A question about pulleys.

[Robin GrahamParticipant @robingraham42208]

Hi. An acquaintance has presented me with a thing labelled "Clarke Motor". This is a 1475 rpm motor coupled to a "headstock spindle" via four-step pulleys on the motor and driven shafts. The whole thing is enclosed in a pressed steel A-shaped enclosure. He wants to get the driven shaft down from its present minimum of 850rpm to around 180. So abount 8:1 reduction from the motor speed. My question is this: given that the maximum (rim, not PCD) diameter pulley that can be accommodated on the output shaft without modifying the enclosure is 100mm, can this be done in one stage, and if so what belt profile would be best? There is almost no torque requirement I guess – he just wants to run an embossing wheel (think single wheel knurler) round leather-hard clay mounted on the output shaft. I think there would be room in the enclosure for a countershaft if necessary, but I'd rather keep it simple if pos.

Regards, Bob

[Robin GrahamParticipant @robingraham42208]

[John HaineParticipant @johnhaine32865]

You obviously need a motor pulley about 12.5 mm diameter and will need a flat belt. Pulleys could have slightly convex profiles to help keep the belt on. There are suppliers around of flat belting, I remember I bought one from somewhere in Suffolk for an Aciera F1 miller I used to have. Look for Anglo Swiss Machine Tools who I think pointed me at the supplier.

[Michael GilliganParticipant @michaelgilligan61133]

Robin,

This is just crying out for a PolyVee conversion.

… as compact as flat belts, but better transmission.

You should find several threads about them on the forum.

MichaelG.

.

Edit: Various spellings … but this should give you a good start.

Edited By Michael Gilligan on 17/06/2014 23:13:34

[Les Jones 1Participant @lesjones1]

Hi Robin,
Some further comments on Michael's PolyVee suggestion. Most washing machines seem to use this method for a very high reduction ratio. The end of the motor shaft is machined with the polyvee grooves but the large plastic pulley on the back of the drum is flat. (Or possibly slightly domed.) You could machine the motor shaft or cut the end off an old washing machine motor.

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Robin,

As an example of the reduction ratios that can be achieved in a compact space … have a look at this Wood Lathe.

MichaelG.

[jason udallParticipant @jasonudall57142]

If little torque required..why not try a dimmer as speed control to motor..

[Bob Brown 1Participant @bobbrown1]

There is a minimum diameter that all belts can run and in this case you will not be able to get to 180rpm in one hit, it will need a counter shaft. The minimum diameter for a Polly Vee "PJ" belt is 20mm, if you had that driving a 100mm pulley the best you'll get is close to 300 rpm. If you install a countershaft and go for 4:1 on each run you effectively have a ratio of 8:1 which will give you around 184 rpm.

Or you could use toothed belts which is a relatively low cost option see **LINK**

Bob

[BazyleParticipant @bazyle]

Try just friction drive with pram wheel onto shaft. The application probably doesn't matter if it slips when overloaded.

[Anonymous]

I was under the impression that a reduction of 4, followed by another reduction of 4, gave an overall reduction of 16, not 8?

Andrew

[Bob Brown 1Participant @bobbrown1]

Andrew

you are correct should have been 4:1 then 2:1

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bob Brown 1 on 18/06/2014 09:14:31:

There is a minimum diameter that all belts can run and in this case you will not be able to get to 180rpm in one hit, it will need a counter shaft. The minimum diameter for a Polly Vee "PJ" belt is 20mm

.

Bob,

Only partly true …

PH section belts are aso available.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 18/06/2014 11:51:36:

PH section belts are aso available.

.

Here is a useful summary of the specification.

MichaelG.

[Bob Brown 1Participant @bobbrown1]

PH minimal pulley diameter is 13mm which you could get away with if you increase the diameter of the driven wheel slightly (+ 4mm) but best of luck finding a suitable belt or pulleys as not that common, hence the reason for PJ profile and it all depends on the power requirements.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Robin Graham on 17/06/2014 22:30:29:

… There is almost no torque requirement I guess – he just wants to run an embossing wheel (think single wheel knurler) round leather-hard clay mounted on the output shaft.

[Neil WyattModerator @neilwyatt]

For such a non-critical application use a hoover belt which can wrap around a pulley only 1/4" diameter if you need it too. I fitted enough of these to hoovers in my youth. Available from your nearest market for pence.

Neil

[Robin GrahamParticipant @robingraham42208]

Thanks for all the suggestions / comments. I had read somewhere that there was a minimum diameter for pulleys, but didn't hunt for 'official' data because I thought they would probably apply to situations where torque transfer is an issue, which it really isn't in this case – hence asking here for more 'what you can get away' figures. Inspired by Neil's remembering of his Hoover belt fitting youth (I'd forgotten about those things) I've had a look at a defunct Dyson which I got off Freegle 'for parts'. The cleaning brush is driven by a half-inch flat rubber belt direct from the motor shaft and is the right sort of length (it's quite stretchy), so I'm going to give that approach a go because it's cheap and simple to do. If it doesn't work, not much lost, and I' ll do it properly with a countershaft. A subsidiary question though – am I right in thinking that for a flat belt transmission the crown should be on one wheel only? I imagine that if both are crowned, and they aren't perfectly aligned, they will fight for control.

Jason, if it would work, the dimmer switch idea would be ideal, but as this an induction motor (I should have said that ) I think it won't.

Bazyle, the friction drive idea had occurred to me but because the input/output shaft distance is 130mm (should have said that too!) it doesn't add up within the space constraints. Thanks anyway – it would have been a neat solution.

Regards, Rob.

[Neil WyattModerator @neilwyatt]

Hoovers used to use round belts running in a grooved pulley, I recall the driving (motor) shaft used to have well-spaced flanges but I may be wrong. On the Dyson the larger, driven, pulley is crowned but has flanges just in case (probably to make sure the consumer fits the belt in the right place!)

The Hoover type belts are MUCH better, they typically last years, I've got through two Dyson belts in a week as if there's a jam up they melt though in seconds. Don't get me on to the world-beating design features of Dyson vacuum cleaners, suffice to say my Mum's hoover in the '90s dated from the '60s, but…

That said, if your arrangement is unlikely to ever stall,the Dyson belt should be OK

Neil

Edited By Neil Wyatt on 19/06/2014 08:46:54

[Ian S CParticipant @iansc]

You can get heat joinable flat plastic belting, in a number of sizes. Think you might find flat belts are often used on machines such as tool post grinders.

I think the manufacturers of the heat join belts recommend that you give them the dimensions, and they will join it for you, it's a wee bit more complex than the round stuff. Ian S C

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