Thread: RPM calculation

Hi Bob,
A search on the forum should yield result's there was a similar thread a while ago and a few gave the formula to working it out and there was a web page also that you could use to do it also. ( will have a look as well see what I can find)
Regards Rod.

Not sure if this will help, but speeds on pulleys (or anything circular) are directly proportional to the diameters. That is if you have one pulley driving another one that is half the diameter, then the second one will be doing double the rpm(because the circumference of the second one is half the first).

Same for grinding wheels: a 6" inch wheel has 3/4 of the circumferential speed of an 8" wheel - when both are at the same rpm. Obviously the same for drill bits and so on.

small pulley/big pulley*rpm=570rpm
110/270*1400=570
or bay this on ebay
LCD Digital Laser Photo Tachometer RPM NON Contact Tach Motor Speed Meter NEW | eBay

Hi team, for what it is worth, I have one of those tachometers, It works OK. I compare it to my mini-lathe with digital read out. Jay

tore has it - 110/270 x 1400 = 570rpm
The same applies with diameter as well as circumference, since only the ratio is important.

I have an optical tacho too, but it's not necessary in this case.

The best calculator I have seen is this one by forum member Blocklayer - Pulley Calculator. RPM, Belt Length, Belt-Surface Speed, Animated Diagrams Metric

Robyn go online there a number of websites that a built rpm calculator, easy peasy.

/www.google.com.au/search?q=rpm+pulley+calculator+download&oq=RPM+&aqs=chrome.2.69i57j69i65j69i59l3j69i60.5059j0j8&sourceid=chrome&es_sm=122&ie=UTF-8

Originally Posted by Ironwood

The best calculator I have seen is this one by forum member Blocklayer - Pulley Calculator. RPM, Belt Length, Belt-Surface Speed, Animated Diagrams Metric

That's the one that I was thinking of Bob,it also has a very wide range of other very useful calculators. I also purchased one of those digital meters and it work's very but it won't tell what size pulley's you need to get a range of RPMs you want to build.
Regards Rod.

thankyou all for your help.at least i know the pulleys i have will do the job for me............bob

Simple method

Motor speed
Divided by driven pulley dia
Multiplied by motor pulley dia

Cheers
Tim