Lathe HSS cutting tools

[Alfie PeacockParticipant @alfiepeacock58331]

I have a few HSS lathe tools from 1/2 inch to 3/8ths unused with a 60 deg angle on both ends. As a cutting tool has a lot less of an angle why have the tools got this 60 deg angle on them. I would like to grind some tools up but this means grinding the angle off, this is a beginners question so any advice would be appreciated,

[Alfie PeacockParticipant @alfiepeacock58331]

[David Standing 1Participant @davidstanding1]

When you say a '60 deg angle', do you then mean they are thread cutting tools?

[Simon Williams 3Participant @simonwilliams3]

Unused square HSS tools come with each end cut off at an angle, 60deg sounds about right. My understanding is that this is to facilitate sharpening the end before mounting it in a tool holder of the Jones and Shipman type, which holds the whole tool at an angle below the horizontal, automatically giving a top rake angle without grinding away the top surface of the tool blank.

Other explanations may abound!

Simon

[SillyOldDufferModerator @sillyoldduffer]

I've wondered about this too. Here's an example of a new HSS tool blank:

On this one, the left hand angle is about 70° and the right about 73°. Whatever the purpose of the angle, accuracy seems not to matter.

Dave

[Thor 🇳🇴Participant @thor]

Dave, the toolbit in your photo looks pretty much the same as the ones I have.

Thor

[mark smith 20Participant @marksmith20]

Ive always wondering the same the angles vary ,heres some i have the ones on the left are cut at a 60-70 degree angle ,the one at the bottom straight across and the ones on the right are cut at an angle but in two directions.

[Clive FosterParticipant @clivefoster55965]

As Simon suggests the angled cut off is provided to reduce the amount of grinding needed to produce a typical tool.

Works for conventional lay flat and boring bar tool holders as well as the Armstrong, J&S et al "up kicked" variety. The proper clearance angle for the material being cut only needs to be applied to a narrow land below the cutting edge. Think typical insert tooling. Once you have clearance between tool and cut surface the HSS is in the wind and air cares not a jot about what the angle is. So long as there is sufficient support for the cutting edge and adequate metal to take the heat away detail shape beyond the active cutting part is unimportant.

Pretty much stuck with a full grind on the flat top as the swarf needs to flow over it. Pro users tended to grind a chipbreaker there anyway.

I have an orphan tangential type cutting tool holder which takes truncated triangle shaped HSS exploiting the same ideas to minimise waste.

Got a cheap chainsaw sharpener on the shelf waiting to be converted into an HSS bit end chopper off. Plan is to fit a 1 mm cutting disk and arrange a suitable adjustable bit holder to put a similar over clearance angle on well used bits so only a narrow land has to be ground or touched up when re-sharpening. As one side of my DE grinder carries a wire brush cutting thus saves swopping between coarse and fine wheels or wasting the fine one on bulk grinding. Doing it by hand is less than accurate.

Clive.

[BazyleParticipant @bazyle]

At one time HSS was very expensive. Since tools are always going to be ground off at least a bit at an angle someone, perhaps during WW2, realised it made sense to cut them at an angle to start with. The potential saving in material and time to grind from new would be worthwhile.

[Clive HartlandParticipant @clivehartland94829]

Grind the tool for a purpose, dont worry about what is there now. Grind the tool to the angles YOU want for standard turning or a rounded point. Cut back as far as necessary for internal cutting. You will end up with a selection of tooling for most purposes.

Clive

[Clive FosterParticipant @clivefoster55965]

Most beginners over grind tools. Don't take any more off than you need to.

Don't get hung up on exact angles.  Sharp matters more.  For our rates of metal removal something close will do just fine.  Especially if its sharp and nicely polished.  To a first approximation the turned surface replicates the cutting edge so a smooth polished edge gives a better finish than rough one.

I've seen a table and diagrams somewhere linking the clearance angle immediately below the cutting edge to the height of the tool when presented straight on to a grinding wheel of a given diameter. Obviously the basic shape of the ground surface is an arc of a circle but this is clear of the turned part surface so doesn't matter.

From a beginners perspective its obviously much easier to simply put a piece of packing on the grinding rest to get the correct angle than it is to sort out an accurate, solid, tilting type rest. Easier to produce a radius on the point of the tool too. Helps with touching up as you aren't reliant on setting up the exact angles on a tilting device. Many amateur ground tools show the remains of multiple nearly the same angles where rest set-up has been slightly different for each grind.

Hopefully someone can find the reference. Its not a universal panacea but it does get you started with reliable, repeatable results.

Clive.

Edited By Clive Foster on 29/09/2017 16:00:52

Edited By Clive Foster on 29/09/2017 16:02:07

Edited By Clive Foster on 29/09/2017 16:02:28

[Simon Williams 3Participant @simonwilliams3]

There is an analysis of presenting the work to the grinding wheel above centre height to achieve a predictable clearance angle in the book of the Quorn. IIRR it crops up in the setting instructions for grinding reamer flutes, also for putting clearance on the perphery of a side and face cutter.

[not done it yetParticipant @notdoneityet]

Yep, Bazyle got it. Economy of material. Simple asvthat. If it was square at the ends, more material would be needed. Saves time too – not having to always grind a square end away!

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