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Quick queston about motors.........

Odie

Odie

Panning for Montana gold, with Betsy, the mule!
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My grinder is 1825rpm, and I'd like to experiment with slower speeds. About half that, or around 900rpm would be good to try. Is this possible? What speeds would be possible?

Thanks, ko
 
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odie said:
My grinder is 1825rpm, and I'd like to experiment with slower speeds. About half that, or around 900rpm would be good to try. Is this possible? What speeds would be possible?

Thanks, ko
Click to expand...

How about 1725 RPM?

There are special inverters that are designed for use with certain types of single phase motors that are used in HVAC applications (blower motors), but I don't think that they will work with the capacitor start type used on bench grinders. I haven't investigated that area because my experience is with industrial three phase motors and inverters.

Just as a WAG, I doubt that you would see any difference at half the speed.
 
Clifton C said:
odie, this contraption came to mind,
http://www.grainger.com/product/DAYTON-Mandrel-6L098
A bit pricy for experimenting, But sometimes I go that route. The right size pulleys or sheaves and you can get pretty close to the speed you're after. You might even have enough parts and pieces around the shop to cobble together a workable prototype.
Just a thought.
c
Click to expand...

Bob Howell said:
I have a mandrel that fits in my #2MT lathe drive end. I use it for a felt wheel but it will take a grinding wheel also.
Click to expand...

Thank you Bob and Clifton.....Either one of these suggestions will work for what I have in mind. I was hoping for an easy way to slow down my grinder, but I guess that isn't so easy. They have some Dayton motors with variable speeds where I work.....I guess that would work too.

Still thinking about this........

ko
 
Sounds like the Dayton motors at your work are 3-phase with variable frequency drives. You can replicate that too: find a 3-phase grinder and fit it with the VFD. You’re likely looking at about $500 to get there.
 
Owen Lowe said:
Sounds like the Dayton motors at your work are 3-phase with variable frequency drives. You can replicate that too: find a 3-phase grinder and fit it with the VFD. You’re likely looking at about $500 to get there.
Click to expand...

Ya, Owen......I think you're right, three phase. I forgot about that. I think there is also a three phase converter that allows 3-phase motors to run off of a regular circuit.....but, I guess that won't apply to my grinder either. $500 is a bit out of my budget for something experimental like this.....:(

I'm such a "know it not" with electrical things!

ko
 
Odie I've been playing with different sharpening methods and consequently different grinders and speeds. I don't think you will notice much difference at all on most normal size tools. I sharpen my really small tools, 1/4" and under by letting the grinder get up to speed and then turning it off. As the wheel slows down I sharpen the smaller tools. At 1725 on an 8" wheel it simply takes off too much steel and on those tools it's too easy to overgrind them. I've been sharpening bowl gouges on my tormek which is quite slow (don't remember what speed) and my 1725. For normal sharpening i don't notice much difference. Once or twice across the face and it's sharp. the 1725 might be removing more metal but i'm using such a light touch I'm not sure there's much difference.
No for reshaping the edge that's a whole different ball game. I often use an older 3450 grinder with a course gray wheel. That gets me close very quickly. Then I can go to the 1725 with a 180 grit CBN and fine tune the shape.
 
Well, the Tormek is too slow. I would guess another alternative would be a DC motor, or using a gear reduction type set up. I did find a place in the Seattle area that can custom make variable speed DC motors to just about any spec you want, but you have to order at least 10.

I did try out a new CBN wheel that I had around the shop, and boy, what a huge difference in how much metal it takes off. My most used set has a lot of sludge on it, but still cuts very well, but the new wheels, WOW. I haven't tried out one of the 400 grit ones from Optigrind though.

robo hippy
 
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odie said:
...I think there is also a three phase converter that allows 3-phase motors to run off of a regular circuit.....

ko
Click to expand...

That is also what a VFD (variable frequency drive) does. In tis case it not only converts the motor to allow it to run off of single phase but also allows variable speed and a host of other features like ramp up/down torque setting, etc. Same as most 220V lathes, 3 phase motor and a VFD
 
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