KMG 3 speed or variable

Pepper55

Member
The grinder I picked up wasn't quite as good of a deal as I thought. Turns out the motor is not tefc and its starting to make noise. Its also 3600 rpm, I believe this grinder was designed for a 1740 rpm motor. I’m shopping for a new motor and trying to decide if its worth the $ to upgrade to variable speed motor. I think I can get a 3 phase motor for about the same price so the extra cost would be the speed control and pulleys. I’m thinking the 3 speed is all I need, but I would appreciate your opinions.

Thanks
 

EdCaffreyMS

"The Montana Bladesmith"
Whew..... It's tough to give any absolutes..... but IMO if you do go with variable speed (3ph motor & VFD) you'll never be sorry you did. When you can infinitely change speed with the turn of a dial...... life is just better. :)

That being said, I don't know your situation or how much $$$ your willing to spend. I can tell you that over the years I have seen folks spend money time and time again to "upgrade" a grinder..... and by the time they get to a "top end"/variable speed machine, they've spent enough to buy 2-3 top end grinders. Just food for thought.
 

Randy Lucius

KNIFE MAKER
Everyone always recommends a variable speed. Mine is a no-weld-grinder with step pulleys. I have a variable speed on my 9 inch disc sander and it’s awesome. When i replace my 2X72, hopefully soon, it will have variable speed.
 

Chris Railey

KNIFE MAKER
In my journey I went from a HF 1x30 to a WAO O grizzly 2x72 then to a Pheer 454 with variable speed and let me tell you it was a huge game changer. If you can do it, get the variable speed or use what you have until you can.
 

Sean Jones

Well-Known Member
If you can afford it definitely get the VFD and a 3 phase motor. I was very reluctant to spend the money on a VFD (I'm retired so money is always a concern), but after doing so, I don't regret it one bit. It is a serious game changer.
 

Austin Thrasher

Well-Known Member
Without a doubt the variable speed is worth any extra money you’ll spend on it. Buy once, cry once certainly applies here.
 

KenH

Well-Known Member
I built a KMG 3 speed clone for my first grinder and didn't understand why folks were spending all that money on variable speed grinders, 3 speeds was all I needed! I had the motor on hand, had the shaft so the pulley was all I had to buy to make the 3 speed. After a couple of year I decided to build another grinder, sold the first for enough to build the next one. Since I was buying a new motor, 3ph was same price so that was a wash. I purchased a Chinese VFD that is NEMA 1, but filters over air inlets. It ran for over 5 yr before going bad so I replaced it with another cheap $60 Chinese VFD. "IF" money is no object, then I'd go with the 27D NEMA 4X VFD.

The extra cost for changing to variable speed in your case would be the VFD only. Just use the existing pulleys - best would be to remove the pulleys 'n shaft and mount the motor as direct drive but that takes a bit of work on the KMG. That is best, but does take some work.

After using the variable speed grinder for a while, I was sold! Wouldn't even consider anything else.
 

EdCaffreyMS

"The Montana Bladesmith"
It just occurred to me.... you might not be aware of the very practical reason(s) for variable speed..... because different grits of belts cut more efficiently, and last longer at different speeds, a variable speed grinder can save you money on belts.

Heavy grits, 34-60 grits, work best a top speeds, as grits become finer, speed should be reduced for efficiency, longevity, and heat reduction. Exact settings depend on drive wheels on the grinder, but roughly.....
24-60 grits FULL SPEED, whatever the drive wheel size.
80-120 grits 50-60% on the speed control dial for a 4" drive wheel (KBAC 2X series VFDs)/30-40% for 6" drive wheel
220-400 grits 40-50% on the speed control dial for a 4" drive wheel (KBAC 2X series VFDs)/ 20-40% for 6" drive wheel
600 and finer grits..... varies based on material being ground and belt type, but I rarely run these grits higher then 25% for either drive wheel size.

Of course, those are the speeds that work best FOR ME. I'd consider them as BEGINNING points for you, with the exception of what you use for heavy grit belts (24-60 grits) which are almost always best used at highest speed, then adjust to your liking. ;)
 

John Wilson

Well-Known Member
It just occurred to me.... you might not be aware of the very practical reason(s) for variable speed..... because different grits of belts cut more efficiently, and last longer at different speeds, a variable speed grinder can save you money on belts.

Heavy grits, 34-60 grits, work best a top speeds, as grits become finer, speed should be reduced for efficiency, longevity, and heat reduction. Exact settings depend on drive wheels on the grinder, but roughly.....
24-60 grits FULL SPEED, whatever the drive wheel size.
80-120 grits 50-60% on the speed control dial for a 4" drive wheel (KBAC 2X series VFDs)/30-40% for 6" drive wheel
220-400 grits 40-50% on the speed control dial for a 4" drive wheel (KBAC 2X series VFDs)/ 20-40% for 6" drive wheel
600 and finer grits..... varies based on material being ground and belt type, but I rarely run these grits higher then 25% for either drive wheel size.

Of course, those are the speeds that work best FOR ME. I'd consider them as BEGINNING points for you, with the exception of what you use for heavy grit belts (24-60 grits) which are almost always best used at highest speed, then adjust to your liking. ;)

THIS IS GOLD.

These are just about exactly the speeds I have found to be just right for me, too... after several years of trial and error! I have wrecked more blades running fine grit belts at too high a speed to count. It took me about five years to be able to use j-weight belt on bevels without getting the dreaded splice bump buggering up my finish. Turns out it was all a matter of speed.

A VFD is worth its weight in gold for saving money on belts. Any belt above 120 lasts about ten seconds if you run it too fast, but will cut for a very long time at low speed with light pressure.
 

Daniel Macina

Well-Known Member
THIS IS GOLD.

These are just about exactly the speeds I have found to be just right for me, too... after several years of trial and error! I have wrecked more blades running fine grit belts at too high a speed to count. It took me about five years to be able to use j-weight belt on bevels without getting the dreaded splice bump buggering up my finish. Turns out it was all a matter of speed.

A VFD is worth its weight in gold for saving money on belts. Any belt above 120 lasts about ten seconds if you run it too fast, but will cut for a very long time at low speed with light pressure.
I did not know that speed could be a factor with that I’m definitely going to half to play around with that because I have buggered up a ton of blades like that.
 

Drew Riley

Well-Known Member
Go variable speed. If you can't afford a KBAC 27d (or similar), then start out with one of the Chinese VFD's. You can get a 2hp VFD for well under 100 bucks now days, and as long as you keep the dust out of it, they'll do the job until you can upgrade. You will need 220VAC to power it though.

I went the step pulley route for years, and when I did finally upgrade to a VFD, I immediately kicked myself for not doing it sooner. It's worth every penny.
 

MTBob

Member
For years I held off getting VFDs for my equipment. Finally I tried a KBAC drive on my lathe and within a year I added 2 more, 1 ea to my mill and drill press. And I now have my 4th KBAC unit on my 2x72 grinder.
I say all that to reinforce how much value i get using (high quality) variable speed drives in machining operations. BTW, the reason I chose KB drives: they are dust proof (critical with a grinder), easily programmable, and tough... and made in the US. The VFDs are some of the best purchases I've made for my shop.
 
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timgunn

Well-Known Member
Try looking at it differently. See if you can find anyone who has posted an “I regret going for a VFD” anywhere without a specific reason (30+ year old motor, poor choice of VFD: cheap unsealed VFD with no manual or sealing, running off a generator, etc). It may help with your decision. I don’t think I’ve ever seen one.
 

Pepper55

Member
All good points, its obviously beneficial to go variable speed. Unless my brother in law gives me a single phase motor (it could happen), I’m in the market for a 3ph 2hp motor. As mine isn’t completely dead yet I’m hoping to find a good used one. My odds of finding the used motor I need locally are probably similar to playing the lottery but its worth checking. When mine gives up the ghost I’ll bite the bullet and get a new one. I’m Thinking a kbac-24 or 27 would be the best vfd, nice that its in a nema enclosure to boot.
 

EdCaffreyMS

"The Montana Bladesmith"
For the past decade+ I've purchased all my 3ph motors and KBAC controllers from: http://www.electricmotorwholesale.com/
My personal choice for motors was Baldor, until the got so expensive I couldn't justify them, then I went to Leeson motors....and to date have had no issues with them. The only motors brand that I can personally warn you off of are Marathon..... I've purchase 3, and all three have lasted less then 6 months! I took one into my local motor shop, and the folks there told me that in their experience, Marathon motors cost more to repair then it would be to buy a new one.....and recommended I steer clear of them. As for VFDs, you simply cannot beat KBAC for simplicity, durability, ease of use, and longevity. For a 2HP motor you'd need the model 24D. I know some folks advocate the much cheaper import versions, but I've had so many bad experiences trying to help others fix those things...... GRRRRR!!

Lately I've noticed that the motors I purchased have/are being phased out, and replaced with (of course) a "new and improved" version, that costs a couple hundred dollars more for the same HP/RPM, etc. :rolleyes: "New and Improved".... just means they changed the label, and it costs more.
 

Self Made Knives

Well-Known Member
I don't know if I can describe it or not, but I have noticed that there are times when I'm grinding that the combination of belt speed, grit, angle, etc. will almost start an oscillation. The blade seems unstable and I feel like it's moving all over the place. Like I can't hold it still. I can reach over to the VFD and bump the speed up or down just a few rpm and it goes away. Smooth sailing then. Ya'll ever notice that? That's a life saver on the VFD for me.
 

Drew Riley

Well-Known Member
FWIW, you can get a brand new 3 phase "IronHorse" motor from AutomationDirect for less than $200 shipped (Or at least that used to be the price, I haven't looked recently.)

I used to shy away from import motors, but I've had zero issues with mine in the years that I've had it. I also used to work in an industrial laundry, and the local motor shop started sourcing an import brand very similar to IronHorse (made in china, same style of label, etc....). Most of those motors were rode hard and put away wet about 10 to 18 hours per day (minimum) and lasted for years without issue.

I believe IronHorse motors also have a 2 year warranty through AutomationDirect.

The only bad thing I will say (or at least caution) about the IronHorse motor I received. Even though it's supposed to be a TEFC, there was one or two openings in my rolled housing that could potentially have allowed dust and debris into the motor. The were small, so I simply put a piece of duct tape over them and called it good.
 

Sean Jones

Well-Known Member
FWIW, you can get a brand new 3 phase "IronHorse" motor from AutomationDirect for less than $200 shipped (Or at least that used to be the price, I haven't looked recently.)

I used to shy away from import motors, but I've had zero issues with mine in the years that I've had it. I also used to work in an industrial laundry, and the local motor shop started sourcing an import brand very similar to IronHorse (made in china, same style of label, etc....). Most of those motors were rode hard and put away wet about 10 to 18 hours per day (minimum) and lasted for years without issue.

I believe IronHorse motors also have a 2 year warranty through AutomationDirect.

The only bad thing I will say (or at least caution) about the IronHorse motor I received. Even though it's supposed to be a TEFC, there was one or two openings in my rolled housing that could potentially have allowed dust and debris into the motor. The were small, so I simply put a piece of duct tape over them and called it good.
I've had no problems with the Iron Horse motor I have. I think it's an excellent choice.
 
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