Clarkson grinder - J section poly v belt

I've just bought a MK1 Clarkson grinder. It needs quite a bit of work, part of which is replacing both crowned pulleys for the flat belt drive. I'm inclined to convert to a poly-v J secion 8 groove belt and off the shelf j section pulleys. The alternative is i make my own crowned flat belt pulleys. Any reason I should stick with the flat belt?

Can’t see any compelling reason to keep the flat belt, I am sure that if poly vee belts had been available when the Clarkson was originally made they would have used them.

Probably the only hypothetical reason to keep the flat belt is that it will be lighter in weight, and therefore have less tendency to fly-out at high speed.

But if you need to replace the pulleys anyway, then there’s a lot of merit in poly-v

MichaelG.

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There is a rather impressive photo of fly-out [captured with electronic flash] in John P’s Album, here:

https://www.model-engineer.co.uk/albums/member_photo.asp?a=38322&p=900793

Edited By Michael Gilligan on 03/11/2021 19:39:27

Poly V belt may be too effective at power transmission for safety on a T&C grinder like the Clarkson with relatively exposed wheels in close proximity to the operator. Make that very exposed for the earlier examples of the breed!

It is said that power transmission should be only just sufficient to spin the grinding wheel and do the job. Hence the belt will slip should a jam up occur or a chunk of wheel escape. A more positive drive may lead to wheel burst or similar undesirable outcomes under such circumstances.

I have a translucent yellow plastic flat one on mine with visible re-enforcement threads. It works.

The four short bar motor mount system is a royal pain to set so to simultaneously achieve correct tension and alignment so the belt stays on the pulley. I modified mine with L shaped brackets replacing the lower short arms. Much more civilised. Drawings and pictures somewhere if of interest.

Clive

I fitted a skimmed down poly-vee belt onto standard flat pulleys on a Clarkson grinder. I ground off all the ribbed section leaving a thin rubber belt. It worked just fine on the original crowned pulleys.

On my surface grinde rI made two poly-vee pulleys and used a standard belt and that too worked very well.

A crude source of flat belts is either toothed or polyvee turned inside out. I suspect polyvee are cheaper, but stand to be corrected

Mine has the full belt guard, ill have to make a wheel guard. I'm going to give it a go with poly V pulleys and belt. I'll try a 4 groove belt gather than the 8 I had in mind initially, but will probably buy 8 grooved pulleys. I may try and recut a crown on the original steel pulley but the alloy one on the motor is too far gone. I need to recut the slide ways for the x axis before I worry about the drive belt.

Mark

When I commissioned my Clarkson I simply recut the sadly worn / abused alloy spindle pulley with two shallow straight tapers derived by measurement from the motor pulley which was essentially unworn. Being steel probably helped. A quick touch with a file to round off the centre peak and take the straightness out of the tapers and I called it good.

20 years on the belt still doesn't run dead centre but the grinder works fine. Inspector Meticulous might quibble and Super Safety Maven object to the minimal change in wheel speed but I shoved them out of the workshop with instructions to "Get a Life!" eons ago.

Poly-Vee are indeed a doddle to make if you take the trouble to make the easy set-up tools first. But for something like this on standard shaft sizes with sensible centre spacing and diameters, I buy, not make. Making is for unobtanium specials in weird sizes.

Clive

Hi Mark, The early Mk 1s were just that but late models incorperated some of the Mk2 items, the most obvious difference was the 2 step pulleys that from memory gave 4000 and 6000RPM ! Depending on what you are intending to do on the machine it might be worth converting the bearings and pulleys to MK2 spec.

I have run a Mk 1 with an inside out poly V belt without incident. for pictures of the Clarksons in all their forms see The bedroom workshop site, very interesting and usefull. Good luck Noel.