Pulleys and SFPM - can you check my numbers?

7

724wd

Joined
Dec 29, 2006
Messages
435
My Coote came on the 16 and I'm trying to work out the pulleys for effective SFPM.

I went with the 8" contact/drive wheel.

with my 1725rpm 1hp non-footed motor, i'm working on setting up the bracket. now, my dad still has the 4:1 reduction box that the motor ran when it powered his automotive paint mixer. I've been trying to work out the SFPM with and without the reduction box. Can someone check my math? (it was NOT my strong suit in school!)

1725 rpm
8" drive wheel
25.13 diameter
using 4/3/2 on the motor and 4/5/6 on the grinder

4:4 pulley
1725 rpm
43353.942 / 12 = 3613 sfpm at 1:1

3:5 .6
1035
27044.55 / 12 = 2253 sfpm at 3:5

2:6 .33
569.25
14305.2525 / 12 = 1192 sfpm at 2:6



using 4:1 reduction box and reversing the pulleys
4/5/6 on the motor, 4/3/2 on the grinder
1725 x .25 = 431.25 rpm

6:2 3
1293.75
32512 / 12 = 2709 SFPM

5:3 1.66
715.875
17990 / 12 = 1499 sfpm

4:4 1
431.25
10837 / 12 = 903 sfpm


If my numbers are right, using the 4:1 box and reversing the pulleys, my top speed would be 1000 sfpm slower than with no reduction box, while my slow speed would be 300 sfpm slower than no reduction box. would this be beneficial, or is the higher top/slow speed a bonus?
 
Why not get individual pullies so that if you guess wrong you can get the speed you want by buying just 1 new pulley? I'm not familiar with how the coote is setup, but I guess the motor powers the contact wheel?

I think you'll be guessing until you power it up and see how the speeds work for you. What you like today will likely change in the next year so be prepared to change things around. Good luck.
 
I had planned on getting step pulleys, hence the questions regarding speed, not individual pulleys.
 
I got a handheld laser tachometer to avoid the confusion.
Place a piece of reflective tape on anything that is going 'round and 'round. Shoot it - get the rpms.
I can place a piece of reflective tape on my belt and check the rpms and then multiply by 6 feet = SFPM.
13 bucks free shipping.

I use mine on all kinds of things just to satisfy my curiosity.

http://www.ebay.com/itm/Non-Contact...559?pt=LH_DefaultDomain_0&hash=item2ecd04e0af
 
724wd said:
I had planned on getting step pulleys, hence the questions regarding speed, not individual pulleys.
Click to expand...

Speed is derived from pulley diameter so you need to discuss both. What I was saying was maybe go with 3 separate pullies in the drive shaft so that you get the versatility of the step pulley but you can create the speed you want rather than trying to find something that works. TB woods pulleys are quite nice and quite affordable. I would recommend pricing out the step pulley and the same diameter individual pullies. This would allow for a more versatile setup. You could create exactly the sfpm that you want.

I would forego the reducer for now. Do you have to commit now? Seems like you are using the same step pullies in both scenarios, so why not try it out first, and if you find it's too fast for you, implement then reducer and see how that goes. Hope this helps.

It doesn't look like there is room for a step pulley on the shaft of the contact wheel. Will you replace the shaft for a longer one?
 
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People try to make a VS grinder with pulleys...that is a fools errand. Using step pulleys, you should get three (or four) speeds that can quickly and easily be changed. If you use three-step pulleys on both shafts, and want more than three speeds, it is going to be counter-productive loosening them and sliding them back and forth. The two sets should be aligned, and the belt moves on corresponding steps on both pulleys. If you set up the motor on a sliding shaft, you only need one step pulley.

One set of three-step pulleys should give you 2:1. 1:1, and 1: 2 speed. That will be sufficient for most work.

Gear box reducers , in my opinion, are not a good alternative to speed control on a grinder. Will they give a much lower speed, yes ....will they last or be worth the hook-up issues...probably not.

Figure what three speeds will do the most good for you and set up the pulleys for those speeds. If that won't work, go with a VS 3Ph system.
 
Thanks chaps.

Stacy, "The two sets should be aligned, and the belt moves on corresponding steps on both pulleys" is how I plan on setting up the grinder.

PT Doc, Mr. Coote recommends step pulleys, so i was thinking there was room. I will have to measure to make sure. thank you for pointing out the shaft length (never said THAT to a man before! :eek: )

My idea to use a 4/3/2 on the motor and a 4/5/6 on the grinder was to try and limit the high speed to something usable for blademaking. I am a stock removal guy doing blades for fun and gifts. Rarely on here did I see anyone advocating high grinder speeds. everyone seems to want to slow them down. using a 2/3/4 on both the motor and machine would produce the ratios Mr. Apelt noted: 2:1, 1:1, 1:2. It seemed through my research that overdriving the machine was not recommended. but as a complete amateur, perhaps I am wrong?

Heath
 
I think that many will grind with slower belt speeds but that doesn't mean that higher speeds are not used. With 2 and 3 hp motors and a vfd, it's easy to slow things down.

I believe kmg comes standard at about 3663 rpm, wilmont is about 5652+ rpm and the tw90 somewhere around 4400. It seems like you are trying to save money with this setup but a 3 phase motor and vfd can be used with any grinder. Get a c face and footed motor and your options will not be limited in the future.

What is the width of the 3 step pulley?
 
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