Buying a Coote - 6 or 8 inch?

7

724wd

Joined
Dec 29, 2006
Messages
435
got approved to buy a new grinder! YAY! my little 1 incher has served me pretty well, but I can't wait to work on a 2x72! I have a 110 1hp 1725rpm explosion proof motor from my dads old paint mixing system, and might be able to get my hands on the gear reduction unit if need be. The wiring in my garage is junk, so i'll probably be running it off my generator like I do my welder.

My knives are flat ground, so the 10" contact wheel doesn't interest me much. Does anyone have any opinions on which would be better, 6 or 8 inch, for handle shaping and whatnot?
 
Your knives are flat ground because, until now, you had no way to hollow grind them. Try it, you might like it.
The 8" wheel is probably the best for general use.
 
I have a Coote with a 10 inch wheel. I have never hollow ground a blade, but I went ahead and got the 10 inch wheel because I thought I may try it later on. A 10 inch wheel makes a high hollow grind, which I'm quite fond of on other peoples knives. That option isn't much more expensive either.

Go ahead and get Norm to get you set up with a glass platen. That thing is a must.
 
Agree with the 10" Coote. I had one for about 5 years, and liked the 10" hollow grind ability. 6", IMHO,is way too small for a hollow grind, and 8" is pushing it unless for folder size blades. Again, just my opinion.
 
Btw, I forgot to say this, but I recognize that you don't hollow grind... But if you did want too in the future, you have the ability to with the 10". If you truly don't wish to EVER hollow grind a blade, then you question on what wheel to choose becomes only focused on how fast you want the belt to run (at a fixed motor speed). Bigger the wheel, the faster the belt moves. Faster = more metal/ wood/ material removed sooner= Higher temps.
 
I prefer the 10. I agree that I wouldn't step down unless on folder blades. Even the 10 seems small sometimes.
 
thanks guys. i've ordered a grinder! :) I asked Mr. Coote about pulley sizes, as i'm a little unsure regarding the setup. he said he usually recommends a 2-3-4 on both the motor and the grinder. using those pulleys, i'd really only have direct drive and underdrive, as overdriving seems to be frowned upon based on my research. therefore, i wonder if it would be worthwhile to try a 2-3-4 on the motor and a 4-5-6 on the grinder, making direct drive, underdrive, and SUPER underdrive?

then there is the issue of my motor. as stated, it's a 110 1hp 1725 explosion-proof. it's not footed, so i'll be fabricating a mount, but my new concern is it is not fan cooled. it came from an autobody paint mixing fixture, mixing MANY gallons of auto paint, using a gear reduction unit. it ran fine in that application, and auto paint is pretty thick stuff! the non-cooled aspect has me questioning whether or not to search for perhaps a footed TEFC motor instead. the attractive part of the one i have now is it runs good and was a freebie! what do you guys think?
 
Those paint mixing machines only run 15min and shut down.Not much chance of overheating a motor with that kind of cycle.You would be better off with the fan cooled motor.
Eddie
 
I would just run it till it goes out, unless you put a lot of pressure you may not over heat. It is designed to do 1hp of work. I run the 4-3-2 on the motor and 4-5-6 on the grinder and like the setup. This sets the high speed at 4579 fpm, and low at 1526, I would rather have a lower speed rather than a higher speed, the 2-3-4 to the 4-3-2 give you a low of 2289 and a high of 9198, this seems fast for me.
 
My grinder should be here on the 16th! YA! went 8" contact/drive.

now, my dad still has the 4:1 reduction box that it ran on the 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?
 
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