HSS Split Dies

Greetinga Addy, It's OK to be a beginner and ask questions. Of course if you do we will all laugh behind your back when you're not looking. :) First of all, you can't put a bar of HSS in a lathe, then turn and thread it. This is because the HSS you buy will be way too hard to do anything to except grind it. You can do this with tool steel however. And then heat treat it. It's good that you want to learn how to make things. Making things that we can buy cheap may not make economic sense in the short run but it is a good way to learn. Especially if the item you make is better than the one you can buy. What you really need to do is buy a copy of Machinery's Handbook. This book has been published since 1913 or 1914. Much of the information in the first edition still applies today. However your best bet is to get either the latest edition or an edition published in the last 20 years or so. Many things have changed fast in the last 20 years, such as the rise of CNC, powdered metal alloys, carbides, and coatings for both carbide and HSS tooling. Most tool steels that are common today were common 20 years ago so all that info will be useful. Threads are another aspect of manufacturing that has been standardized for a long time. Machinery's Handbook has all kinds of thread data. Thread form, size, class, gauge form, etc. If you want to make taps and dies from scratch using tool steel then all the information you need is in Machinery's Handbook. Which steel to use, how to grind cutting tools, how to heat treat the dies, and so on. The newer editions will have much more metric and international standards information. It will set you back about $70.00 US and this book is well worth it. EVERY Machinist should own at least one copy of this book. Cheers, Eric R Snow

Addy wrote:

I've made split button dies for threads I had taps for but dies weren't available. I used 1" O1 steel, annealed HSS COULD be used, but I have no idea where to get such and it would require some fancy heat treatment equipment. If you get annealed HSS, it should come with heat treatment instructions and tables. 1" O1 drill rod is readily available from most any tool supplier and has stood up to the limited uses to which I've put it. The method I used is rude and crude, I ddin't have a whole lot more equipment than a lathe and drill press, plus a Dremel. Cut a slice off the bar, face both sides, bore a tap-sized hole and tap using a GOOD cutting lube. Countersink one side a couple of threads worth for starting purposes. I used an existing button die to lay out the holes that actually determine the cutting edges. I used a rotary table on one die on the drill press to do the drilling, on another I just center-popped and eyeballed it, didn't seem to make a lot of difference in cutting qualities. At this point you could harden and temper the thing or put in some divots on the periphery to hold the die in the die stock. Don't use any steel for which you can't get a hardening table. I used some anti-scale compound on the threads, heated it up with an air-acetylene torch and quenched it in oil. Cleaned it up and tempered in an electric fry pan for a couple of hours and let cool. I used a Dremel with a cut-off disc to slice the adjustment slot. I used a round india stone to clean up the burrs and hone the cutting edges. Worked fine for what I wanted.

It'd be a pain trying to do it with just a mill, but if you were very careful about centering up and boring, I imagine it could be done. Facing cut blanks parallel front and back might be interesting with just a mill.

Stan

================= From the old machining books, at one time it was expected that as part of their apprenticeship, machinists/mechanics would make a set of taps and dies for their "kit."

HSS is of benefit only if the tool is operated at a high enough speed so that it becomes hot enough to "pull the temper" of a high-carbon tool, which is unlikely with a hand operated tap or die. While I have not verified this, the literature indicates that high carbon steel is actually (or can be made) harder than HSS, and gives a better surface finish than HSS, all other things being equal, albeit at a much lower SFM.

You actually have far more equipment than you need.

The suggested materials, assuming you don't want to forge your own blanks from high carbon steel, and/or case/pack harden is drill rod [silver steel].

In the US this is available in 3 grades, W1, O1, and A1, standing for the quenching medium, i.e. W for water/brine, O for oil, and A for air. The price roughly doubles for each increase from W to O to A. Drill rod [silver steel] is essentially high carbon steel in the annealed condition.

Heat treating may be your biggest challange, and a whole seperate topic. However, the oldtimers did manage to do this, even with case/pack hardening of mild steel. What is not recorded is how many pieces they ruined before they got one right.

I suggest using A1 as the scaling will be much less if you can use a stainless steel wrap or heat under salt/flux, and the distortion is minimal as only an "air" quench, possibly a fan blowing on the part while still in the stainless steel wrap or covered with flux/salt is required for full hardness.

I suggest you buy some of the old maching books now available as reprints. Even if you don't make any dies, these are a good read, and will greatly increase your respect for the people in the craft before us. (At least they did for me.)

"Advance Machine Work" by Smith has 2 pages (12-80, 12-81) on making dies, but this requires a "relieving attachment." Given that dies were being made and successfuly used far earlier than "relieving attachments" this does not appear to be necessary, although helpful.

Some of the other reprints also show elaborate mechanisms to slightly alter the thread lead on a lathe, e.g. from 20 TPI to

20.01 TPI or 19.09 TPI. Apparently you made a tap or die, hardened it, measured the lead, and then went back and made another one, this time adjusting the "lead compensator" for the change in lead due to hardening.

see:

Let us know how you make out.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

I suppose that's true in the sense that a hand tap may not get hot enough to take advantage of the red-hardness of HSS, but HSS steel does have other desirable properties lacking in the usual tool steels, wear resistance being one of the most important. For example...

D2 rates near the top in wear resistance among the standard cold work steels, but M2 HSS has about twice the wear resistance. M4 HSS is more than 5x as wear resistant and 2x as tough to boot. T15 is even more wear resistant, but no tougher than D2.

This is probably not important for a homemade die for occasional use, but explains the use of HSS in many applications where the need for red- hardness is not apparent. Personally, if I wanted to experiment with making dies I'd use O1 if torch hardening, and A2 if a furnace were available.

Ned Simmons