L.A.Van Royen Twist Drills and their Grinding

The old model engineering myths are still the best.

Sharpness will depend upon grain size. I suspect that no specific material has a overwhelming claim to be the sharpest. Although sub-micron carbide cutters are really sharp. When I first opened one it was immediately followed by a visit to the bathroom to get the first aid kit.

Silver steel after quenching is around 65Rc, and gauge plate is around 63-64Rc, borne out by measurements after I've quenched parts in brine. A low temperature tempering, for cutting tools, may knock a couple of points or so off the hardness. Looking at datasheets M2 HSS has a maximum hardness of around 64Rc whereas M42 is nearer 68Rc. Hardness measured by the depth of an indentation is not particularly accurate, so all the values mentioned could have several points of variation.

So I think it's a myth that carbon steel is harder than HSS, unless somebody can come up with quantative proof.

Andrew

In my defence I'm about 6 months behind in reading both MEW and ME.

Andrew

Now I wonder where I got that from? I was confident it was a fact but now my reputation is on the line I can't find anything authoritative to support it.

Machinery's Handbook (20th Edn) has a table of properties 'sort-of' implying Carbon Tool Steel holds a better edge, but reading the words in the rather complicated discussion suggests to me that the choice between plain and alloy tool steels is more to do with cost than superior hardness & sharpness. As there's also a table showing two of the HSS alloys are harder to grind than the hardest carbon tool steel, I may have to plead guilty!

Very broadly, carbon tool steel it seems is fit-for-purpose and value-for-money when you are cool-cutting, like tapping or filing. But as soon as the tool edge gets hot or an extended tool-life matters, HSS is worth paying for. Like many other engineering design decisions, selecting the best cutting option for a particular job ain't simple - Machinery's Handbook tabulates 75 different tool steels, each with tuned characteristics - hardness, heat hardness, toughness, machinability, ease of heat treatment, cost, abrasion resistance, depth of hardness etc. Fortunately the general purpose tooling bought from the usual hobby suppliers is effective in my amateur workshop - mostly!

Dave (in Sackcloth and Ashes...)

Well this link suggests carbon steel is harder than HSS at low temperatures **LINK**

Tubal Cain (the English one, not the American upstart) quotes 850/860 Vickers for a carbon steel lathe tool tip. This link https://www.icscuttingtools.com/Tooldata.htm suggests 63 to 65 Rockwell for HSS , which is 775/825 Vickers (see https://sij.ravnesystems.com/assets/Uploads/Hardness-Conversion-Table.pdf for conversion chart) so not much in it. I often use carbon steel in small boring bars (broken taps reground), but I couldn't be bothered trying to source carbon steel squares when HSS is so readily available and even with gentle treatment will last longer and be less susceptible to drawing the temper whilst being sharpened.

There was an article in ME not too long ago about making turning tools out of old files

Dave, you can lose the sack cloth.

Edited By duncan webster on 10/01/2019 20:11:04

Edited By duncan webster on 10/01/2019 20:13:24

It has cropped up every now and again for as long as I can remember. It might possibly have been true, to some extent, in the early days of HSS in the 1900s. But not now with more complex types of HSS with better heat treatment and understanding of the metallurgy.

Whatever the answer, I use carbon steel, HSS and carbide tooling as needed to suit the job and machine.

Andrew

You can read my articles in MEW about drill sharpening (the Van Royen is discribed as conical clearance). Issues N° 245, 246, 247. Issue 251 for small drills, and issue 256 for web spitting. I'm still working on the subject for further articles.

J Maurel

I have quite a collection of 'carbon' tools and often use them in preference to HSS tooling when working brass - either on my smaller lathes or the hand shaper. They take a very good edge where fine cuts are required and many are forged to particular shapes that can be convenient on the shaper. They don't get hot enough to lose their hardness, which is more than sufficient for non-ferrous work.

As always these things depend on the context - horses for courses.. If I'm roughing out mild steel then obviously HSS holds up much better - but for shaving thous off brass, then a nicely honed carbon tool works very nicely and I've never had to worry about its "Rc" value!

I haven't got the math to understand most of the discussion here - but when those who 'do have' decide what's best - a simple "do it this way" would be quite good enough for me. All I want is something that drills to size and produces those lovely twin spirals of swarf. Sounds simple enough...

Regards,

IanT