Grinding lathe tools

[WolfieParticipant @wolfie]

Good questions…

[David LittlewoodParticipant @davidlittlewood51847]

Peter,

1 White is normal for aluminium oxide (alumina) wheels; these are perfectly normal for grinding HS tool steel – it's what I use on my grinder. Size depends on your grinder, not sure what grade is recommended, you'll have to do some research (or ask the seller, they should know).

2 Again, depends on your grinder; I use a cup wheel and this automatically gives me a flat face to use. This is far and away the most recommended way; if you use a disc wheel you shouold only grind on the periphery, which gives you a concave tool face which is weaker than it needs to be. You can in practice get away with some light finishing cuts on the side, don't tell anyone I told you.

3 Ditto (except for the bit about the side – they don't have one, you have to use cup for flat face).

4 Fitting abrasive wheels to grinders is something to be done with care; there is an HSE guide on this, probably rather paranoid, or the instructions which came with your grinder may help. Basically you need to be sure you have an arbour of the right size for the hole, and use thick paper washers to avoid cracking the wheel (VERY dangerous). With the diamond wheels referred to above there is no real problem, as they are a thin layer of diamond compound on an alloy disc or cup, no cracking problem.

5 Get hold of the Workshop Practice series book on tool and cutter grinding – it's only a few £ and will give you a good grounding (if not grinding).

6 A used Clarkson Mk1 tool and cutter grinder can be had for less than the price of the kits to make ones like a Worden, and will be far superior.

David

Edited By David Littlewood on 18/07/2012 13:00:49

[gerry maddenParticipant @gerrymadden53711]

Thanks all for your interesting input to this thread. I am 90% of the way through making an HH rest and soon to be thinking about wheels and motors. Just one point I have not seen mentioned…. what does one use to dress a diamond wheel ? Does the fact that they have metal location bores mean that runout is less and therefore dressing not necessary ?

Gerry

[Robert DoddsParticipant @robertdodds43397]

Peter,
In addition to David Littlewood’s notes on mounting wheels be sure to keep the clamping washers as matched pairs.
The clamping faces will often be in the form of two annuli and the O/D and I/D of each half should match so that nothing but plain compression is applied through these faces and the thick paper washers onto the grinding wheel.
Any mismatch in dimensions will potentially lead to cracking the wheel.

Bob D

[colin hawesParticipant @colinhawes85982]

You don't need a cup wheel to sharpen general HSS turning tools. They can be done very satisfactorily on any offhand grinder using a 60 -grit wheel even without using a toolrest. In fact it is easier to get suitable angles without the rest . Colin

[David LittlewoodParticipant @davidlittlewood51847]

Posted by colin hawes on 18/07/2012 16:13:08:

You don't need a cup wheel to sharpen general HSS turning tools. They can be done very satisfactorily on any offhand grinder using a 60 -grit wheel even without using a toolrest. In fact it is easier to get suitable angles without the rest . Colin

Expect to get very hot fingers though!

And Gerry, you would not (normally) need to dress a diamond wheel, in fact the abrasive layer is pretty thin and there would not be much to take off anyway. If you did, it wouldn't be difficult as the diamond dust is embedded in some fairly soft matrix material. It does perhaps mean you have to take even more care over mounting it true, as you can't true it up by dressing afterwards.

David

[Peter Wood 5Participant @peterwood5]

Thanks for all the advice. However I still have a question about grinding tools.

I have an HH toolrest mounted in front of the grinder. I use the HH work holders to present the tool to the grindstone, partly for accuracy, and partly to keep my fingers out of harms way. However this means that the side and top rakes have to be ground on the side of the wheel!! This goes against all the safety advice.

In my defence, all the photos in HH's book, Tool and Cutter Sharpening, show the side of the wheel being used.

Mounting the toolrest at the side of the wheel might solve the problem but I would still have to grind the front clearance on the side of the wheel.

What is the correct techniquer?

Peter

[David LittlewoodParticipant @davidlittlewood51847]

Petr,

Is there any reason why you can't fit a cup wheel? That is the "correct technique". I suspect we have all used the side of a disc wheel – I know I used to do it before I got a proper T&C grinder – but it does not do the wheel a lot of good; it is very difficult to dress it effectively to get a good surface, and places stress on it in ways it wasn't designed to take, so increasing the risk of a dangerous fracture.

David

Edited By David Littlewood on 20/07/2012 11:39:14

[David Clark 13Participant @davidclark13]

Hi Peter

I have worked in many factories. I would say that in every one the side of the wheel was used to grind tools and I have never seen an exploded wheel. I have seen some that were worn to half their original thickness.

I am not recomending grinding on the side of the wheel but the operator must weigh up the risks and decide for himself whether to do this.

Also, bear in mind that if you grind on the side of the wheel, you don't want any end float in the spindle.

When people write books and articles on engineering do they say "don't grind on the side of the wheel" because they don't do this or is it because they feel they must point out the correct and safe way?

regards David

[Russell EberhardtParticipant @russelleberhardt48058]

Peter,

The normal technique is setting the rest to a degree or two from the side of the wheel so the tool being ground is normally only in contact with the corner of the wheel as it's advanced. Sometimes however, such as for drill grinding you do use the side of the wheel but carefully – don't apply too much pressure.

As everyone says though a cup wheel is better. I keep a white 60 grit cup wheel on one end and a diamond wheel on the other.

Russell.

[Peter Wood 5Participant @peterwood5]

David L and David C.

Your two responses illustrate my dilemma. Excuse my paraphrasing but David L says don't use the side of the wheel, with a very good argument about the difficulty of dressing, as well as perceived safety. David C argues that in practice everyone does use the side of the wheel and that the risk is small.

In my working career I was, for a while, in charge of H&S at a dozen large bakeries making a well known brand of bread. I soon learnt that most accidents were down to operatives doing the wrong things for the right reasons. That is they wanted to keep the job going so they took short cuts. I guess the same pressure is on people in engineering factories. Now I am not a 'jobsworth' about H&S but the best way of assessing risk or danger is by multiplying likelihood of an event against the consequences. That is when I come unstuck on this issue, because I cannot gauge the likelihood of a wheel shattering.

However, end of rant. David C – how about an article in MEW on the different approaches to tool grinding ie disc wheel techniques, use of cup wheels, choice of wheels etc.

Regards

Peter

[David Clark 13Participant @davidclark13]

Hi Peter

Yes, if someone would like to write a definitive article on tool grinding I would be pleased to publish it. I can't because all my knowledge on this subject is going into my new book. However, I will be able to add bits into Ed's Bench etc. I did a few words about the Axminster supplied grinding rest and recessed wheel recently.

regards David

[jason udallParticipant @jasonudall57142]

Have to add.

Bench grinders and wheels..terrify me.have seen a wheel come apart .nevver want to see it again.

Ok as to use of side of wheel.

1 speed not constant ..effects result

2 thining through dressing or use weaken the wheel at a point of max stress. A deep grove in middle of rim has a simular risk to the groving the side of the wheel..

3 work piece can snatch and fly …very much more so on the edge..( workrest)

But finishing cuts on the side of the wheel are normally very light and not the risk people think..

In truth TOOL SHARPENING might be ok but roughing out and bulk removal never.

Judge for your self but if wheel starts to need dressing on side then you need a new wheel

BTW you do "ring " your wheels don't you ?

[Harold Hall 1Participant @haroldhall1]

Thanks Peter for making my grinding rest and purchasing my book Tool and Cutter Sharpening, unfortunately though you seem to have bypassed page 31.

This explains, and shows in Sk 1 E, that when the tool passes down the side of the wheel it has to move at a slight angle to the wheel and actually only contacts the wheel on its corner. Similarly, if passing the outer diameter, then it also moves at a slight angle and again contacting just the corner.

In theory therefore, when the tool passes down the side it cuts on the outer diameter of the wheel and moving across the front of the wheel it cuts on the side. This is clearly indicated, much exaggerated, by Sk1 C and F. In practice though, with the depth of cut only being in the order 0.01mm, and the wheel having a minute radius on its corner, it is neither. Because of this the pressure on the wheel, which is minute for T and C grinding, will no doubt be at an angle of 45 degrees, nominally.

When sharpening tools they should not, ideally, slide along the face of the wheel, side or front, as this causes more heat to be generated and requires a greater force to make the wheel cut.

For viewers who do not have my book, see my website on the subject of tool and cutter sharpening, especially SK1. The link to this can be found page two. I have though used different references to those in the book, SK1A is the correct method, SK1B is the wrong method.

As to using the side of the wheel, the rule that this is a no no seems to be to me a rule that has been passed on from generation to generation without qualification as a result becoming absolute. Even some hand books provided by those manufacturing grinding wheels imply that it is OK for light duty tasks.

For me, this means that if you have welded up an assembly and need to dress some poorly made welds, one is likely to apply substantial pressure to speed up the task and is obviously a task NOT to be undertaken on the side of a wheel. On the other hand, sharpening a drill using a drill grinding accessory will present very little pressure and is without doubt perfectly acceptable. This provided that the wheel has not been dressed on the side to a point where it is becoming dangerous anyway, say 3/4 its thickness. In the home workshop, with the limited use a grinder will get this is unlikely.

I have been composing this away on my word processor before adding it here, since which I see Jason has added his contribution, to which I totally agree.

Harold

[David Clark 13Participant @davidclark13]

Hi Harold

Well said, common sense.

I have never personally dressed the side of the wheel, they invariably run true.

regards david

 

 

Edited By David Clark 1 on 20/07/2012 15:36:43

[Peter Wood 5Participant @peterwood5]

Harold

Thanks so much for your posting. At last I have a clear understanding of the correct way to use the grinding wheel.

I really should have gone back to your book and studied it more closely.

Furthermore the photos on your web site have now clarified how a cup wheel should be used.

Thanks again.

Peter

[TerrydParticipant @terryd72465]

Hi,

In defence of grinding wheels, I would say that you shouldn't be terrified of them, just read and understand their use and dangers then treat them with great respect. As for advice about grinding on the side of the wheel, that really is to prevent heavy usage such as dressing welds as Harold says, or for rapid metal removal. I have seen some really well worn wheels in industry which have been misused by some of the gorillas that use them. Personally I use a hand held grinder for that type of work with the job held firmly in a heavy vice if needed (I do it outside as I have a vice on a movable bench with normal grinders and vice) and keep my bench grinder for tool grinding. It is modified as per Harold Halls book and it works very well.

Previously I used the bench grinder in it's unmodified form. Initial shaping of the tool was done on the front of the wheel as normal but I must admit to using the side of the wheel for very light final touching up of the tools cutting edges, followed by honing. Once you have a set of HSS tools ground up they should only need roccasional touching up with a fine hone and rarely need grinding except for mishaps. It is interesting (but not essential) to understand how a single point cutting tool actually removes metal – I include milling cutters in that classification as they are merely a series of single point tools.

Best regards

Terry

Edited By Terryd on 23/07/2012 10:39:35

[Richard ParsonsParticipant @richardparsons61721]

May I put in my ½ pen’oth (In old money where 1/2d was 1” Dia).

I never regrind the indexable tipped tools. I will touch them up with a solid flat diamond file or on a diamond plate, taking care to keep the surface dead flat. I also just touch the finished edge with the diamond to ‘break the kerf’ NB take of no more than 0.001 mm)

Brazed tips I will touch up with the same diamond tools mentioned above. If they become badly chipped I clean them up with a 60 or 80 grit diamond stone cutting wheel which is backed up with a disk of ½” thick alloy to stop it flexing. Here I make no more than 3 passes before I dip in the water tin. I long ago abandoned ‘Green (bauxite) wheels, they made too much dust and mess. Diamond stone cutting wheels are dirt cheap and last a very long time

HSS tools are sharpened or rather honed as for indexed tips on diamonds/carborundem oil stones. If they are too far gone for that or are badly chipped I use my little 'off hand' grinder with 120 grit wheel to re-set them. Two passes then dip in the water and repeat. I finish them by honing as above. Do I use the sides of my wheels? Yes I do, and I also use the front of the wheel taking care to use the whole face to stop groves forming. I also use one of several rests. I have made one set at 10° below the right angle, one at a right angle and one at 2° above the right angle the stone.

To grind a new tool from a new bit of HSS stock by the hand held method can take an hour or more. For this I use the coarse (80 grit) stone to get the general shape. I bought my little grinder in 1970 and have as yet not had to get new wheels for it! This shows just how light my touch is.

The secret is like many other things “Softly softly catchee monkey” slow and easy. You do not need to be a gorillaoid to grind and sharpen lathe (or any other tools for that. A light touch, a good look and a little patience is good.

Rdgs

Dick

How do I know my tools are sharp? I touch them gently on my thumb nail!. Try it you will soon see when they are sharp.

[David LittlewoodParticipant @davidlittlewood51847]

Richard,

I believe the green grit wheels are silicon carbide (carborundum) not aluminium oxide (alumina) – the latter is used in white (and IIRC pink) wheels, but not green.

A light touch is all very well, but try doing that when roughing out a 16mm HSS tool – you'd be there all year!

I generally consider a tool (whether a lathe tool or a woodworking one) sharp if I can't see a noticeable line of light reflected from the edge.

David

[WolfieParticipant @wolfie]

Excellent and informative discussion, thanks chaps.

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