Crowning a pulley for a flat belt Question

[Anonymous]

Posted by JasonB on 04/03/2021 07:26:10:

This has always been the traditional model engineers way of doing it………..

Just as well I'm not a model engineer. For the crankshaft governor pulley I used a hydraulic copy unit with a hand filed pattern:

To keep the traditionalists happy the governor end pulleys were done with files:

The pictures of full size engines that I have show that both ends of the governor belt have crowned pulleys.

Andrew

[Martin KyteParticipant @martinkyte99762]

Once most people have a copying attachment or a CNC lathe that becomes the 'Traditional" way. Nice bit of turning as usual Andrew.

regards Martin

[JasonBModerator @jasonb]

Posted by Michael Gilligan on 04/03/2021 08:58:31:

Posted by JasonB on 04/03/2021 08:49:48:

Posted by Chris Evans 6 on 04/03/2021 08:41:17:

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?

.

… but you only emboldened part of the text !

Try adding some mathematically relevant parentheses to what Chris wrote.

MichaelG.

yes that is what I was trying to make sense of, there are several ways it could be written which would give a different outcome, I would actually have expected some trig in there, hopefully Chris will come along with the details as I can't make any of those 3 options work. But r – square root of (r squared – d squared) does give the infeed for a given stepover

Out of interest for a 25 x 25 pulley using the table you linked to the radius that a ball turner would need to swing would be 98mm and the tangent angle in the region of 4deg, quite different to the 1.5deg that looks right.

Edited By JasonB on 04/03/2021 13:38:02

Edited By JasonB on 04/03/2021 13:43:29

[JasonBModerator @jasonb]

Just to try it out with the formula that made sense to me for a stepover at 7mm from ctr line

[Howard LewisParticipant @howardlewis46836]

1.5 degrees looks to be not too far from correct

Kempes Engineers Year Book, in section E9/3 advises:

That pulleys should be cambered to keep the belt tracking properly, in spite of errors in alignment of shafts and lack of truth in the belt.

The profile of the pulley should be a smooth curve, or of two symmetrical two smooth curves with a flat central portion not exceeding half the width of the belt.

The advice is that where the pulleys differ markedly in size, it is good practice to leave the smaller pulley flat, and to apply camber to the larger.

Pulley width should be 15% greater than that of the belt

Maximum camber should be about 1% on diameter., or 0.2 in per foot of pulley width, whichever is the lesser.

By my calculations this suggests an angle of 1 Degree 8.7 Minutes, so I degree would probably suffice.

Flat tapers should not be used because they cause local strains in the belt, and impair contact between belt and pulley. .

For simple souls like me, the calculation shown can be made a little easier..

The square root of ( R^2 – d^2 ) involves the difference of two squares, so the calculation becomes the

Square Root of (R + d ) * (R – d )

HTH

Howard

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