Wonky threads using die

" for example using metric drills (available in straightforward 0.1mm increments) rather than Imperial Letter and Number drills, which are bonkers illogical. "

I have often wondered how number and letter drill sizes came about. does anyone know or is it lost in history?

A mixture of metric, imperial and letter / number drills does give you even more choice for fine tuning sizes.

Best answer I've heard is the sizes come from the way wire was originally handmade by pulling metal through dies.

The apparatus consisted of a stout bench with a large lever at one end. At the other a long bar was bashed through a fixed die until the end could be gripped and the rest drawn through the die by heaving on the lever. The diameter, or gauge, of the die was limited by the maximum force the lever could apply to swage the metal down to size without breakages.

Smaller diameters were made by pulling a large gauge wire through a smaller die, with the size of the hole adjusted again to avoid breaking anything. Thus wire gauges step down through a series of diameters that don't have an obvious numeric relationship - they depend on ductility, the strength of the metal being pulled, the strength of the die, and the power of a manually operated lever. The sizes were found by experiment, not calculated, and the resulting series of gauges became de-facto standards.

When the Victorians upgraded to drawing wire with steam they could draw wires in any diameter. But because many customers were committed to the old gauge sizes, they carried on producing them. There were dozens of different gauge systems, and my 1948 Engineer's Handbook spends half a page introducing them: quite easy to order the wrong one. Gauge sizes have gradually been supplanted by rational diameters but there are still survivals.

They say the gauge of modern railway track is derived from Roman Chariots axles for much the same reason: once a standard is embedded they take forever to change, even if the original reason has become daft!

Dave

Die holders seem to have mostly metric sizes BA and small Whit & Bsf that i Have are 15/16 which from memory will only go to 1/4 Whit 5/16 Whit and similar go to a 1. 5/16 Die holder which i think stops at 1/2 whit. I also have some BA Dies that go from 10BA to 4BA that are 9/16 Dia . To get a perfect fit you may have to make small ring to fit your Die to then hold your Die , A poor fit may break your die? I maybe slightly wrong about these sizes as i am reliying on my memory

Good luck and time you will win.

right, I have changed my mind, i am making a tailstock die holder. The reason I was hesitant was that I am not confident in turning a morse taper. But I realised I have an MT2 collet which a die holder could easily be fitted to. If I can’t turn a die holder shaped thing with a rod sticking out the back I may as well give up.

What is the handle that sticks out if the back of the die holders for?

Ideally, the Tailstock Die Holder should be able to "float" on the arbor, so that the chamfer on the end of the work centres the Die, and the newly cut threads do not have the task of pulling the Tailstock along the lathe bed.

(With fine threads that is very likely to strip the thread; certainly with ME 40 threads which are only 0.016" (0.406 mm ) deep ).

I ensured that my Die Holder body, and the Tap Holder body were a loose fit on the arbor for just that reason.

Howard

That is interesting. Do you have any pictures of it? Or is there something similar online?

my 1.5” bar I bought to make it is coming tomorrow!

thanks

Steve

Ok, I just watched blondiehacks video on the subject and I think I know what to do now.

The Arrand tailstock die holder allows the actual die holder to be adjusted to be axially true, this is achieved by the holes for the attachment screws being oversized to allow the holder to be perfectly aligned before tightening. Although Arrand has closed as far as I know there is still some available, I think Rotagrip listed them not long ago.

Mike

I am a coward where turning Morse Tapers is concerned, on the grounds that I may not get the angle right, and the turned surface finish will certainly be inferior to that of a commercially ground one.

So the Stub Morse Taper arbor is mounted in the Headstock spindle and drilled / reamed /bored to suit the arbor that will be fitted.

Often the arbor size is determined by the size of material available, quite likely to be Silver Steel.

The arbor is then chamfered and faced to length, and pressed / Loctited into place.

The bore in the body of the Holder is then deliberately made a few thou over size, relative to the arbor, so that it can float to self centre on the chamfer on the end of the job.

The Holder is bored to take the largest OD Die, and holders made that have a spigot the same OD, and length as the largest Die, with a bore that accepts the smaller OD Dies.

The holders are drilled and tapped with three holes for grubscrews, at 45 degree spacing around the circumference.

Or you can cheat by making your main holder body and buying the smaller Die Holders

I put a tapping into the OD of the main holder body, so that a stud can be screwed in, to rest against the edge of the Toolpost, to resist rotation whilst in use.

I made a similar holder taking ER collets, to hold Taps . There is a chanfer on the end of the bore, to help the Tap to self centre on the bore.

Sometimes the torque required is such that the Tap slips inn the collet. In such case the Tap is usually sufficiently engaged for the work to be transferred from chuck to vice, so that tapping can be completed by carefully using a Tap Wrench and muscle power

Although this entails cutting a 1.5 mm pitch thread for the size of collets that you choose.

(It seems that the thread dia is that of the next collet size up. 25 mm for ER 20, 32 mm for ER25, and so on. )

Howard

Well, I sorted it out for now…

I got a ER25 collet that fitted the lathe, and used the tailstock to hold the die stock in position. After a few goes I got fed up with turning by hand and engaged the motor on the lowest speed.

It worked pretty well, maybe not perfect, but pretty close and much better than trying to thread on my voice. I have some steel rod coming to make a die holder at the weekend.

It worked pretty well, maybe not perfect, but pretty close and much better than trying to thread on my voice. I have some steel rod coming to make a die holder at the weekend.

see below, old bent one and new not bent one.

Thanks to everyone who gave me advice.

It's easy to turn a Morse taper if you already have a male taper you can copy. Set a dial guage on the tool post and rotate the compound slide until it tracks the taper accurately. If you do it that way you don't need to worry about the taper angle dimension.

Morse taper blank end arbors are available (Arceurotrade from just over a fiver?). These are accurately ground to size and sold for making items such as you are proposing. Morse tapers need to be precise (fitted using engineers blue) preferably with a hard ground surface. I don’t make Morse tapers ‘cos they are cheap and accurate - I always try to keep a couple in stock for making arbors as and when required (otherwise shipping adds to the cost).

I have one commercial Morse taper (my last ever purchase from ‘ban good’ for anything that must not be a substandard item). It would have destroyed anything that was associated with it, if used.

Ajax might well say it is easy. But it does require a bit of expertise when setting the taper angle, so not recommended (by me) for a beginner.

Setting the topslide to a precise angle can be frustrating - repeatedly this way and that (or "et patati et patate" as the French have it) - but the problem can be simply eased with a GHT-type screw adjuster: