Grinding tool bits

Hi all

Another beginner thread I’m afraid. There will be more.

After my last thread on finish I realised that I’m going to need to grind lathe tool bits. I got hold of some 20cm 10mm HSS blanks. The first thing I realised is that HSS is really hard. My hacksaw basically bounced off. So I cut it with a diamond blade on my angle grinder, but it still took ages and overheated the steel. Any tips for cutting HSS?!

At the grinder, I am lucky in that I already have an adjustable tool rest with an angle fence (used for plane and chisel blades usually). The problems I’m experiencing are:

1) It takes ages. HSS seems to be much harder than plane blades.

2) when grinding a plane blade, of course the grinding wheel leaves a small amount of curvature. But I just hone this off on the sharpening stone, through several levels of grit and then strop it for a “scary sharp” finish. But on the lathe bit, the area I’d need to hone is much bigger, and I don’t have a nice sharpening jig to keep it perfectly flat against the stone.

The result is a curved point (see pic). It isn’t possible to grind a consistent and small radius on this. The radius either ends up as “triangles” at either end of the cutting point, or a larger “saddle” shaped radius across the whole point.

I’ve watched a few YouTube vids but none I’ve seen properly address this.

I could get a bigger grinder, which would reduce (but not eliminate) the problem.

I could get a belt grinder with a circular sanding disc on the side, but I’m not sure they will be man enough for HSS.

Most likely thing is I am doing this wrong!

Any tips ?

thanks

Steve

Why do you need to cut HSS ?

Roy

Cos the two blanks I bought are 20cm long and I was expecting to make 4 tool bits out of them!

Not something I will do again.

Steve

You can buy blanks that are much shorter than 20cm! Then you will not need to cut them. Try this video about tool grinding - It is excellent and takes you through the process slowly with a full explanation of "how and why". Here

You could do worse than follow the Blondihacks series of beginner videos by Quinn Dunki found here. Not saying everything is gospel and never to be deviated from, but it's a good start.

With 20cm blanks I'd cut them in half and grind a tool on each end (which is probably what you were doing anyway).

Links to https://www.youtube.com/c/Blondihacks/playlists

Rob

HSS is hard: that's the whole point of it, and is the reason why it can cut other steels. And yes, it does take time to shape it.

Heat won't damage the HSS properties, indeed HSS was formulated to resist the heat softening caused by too rapid grinding of standard high carbon steel tools, eg Silver Steel.

I've never tried actual cutting of HSS, but then I've never had a 200mm long piece of it, but if I was, I'd use a 1mm thick grinding/cutting disk in, say a 5inch/125mm angle grinder. I have successfully cut old file like that, and then converted them into lathe cutting tools.

Might I suggest that you invest in a double ended grinder - they are not that expensive and will be better than an angle grinder. And they do have, as a rule, both a coarse and a fine grinding wheel - use the coarse for initial shaping and the fine for the final shaping. FWIW, I used a diamond disk on some HSS - never again, as I think I've damaged the diamond!. Also, although there will be adverse comments about this, some authorities recommend grinding on the side of the wheel in order to achieve a flat surface - whan all said and done, you will not need high pressure, indeed, a light pressure will achieve a smoother surface of the HSS.

Might I also suggest a book: Harold Hall's Tool & Cutter Sharpening in the Workshop Practice Series, No. 38.

Good luck,

Peter G. Shaw

To break HSS toolbits I grind a groove around the blank, put the blank in the vice covered with a cloth, and wallop it with a hammer. For more delicate stock removal HSS can be milled with carbide endmills.

Tool grinding is not complicated. Almost all my HSS tools are ground freehand with an aluminium oxide wheel. You don't need fences and fancy rests unless you need specific angles or shapes. The basic clearance and rake angles are non-critical and can be ground by hand. I don't worry about curvature on the clearance faces, although I also grind on the side of the wheel. That's lit the blue touch paper, now to retire to a safe distance!

Andrew

I sharpen most of my tools on a belt & disc sander and it works fine. I normally use an 80g belt but if I want a nice polished edge for any reason I’ll finish off on a 240g.

Your picture looks like a nicely ground bit for a Diamond tool holder! Try clicking on the Eccentric Engineering link on the right. These are very good, you can make your own "tangential" toolholder, you only need to grind one angle on the tool, easy to hone, and give a good finish. The hollow-ground face is not a problem.

At a couple of pounds each cutting HSS blanks is more trouble than it's worth. If you must, grind. I've done it with a Dremel. Also possible to machine HSS with Carbide.

The world of Model Engineers divides into those who find it easy to grind HSS and those who don't! Them as can find it incomprehensible that anyone else struggles. Actually, I suspect not everyone has the necessary eye-hand coordination. Practice helps, but my own efforts, though serviceable, are multi-faceted in a bad way!

Many prefer Carbide Inserts to HSS, but they're not a straight substitute. Carbide 'prefers' fast deep cutting, for which a stiff powerful lathe is needed. I use carbide inserts for about 80% of what I do, and switch to HSS if I can't get a good finish, need to take very fine cuts, or require a specially shaped cutter. Hint: a useful amateur trick is to use the sharp carbide inserts designed for non-ferrous metals on steel. Sharp inserts are better suited to lathes designed for HSS.

Otherwise the answer with HSS is practice, practice, practice. You might take to it like a fish to water, or it might take time. Persist!

Practice is important, especially if self-taught. Quite a lot of machining, especially with hobby or worn machines, requires the operator to compensate for shortcomings. A bit like learning to ride a bike. Several things I once found difficult, like parting off, suddenly became much easier after several attempts. Experiment and ask - although it's not rocket science, there's a reason turners once served long apprenticeships.

Dave

Steve's Workshop has quite a useful page on ** HSS Tool Grinding ** plenty of useful pictures and diagrams.

John

Excellent video, thanks. I get it now. The honing doesn’t need to flatten the entire surface like one tends to (but again doesn’t need to) with woodworking tools. I loved the honing machine at the end.

I’ve watched her videos so much I am beginning to feel guilty! She’s great, but didn’t quite answer my question on this one.

You really need to get a general workshop book that just covers the basics.

If you check whats written on a good hacksaw blade, you'll read bimetal + the tooth count that means the teeth are HSS and HSS wont cut HSS.

Wood likes a scary sharp blade, but metal will smash the edge quickly if you use the same angles.

Removing the hollow ground effect is a waste of both money and your time and you don't need the double edge look on a metal cutting blade either. Leaving the hollow on a wood blade means the oil stone is usable a lot longer before you need to grind again.

You just rotate the edge of the blank as you lightly touch it on the fine wheel. Touch up with a hand held stone to keep the edge as and when needed.

By all means use an coarse disc on the angle grinder to rough shape a tool

after having watched a few more videos I can see that tool rests etc are not actually required, just a steady hand. But given I already have one, seems to make sense to use it, particularly in the early days as I try to figure out what I’m doing. Actually I’m thinking now that my cheap grinding wheel, which is fine for chisels, isn’t really up to the task of HSS tool bits.

What you showed in the first picture is what you get when you grind for a Tangential turning tool, (marketed by Eccentric Engineering as the Diamond Turrning Tool

Most bench grinders come with medium and coarse carborundum wheels, which are quite suitable for grinding HSS.

If you read L H Sparey's "The Amasteur's Lathe", Ian Brafley's m"The Amateur's Workshop" or Harold Hall's Workshop Practice Series No. 38 "Tool and Cutter Sharpening", thes will advise and illustrate how to grind tools.

You will also find Tubal Cain's "Model Engineers Handbook" a very useful reference on many aspects of Model Engineering and machining.

If you do not have a copy of Zeus Charts, you find that another reference booklet, in almost constant use.

HTH

Howard

I have just sharpened my first hss blank I followed This Old Tony on u tube he does his very much like Mr Crispin video, I have just used it to turn some Ali with great results and some great chip breaking rather than long strings.

This also gave me the chance to see what the dials are set at in as much that when I dial in 10 thousands it cuts off 10 thousands (5Thousands per side)

10mm sq. HSS is OTT for most jobs on a Zyto and grinding that sized stuff on a typical hobby grinder is a tedious job.

6mm. is perfectly adequate for most work, considerably cheaper and much quicker to grind to shape.

They can be mounted in a 4-way toolpost or in a home-made holder with built-in top rake.

That’s interesting. I have a 4 way tool post, which accepts 1/2 inch bits, but I don’t think it is original. I had been shimming up 8mm bits before I started grinding my own. Perhaps I will invest in some smaller blanks. As you say, it is tedious to grind the 10mm HSS.

There is always a place for HSS tool bits in your kit and the satisfaction gained from a well finished part made with a tool that you also made is for me the best part of the hobby.