Grinding HSS Lathe Tools - Advice please

I am a newcomer to lathe work and thought it would be useful learninmg exercise if I tried to make a lathe tool out of a 3/8" HSS blank. I have been following the instructions from one of the many write ups on the Web but it seems to take ages to grind the steel. Is that normal? I am using a new 6" 36 grit aluminium oxide wheel on my old Wolf light industrial grinder and have dressed the stone.

Any advice would be much appreciated. Thanks. NIck

Hi Nick,

It will take considerably longer than grinding mild steel.

Stick with it, don't burn your fingers and don't dip it in water when it gets hot - you can't overheat HSS on a grinder. Try holding it in a clamp rather than your fingers.

Neil

Hi Nick,

Others will probably give you much more chapter & verse, but for what it's worth, my take is that a) yes it will take a long time; and b) the tool will get darned hot.

Now, I can't comment on this because I haven't that much experience, but apparently if you attempt to cool a HSS tool that's hot, as when grinding, you run the risk of causing cracking.

It may be advantages to use a coarse grinding wheel first to rough out the shape you want, followed by the fine wheel to smooth out the grinding marks left by the coarse wheel.

Good luck.

Peter G. Shaw

Cubic boron nitride (CBN) plated wheels are the best for HSS but they are initially expensive. However they last a long time.

Dunno why my last came out green!

Which shape are you making ? there isn't much to take off a 'knife tool'.

Nick,

There's a lot on the web about tool shapes and different methods of achieving them. I don't know what kind of work you are intending to do but I'll give you this very simple thought. Getting a 1/8th HSS tool into "initial" shape is much easier and quicker than doing it with 3/8th HSS tooling ! This will be true every time you need to re-sharpen them too.

I've pretty much standardised on 3/16th HSS (I happened to 'acquire' quite a bit of it - otherwise I would use 1/8th)

I do use heavier section HSS for a few applications (e.g. some shaper tooling) but only when I really need to.

Try it and I think you will find smaller section tools are much easier to sharpen (and to keep sharp) and that they are perfectly usable for most hobby uses.

Regards,

IanT

I've ground some according to 'toms techniques' youtube vids and they work OK.. and he cools his as do I (mine in a mix of collant wash). But it is tedious to do and frustrating if you bog up near the end. I've tried using my tormek wet wheel that i use for wood carving chisels but that really is slow. I've also used my belt sander but you can't get just the edge of the front of the tool at it properly without tripping over the belt sander;s own edges (as in the belt is a centimeter in).

I;ve just ordered a 60 grit diamond disc to try on the belt sanders disc face which has no rim. if that works then i;ll build a holder to sit on the platform there for compound angles. It was about a tenner on ebay from china so it'll be interesting to see what it's like.

As for the cooling argument.. well frankly I don't think that the difference between the heat needed to burn my pinkies and a dunk in room temp water is enough to matter - guesstimating a drop from less than 100C to 20C. And you can dunk before you start.

Some things not mentioned thus far is the need to dress a conventional abrasive wheel frequently and let the wheel cut rather than forcing the tool into it. I find a white wheel far better than the dubious quality grey ones often supplied with low cost bench grinders.

Use an angle grinder fitted with a thin cut-off disk to rough shape the tool first. Three or four slices at most will get you close and save lots of grinding. Especially once you get the knack of judging angles to slice at slightly too great a clearance angle on the cutting edges so only a small part of the tool depth needs to be ground at the correct clearance angle. A millimetre or so at the correct angle is plenty.

Up-tilted tool holders, Armstrong et al style, make life much easier and more economical because the top rakes are produced by flattening off the top as required rather than grinding down into the tool bit.

You need two grinding wheels. One coarse for rough shaping and one fine for final sharpening. Best to have a slipstone or diamond for the final touches. The finish on the work matches that of the cutting tool so the bits that do the work need to shine.

Clive

Edited By Clive Foster on 20/02/2015 00:12:21

Thank you all for your helpful comments. I am a way off actually using my Boxford CUD as I am still fitting out the workshop. This tool grinding exercise is very useful in the mean time. Best wishes. NIck

Nick, you may find Harold Hall's book 'Tool and Cutter Sharpening' (Workshop Practice Series # 38) handy.

Best $20 I spent - very educational and easy to follow. Highly recommended reading.

* Danny M *

Just do the roughing with an angle grinder, either a cut-off wheel as suggested or a grinding wheel. They are cheap ones which will do the job. HSS should not suffer at all by getting hot, no need to quench.Finish on a white oxide wheel and a slip stone for polishing and putting on radius at the tip.

I use a tangential tool - so easy to sharpen - small tool bits with supplied sharpening jig and to me it is worth every penny I paid for it.

I do not worry about angles - the jig sets them for me with only one face to grind.

My home-made tool rests for both course and fine wheels are both set level

So my 14 QCTP's sit on the shelf and are rarely even looked at.

And now I have made that marvellous tool height gauge from last month's MEW

sharpening and resetting the tool is just a few seconds work.

Richard.

Agreed. I use 1/4" HSS nearly all the tome on my 5" lathe. Just make sure they don't project far from the tool holder or, if necessary, support them with some mild steel bar underneath.

Russell.

You can let HSS turn blue when you are grinding it, as pointed out by a recent article in Home Shop Machinist.

Neil

Nick, I mainly use 1/4" tooling, although I do have some 3/8", 1/2" and 5/8" stuff. If you look at most tool blanks, you will see that they are cut off at an angle when you get it, and a tool can be ground up from there without much effort, but I agree that with tooling above 1/4", an angle grinder is the way to go, but be careful with the thin cut off wheels, if you use them don't cut on the side of the wheel.

Ian S C

.

I cheat.!!!!

Mostly use the Eccentric engineering tool holder and their associated grinding jig. (I have no shame )

Makes even a tool grinding retard like me able to produce good HSS tools. However I still t times need to grind a 'special' tool.

Nick