Re: How to measure pulley diameter

Bob Engelhardt wrote:

To measure the blade's pulley "pitch diameter": make a chalk mark on the pulley and belt just where the belt "exits" the pulley, rotate the pulley one revolution so the belt's chalk mark moves away from the pulley, and measure the distance on the belt from its chalk mark to the pulley's chalk mark. This is the pitch circumference, divide by pi for the pitch diameter.

Buy a new pulley whose pitch diameter is twice this. Pulleys *are* sold by pitch diameter. Maybe not the ones on the rack at Ace Hardware, but the ones at MSC, McM-C, etc.

Bob, that is a very clever trick, and one I never thought of when I had
this problem!

I actually disagree with you about pulleys being sold by PD, though. If I
go into my local Ace and measure the OD of what they sell as a 5" pulley,
it will read 5" and it will be made by Chicago Die Casting. If I order a
3/4" bore 5" pulley from MSC it will also be made by Chicago Die Casting
and it will also measure 5" across the OD. And it may well have 1/32" of
runout both radially and axially. I've bought and returned pulleys from
MSC.

Maybe if you step up to Browning, Morse, don't know.

It is possible to take such a pulley and mount it by its bore in a lathe
and true it up. I did this when I replaced a Shopsmith drive pulley awhile
ago and the trued up el cheapo zinc pulley runs dead true.

Grant
.

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