Lathe Tool grinding

[Simon RendallParticipant @simonrendall97987]

Wheel rotation’

[Simon RendallParticipant @simonrendall97987]

I am trying to make a 40 degree point tool for a poly V pulley.

Does it make any difference if you use the front of the wheel ie. wheel going downwards or the back of the wheel ie. wheel going upwards as I can’t see how to do it otherwise, either on a diamond cup wheel, as it only has diamonds on one side or a plain disc where there is no room at the back of the wheel to get the tool in.

thanks, Simon

[egaParticipant @ega]

You don't say what grinding equipment you have but if it's an ordinary bench grinder I can suggest two things to help with this:

1. Get or make an adjustable tool rest

2. Install one or two depressed centre wheels so that you can grind on the side of the wheel.

[egaParticipant @ega]

PS I have some notes about tool shape and machining methods for Poly Vee pulleys which I can share with you if you care to PM me your email address.

[EmgeeParticipant @emgee]

Simon

As said by ega if haven't got a rest that can be adjusted to centre height of the wheel.
You don't say if HSS or other material but before using your diamond cup wheel you need to rough grind the tool to the shape needed on a white, grey or a green wheel if carbide.
Finish grind the tool with your diamond cup or a fine white wheel if HSS.

It is best to grind with the wheel rotating in a direction to cut the tool from top to bottom which leaves a clean cutting face.

To get your included angle correct you need to bring the tool to the wheel at 1/2 the included angle so 20 degrees, keeping at the same angle in relation to the front of the wheel move the tool from right to left on the face of the wheel until to halve tool thickness, do the same grind approaching the wheel left to right at the same 20 deg angle until the 2 faces ground meet at the tool tip.

If you want to use top rake on the tool you should grind that before finish grinding, it depends on the material being cut whether you need top rake, none on brass and 10-12 degrees for aluminium but less for steels.

This will provide side rake to the tool so when finish grinding you will not have to grind the full tool thickness but you will need to adjust the rest to suit a smaller angle clearance than already ground, saves wearing out the diamond wheel.

I usually use a white wheel for HSS and a green for carbide, if I need to it will be finished with a diamond wheel but mostly use an Arkansas strip by hand to remove any flashes on the cutting edges.

Search on Youtube for tool grinding videos, there are some very good videos but some that don't provide such good information.

Emgee

Edited By Emgee on 04/01/2022 12:50:13

[Nigel Graham 2Participant @nigelgraham2]

More generally, it would be worth buying Harold Hall's Tool and Cutter Sharpening. The author not explains tool-sharpening but gives a range of tool rest designs to enhance a straightforward off-hand grinder for sensibly accurate, repeatable results .

Though I've completed a Hemingway Kits 'Worden' T&C grinder, Mr. Hall's book's most advanced projects would turn the ordinary bench-grinder into something not very far less than that machine, for drills, lathe-tools and to a limited extent, milling cutters.

[Clive FosterParticipant @clivefoster55965]

Simon

No need to overthink this. Use the periphery of an ordinary grinding wheel and push the tool against it at 20° left and 20° right to get the angle. Faces will be hollow ground which matters not a jot. Actually makes it easier to hone for a real sharp edge.

Top will be flat so the depth of cut you can take without chip crowding is limited but 20 thou / 0.5 mm at a time will get the job done. More if you lubricate. Not a bad idea to leave a few thou when forming the basic pulley then honing the tool before coming back to finish. Don't forget you need a bit of clearance between belt and pulley at the ends of the Vee grooves to accommodate squidge. A belt bottoming out at the tips and bases of its ribs tears up fast. I usually go a tadge undersize on diameter and run a thin blade (hacksaw) round the bases of the grooves adding another 10 tho or so just to be sure.

At least you don't have to worry about geometrical effects due to back rake which alters the effective side angle of the groove to being cut. In practice not enough to worry anyone except Inspector Meticulous on a bad day but some folk will bang on about such things.

My view has always been that just getting on with the job using an OK near enough tool is a lot quicker than faffing around with trying to get a perfect to book shape. Book is about getting longest tool life and most jobs out as fast as possible under industrial conditions. We will never make anything like that many parts but have only limited time to make best use of. Less time on grinding / preparation but more on the job is frequently better for us.

Real sharp beats perfect shape for us.

Clive

[Thor 🇳🇴Participant @thor]

Hi Simon,

I only use my diamond wheel to grind carbide tools, and Aluminium Oxide wheels for HSS tools. Here are a few websites about tool grinding if you haven't already found them:

***Link***

***Link***

***Link***

Thor

[Simon RendallParticipant @simonrendall97987]

Many thanks everyone, very helpful and some good points.

I already made Harold Hall’s simple rest and have his book on sharpening.

Does it matter if the final fine sharpening of the tool uses the upgoing side of the wheel or the downgoing side of the wheel. My grinder is one ended so I can’t move from end to end.

Simon

[MikeKParticipant @mikek40713]

The thinking is that an upgoing wheel can lift a burr on the cutting edge. The downgoing wheel won't, which will also force the tool more onto the table. Minor, but not insignificant? I hone the edge with a diamond lap no matter what.

[egaParticipant @ega]

I agree that grinding away from the edge produces a different burr from grinding towards. Another point is that grinding away (upgoing) typically directs the sparks towards the operator (and his PPE).

[John ReeseParticipant @johnreese12848]

Conventional thinking is that the wheel should turn into the cutting edge. If you stone the cutting edges after grinding it really does not matter which way the wheel turns.

[Simon RendallParticipant @simonrendall97987]

Thanks for all that. I will have to hone my lapping skills as I usually make the tool blunter when I do it. Do you hone across the top of the tool as well as the sides and of course rounding the tip a bit?

simon

[Mike HurleyParticipant @mikehurley60381]

Posted by Nigel Graham 2 on 04/01/2022 13:41:24:

More generally, it would be worth buying Harold Hall's Tool and Cutter Sharpening. The author not explains tool-sharpening but gives a range of tool rest designs to enhance a straightforward off-hand grinder for sensibly accurate, repeatable results .

Yes an excellent book, my go-to all the time! One comment though, his basic adjustable tool rest design – I made one of these some time back and was generally pleased. One anomoly though seems to be the way the table is attached, being on a ball mount. This obviously makes it very versatile as you can move to any angle in any plane should you so wish. However, I find that the vast majority of times I want the table horizontally level with a specific vertical angle to the grinding wheel and I find it difficult with this arrangement – I get it horizontal then when trying to set the vertical angle it slips out of the horizontal and so on. I was considering changing the ball arrangement to a flat spacer that would allow the table to sit level across the grinding wheel face but still allow it to angle up/down.

Anyone done anything similar, or have thoughts on why this might be a bad idea?

regards Mike

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