lulu
off to a rocking start
Member since January 2017
Posts: 9
|
Post by lulu on Dec 29, 2021 18:50:26 GMT -5
is a V belt pulley size determined by the outside diameter of the pulley or the diameter of where the belt rests?
|
|
|
Post by Son Of Beach on Dec 29, 2021 19:15:10 GMT -5
Typically, the belt length is determined based on the diameters of each individual pulley and the the distance between shaft centers. Luckily, there are a lot of resources to help you figure out what setup you need with different measurements. Something like this durabelt.com/beltlengthcalculator.php will help answer your question.
|
|
lulu
off to a rocking start
Member since January 2017
Posts: 9
|
Post by lulu on Dec 29, 2021 20:48:51 GMT -5
I have all kinds of different size belts so thats not the issue, what I was wanting to know was if pulleys were measured by outside diameter or where the belt rests
|
|
|
Post by Son Of Beach on Dec 29, 2021 20:53:51 GMT -5
I have all kinds of different size belts so thats not the issue, what I was wanting to know was if pulleys were measured by outside diameter or where the belt rests In the field it supposed to be where the belt rides/rests, but in general most of the time people talk about the outside diameter. 99% of the discussions I had with customers was about the outside diameter. Belt width matters as well...I would assume you are running a 3/8" or 1/2" belt?
|
|
lulu
off to a rocking start
Member since January 2017
Posts: 9
|
Post by lulu on Dec 29, 2021 20:57:51 GMT -5
3/8th. Do you think the charts telling you what size pulleys to use to get the correct speed for the size blade your using goes by outside diameter for the pulley size?
|
|
|
Post by hummingbirdstones2 on Dec 29, 2021 21:50:29 GMT -5
Technically, it's where the belt shoulders ride in the pulley.
Try an online calculator (I cheat and use them) to compare the results using the OD against the results using the actual contact point diameter.
The difference in the blade rpm will be small relative to the recommended rpm ranges given for your blades.
|
|
|
Post by Rockoonz on Dec 30, 2021 1:42:20 GMT -5
lulu pulleys are sold based on OD and the most accurate speed calculations are made using the OD's as long as the widths are relatively equal.
|
|
jamesp
Cave Dweller
Member since October 2012
Posts: 36,607
|
Post by jamesp on Dec 30, 2021 7:54:19 GMT -5
Exact speed may not be an issue with most lapidary equipment. It's not going to make much difference if a tumbler is turning at say 35 rpm +/- 5 rpm. Or a rock saw blade is running at 800 rpm +/- 50 rpm. Lapper at 900 +/- 50 rpm. etc
If there is a large reduction it may be more important, in that case focus more on measuring the small reducing pulley on the motor most accurately. Being off by a 1/4 inch on a 1 1/2 inch reducing pulley has big percentage influence on the ratio and therefore the output speed. It is less critical to get dead accurate measurements on the larger pulleys.
A good example is using a 1/2 inch shafts verses 1 inch shafts on a rock tumbler. The one inch shafts will rotate the barrel twice as fast as 1/2 inch shafts for a given shaft speed. Doubling the speed of a tumbler can be a detrimentally large increase in barrel rotation.
|
|
|
Post by hummingbirdstones2 on Dec 30, 2021 9:05:44 GMT -5
Yep, Rockoonz , once again engineers and "real" people differ.
Pulleys/sheaves are sold by OD, but the engineers want to use a point that can't be easily measured by the rest of the world for their calcs.
And, as jamesp said, it usually doesn't matter much for most lapidary applications - unless you're an engineer. Engineers would lose sleep... .
|
|
jamesp
Cave Dweller
Member since October 2012
Posts: 36,607
|
Post by jamesp on Dec 30, 2021 9:42:29 GMT -5
Yep, Rockoonz , once again engineers and "real" people differ. Pulleys/sheaves are sold by OD, but the engineers want to use a point that can't be easily measured by the rest of the world for their calcs.
And, as jamesp said, it usually doesn't matter much for most lapidary applications - unless you're an engineer. Engineers would lose sleep... . Lol. I would like to think of myself as an unengineer @2, an engineer with at least 2 ounces of very valuable common sense.
|
|
|
Post by Rockoonz on Dec 30, 2021 12:38:37 GMT -5
Yep, Rockoonz , once again engineers and "real" people differ. Pulleys/sheaves are sold by OD, but the engineers want to use a point that can't be easily measured by the rest of the world for their calcs.
And, as jamesp said, it usually doesn't matter much for most lapidary applications - unless you're an engineer. Engineers would lose sleep... . The possible variation in the drive motor RPM is probably more than the calculation error using the pulley OD. A member from the club in Oregon who is a Millwright and math geek gave me a spreadsheet called mathmagics that is fantastic for calculating speeds, pulleys, belt lengths and everything. That's just one of several pages, lots of other fun geometry there.
|
|
|
Post by Peruano on Dec 30, 2021 13:29:25 GMT -5
I have a friend whose son encountered a play friend who boasted that his dad was a doctor. My friends son replied, my Dad's a thinking doctor. Whether that makes him a real people is debatable. RPMs are like grenades. Close is good enough. Me I'm playing with mixing 6" and 8" wheels on the same arbor. Ideally the 6" will be contacting the stone at a slower speed, a desired situation for polishing some stones.
|
|
lulu
off to a rocking start
Member since January 2017
Posts: 9
|
Post by lulu on Dec 30, 2021 14:40:08 GMT -5
Thank you all for all the input!
|
|