Crowning a pulley for a flat belt Question

Crowning a pulley for a flat belt, been trying on some ali before moving onto brass using the top slide set at 1° + and then set at 1° - and it ain't an easy exercise to achieve a simple crowned pulley!

Any hints on how to do this? I thought this was going to be really simple, its kicking my arse!

Think of the crown as part of a sphere ...

Then produce a suitably dimensioned ball-turning tool.

MichaelG.

If I'm stuck on making a small crown and its kicking my **** to "produce a suitably dimensioned ball-turning tool" is probably going to kick my bruised **** out my shed door
I need a much easier method than that, I'm close to getting some files out.

Edited By JasonB on 04/03/2021 06:57:33

Edited By JasonB on 04/03/2021 06:58:34

Try planning it as series of cuts like a manually operated cnc process to get the profile, then blend it together with a file, Jason the moderator has some photos carrying out this process, I'm sure he'll explain in more detail when he sees your post.

Posted by Blue Heeler on 03/03/2021 23:29:29:

I need a much easier method than that, I'm close to getting some files out.

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You haven’t even mentioned what size the pulley is ... but the ball-turning tool need not be much more than temporary tool-post on a pivoted lever.

MichaelG.

Posted by Michael Gilligan on 03/03/2021 23:42:12:

Posted by Blue Heeler on 03/03/2021 23:29:29:

I need a much easier method than that, I'm close to getting some files out.

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You haven’t even mentioned what size the pulley is ... but the ball-turning tool need not be much more than temporary tool-post on a pivoted lever.

MichaelG.

Sorry Michael I should have been a lot more clearer mate.
I'm trying to make (in the end) a drive pulley out of brass approx 1" in diameter and 1" wide and bored for a 6mm shaft out of bar stock with just a gentle crown in the middle to take a small flat belt (its to drive a model steam accessory).
Chucked up the brass and thought it would be a super simple and quick job. Found out that it wasn't working out like that and stopped wasting brass and went to ali to try and work out how to do it.
Not sure if I'm just having a brain f**t here, but its got me stuffed.

Edited By JasonB on 04/03/2021 06:58:12

Thanks Pete.

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At those proportions you will need your surface to be much bigger radius than the pulley, but the principle is still good ... You might be pivoting the lever on the shed wall though, rather than clamping it to the lathe

Not really relevant, but here are some notes about the ‘crown height’ on full size pulleys.

**LINK**

http://www.visusa.com/belt_tracking_m01.htm

MichaelG.

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Edit: The first few seconds of this woodworking demo are probably all you need to understand what I am wittering on about : https://youtu.be/fmzD8wI8RIA

Edited By Michael Gilligan on 04/03/2021 00:30:36

Thanks for the link Michael.

Thanks all, managed it finally, that camber is 1.5° -

having spent enough time toning down the language used I not go through it again, if you search "crowning jasonB" on the homepage search box you will find several threads like this about crowning pulleys & flywheels and also fish bellies on conrods.

This has always been the traditional model engineers way of doing it so no need for large radius ball turning tools and you were right in your first post about getting your files out.

Hi MichaelG, I'm not really into wood turning, but a very interesting demo you've linked too.

Regards Nick.

If it’s for authenticity, OK. But for a normal flat belt I would stick to a pulley with side guides and make full use of the contact area. Worked well enough on our Massey Harris 701 baler.

Faced with this type of calculation again do it in steps as suggested. The formula is the square root of radius squared minus distance moved (step over) squared. Hope this makes sense.

is that not just the radius?

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That looks good

MichaelG.

Hand turn it against a prifile guage.

regards Martin

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... but you only emboldened part of the text !

Try adding some mathematically relevant parentheses to what Chris wrote.

MichaelG.

I seem to remember that the pre-war Austin 7 dynamo pulley was like this but also had a degree of crowning?

Belt and braces!

General practice with belt drives ,in our sphere of vintage steam and oil engine belt drives ,was if the motive power runs at a higher speed than driven machine ,the large pulley on the machine would be crowned and the small pulley on the engine would be parallel, where it was the other way round ie a traction engine driving a faster rotating small pulley on sat a threshing machine then the T/E flywheel would be crowned and the small pulley would be parallel and very often with raised sides to stop the belt slpping off as the threshing machine was never in perfect alignment as it was on rough ground, Now on oil engines as they very often ran faster than the driven machine the engine belt pulley was parallel and I have not come across any genuine manufacturers pulley that was crowned,with the exception where they had to drive a generator or thrashing machine and these would be vey large pulleys. Where it was common in steam practice for portable and traction engine to have crowned flywheels ,oil engines tended to have flat face flywheels only one of my oil/lgas engines has a crowned flywheel, So for a small pulley is crowning essential,?