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Thread: RPM calculation
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14th July 2014, 09:41 AM #1human termite
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RPM calculation
is there someone out there who can help me ? i am wanting to know how slow my lathe will turn on its lowest speed,hope this drawing is ok..........bob
thankyou in advance
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14th July 2014 09:41 AM # ADSGoogle Adsense Advertisement
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14th July 2014, 10:44 AM #2GOLD MEMBER
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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.
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14th July 2014, 11:37 AM #3
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.
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14th July 2014, 12:16 PM #4Senior Member
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rpm
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 | eBayLast edited by tore; 14th July 2014 at 12:19 PM. Reason: adding info
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14th July 2014, 12:50 PM #5Member
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Re Tacho
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
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14th July 2014, 01:12 PM #6
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.... Steve
-- Monkey see, monkey do --
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14th July 2014, 05:51 PM #7
The best calculator I have seen is this one by forum member Blocklayer - Pulley Calculator. RPM, Belt Length, Belt-Surface Speed, Animated Diagrams Metric
Brad.
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14th July 2014, 06:48 PM #8
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-8Inspiration exists, but it has to find you working. — Pablo Picasso
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14th July 2014, 07:12 PM #9GOLD MEMBER
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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.
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15th July 2014, 08:34 AM #10human termite
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thankyou all for your help.at least i know the pulleys i have will do the job for me............bob
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15th July 2014, 11:08 AM #11SENIOR MEMBER
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Simple method
Motor speed
Divided by driven pulley dia
Multiplied by motor pulley dia
Cheers
TimSome days I turns thisaway, somedays I turns thataway and other days I don't give a stuff so I don't turn at all.
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