My homemade 2x72 Grinder

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Piper2328

Joined
Feb 26, 2020
Messages
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My new grinder seems awfully slow! I have a 1800 rpm dc motor and a 4” drive wheel. It’s gonna take forever to grind a blade! Is changing to a larger drive wheel the only option? What kind of spfm am I running?
 
Try posting this to maintenance, tinkering, and embellishment or the custom & handmade sub-forum
You'll get more/ better answers than in General Discussion
Very knowledgeable folks around here if you know where to look.
 
I’m running an 1800 rpm DC motor https://www.automationdirect.com/ad...ors_(up_to_2hp)/general_purpose/mtpm-1p5-1l18 with a super controller. https://www.ebay.com/itm/120-VAC-To...-130-VDC-PM-DC-Motor-Up-To-4-HP-/303159304376 Plugged into 110v AC power. Is there any way to get more voltage into this motor to double the rpms? Or is the only option to make a larger drive wheel. I’m currently running a 4” drive wheel. By my calculations that’s around 1884 sfpm. I’m gonna be taking quite a while to hog off unwanted steel. Any suggestions would be appreciated.
 
Piper2328 said:
I’m running an 1800 rpm DC motor https://www.automationdirect.com/ad...ors_(up_to_2hp)/general_purpose/mtpm-1p5-1l18 with a super controller. https://www.ebay.com/itm/120-VAC-To...-130-VDC-PM-DC-Motor-Up-To-4-HP-/303159304376 Plugged into 110v AC power. Is there any way to get more voltage into this motor to double the rpms? Or is the only option to make a larger drive wheel. I’m currently running a 4” drive wheel. By my calculations that’s around 1884 sfpm. I’m gonna be taking quite a while to hog off unwanted steel. Any suggestions would be appreciated.
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Buy a motor controller with a higher output voltage? Doubling the voltage will double the RPM. However you'd need to make sure your motor is rated for that doubled voltage or it wil probably have a pretty short life. Failing that the only option is to change the drive wheel size. That would be my suggested option.
 
A 4 inch diameter wheel is approximately 12 inches in circumference. 1 foot per rev times 1800 revs/minute is 1800 SFM. Very slow for grinding metal.

Discussion on belt grinder SFM here: https://www.practicalmachinist.com/vb/general/sfm-belt-disk-sander-metal-272217/

One guy's take: When I built my 2x72" belt grinder I shot for a range from 600-6000 sfm. Often I hog steel at around 4500 sfm but some belts like to run up to 6000 so it's nice to have it. However, when you put on the super-fine grit belts (2000 grit for example) you cannot run those belts at high speed because it will just peel the abrasive off the belt. For those kinds of grits you have to go down in the 600-800 range. That's why belt grinders are made to also be able to go slow.
 
Yeah being able to adjust the speed is crucial in my opinion. My controller will slow me way down and still have decent torque. I just bought a 8” dia drive wheel. To speed me up for now. Hindsight I should have found a 3600 rpm dc motor. But with the 8” wheel I should be able to take metal off at a decent rate for now. Thanks for the help!
 
I use a 7 inch drive wheel for 1800 rpm motor and it is pretty nice, I am new to grinders so hopefully someone with expert knowledge will chime in. My motor is 1 hp and direct drive, not variable. Getting a 5 inch to slow it down for detail, final sanding.
 
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