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.

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

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.

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.

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.

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

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.

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

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

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

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