Spindle for diamond grining wheel

[gerry maddenParticipant @gerrymadden53711]

Hi, I have just obtained a 100mm x 200 bore diamond grinding wheel to clean up a few carbide tipped tools. According to the Arc website, this kind of wheel can run up to 9000RPM.

On what should I mount this wheel ?

Generally for grinding people seem to use small induction motors. But these only run at around 3000RPM and probably have a lot of runout.in the shaft. Significant runout would mean I would probably have to dress the wheel and I'm not sure it would take much of this before the abrasive coating was worn through.

Any advice on what would be the best way to support and drive this wheel would be most welcome.

Gerry.

[gerry maddenParticipant @gerrymadden53711]

[AjohnwParticipant @ajohnw51620]

The best simple arrangement for a spindle I have seen is used on the later unimat. Just 2 ball races and a stack of thin disk springs to provide the pre load. Those can be found on the web. The bearings are located on circlips so can be machined in the same setting as the bore – ensuring it's all as good as it can be on a given machine.

Used this way the ball races are effectively being used in a sort of angular contact mode. They last a fair old time on a unimat so personally I don't see the need to use angular contact bearings. The arrangement is cheap and simple and works rather well.

I'd use the same bearings as the unimat and compress  the springs via a screw in part. I started heading in this direction for a toolpost grinder and then found I had one. It need some work but if the spindle proves to be a problem out will come the unimat stuff.

I would have thought that circa 4,000 rpm would be enough even for other types of wheel.

John

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Edited By Ajohnw on 18/12/2016 13:40:36

[JourneymanParticipant @journeyman]

These wheels may be rated up to 9000rpm but that would probably be too fast a cutting speed. Looking at the Norton information for tool and cutter grinding the cutting speed (surface) speed range should more likely be in the range of 15 to 25 m/s for a 100mm wheel this would equate to 3000 to 5000 rpm (if my maths is right, it often isn't). The slower speed for dry grinding and faster with coolant.

John

[gerry maddenParticipant @gerrymadden53711]

John and John, thanks gentlemen for your replies. I would certainly cut dry as all my 'playing' is indoors and the mess and smell isn't welcome. This being the case and your suggestion that 3000 RPM would be sufficient, I can probably get away with direct drive from an induction motor provided it has a good bearing arrangement.

On the other hand, I do quite like the idea of a separate spindle unit and might be able to get my hands on a Unimat headstock assembly. From memory this contains a couple of 6203s set up with a controlled axial displacement of the rings, retained in position by interference fit friction. This probably isn't ideal, but seems to be good enough with the only obvious downside being that there is a little more friction torque than one might expect from a spring-preload arrangement. Anyway, I will let you know how I get on.

Gerry

[AjohnwParticipant @ajohnw51620]

I don't see where the worry about increased friction comes from Garry. Bearings on spindles should be run preloaded. Where it's possible disk springs are ideal. They tend to be far cheaper than springs that look the same and are sold for preloading bearings. Most disc springs are way too strong but there are thin ones about. They wont deflect much which is why a stack of them are used. From memory the unitmat uses a stack of convex to convex pairs.

I'm not going to think too hard about that. They face each other so that the pressure is applied to the bearings as intended without the need for additional bits. I think that means the rim of the springs contacts the bearing's outer and each pair also contacts the other via the rim but you'd best sketch it out and think.

John

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[Gray62Participant @gray62]

I use a diamond wheel on my Worden T&C grinder, that is directly mounted on the motor spindle, never had a problem with runout or vibration using it that way.

The motors for the Worden that are supplied by hemingway are very good quality if you don't already have one, it may be worth a call to them, they will sell the motors separately. (or they did the last time I enquired).

Graeme

[Neil WyattModerator @neilwyatt]

I used the spindle of a small 6" bench grinder. I fitted and aluminium hub and used the existing centres to finish turn it in place. It spins the diamond wheel so smoothly you can put your finger on it and barely feel it moving.

Tea stains optional…

Neil

[AjohnwParticipant @ajohnw51620]

I have a brooks external capacitor motor for mine. If it gets done. It's nice and compact.

Problem though I found I had a toolpost grinder recently. I am not too sure how I obtained it but must just have stuck it in the garage where it promptly got buried. The only source I can think of was several things bought from some one who was giving up.

Either way a grinding spindle can be used for grinding tools and as a toolpost grinder so if made I would use preloaded bearings. The unimat design is very easy to make. I'm not sure I would of thought of using circlips as shoulders for things to press on. Nice idea 'cause all can be machine in one setting so it is likely to turn out with everything concentric and square on with no really tricky work other than getting the bore right.

John

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[Niels AbildgaardParticipant @nielsabildgaard33719]

Posted by Neil Wyatt on 23/12/2016 18:43:24:

I used the spindle of a small 6" bench grinder. I fitted and aluminium hub and used the existing centres to finish turn it in place. It spins the diamond wheel so smoothly you can put your finger on it and barely feel it moving.

Tea stains optional…

Neil

This is so simple and beautifull that I am going to make one straigth away.Put a VFD on and it is perfect

[Neil WyattModerator @neilwyatt]

Posted by Niels Abildgaard on 25/12/2016 17:10:56:

This is so simple and beautifull that I am going to make one straigth away.Put a VFD on and it is perfect

Thanks Although I'm not sure 'beautiful' is the right word!

The slide fits to a stepped disk in a hole in the plate, exactly the same as the top-slide mounting on a mini-lathe so you can use the mini-lathe topslide to grind lathe tools.

The table pivots up and down and the whole assembly moves back and forth on angle-iron 'rails'.

Neil

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