Cutting Tool Steel

[WolfieParticipant @wolfie]

I was given a handful of large lathe tools for my bigger machine by someone in my local SME. Thing is, they are pretty far gone and need regrinding.

 

One or two of them appear to have some kind of tip on but its blunt and difficult to grind. The rest are in a bit of a mess so I thought best thing to do is simply cut the old ends off and start again. But unsurprisingly they are resisting my hacksaw so how do I go about cutting myself some fresh ends or do I have to grind the old ones off?

[WolfieParticipant @wolfie]

[Anonymous]

If we assume that the tool bits are HSS (high speed steel) then you’re not going to cut them with a hacksaw, or anything else for that matter. You’ll have to reshape them by grinding. They have to be worked in the hardened state. The hardening and tempering method for HSS is complex and not possible to do in a home workshop.

 

The tool bits that have tips on them that are difficult to grind are probably brazed carbide tools. These were common in industry before indexable carbide insert tooling took over. They normally consist of a straight carbon steel shank with a carbide cutting tip brazed on the end. The carbide tip will need a ‘green grit’ grinding wheel; these are silicon carbide (and are often green ) as opposed to the normal aluminium oxide grinding wheels.

 

(If you need to shorten a HSS tool bit you can grind a groove around it, put it in a vice and wallop it with a hammer to fracture it. But, wrap it in a cloth first, and wear proper goggles, because it may well send shards everywhere at high speed.)

 

Regards,

 

Andrew

[David LittlewoodParticipant @davidlittlewood51847]

Diamond wheels are the modern, and superior, alternative to green grit for sharpening tungsten carbide tools, for example one of these: Diamond wheels

 

David

[Chris TriceParticipant @christrice43267]

I can vouch for diamond wheels. I generally use HSS or tooling with separate tips but I found an old set of brazed TC tipped tools and sharpened them using a diamond wheel as linked to and got them sharper than they were when new. They now sit on the shelf above the lathe ready to step in when needed or for machining particularly tough material.

[John OlsenParticipant @johnolsen79199]

For cutting small sizes of HSS those small cutoff wheels that they make for the Dremel tools are very good. The wheels I mean are about an inch or so diameter and are very thin. They do want a steady hand as the wheel will bust very easily, so decent goggles are vital. You don’t have to cut right through, they will make a nice groove for breaking as described above.

 

regards

John

[adyParticipant @ady]

Ditto on the dremel tooling, but you have to set things up properly.

 

I put the cutting disc in the lathe chuck and the HSS in the toolpost and then cut carefully through the hss.

 

Any kind of inaccuracy and the dremel disc will shatter.

Once set up they do a good job too, cutting off bits of HSS for boring tools etc

Edited By ady on 28/11/2011 07:01:45

[Gordon WParticipant @gordonw]

If the ends are not to bad, just regrind on your standard bench grinder, Easiest way to cut HSS is a thin cutting disc in angle grinder, I use grinding disc in ang. grinder to rough out the end of larger Hss tools, just to save my expensive wheel. The hard tipped ones you have may be welded hard facing type material, best just chuck ’em.

[Chris TriceParticipant @christrice43267]

Dremel do fibre reinforced cut off wheels too. They’re slightly more expensive but last longer and have far less tendency to break.

[Michael Cox 1Participant @michaelcox1]

I have made a small stand for my Dremel type rotary tool that facilitates cutting of tool steel and other hard materials, see:

 

http://mikesworkshop.weebly.com/rotary-tool-stand.html

 

Mike

[chris stephensParticipant @chrisstephens63393]

Hi Andrew,

If we assume that the tool bits are HSS (high speed steel) then you’re not going to cut them with a hacksaw, or anything else for that matter.

Au contraire, mon ami.

HSS responds well to being milled with solid carbide end mills.

chriStephens

[Chris TriceParticipant @christrice43267]

Hmmm… interesting. Heads out to workshop to experiment.

[chris stephensParticipant @chrisstephens63393]

The cutter in this photo was shaped with a carbide end mill, although it was sharpened on a grinder. If any of you want to see it and going to Sandown, all being well, it should be on the SMEE stand

chriStephens.

[Tony Pratt 1Participant @tonypratt1]

Posted by chris stephens on 28/11/2011 13:18:47:

Au contraire, mon ami.

HSS responds well to being milled with solid carbide end mills.

chriStephens

Hi Chris, so you are saying you can machine hardened HSS with Tungsten Carbide, would you like to elaborate on this for us “amateurs” so we can give it a go.

Tony

[Sub MandrelParticipant @submandrel]

HSS can be cut, albeit slowly, with a carbide cut-off wheel ina dremel (or in my case Woolworths) mini tool.

 

> The hardening and tempering method for HSS is complex and not possible

> to do in a home workshop.

 

J A Radford describes several tools he made at home from un-tempered HSS. I understand that hardening needs two things – a means of keeping the metal at white heat (oxy torch or fierce muffle furnace) and a source of an air blast for quenching.

 

Neil

[Robert DoddsParticipant @robertdodds43397]

Wolfie,

Its difficult to be sure without seeing your large old tools but there used to be a range of Butt welded tools, Stag Major from Edgar Allen is one make I recall. They consisted of a shank, 7/8 x 3/4 in tough carbon steel with approx an 1″ length of HSS butt welded on the business end. Shanks were painted red or yellow I think.

After much use and many regrinds you could finish up exposing the shank and it didn’t cut as well.

Perhaps you have inherited some of these so beware when you do find a way of cutting the ends off

Bob D

[Anonymous]

Posted by chris stephens on 28/11/2011 13:18:47:

HSS responds well to being milled with solid carbide end mills.

 

Chris: I’ll have to put that on my list of things to try; any advice regarding speeds and feeds?

 

Posted by Stub Mandrel on 28/11/2011 21:10:40:

 

J A Radford describes several tools he made at home from un-tempered HSS. I understand that hardening needs two things – a means of keeping the metal at white heat (oxy torch or fierce muffle furnace) and a source of an air blast for quenching.

 

 

I agree that tool steels such as D2 can be hardened by heating to about 1000°C and then oil or air quenched. The same is true of HSS such as M2, although the hardening temperture is about 1250°C. These will give hardness in the range HRC60-65. However, for cobalt based HSS, such as M42, to get the full hardness (about HRC68-70) you need to heat to about 1200°C and then (this is the difficult bit) quench in a salt bath at about 550-600°C before air cooling and then tempering.

 

Can’t say I’ve ever tried it though. May be I should get my hardness tester up and running and then do some experiments! Minus the salt bath of course; a bit too dangerous for me.

 

Regards,

 

Andrew

[chris stephensParticipant @chrisstephens63393]

Hi Tony and Andrew,

The advantage of being an amateur is that no one has told you that you can’t do something, so you find out for yourself.

I first tried milling HSS when I wanted to square off the dovetail on an Eclipse parting blade and it worked to my entire satisfaction.

The thread cutting tool in the picture was milled with one of Jen’s from JB, a 10mm four flute milling cutter running at 800 RPM and roughly 0.5mm depth of cut. As it was an experiment, what the first E in SMEE stands for, I used an odd bit of bogstandard HSS that had become too short for normal use. It now has a new lease on life as a “self retracting” thread cutting tangential tool. My reason for wanting to use a milling machine for shaping was to get precise shape, I could have used my surface grinder, but milling is so much quicker.

chriStephens

Edited By chris stephens on 28/11/2011 23:32:59

[mgjParticipant @mgj]

I think if I were in this game I’d try one of two approaches.

 

If I had cobalt endmill, then that is the best and quickest way to reshape. And if CS says it works, he of the tangential tooling, praise be upon him, you can bet it does. I keep meaning to get a couple for roughing all my tool steel (but since I don’t use so much these days…)

 

Failing that, I would rough out with the 1mm cutting discs in an angle grinder – fast (very), waste little material and put little heat into what is being cut. And they don’t take the angle grinder under gyro forces. Then I’d grind with a proper tool and cutter grinder – or a grinding wheel if I didn’t have the other..

Edited By mgj on 29/11/2011 00:09:05

[chris stephensParticipant @chrisstephens63393]

What Ho MGJ,

You flatter me but remember flattery does not work on me, I am too used to it.

 

1mm angle grinder discs are fantastic for shortening HSS. When I used to make light pull drives, for a well known woodturner, out of 8mm HSS end mills I used them to cut off the overly long shanks, it took mere seconds.

 

I think you might mean Carbide not Cobalt, but we get the idea. I am not the only one to mill HSS, Mike Crisp has had a go and used the technique to rough the blanks for a recent grinding course at SMEE. As with most of you lot he had not thought to try it, well lets face it Industry has no need for it, but found it to be a useful addition to a home machinists arsenal.

chriStephens

[mgjParticipant @mgj]

Shortening, and roughing. Use mine to put aproximate angles on sq HSS before grinding.

 

Biggest I go to is 3/8 sq.

 

I will see you at MEX – I doubt I shall miss you.

[Anonymous]

Chris; thanks for the information.

 

However, I think you are wrong about industry having no need for it. I use Garr carbide milling cutters, as it is what my local tool supplier stocks. Their catalogue has several pages in the back dedicated to feeds and speeds for use in hardened steel up to 70 HRc, which I suspect is about as hard as HSS gets. As I understand it the driving force is the machining of pre-hardened mould dies, to avoid heat treatment distortion that may occur if the mould is hardened after machining.

 

Regards,

 

Andrew

[chris stephensParticipant @chrisstephens63393]

Hi Andrew,

What I meant was that industry does not need to machine HSS in its hardened state. If there were a need it would be easier to do batches in the “soft” state and then harden.

I quite see that there is a need for machining hard metals, apart from my playing.

chriStephens

[Chris TriceParticipant @christrice43267]

So as a rule, what sort of speeds are we talking compared with say machining a carbon steel?

Edited By Chris Trice on 01/12/2011 01:50:36

[Anonymous]

Chris S: I don’t disagree with you.

 

Chris T: According to my Garr catalogue they recommend the following for 60-65 HRc. Normal machining is at 75fpm, so for a 1/2″ cutter 575rpm and 0.0012″ chip load. For high speed machining at the same hardness they recommend 450fpm, 3450rpm and 0.0009″ chip load for a 1/2″ cutter. Airblast is recommended, but dry machining is acceptable. Seems pretty fast to me, but I assume the idea is to run the chip shear zone hotter than red heat, so softening the metal.

 

Regards,

 

Andrew

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