Grinding your own hss lathe tools. Tips & tricks?

[samuel heywoodParticipant @samuelheywood23031]

Sorry, yet another question…i'll stop asking soon, least for a while, seem to have a head full of engineering at present.

Please share your toolbit grinding tips & tricks, i'm sure quite a few beginners would benefit from it.

When i bought my mini lathe, ooh, must be 10 years+ ago now, pre ground hss tool bits didn't seem to be available.

I started with some Chinese brazed carbides,,,,less said about that the better!!!!

So i quickly needed some hss blanks & a cheap grinder.

According to the specs, my mini lathe would take up to 3/8" toolbits.

Working on the theory bigger is stiffer that's what i went with along with (intuition must have prompted me ) some 'half size' 3/16" ones, just your basic chinese hss.

Some might scoff but i've found these to be adequate for most things, a couple of times i've machined unknown quantities which have quickly blunted the chinese hss & i've had to dig deeper. Trueing up my spindle register was one such occasion (had burrs roundthe bolt holes for starters)

Plenty of info on the WWW about grinding basic turning tools, so don't be lazy~go look!

After grinding a couple of 3/8" bits i kinda realised why smaller bits in toolholders are often favoured~ it takes forever!

That's my tip #'1~ use the smallest bit that's realistic.

Am i doing something wrong??

Literally hours to grind a 3/8" bit , don't ask how long a hssco8 took!

I have got the patience,I just don't want to upset the neighbours excessively.

Really am i getting something wrong? Any way to speed things up a bit?

That's another tip for beginners~ wear ear plugs, the bench grinder should run fairly quiet but once you get that hss engaged it gets pretty vocal!

Tip #2 if you're grinding an external threading tool definitely use a smaller tool bit, the cutting forces should be fairly low so no iron girder required~ it will enable you to get closer to that often present shoulder…& don't set the point to the midpoint of the tool either (I got that right 2nd attempt )

Pre ground tool bits now seem more readily available, tried a couple from Arc recently, decent enough~ hardly seems worth grinding your own for the price? except you may need something not available off the shelf.

I've barely scratched the surface grinding my own as yet (no pun intended), It is kinda fun & rewarding (was very suprised & pleased with my home grown threading tools) but it does seem rather tedious.

My two favourite home grown tools are vertical shear (fine finishing) & a neutral/chamfer tool which i elected to use zero top rake on~ it still cuts steel ok,so long as i don't push it hard. See below as to why.

Both these tools are more or less infinitely re~grindable/ re~honeable. They will outlast their maker, that's for sure.

Please kindly share your tips & tricks.

Forgot one more tip #3~ I usually use 4" blanks~ if you think about what you are doing & grind appropriately you can have a tool at each end & a quick rotation of the toolpost will bring the second one into play. MIND THOSE FINGERS THOUGH!

[samuel heywoodParticipant @samuelheywood23031]

[Kiwi BlokeParticipant @kiwibloke62605]

Really, I think you should do your own research. you will find out more that way, and avoid (some of) the misinformation that clogs up the internet – and, mercifully fairly rarely, even this forum. There are plenty of appropriate books out there (remember books?).

A 'cheap grinder'? '…fairly vocal'? Well, goodness knows what sort of wheels come with a cheap grinder, but they almost certainly won't be well suited to the task. Perhaps OK for putting an edge on a mattock… And, in the 10 years of taking 'literally hours', trying to grind HSS, the wheels are probably glazed. Glazed wheels won't cut.

So, tips: 1, read – buy books; 2, get appropriate wheels; 3,mount the wheels properly; 4, dress the wheels; 5, sort out a sensible tool rest – what came with the grinder will be hopeless. 5, read more. Then, if you're still stuck, ask…

Oh, and balance the grinder and the wheels…

[Lee RogersParticipant @leerogers95060]

Kiwi Bloke points out the inadequacy of standard tool rests on grinders. Replace it with the simplest one you can think up. Mine just has an adjustable fence and I only use that for the final cuts and as a visual reference for initial cuts. The satisfaction of your first job done with a tool that you ground yourself is priceless.

[derek hall 1Participant @derekhall1]

Kiwi gives good advice,!

Does sound like your wheels are glazed where they are not cutting and you force the HSS into the wheel.

A simple double wheeled bench grinder is one of the most dangerous (and neglected) peice of kit in the workshop….

Regards

Derek

[pgk pgkParticipant @pgkpgk17461]

There's folk on here with a heap more experience than myself. I followed 'Tom's techniques' (although he stopped posting) ..off hand grinding just resting a hand on the grinding rest rather then using it as 'the rest'
Also one can cut chunks off with an angle grinder or cut-off dremel to get closer to the shape wanted – or use a carbide tool. Joe pie showed that recently or a specific internal radius form tool.
It's all about practice.

pgk

[JourneymanParticipant @journeyman]

There is some useful info and a downloadable wall chart at *** Steve's Workshop *** which you may find useful.

John

[Bob WorsleyParticipant @bobworsley31976]

In my experience you will notice a definite improvement if you find yourself a grinder with 8" stones. The motor will be powerful enough to actually grind! Mostly 3ph but practice doing 230/400V converters!

Keep the gap from wheel to rest to a minimum, especially with an 8" grinder.

Use good quality white grind stones.

Get a devil stone, for cleaning the wheel in bulk, and a 1ct diamond for precision cleaning.

[Mike HurleyParticipant @mikehurley60381]

1. Buy the Workshop Practice series book no 38 'Tool & cutter Sharpening' for about £8

2 Make a versatile tool grinding rest as detailed therein – (excellent general machining practice anyway)

3. Keep the grinding wheels unclogged

4 Practice lots

Simples!

[Nick WheelerParticipant @nickwheeler]

I haven't done much grinding because tipped tools do virtually everything I need, but 10mm tools on a mini-lathe is daft when you won't get to the limit of a 6mm one. That immediately saves money, time and effort. I do a lot of work with a 3mm tangential tool.

Rough out the tool with a coarse wheel or angle grinder and finish on the fine wheel. De-glaze it often.

A larger, tiltable table makes grinding the tool much easier. Draw or scribe some lines on it to give a better idea of the angles.

Practice with mild steel of the same size before getting too involved with the HSS.

[IanTParticipant @iant]

Well, on the Myford a Diamond tool holder does a great deal of my day to day work, the main reason being that it's very simple to keep the tool sharp.

On my small EW I use 'Rose' blocks generally and (like yourself) decided that 3/16th HSS was quite robust enough for that lathe. One thing I do not bother with however is back rake. I have tools for both steel and brass. The former have side and top rake, the later just side rake. The first grind is such that I keep the cutting edge level with the top surface of the tool – obviously easy with the brass tools as they have no top rake but a bit more care required for the steel cutting ones.

Once you have this then the tool is simply sharpened (in it's holder) on the front face, the wheels' curve giving front clearance. It's quicker to do than even a 'diamond' tool and cutting height is not effected. The only variable is how much angle to put on the front face and usually I put very little on (just enough for clearance) as this gives a stronger cutting edge. They are lightly stoned to round the front leading edge.

It may not be too obvious in the photo below but the top (furthest away) block has a l/h steel tool and the middle block a r/h brass tool (so the side clearance is on the camera side). The bottom tool was used to trim plastic btw. I do grind special tools but these 3/16th ones work well for most jobs on the EW. So not what the books say but it works for me. A quick and convenient way to keep tools sharp.

Regards,

IanT

[noel shelleyParticipant @noelshelley55608]

The degree to which many bench grinders wheels are out of balance makes them difficult to use accurately. If the grinder was cheap then the wheels will be even cheaper, and of little use for tool grinding ! Fit a white wheel for tool steel and a green wheel for Tcarbide. If the wheel has plastic bushes for a smallerl shaft then make a carrier for the wheel so it can be balanced before fitting to the grinder. A glazed wheel will generate heat rather than cut metal, so a star wheel dresser is handy. Noel.

[VicParticipant @vic]

Posted by IanT on 06/02/2023 09:55:18:

Well, on the Myford a Diamond tool holder does a great deal of my day to day work, the main reason being that it's very simple to keep the tool sharp.

On my small EW I use 'Rose' blocks generally and (like yourself) decided that 3/16th HSS was quite robust enough for that lathe. One thing I do not bother with however is back rake. I have tools for both steel and brass. The former have side and top rake, the later just side rake. The first grind is such that I keep the cutting edge level with the top surface of the tool – obviously easy with the brass tools as they have no top rake but a bit more care required for the steel cutting ones.

Once you have this then the tool is simply sharpened (in it's holder) on the front face, the wheels' curve giving front clearance. It's quicker to do than even a 'diamond' tool and cutting height is not effected. The only variable is how much angle to put on the front face and usually I put very little on (just enough for clearance) as this gives a stronger cutting edge. They are lightly stoned to round the front leading edge.

It may not be too obvious in the photo below but the top (furthest away) block has a l/h steel tool and the middle block a r/h brass tool (so the side clearance is on the camera side). The bottom tool was used to trim plastic btw. I do grind special tools but these 3/16th ones work well for most jobs on the EW. So not what the books say but it works for me. A quick and convenient way to keep tools sharp.

Regards,

IanT

Nice job Ian, those holders look very smart.

[HopperParticipant @hopper]

Couple of tips I would offer:

1. Buy yourself a copy of LH Sparey's book The Amateur's Lathe. It has the best description I know of how to grind lathe tools. Start with his "Knife Tool". 8 Quid from Tee Publishing. Well worth every penny.

2. Don't let the HSS overheat enough to turn blue. You've lost the temper if it does. Keep a large tin of water by the grinder (2 litres at least) and dip the tool in frequently before it gets hot on the end. Keep it in there until stone cold.

3. Use 1/4" square HSS and sit it on suitable 1/8" packing in the toolpost to bring it up to 3/8" high. Much quicker and easier to grind than huge chunks of 3/8 HSS. And thus does not get as hot. See point 2.

4. Use a good quality 6" bench grinder with good quality wheels. Get a diamond wheel dresser and use it when needed.

5. If using carbide tooling use the ground inserts that are coded for instance CCGT rather than the standard CCMT etc etc. These are made with a sharp edge for turning aluminium but work well on steel in small lathes.

Edited By Hopper on 06/02/2023 11:39:01

[BazyleParticipant @bazyle]

Lots of small grinders available second hand. We sent half a dozen off to the 'tools for Africa' place last year. They should be cheap then you can spend money on the new wheel. Otherwise the Titan 8in from Screwfix is good out of the box.

Don't get intimidated by it being a 'black art' or any more difficult than making decent tea. eg over stewed tea = overheated bit etc.

You don't need a fancy adjustable toolrest until you are sharpening end mills.
Find the references on this forum to a stack of wood blocks and the height above wheel centre creating the grind angle.

You only need one angle to all faces = 10 degrees. Just do everything to 10 until you really have a reason to deviate. (obviously not thread tools)

To save carving off huge chunks of a new blank get a pack of used tools off ebay which will have much of the work done so only need finishing off.

If you find that you 'need' a more powerful motor on your grinder as indicated in an earlier post you are using the wrong grade wheel and it is clogged.

[mgnbukParticipant @mgnbuk]

I started with some Chinese brazed carbides,,,,less said about that the better!!!

Did you grind them first before use ?

All of these that I have come across (square section lathe or round section boring tools) have just been square section carbide blanks brazed to the shanks with no clearance angle ground in, as though they are supplied "semi finished". A couple of minutes finishing them off on a green grit wheel to put some clearances on makes them functional – if you used them straight out of the packet I would not expect very good results !

Nigel B.

[Dave SParticipant @daves59043]

2. Don't let the HSS overheat enough to turn blue. You've lost the temper if it does. Keep a large tin of water by the grinder (2 litres at least) and dip the tool in frequently before it gets hot on the end. Keep it in there until stone cold.

Why wont this myth die? HSS holds its hardness at red heat. Thats the whole point of HSS.

It is *very* unlikely you will be able to temper a piece of HSS using a bench grinder.

Dave

[IanTParticipant @iant]

Why wont this myth die? HSS holds its hardness at red heat. Thats the whole point of HSS.

It is *very* unlikely you will be able to temper a piece of HSS using a bench grinder.

Dave

I generally agree Dave but I think there could be an issue with getting HSS tooling quite hot and then dunking them into cold water. I've read of "micro-fractures" being caused by the sudden temeperature changes, especially on the cutting edge(s). The tool tip is then more fragile and probably won't bear up as welll. I work on the general rule that if the tool is too hot to hold then you should probably let it cool. I also tend to do tool grinding in batches, so it's easy enough to rotate through them.

I guess it mght be worth mentioning that for my 'Diamond' holder I have spare toolbits, so I can just swop them out as needed, much easier than just using the one.

Another advantage of the 'Rose' blocks is that they act as a heat-sink for the smaller 3/16th tools. I also have 'spare' 3/16th tools but they are still placed in a block to be sharpened. This helps with cooling and of course also gets the grinding height right (for the front clearance). May be worth mentioning that you can do all this work on the front of the wheel – which is not only safer but is also the only part of the wheel that you can dress.

So I agree but whilst I don't think 'Blueing' HSS tools is a huge problem, I still prefer to avoid it – and dunking very hot tools into cold water is probably not a good idea either…

Regards,

IanT

[Mick B1Participant @mickb1]

Posted by Dave S on 06/02/2023 13:47:59:

2. Don't let the HSS overheat enough to turn blue. You've lost the temper if it does. Keep a large tin of water by the grinder (2 litres at least) and dip the tool in frequently before it gets hot on the end. Keep it in there until stone cold.

Why wont this myth die? HSS holds its hardness at red heat. Thats the whole point of HSS.

It is *very* unlikely you will be able to temper a piece of HSS using a bench grinder.

Dave

Good comment. I can't remember ever wrecking a tool that way. I just use a little plastic beach bucket looted from the grandkids' surplus as a dip tank.

| Posted by Bazyle on 06/02/2023 11:54:44:

|…

| You only need one angle to all faces = 10 degrees. Just do everything to 10 until you really have a reason to | deviate. (obviously not thread tools)

|…

This too is true – though TBH I'd just say 'a few' degrees. You need more than about 3 or 4 to be sure you've actually got definite rake and clearance, while more than about 12 makes your edge a bit fragile, and adds the risk of 'inward drag' in the case of rake – but in most cases there's no need for particular exactitude.

I'm a bit tempted myself by the idea of an 8" grinder that's good straight out of the box, again as recommended by Bazyle – but up to now I've coped well enough with cheap 6 inchers, replaced every 15 years or so by another cheapy. I think I'm on my 3rd, or perhaps 4th.

The real effort that IMO is unavoidable is putting in the time. I did a government training centre course on centre lathe in 1975, and I think I put most of a week of the 26-week course into learning tool and drill grinding on the bench grinder, and still think it was a good use of the time.

[Dave SParticipant @daves59043]

I tend to hold the HSS toolbit in a pair of mole grips, grind away and then use. Saves both time and burnt fingers…

I have heard the micro crack theory, but not seen it happen. Dunking a piece of red hot silver steel to harden it doesn't tend to cause issues, so I don't see why a much cooler piece of tougher steel would fail.

I suspect that the micro crack 'myth' (going to call it a myth for now) propagates from the cemented carbide world – where certainly older carbides were prone to premature failure if the coolant supply was intermittent.

Dave

[Iain DownsParticipant @iaindowns78295]

Thanks for starting this thread, Samuel.

I've been using self-ground hss since I started this (only the last 10 years or so – a beginner still).

I find that sometimes my tools work well and sometimes the edge / tip just rubs away. All comments about rake above and in the literature have been taken into account.

I was going to post and ask about the heating effect on HSS as I find it hard to avoid getting the tool hot enough to generate colour. Even with very short application of the wheel (grey wheels on a cheap bench grinder).

I think I've learned that I need to dress the wheels and that I shouldn't get too concerned about the tool getting warm – even to blue(though I have read conflicting views on that).

What I'm less sure about is if I should dump all my blanks of uncertain origin and just get some fresh from a known good source.

Is the steel likely to be an issue for me?

Iain

[Iain DownsParticipant @iaindowns78295]

As an example of my issues, here are some pictures of a very fine tipped toll I ground, put to work to cut 3 grooves.

Sadly I don't have any before pictures, but the profile was reasonably square from the top and of course there was a point from the side. The end flat was originally about 0.35mm – the images are considerably enlarged!

In this case this end is the opposite end from the pointy end of a parting off blade which I'm reasonably sure was sourced from ARC and thus should be of decent quality.

All three cuts were in stainless. The first in 304 the last (when I noticed the quality is of uncertain consistency.

I expect that the tip got to blue temperature at some point in the grinding process.

Any idea what I can do to fix this?

Many thanks

Iain

[SillyOldDufferModerator @sillyoldduffer]

Posted by Dave S on 06/02/2023 15:08:37:

…

I have heard the micro crack theory, but not seen it happen. Dunking a piece of red hot silver steel to harden it doesn't tend to cause issues, so I don't see why a much cooler piece of tougher steel would fail.

I suspect that the micro crack 'myth' (going to call it a myth for now) propagates from the cemented carbide world – where certainly older carbides were prone to premature failure if the coolant supply was intermittent.

Dave

Difficult to see microcracks because they're too small. The effect they have is rapid wear, not catastrophic failure. Plenty of cracking to be seen on TV's Forged In Fire programme.

Not so sure overheating whilst grinding is a myth either. Although the body of an HSS blank is unlikely to get red hot, the point, edges and surfaces in contact with the grinder have much less volume and could easily get much hotter. Notice any sparks? The fine fragments of HSS cut off by a grinding wheel can get hot enough to catch fire.

Overheating and microcracking probably only damage HSS near the edge at the hot end, so gently removing a couple of millimetres should get back to safe metal.

Wear on cutters can't realistically be assessed in home workshops because the conditions are so variable. Noting tool life in hours at a fixed cutting rate isn't what we do, but when tested properly it's found that cool sharpened tools last longer than overheated and temperature shocked tools. Unlikely to matter in a home workshop, because our mixed work load makes it difficult to optimise tool life, and we re-sharpen as necessary.

Nonetheless I feel it's hardly worth taking the risk of burning when backing off slightly and frequent dunking is so easy to do.

Dave

[Howard LewisParticipant @howardlewis46836]

IME , HSS tools do not need to ground absolutely accurately with regard to clearance angles , unless you nare machining something quite different from mild steel.

I tend to use Zero top rake , especially for parting tools, to minimise the risk of dig ins, just front and side clearance of about 5 – 10 degrees.

Avoid excessive angles, they weaken the tool and reduce the amount of metal to conduct away heat from the cutting edge..

You are not chasinbg seconds of arc; scarcely whole degrees even!

If the toolbit gets too hot to hold, take a rest and let it cool. Even, make a holder to make holding the tool safer and easier. Quite easy, may need asome filing and and a tapping, but a useful accessory.

Grinding a tool should not take hours.

I am now fortunate to have made a cutter grindeer, so can grind very small amounts at a time, but usually it only takes a few minites from a blank toolbit to one ready for use.

Off bhand grinding tends to be quicker and less maccurate, but stoll, does the job.

Buy and study the WPS book on tool grinding, also L H Sparey, Ian Bradley or any of the other authors of books on basic lathe work (Stan Bray, Harold Hall, Dave Fenner, David Clarke – all former MEW editors, and the current one, Neil Wyatt.

Get the basics right, a suitably ground tool, set at centre height and with the speeds and feeds, somewhere near right, things should work out OK.

If the machine is not set up correctly, it doesn't matter how you grind the tool, the resu;ts will be less thatn good..

You can do an awful lot of work with a basic knife tool, possibly with a small radius on the cutting edge (But be careful that the radius extends far enough down that the tip contacts the work rather than rubbing below the tip.

I tend to use a Tangential tool for a lot of work. That needs a holder / jig for grinding, and only one face needs to be ground..

HTH

Howard

[Roger WoollettParticipant @rogerwoollett53105]

You may be interested to know that SMEE do a one day course that covers this. The offhand grinder is covered with safety, choice of wheel and dressing to preserve the cutting surface discussed. Students then get to finish a knife tool having been shown how to get the desired clearance angles accurately.

The next course is on the 23rd September.

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