined from solid so sizes OK.

Hi Juddy, sounds a possibility, die holder is a sng fit, no adjustment.

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

Martin, Thank you.

Using Tracey tools, all ordered and arriving to him tomorrow.

Thanks for the recommendation though.

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

I went with what I have used in the past but that was 25 years ago. I will report back when the job is done.

Thank you all.

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

No Martin, power in then die locks up and bar spins in chuck.

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.

5/16 x 32 in brass should not be a problem under power, if it is slipping then die is blunt of chuck not done up/worn

Hard brass should not really need backing off as it produces small chips anyway

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

I had a set of dies from Tracy Tools many years ago that would strip threads, turns out that their supplier had got hold of a batch of solid dies and was slitting them with an elastic wheel, trouble was they were twisting and going out of pitch. Must admit that stuff I have purchased from them recently is all ok.

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

H

I've had an Apex carbon steel die in that size since the early '90s. I'm guessing I bought it from Chronos though TBH I can't remember. I used it to cut the air connector thread on the inlet pipe for the stationary engines I've built, in whatever steel or brass I happened to have convenient, and it seems to've worked fine.

I think Nigel Graham 2's account is probably pretty much on the money.

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.🙂

I have a tailstock die holder set from Arc that has metric holders and imperial holders.

I would like to know what the "target" internal dia of these holders are supposed to be and tolerances.

It is a very good piece of kit but I find that when a die is inserted into a holder there is not much space to open up the die slightly with the adjusting screws.

I am wondering if i should bore out some of the holders slightly to give me the degree of adjustment that a hand die stock generally gives...

Regards

Derek