Soft high speed steel

[John MCParticipant @johnmc39344]

Does anyone know of a supplier of HSS in the soft (machinable) condition?

The reason I ask is that I want to make some new “cutters” for a rotary broach I made many years ago.  I’ve used silver steel for the cutters but they lack toughness when hard enough to cut.  Inevitably, in the smaller sizes, around 3 to 6mm diameter/AF, the cutters eventually break when being used in steel, long before blunting.

I’ve read the recent thread on annealing HSS, I agree, difficult to do.  I’ve tried, using the (solid fuel) central heating boiler.  Not that successful, the very slow cooling is the problem.  Hardening is much easier!

So, over to you.

 

[JasonBModerator @jasonb]

The shanks of old HSS drill bit smay be an easy to come by source as they are soft enough to get torn up if the drill slips in the chuck.

[BazyleParticipant @bazyle]

Despite the red glow if the stove gets hot enough to reach the annealing temperature the firebars will melt.

[VicParticipant @vic]

D2 Steel is sometimes used for items like this and is readily available.

https://www.steelexpress.co.uk/toolsteel/D2-Steel-properties.html

[Graham MeekParticipant @grahammeek88282]

D2 would be fine, but if I remember correctly it should be Vacuum Hardened.

Regards

Gray.

[SillyOldDufferModerator @sillyoldduffer]

Everything I’ve read about HSS suggests heat treatment is well beyond amateur means.

It’s difficult to anneal and difficult to re-harden without following an elaborate recipe, which varies alloy by alloy.

More than one oven, because the process calls for soaking at, say, 1200°C then transferring immediately to an 800°C oven for another soak.  The 400°c drop is a high-temperature quench needed to reorganise the alloys internal structure ready for the next move.   Few of us have the gear needed to quench at anything other than room temperature!   Temperature and timing are both critical over a number of stages.  And the recipes don’t seem to be in the public domain.

HSS is much more difficult to heat treat than Tool Steel or Silver Steel.  Certainly possible to ruin HSS by blasting with a torch or leaving it on a fire.  Very unlikely it can be returned to factory condition. Much more to it than “slow cooling is the problem”.  HSS is supplied hardened, and we have to grind it.

D2 looks much more practical, but more elaborate than silver steel.

I wonder if the silver steel breakages are due to sub-optimal heat-treatment?  My results vary, and I put it down to me not quite getting all the ducks in a row. Silver Steel is forgiving, not SOD proof!

A known mass/thickness of metal has to heated for the correct time, then instantly quenched.  What exactly is “Cherry Red” and “light straw?  Both colours vary depending on how the workshop is lit.  I’m not sure what they are and a proper thermometer would tell me.

Though tempering with a torch usually works well enough,  I find a hot kitchen oven works best.  Put item in, wait until the oven comes back up to temperature after having the door opened, then turn off and leave inside to cool.

Dave

 

 

 

[FulmenParticipant @fulmen]

I agree with Vic and SOD. Silver steel is a pretty basic carbon steel, jumping straight to HSS seems overkill unless you actually need the higher cutting speed.

[DiogenesParticipant @diogenes]

Can’t you make a jig to grind them from an HSS toolbit, or set them up to grind in a lathe/mill?

EDIT – also, what relief are you using on the existing cutters? ..are they snapping off at the base or splintering from the tip?..

[VicParticipant @vic]

I’ve done a very limited amount of milling/turning HSS and it can be done with carbide tooling. I wouldn’t want to attempt to remove a lot of material though. At least not with the equipment I have.

From what I’ve read it’s virtually impossible to Harden HSS in a home workshop. D2 should be somewhat easier though?

[FulmenParticipant @fulmen]

Even if you do manage to harden it I’m not convinced it would be any better than a simpler steel. They would not go through such a complex process if it wasn’t absolutely needed.

As for milling I have done it with a solid carbide endmill, but only in a very rigid setup. Grinding would be the best option.

[HuubParticipant @huub]

If you can grind the rotary broach cutters the use HSS blanks. If not, use silver steel, O2 or C45. Quench silversteel in water and do not relieve the cutters. Than they are pretty hard and should not break in a rotary broach.

I grind my rotary broach cutters on the CNC lathe using a small (50 cent) diamond disk. They have a relieve angle of 6°.

 

[JasonBModerator @jasonb]

For what you can buy an HSS rotary broaching bit for off the net these days I’d be inclined to buy and get one with making the actual part you want. Infact you can buy a whole tool for only £10 more  EDIT LESS than what a Hemmingway kit of metal costs.

Really depends on what your interests are, do you like making tools or are the tools just something needed to make what you really want/need.

[bernard towersParticipant @bernardtowers37738]

surely thats true of lots of tools being able to buy for less than the making but thats not the point is it?

[HollowpointParticipant @hollowpoint]

I’ve just purchased a rotary broach from China (not got it yet). I looked at the Hemmingway kit first but the Chinese one was only about £20 more and obviously I don’t have to make the damn thing first.

What sealed the deal for me though was that the cutters are a much more common metric shank size, and are dirt cheap. I bought 5 cutters with it, which worked out at around £5.50 each! And of course they are HSS and will likely be better than I could ever make myself.

[not done it yetParticipant @notdoneityet]

Isn’t HSS an alloy <u>designed</u> be both hard and tough, even after raising to elevated temperatures?  To me, machining HSS appears to be the equivalent of ‘taking coal to Newcastle’ was in past generations.

Calling HSS as readily machinable, when it is used to machine other metals seems a bit like an oxymoron!  If it is soft, it is not HSS!

 

[bernard towers]

On bernard towers Said:

surely thats true of lots of tools being able to buy for less than the making but thats not the point is it?

That is why I wrote the second paragraph but you obviously did not get the point.

“Really depends on what your interests are, do you like making tools or are the tools just something needed to make what you really want/need.”

Yes some people like making tools as I said in which case they can buy the materials and make the tool. Others like Hollowpoint’s post above just want to use the tool. I don’t know what the OP’s preference is but he may want to consider my suggestion as may others reading this thread.

But if you can point the OP to a source of what he is after I’m sure that would be helpful to him and others wanting to do the same. A few notes on how best to harden would not go amiss either. So far the only poster who has answered the question and suggested a suitable source in this thread is me!

[BazyleParticipant @bazyle]

Be aware that not all HSS is HSS. A few years ago I bought some round HSS off ebay and found in practice it was as soft as silver steel. Not even hardened silver steel in the temper supplied. Some suppliers either don’t know or don’t care what they are supplying.

[JasonBModerator @jasonb]

For anyone who wants soft HSS as I said a drill shank is a good source, there are plenty of suppliers of HSS drills if you don’t have any old ones laying around.

Easy to turn down to the required diameter with carbide, this was probably a Korloy CCGT 060208, 0.5mm DOC (1mm offdia). Equally as easy to mill with a £1.69 4-flute 6mm carbide cutter taking a 1mm deep cut.

A Presto 13/32″ HSS drill was sacrificed for this video as I don’t use imperial much these days.

[bernard towers]

On bernard towers Said:

surely thats true of lots of tools being able to buy for less than the making but thats not the point is it?

I assume Bernard is commenting on Jason’s comment “do you like liking tools or are the tools just something needed to make what you really want/need“?

Terse is good, but don’t overdo it. I refactored Bernhard’s comment to: ‘It is true that lots of tools can be bought for less than the cost of making them.   But that’s not the point, is it?”   Apologies if that’s wrong!

It very much is the point, though why depends on what Model Engineering is.   In my opinion, ME should be a very broad church, covering all forms of making from restoring full-size machines to any kind of tinkering for pleasure. It includes collecting tools and never using them.   Armchair engineering, in which people think rather than do, is allowed.   So are CAD, electronics, chemistry, electrics, software, radio, materials science, design and economics.

Professional engineering is strongly focussed on economics, or should be!  I believe it was George Stephenson who said:

“An engineer does for a guinea what any fool can do for a pound.”   (The internet disagrees: they find the first expression in  Wellington’s 1877 book “The Economic Theory of the Location of Railways”.  Wellington said “To define it rudely but not inaptly, engineering is the art of doing that well with one dollar, which any bungler can do with two after a fashion.”

The problem with making tools rather than buying them, is cost:  time as well as money.  Making tools is legitimate when Model Engineering is staving off boredom as a hobby.  Beware believing that home-made tools are cheaper;  in general they aren’t. (Do a full analysis!)  DIY tools are time expensive, and the time might be better spent on actually making things.

Some folk buy a mill and lathe and only use them to make accessories.  A full-time occupation because there are so many! Broaches, die holders, file rests,  fly-cutters, knurlers, boring heads, vices,  rear tool-posts, QCTP, slotters, spotters, grinding attachments, trepanners etc.   And then build a Quorn…  These folk aren’t daft, but I have different goals.

I make things in support of experimental interests, not tools, miniature replicas, or chuff-chuffs.   Making parts is secondary, and making tools wastes time needed elsewhere.  Therefore I only make tools when they’re not available off-the-shelf,  or I really can save a lot of time and money, or for self-training.   I buy tools for a purpose: provided they do the job I don’t care about ‘quality’, and I have better things to do than make them!

Both approaches are allowed.  I fight boredom by experimenting, others fight boredom by tool-making!   There is no one size fits all, and we shouldn’t criticise how others choose to exploit “Model Engineering”.

We can, and should, point out mistakes, dogma, wishful-thinking, conflations, prejudice, and errors of fact and logic.   Ignorance is always bad, as is stubbornly clinging to the past, perhaps hoping a return to traditional methods will somehow make British industry top-dog again.  Fraid not.  British industry has to meet tomorrow’s needs, and modern engineering is not, repeat not, simple.

Dave

[JasonBModerator @jasonb]

Quite good posts over on HMEM about how a member goes about hardening HSS in his home workshop. Start making that oven and quench tank now😉 He also mention show to anneal it further down the page. At least a few old drill bits won’t cost you anything to practice your hardening with.

[John MCParticipant @johnmc39344]

Thanks for the replies.   Some more background might help.  I made the tool in the mid 1980’s, pre-internet for most.  The idea came from watching a very expensive rotary broach being demonstrated at a machine tool exhibition.

Bit of a head-scratcher sorting out the geometry of the device but managed to make a tool that works well.

No chance of being able to afford commercial tooling at that time so I was on my own with regard to cutters.  I chose 12mm diameter for the mounting diameter.  Cutters are now available with that “shank” size at reasonable cost.  Problem is the length of the cutter, for what I hope are obvious reasons.  This being the reason I need to make my own cutters.

I like Jason’s idea of using HSS drill shanks, would need an adaptor making unless sacrificing a 12mm drill every time I wanted to make a cutter!

The reason for wanting HSS or something better than Silver Steel (drill rod) is, as I stated in my first post, is that I want a cutter that is hard and tough, not a property possessed by Silver Steel.

Grinding hard HSS , while I have a tool and cutter grinder, it would take forever to make a tool.

Hardening HSS.  Its an involved process to get the best performance.  But, it is possible to get a reasonable result with the “conventional” quenching and tempering, just be careful with the temperatures.  I have a low cost non-contact thermometer that is fairly accurate that has enabled me to get good results with heat treatments.

Vic, thanks for the link, I’ll give D2 (or similar) a try.

One final point.  My solid fuel boiler has been very useful for annealing steel, heating steel well into the annealing range, 800 – 1000 degrees C, sometimes even hotter.   The grate hasn’t melted!  Why?  Because the grate is constantly cooled by incoming air.

 

[JasonBModerator @jasonb]

Many a boot sale or ME show has second hand drills at reasonable cost rather then having to sacrifice what you already have, even taper shank ones cpuld be turned down and the makers are nice enough to add a ctr drilled hole for tailstock support in many cases. Certainly less than a half decent 12mm HSS toolbit would cost.

Roughing down to shape with an angle grinder would be quicker than using a T&C grinder to do it all, save that for the final profiling to size.

[not done it yet]

On not done it yet Said:

Isn’t HSS an alloy <u>designed</u> be both hard and tough, even after raising to elevated temperatures?  To me, machining HSS appears to be the equivalent of ‘taking coal to Newcastle’ was in past generations.

 

Well, John’s idea isn’t unreasonable.  Many steels can be annealed and re-hardened just as he wants.

It’s one of the reasons steel is so useful; any combination of hard / tough / brittle / malleable to meet the need, just by heat treating.

Unfortunately hardened ordinary steels aren’t heat proof, so a very good carbon steel file is destroyed well below red-heat. Carbon steel cutters don’t last long on a metal lathe, and wood can soften them too.

HSS remains tough and hard at much higher temperatures.  It’s achieved by putting certain alloy steels, not carbon steel, through a very complicated time and temperature critical heat-treatment. Could be done with the right equipment and full instructions, except home workshops don’t have either.

So in practice, wanting to change HSS becomes coals to Newcastle!  Good idea, very difficult to do, therefore try something else!

Silver-steel is a good compromise:  easy to harden with moderately good heat performance.  Not as good as HSS, but then HSS is inferior to Carbide, which isn’t as good as CBN…

Dave

[HollowpointParticipant @hollowpoint]

Another option might be to harden the cutting edge of the silver steel very hard and leave the rest of the shank unhardened. It might help prevent breakages at least.

[bernard towersParticipant @bernardtowers37738]

I am really surprised that you say it takes forever to grind a tool on your cutter grinder, may be you could explain?

[Author]

Posts