Need advice on a Grinder

[JeffL]

I am using an 8" grinder to do my buffing, but seems to take quite a while to build up heat cause I can't put much pressure on the wheel without it slowing down or almost stopping.It's 3/4 hp. spinning at 3450rpm.I figure if I go to a 10" 2hp, 1750rpm,& put an 8" wheel on it to give me 3500rpm(if the math is right)I put put some real pressure on the part to crate a lot of heat to cut.Is my thinking correct or should I stay with what I have?

[sswee]

Your thinking about it in reverse. The size of the wheel doesn't matter to the RPM only to the SFPM. The 2 hp motor will still only turn 1750 RPM's with a 8" wheel but you would slow your SFPM down and go the opposite way you are wanting.

A 8" wheel at 3450 RPM turns 5131 SFPM
A 10" wheel at 1750 RPM turns 4581 SFPM
A 12" wheel at 1750 RPM turns 5497 SFPM

If you go to the slower 2 hp motor with a 12" wheel, you would be getting more surface feet per minute and more the direction you want to go.

Hope this helps.
SS

[mikekozura]

Originally Posted by sswee

A 8" wheel at 3450 RPM turns 5131 SFPM
A 10" wheel at 1750 RPM turns 4581 SFPM
A 12" wheel at 1750 RPM turns 5497 SFPM
SS

I'm confused now I though it was wheel size times 3.14 times RPM divided by 12 = SFPM. And your looking for 6000 to 8000 ?

The 10" & 12" come out to yours but I'm getting 7222 SFPM on the 8" wheel @3450

[sswee]

Your right, I must have miss keyed because I get 7225 SFPM also. Thanks for catching it.
SS

[thesound]

Maybe you could talk Caswell into special ordering you one of the 2hp buffing machines they used to sell. I love mine. 3360rpms@8.90 amps. I had to buy a 3,000watt 110v/220v AC to AC converter to run it because it has a european style 3 prong plug and needs 220v to run, but it was worth it. The amount of torque this thing puts out makes it possible for me to lean on it with all of my weight and build up so much heat that a part gets too hot for me to hold even with insulated gloves on. (Not that this is necessary, just shows how powerful it is.) If the thing never craps out on me, it'll be the last buffing machine I'll ever buy.

[JeffL]

Where did you get that formula? The formula on the buffing & polishing booklet says....1/4xDia. of wheelxrpm.That would give me 6900 sfpm. on an 8" wheel. And 5250 on a 12" wheel.But it is certain that which ever formula is used, the 12" wheel is going to spin slower.Am I still going to benefit using the bigger grinder at slower speeds, but being able to put more pressure on the part, & making more heat?

[mpierich]

Originally Posted by JeffL

Where did you get that formula? The formula on the buffing & polishing booklet says....1/4xDia. of wheelxrpm.That would give me 6900 sfpm. on an 8" wheel. And 5250 on a 12" wheel.But it is certain that which ever formula is used, the 12" wheel is going to spin slower.Am I still going to benefit using the bigger grinder at slower speeds, but being able to put more pressure on the part, & making more heat?

Jeff,

There is no way that the larger wheel is moving slower (at the same rpm's) on the same machine. They are moving at the exact same rpm's - and since the larger wheel's surface has to travel farther in the same time, it's surface will be moving at a _faster_ fpm (feet per minute).

8": 1/4 x 8" = 2.....2 x 3450 rpm = 6,900 fpm.

12": 1/4 x 12" = 3....3 x 3450 rpm = 10,350 fpm.

Be careful...several of us feel that excessive wheels speeds makes it very dificult to achieve a good final color.

Unless you mean it'll move slower when you lean on it - that's very possible since the larger diameter gives you more leverage relative to the center of the wheel.

[JeffL]

Sorry for not clarifying my answer.The 12" wheel is spinning at 1750rpm on a 2hp grinder. The 8" wheel spinning at 3450 on a 3/4hp grinder.....thats why sfpm are slower. Was wondering if it was worth putting out the money for another grinder, or putting the money toward something else.

[mpierich]

Originally Posted by JeffL

Sorry for not clarifying my answer.The 12" wheel is spinning at 1750rpm on a 2hp grinder. The 8" wheel spinning at 3450 on a 3/4hp grinder.....thats why sfpm are slower. Was wondering if it was worth putting out the money for another grinder, or putting the money toward something else.

Whatever you get, the more HP the better, and the longer the shaft the better for clearance. 3/4 HP is a little weak. Also, since most of your work will be on the underside of the wheel, hanging the motor from an arm will give you the best clearance of all. And don't forget about the apparent problems of excessive surface speed for coloring. I'm heading toward a two-speed motor or a dual pulley system for that reason.

[JeffL]

thanks guys!!!!