Pulley design

I need to make rather large pulleys (140-200mm) for standard 10 mm V-belt.

Grove is to be 9.7mm wide on the top and 11mm deep as theory and published projects are saying.

What are correct grove angles?

What I have found that tor a small pulley (up to ~3 inches) correct grove angle is 32 deg and for larger pulleys it is 38 deg.

I understand it, as it seems logical that due to larger contact area of big pulley frictional force per unit of contact area does not need to be so high because total contact area is larger.

I am aware that many people are making pulleys with 30 deg angle, regardless of size.

So what is correct angle for large pulleys?

38 deg or perhaps less?

Page 2 on this PDF should give you the dimensions you require.

http://www.bearing.net.au/wp-content/uploads/2014/07/SKF-Pulley-Catalogue.pdf

Phil

I'm not sure the angle is to do with pulley contact area. I think its to do with the distortion of the cross-section of the belt as it bent. The tighter the bend the more the distortion.

I got so confused by data on the net so when I made some pulleys I bent the belt into the working radius of the pulley and measured the resulting 'v' angle on cross-section. My measurements seemed to agree with some of the internet guidance and after making them they seemed to work too!

Gerry

It probably isn’t too critical in a hobby workshop application. Belt slip is unlikely and premature wear of the belt or pulley is also unlikely to be serious. If you want to transmit full load 24/7 then the belt manufacturers recommended specifications would be best adhered to but as long as you are in the right area it will be satisfactory.

Mike

For hobby use, I'd go along with Gerry. Just make sure the belt doesn't bottom out in the groove.

Thanks for all your comments. I will go for 36 deg., not exactly what industrial art calls for larger diameters (38 deg) but more than usually modellers are doing (30 - 32deg).

Reasoning is that pulley will be used quite a lot but because it is going to be made of aluminium, then this angle will be a little bit steeper to accomodate for wear.

Martin

According to Kempe's Engineers Year Book, section E9//5 Z, A , B and C section belts have angle beteen 34 and 38, so 36 looks about right.

Howard

Hi Martin

Have you considered using "Poly Vee Belts" for much better performance than "Vee Belts" as an alternative. Much easier to fabricate with the ability to use much smaller driver pulleys. Classic example is Wood working hand held power planers.

Eric

P.S. Poly Vee Belt Drive lives at my house

@oldvelo,

System will be used for motor speed reduction, so sizes of pulleys have to stay as designed.

Smaller pulleys are already rather small and further size reduction would only bring unnecessary strain..

But yes, I do use poly-v belts because they perform so much better.

Martin

@oldvelo,

I think, I misunderstood you.

Do you mean belts like those used for example in washing machines?

`Hi Martin

Yes washing machines, motor cars, and almost all modern machines use Poly Bee Belts