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Grinding lathe tools

How critical is the angle?

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Wolfie16/07/2012 09:52:28
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502 forum posts

OK now that the first engine is done I need to address the things the build threw up for me.

The main one is that I'm struggling to cut decent lathe tools that give me a good finish. I've had a couple that have worked well (luck probably) but when I sharpen them they're never as good.

Now I'm building a grinding rest so that I can grind better ones, now when you look this stuff up on the net you get a load of stuff about rake angles. How critical are these angles or is it just enough so that the tool clears the job?

And what tools would you have in your everyday arsenal to do turning and facing to a decent standard. By that I mean what shape.

I only have a bog standard twin wheel bench grinder and it probably needs new wheels. Can I use this with Harold's grinding rest?

Edited By Wolfie on 16/07/2012 09:53:25

Ady116/07/2012 10:55:44
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3463 forum posts
513 photos

A simple grinding rest would be a good start, and see how it goes.

Have you used those carbide tipped tools yet, with a green grit wheel?

I always think carbide first nowadays because it's so much tougher than hss.

Russell Eberhardt16/07/2012 11:45:44
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2465 forum posts
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Wolfie,

The angles are not critical. Clearance angles (front and side) are usually between 5 and 10 deg. Rake angle zero (ie flat topped) for brass and cast iron and about 20 deg for steel.

You will find a straight knife tool wil cope with 90% of your work and you can grind others as and when required.

Yes, you can use an ordinary bench grinder with Harold's grinding rest. If you look at his book "Tool and cutter grinding" he tells you how to improve it. I use my rest with a cheap 15 euro grinder fitted with cup wheels but straight wheels will handle most jobs.

Ady,

Carbide tools are harder than HSS but certainly not tougher. They can easily be chipped if abused. HSS will also be easier to grind.

Russell.

jason udall16/07/2012 12:18:33
2010 forum posts
41 photos

and remember.. the finish of the tool shows up in the job...so hone your tools after grinding..

Often a blunt tool is stoneable back without regrinding...I make it a habit to stone after use ( and funnily before too ! )..

I can't grind drills for toffee even with a jig.. one chap at work can tune a drill to perfection...to 0.05 mm conc at 18 x dia...as good as out of packet.. and also cut over size if needed....must be a kind of majic .( or 40 years of practice) .. yes I do know, just can't do it by eye.( or otherwise).

As to angle of lathe tools...the jigs will give consistensy and nice finish the angles them selves are as said "between this and that" ideal angles for a pair of mataerials not even say all steels...

even inserts have odd days... one insert, or even point , just doesn't give finish the the previous one did for 100 parts ( yes I know first cuts with new insert etc.)..go figure.

Tool grinding is much like most of this hobby.. frustrating AND rewarding...experience leads to improving the ratio.

David Littlewood16/07/2012 12:47:15
533 forum posts

Wolfie,

For most of my routine turning I use inserted tip tooling. I have rather a lot of holders probably far more than I need - but the most useful ones are these:

SCLCR holder, takes CCMT tips; the most used, basic knife tool, will do turning and facing.

SCLCR boring bar - similar shape to above, but on longer shank and geometry optimised for boring

Q-cut parting tool - the best parting tool I have used, by a country mile.

You can find most of these on the Greenwood website, **LINK**

A word about quality and price. The Greenwood prices are high, but the special offers are a good deal less. You can get Glanze tools much cheaper from Chronos; the quality of the holders is OK - not as good as the Greenwood ones, but acceptable. The tips seem to be much more brittle than the more expensive ones, so I don't like them. The Greenwood site is well worth reading for the helpful guidance.

For really fine shaving cuts, a good sharp HS toolbit is slightly better - not as much as some would have you believe, I have done tests on mine and found a 0.5 thou cut with carbide is relatively easy, less than this and they are inclined to rub. I generally have a conventional knife tool and a 45 degree chamfering tool in HS set up for both my lathes.

Other points:

(1) Ady suggests sharpening TC tips on a green grit wheel. Don't waste your time, green grit is a total PITA, get a diamond wheel, they are cheaper, work better and are virtually indestructible:

**LINK**

Use a cup wheel for preference.

(2) You can find toolholders and tips quite cheaply on eBay - but take care, a lot of them are surplus industrial-sized tools and may not fit on your lathe. If you do find some common tips, for example CCMT 0602 or 0604, from a good maker (e.g. Sandvik) at a good price, snap them up even if you have to buy 10.

(3) You can get holders which use the obtuse corners of tips for rough turning, they won't cut to a shoulder but will happily chew massive cuts off in straight turning.

(4) Even carbide tips can be freshened up with a diamond hone.

(5) Your best course may be to buy a cheap set from Chronos and then experiment to see how you get on - for example:

**LINK**

I think you have a Myford 7 - if so, the 10 mm size will be the one for you.

David

Edited By David Littlewood on 16/07/2012 12:49:03

Russell Eberhardt16/07/2012 15:00:54
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2465 forum posts
83 photos
Posted by David Littlewood on 16/07/2012 12:47:155) Your best course may be to buy a cheap set from Chronos and then experiment to see how you get on - for example:

**LINK**

Depends what you call cheap! Compared to this that is **** expensive.

Russell.

Terryd16/07/2012 15:44:15
1926 forum posts
179 photos

Hi Wolfie,

HSS is an excellent choice for lathe tools. It is cheap, easy to grind to shape, rarely breaks or chips, can run hot and cuts beautifully. I have gone back to good old HSS after a few months using indexable carbide tools. Some swear by them but HSS (and high carbon tool steel such as silver steel) has been used for many years by some of the best. Once you have the basic shape and angles ground they are very easy to touch up with a small oilstone (slipstone) from time to time, even still mounted in the toolpost. A simple grinding rest is adequate but Harold Halls is very good but you will need to fit a cupwheel to one end of your grinder. I managed without any modification, just remove the guards and wheel from one end.

Also as Russell says, carbide tools are harder but not tougher than HSS and as he says are very easily chipped.  Remember toughness is not the same as hardness, carbide is like glass, very hard but brittle, HSS may not keep it's edge as long as carbide but as I said, is very easily touched up by honing with a slipstone in situ.

As for shapes and angles, Sparey in 'The Amateurs Lathe' shows the three basic shapes needed. Here is a copy of part of his sketch:

lathe tools.jpg

A) is a right hand knife tool

B) is a 'corner tool'

C) is a round nose tool and

D) is an example of a knife tool used for brass, you should have a round nosed and corner tool as well for brass (and CI)with the same reduced top rake.

The angles are not critical but it doesn't hurt to get as close to the theoretical ones as possible. I would add a LH knife tool as well.

There are others but these shapes will manage for 90% of any work you do. Here is my version of the HH grinding rest before it was damaged in my garage fire:

Grinding rest

I have since managed to resurrect the poor thing

Best regards

Terry

Edited By Terryd on 16/07/2012 15:53:46

Terryd16/07/2012 15:46:21
1926 forum posts
179 photos

Hi Wolfie,

Congrats on a lovely engine by the way, credit to you.

Regards

Terry

colin hawes16/07/2012 16:05:36
496 forum posts
18 photos

Forget recommended angles on HSS turning tools they are not the best for amateur work. Increase the angles a lot then most steels will cut a lot better. Always keep your tools SHARP. The " recommended" angles are meant to give the longest life for production runs.You cant easily see 2 thou wear on the tool's cutting edge but obviously you cant take a clean 2 thou cut with it because you are trying to cut with a round bar 4 thou in diameter instead of a blade. If the turning becomes rough it is neary always because the tool is not sharp ENOUGH , even if you cant see or feel it. Stoning is risky as you are likely to radius the cutting edge giving the above result. Avoid it. Stoning the cutting edge of the tool does cannot help as its only producing waste swarf ; only the extreme tip of the tool leaves the required finish and a small, well-relieved radius there will improve the finish. Colin

Robert Dodds16/07/2012 16:18:12
263 forum posts
29 photos
Hi Wolfie,
Liked you little engine.
You mention that your grinders wheels are shot. Are they truly at the end or simply need a new lease of life with a diamond dresser. (?5-6 off ebay)
A quick trim across the wheel face will rejuvenate your old wheel. It gets rid of all that rubbish in between the grains of carborundum and presents fresh grit to do the cutting.
I too like HSS but if you do hone by hand after sharpening take care to keep your stone flat to the tool and don't round the edges of your tool. That's worse than cutting with a blunt tool!

Bob D

Edited By Robert Dodds on 16/07/2012 16:19:08

David Littlewood16/07/2012 16:47:39
533 forum posts

But if you do take a diamond dresser to your wheel, keep it well away from your lathe (and other tools) when you do it, the dust is very abrasive.

David

Wolfie16/07/2012 18:22:50
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502 forum posts

Thanks all, similar advice to what I've read. However the thing about a sharp tool...

Everytime I grind one dead sharp it almost cuts a thread in the work and I have to round the nose off slightly.

colin hawes16/07/2012 19:02:57
496 forum posts
18 photos

Sounds like you're running the lathe too slow. Colin

Stub Mandrel16/07/2012 20:32:00
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4306 forum posts
291 photos

Wolfie,

That's perfectly normal - you should have a flat or rounded end to the tool such that it makes a cut about 1 1/2 times as wide as the feed per revolution.

I used to do most of my cutting with a knife tool like terry's "A", but with a freater angle looking down from above so it could be mounted at a slight angle and used for both turning and light facing cuts. I also make regular use of a similar tool with a bigger radius in the end.

Now I have a tangential tool and use that for 90% of turning.

Neil

colin hawes16/07/2012 20:48:27
496 forum posts
18 photos

Just a thought, Wolfie, that the tool is much less likely to give a"thready" finish if the cutting face is parallel to the chuck face or, preferably, the point trailing the face so that the side of the tool tends to push away from the cut rather than being drawn or digging in to it even if it means resetting the tool to finish a face. Colin

Terryd16/07/2012 20:48:42
1926 forum posts
179 photos
Posted by colin hawes on 16/07/2012 16:05:36:

Stoning the cutting edge of the tool does cannot help as its only producing waste swarf ; only the extreme tip of the tool leaves the required finish and a small, well-relieved radius there will improve the finish. Colin

You don't hone (not 'stone) the cutting edges, only the flat surfaces, usually the top face of the tool to refine the inevitable ridges induced by grinding (even with a fine wheel - see micrographs of ground tools). Honing a cutting tool is rather like 'stropping' an old fashioned razor. And if it is not effective why have generations of excellent machinists and 'mechanicians' (see Henry Maudslay) carried out the procedure successfully.  However, what does know after only 49 years experience - I was the one who was asked to prepare the tools for the toolroom, I'm still willing to learn though.

Best regards

Terry

Edited By Terryd on 16/07/2012 20:51:31

John Haine16/07/2012 21:25:31
2577 forum posts
133 photos
No one mentioned tangential tools....
Versaboss16/07/2012 22:27:35
414 forum posts
50 photos

If you want SHARP HSS (and inserts also) tools, there is nothing better than one of the small Diamond wheels from Eternal Tools:

**LINK**

I use the very fine D9 grit. This is only suitable for giving the razor sharp, shiny edge. For removing material a much coarser grain is necessary. I have the toolrest set to 6-7 deg. (clearance) most of the time. I make the wheel moist and clean it (often!) with a brown Scotchbrite and soap. Maybe not what E.tools write, but it works for me. This fine wheel, although not really cheap, lasts indefinitely.

I use this wheel in a (kind of) old T+C grinder, but it could easily be done in the lathe (couple of newspaper over the ways if you use water). Or cobble something together, Worden-like, with a small motor.

Just a satisfied customer...

Greetings, Hansrudolf

Russell Eberhardt17/07/2012 13:33:13
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2465 forum posts
83 photos
(4) There is nothing like trial and error for fast learning about turning and grinding tools - if one set up doesn't work try another .

Probably the best advice so far!

Russell.

Bazyle17/07/2012 16:30:26
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4656 forum posts
185 photos

re (3) above the well known Boxford book recommends just above centre without giving a reason but probably to provide a small outward thrust when facing to take up the play in the nut.

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