Are Disk Grinders Really That Awesome?

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Nov 15, 2005
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110V 3 phase motors don't really exist (yes, there are a few out there, but the vast, vast majority of 3 phase motors are 230V/460V). I'd recommend getting a VFD that outputs 230V 3 phase power like the KBAC-24D. A TEFC (totally enclosed fan cooled) motor is what you really want for longevity. While it may not see as much dust as a belt grinder, it will still accumulate some over time and a properly sealed motor will survive in those conditions indefinitely.

Edit: You'll want a frame 56 or 56C motor; they are the only NEMA motor frame sizes that have 5/8" shafts.
Thanks for the info! Happy I asked… I was getting confused with the options out there.

I have a KBAC-27D on my NorthRidge 2x72 wired for 110. I’m guessing that motor is a single phase then.

So I guess if I want to run on 110, I’ll be looking for a single phase TEFC ~1800RPM motor and a VFD that outputs single phase like the KBAC-27D.
 

Hubert S.

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Thanks for the info! Happy I asked… I was getting confused with the options out there.

I have a KBAC-27D on my NorthRidge 2x72 wired for 110. I’m guessing that motor is a single phase then.

So I guess if I want to run on 110, I’ll be looking for a single phase TEFC ~1800RPM motor and a VFD that outputs single phase like the KBAC-27D.
That motor on the NorthRidge must be a 3-phase, the KBAC converts your 110V to a higher voltage. You want a 3-phase motor to connect to a VFD. Your motor should have a plate on it with all the specs.
 
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Just to clarify, the KBAC-24D and 27D are dual voltage VFDs, quite uncommon actually. They'll take either 115V (110V, 115V, 120V are all synonymous in this context) or 230V single phase input and output only 230V three phase power. VFDs can only power three phase motors and your single phase wall power can only power single phase motors.
 
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Thanks for the help guys. Someone needs to make an “electric motor cheat sheet”… For us clueless guys!

From what I gather:

1.) Get a hybrid KBAC VFD (24/27) (single phase 110 in and 3 phase 220 out)
2.) Find a totally enclosed, ~1800 RPM, 5/8’’ shaft, 220v 3 phase motor ~1.5HP so it can be downgraded to around 1HP
 
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Jun 14, 2013
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The 24D is for up to 1hp motors and the 27D is for up to 2hp. So, if you wanted a 1.5 motor you'd need the 27D.

For my 9" disc grinder, I used the KBAC 24D and a 1hp motor. I think that's enough for a disk that size. I use it with light pressure.

d3ZO4pO_d.webp
 

Hubert S.

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Thanks for the help guys. Someone needs to make an “electric motor cheat sheet”… For us clueless guys!

From what I gather:

1.) Get a hybrid KBAC VFD (24/27) (single phase 110 in and 3 phase 220 out)
2.) Find a totally enclosed, ~1800 RPM, 5/8’’ shaft, 220v 3 phase motor ~1.5HP so it can be downgraded to around 1HP
Not sure why you want to downgrade a 1.5 HP to 1 HP? With a KBAC-27D, you can run a 1.5 HP on 110 V, or downgrade a 2 HP to 1.5 HP.

If you are getting a new VFD for a disk grinder to run on a 110 V outlet, my choice would be the KBAC-24D and a <=1HP TEFC 3-phase motor. The IronHorse 3/4 HP 1800 rpm is probably one of the cheapest options at $175. As far as I know, there are no other VFDs that run on 110 V. If you have 220 V, there are more choices, but if you want a NEMA-4 (dust-proof) enclosure, there are no great cost savings compared to the KB drives.
 
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Not sure why you want to downgrade a 1.5 HP to 1 HP? With a KBAC-27D, you can run a 1.5 HP on 110 V, or downgrade a 2 HP to 1.5 HP.

If you are getting a new VFD for a disk grinder to run on a 110 V outlet, my choice would be the KBAC-24D and a <=1HP TEFC 3-phase motor. The IronHorse 3/4 HP 1800 rpm is probably one of the cheapest options at $175. As far as I know, there are no other VFDs that run on 110 V. If you have 220 V, there are more choices, but if you want a NEMA-4 (dust-proof) enclosure, there are no great cost savings compared to the KB drives.

I just mean that running a 220v motor on 110v input would likely provide less power than the spec plate says it will? So a 1.5 HP 220v motor would really provide around 1HP? Just guessing here.
 
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Nope, the VFD is up converting the 110v single phase to 220v three phase. Your motor will run at name plate specs. The 24D on 110v or 220v will power a 1 hp motor perfectly. The 27D on 110v will power a 1.5 hp motor perfectly and the 27D on 220v will power a 2 hp motor perfectly.
 

Stacy E. Apelt - Bladesmith

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For those who don't understand the setup, buying a combo is wise.

For a budget disc grinder, this 1/2HP motor/VFD combo will work fine:

For a more robust KBAC 24D unit, this supplier is great::
 
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I have the 27D and run a (I believe) 3/4HP motor off it for the disk and my 2HP for the belt grinder. Both are 220V. Do you not have 220 in your shop for your belt grinder now? I run an extension cord I wired up from the laundry room into the garage.
 
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I'm planning on putting a 1/2 hp motor on the same VFD as my belt grinder. Saves a good chunk of money. Then I just need a disc grinder plate to attach. The motor is less than $150 and the disc is like $90. I think all the wiring and switches would be about $40 total. It's the cheapest way I've figured so far, but I haven't gotten it all together yet. Good luck with yours
Yep. This is what I did. I made my own disc grinder plate as well. Really good for thinning kitchen knives.
 
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I want to button up this thread from 2021 for history's sake...

I did end up building a disc grinder this month (6-2022) and wow... It's a pretty amazing piece of kit. I can't wait to incorporate it into all my builds going forward.

I went with a cheap VFD and custom enclosure coupled with a 1.5 HP motor. Wired up for 110. I have a full set of links to the items used in the description of this build video for those looking to put one together. I also go though all the wiring in this video to demystify the process.


The chassis was sent to me for free from Beck's Armory. So far I like it. Seems pretty versatile.

Cheers,
RBO
 
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Thanks for the update on the project. You've added another source of a 120 vac input VFD at a decent price. The motor source has some good prices on the 3450 rpm motors also. The price structure on those motors sure is interesting.
 
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Thanks for the update on the project. You've added another source of a 120 vac input VFD at a decent price. The motor source has some good prices on the 3450 rpm motors also. The price structure on those motors sure is interesting.

Brian at House Works turned me on to that VFD. I was shocked at the price. DIY enclosing it is a little bit of a pain, but not too bad. The motor seems well made... my motor mount was bent due to shipping, but I wasn't using it anyway. Defiantly cheaper than I thought it would be as well. Cheers sir.
 
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Feb 4, 2013
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I run one KBAC to a 4 way rotary switch and then am able to control 3 disc grinders + a 2x48 off the same VFD. I use disc grinders constantly for various tasks. One other tip is to wire in a momentary on/off pedal in the normally clawed position to the stop / start switch area on the KBAC and then you can stomp on the pedal to stop the disc. It makes for easier placement and removal of handle material on the disc (so you do t round a corner during placement and removal).
 
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I run one KBAC to a 4 way rotary switch and then am able to control 3 disc grinders + a 2x48 off the same VFD. I use disc grinders constantly for various tasks. One other tip is to wire in a momentary on/off pedal in the normally clawed position to the stop / start switch area on the KBAC and then you can stomp on the pedal to stop the disc. It makes for easier placement and removal of handle material on the disc (so you do t round a corner during placement and removal).
I'd love a picture of that set up! Sounds awesome.
 
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I love and use my disc sander for lots of stuff. However I don't understand folks thinking they have to have a individual VSD for every device. I have my NR grinder mounted on a moveable roll able stand that also has my disc FLAT sander on it. With simple cord connects I use the same KBAC to power BOTH. Someone once mentioned having a KBAC feeding a 3 phase panel and it feeding multiple 3 phase motors. Of COURSE you can only use one motor at a time but seems useable to me other than having to got to VSD to adjust speeds. Keep in mind your only going to use a disc sander at incredible slow speeds. At least I do.
 
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