Converting a KMG to direct drive...?

Matthew Gregory

Matthew Gregory

Chief Executive in charge of Entertainment
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Jan 12, 2005
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There's a handful of nit-picks I've got with my KMG, but without question the one aspect of it I despise is the pulley system. Hate it. Noisy, vibrates like hell, inefficient and just plain sucks. I can stall the same 2hp motor I was using on my Wilton, and using no where near the same degree of force it took on that old machine. As far as I can see, there's no reason I can't snag a decent piece of 1/2" or thicker plate, perhaps 8"x8", square it up, cut a c-face mounting hole in it, and bolt it to the existing subframe and get back to work.

Has anyone else done this? If I don't have to reinvent the wheel or run into snags, I'd much prefer hearing about what I'm NOT thinking of, rather than diving in and shutting myself out of business until I return it back to pulleys...
 
I just emailed Rob about direct drive on mine because I had a belt slipping, but the motor still turned.
He mentioned a motor coupling or a shaft coupler.
He told me he didnt like direct drive, but didn't elaborate.
I assume so people can use single phase 3 speed motors.
 
Fred.Rowe said:
I can't picture what you are trying to accomplish. Is the motor VS?
Click to expand...

Sorry, Fred. Yes, it's direct drive. My thought is to eliminate the entire pulley assembly, mount a plate to the far right side of the grinder (about where the existing shaft bearing is, just before the drive wheel), and be done with it. Does that make more sense?

I'm not planning on relying on Rob for much of anything, with a project like this. For whatever reason, he seems entirely unwilling to revise or update his product line...


I should also add that I've used a number of other grinders, including other KMG setups in various configurations, and mine is no different. They're all noisy and fraught with vibration, especially when compared to other manufacturer's machines (Bader, Weurtz - heck, even my old Wilton!).
 
There have known of a few folks who converted to direct drive. I know of one who used a lovejoy type coupling to connect motor shaft to the drive shaft. NOT my favorite way of doing that - I'd prefer to remove all pulleys/shafts, mount motor direct to a base plate with drive wheel mounted to motor. Mount motor in such a way the drive wheel is in line with sanding belt. You could adjust the the motor so the wheels all line up making belt run true. This WOULD require a 3 ph motor with VFD so you could control speed - UNLESS you're wanting only a high speed grinder.
 
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I really am doing a horrible job of communicating lately. Wow.

Yes, I have a C-face motor, 2hp 3ph with a vfd. My thought is to eliminate the pulley and bearing kit entirely and put the motor right where that stuff is, with the drive wheel in the same vicinity of the original.
 
I just did that upgrade to my kmg, I unbolted the rear pulley set-up and got rid of the base plate and replaced with 1/2" aluminum plate and bolted the motor down to the plate where the pulley setup used to reside.
If I had to do it again I would go with thicker plate because when you tension the belt it flex's the plate like a bow.
I will post a video of the mod tomorrow.
I also have a c face motor but just bolted it down to get started, I'm waiting for a big chunk of angle to make a bracket to bolt on to the grinder body.
Use this opportunity to square up all the pulley's with a straight edge.
I also did a tilt mod so you can flip it on it's side.
 
what barrings are cheaper to replace the ones on the KMG or the ones in the motor ;)
i have a coupler (like a castle nut but 3 lug with a rubber saftey thing)
the funny thing is i have been thinking aobut going to a belt drive 2 speeds with the VFD tuning for a wider band of power and speeds depending on if i want to sharpen or if i want to act like i have a 6" drive wheel and still option even more speed using the VFD
 
Matthew have you tried those linked belts? Might be able to get more tension with one. I've used several direct drives and several KMGs and personally didn't notice a noise difference, though I've never owned a direct drive so maybe I wasn't paying enough attention.

I'll add two things: First, when I got my KMG the belt slipped and I thought it was my motor. After diagnosing the issue as too little tension, I remounted the motor and got the belt as tight as possible and now you can stall the motor before the belt will slip. Which isn't easy, its 3HP and 80lbs.

Second, I have an old delta 6x48 my pops loaned me. The belt has too much slack and that thing is noisy, moves around when in use and drives me insane to the point I barley use it, even when it would come in handy. So if that is what you are dealing with I feel your pain and hopefully you can find a reasonable solution.

-Clint
 
I've tried a variety of things, and can't get satisfaction. Standard v-belts, link belts, different pulleys and pulley sheaves. This machine is nowhere near as vibration free as my Wilton was. I can't rule out something being out of true, such as a bent shaft or something, but what areas I can measure don't display any runout worth mentioning.

Also, my experiences with all the rest of the KMG's I've encountered leads me to think it's just the result of belt drive. I can't say, however, that the KMG's were set up any better than mine, though.

Butchie, I don't think your bearing argument holds much weight. I don't think I've EVER heard of anyone roaching a set of bearings in a grinder. Not to say it hasn't happened, but I highly doubt applying tension with a grinding belt is really any more or less of a load than a v-belt on a pulley system. Also, my vfd allows the ability to double frequency, so if I want additional speed I change a jumper in it.

Meatrobot, I think I understand what you did, but I'm looking forward to your watching your video. I agree wholeheartedly about lining the wheels up - I spent WAY too much time doing that on this machine. Looks like I'll be doing it again.
 
Robot - you use 1/2" plate and it flexed with just belt tension? You must be putting heck of a LOTS of tension on the belt - but maybe there's more stress than I ever realized on the baseplate?

Matt - you got 3 ph and VFD? Go for it! Just like you said, use a baseplate to bolt motor to. The first 2X72 grinder I built used pulleys and worked good, but after I did a direct drive there was no comparison to smoothness and quieter running. Somewhere I have a video of it running at 4,000 SFPM with a quarter balanced on tool arm.

Ken H>
 
It seems to me that the big problem with going to direct drive is the size of the drive wheel. If you use a 1725 RPM motor with a KMG the pulleys double the RPM before the 4 Inch drive wheel . You could double the RPM by using a 8 inch drive wheel but the SFM would still be less than the standard KMG setup. OK, you can set the VFD to double your speed but that is not preferable because of the loss of torque at lower speeds OR you could use a 3450 RPM motor and still lose lower speed torque. I have a KMG and love it. I also built a direct drive Polar Bear Grinder with a 2 hp 3450 RPM motor and it works ok but I really prefer the KMG. I would suggest you check the tension on you belt and use cast iron pulleys like Beaumont Metal Works supply. If you have to go direct drive consider buying a second grinder or sell yours and get another. Good luck. Larry Lehman

zYmxqSG.jpg

gpQo5ll.jpg
 
Larry, I promise to once again do the diligence and examine everything before I proceed. I have a Hardcore 7" drive wheel, and was planning on using that. Guess we'll see where all of this leads, but it's difficult not to allow my experiences with other machines NOT reinforce my position against belt drive. We shall see!
 
Mines only 4 years old but it still balances a dime on the tooling arm wide open for a while, before it start spinning.It may be that the KMG needs a much more sturdy bench than some of the other grinders.
 
The bench I've got it mounted to is bomb-proof. This issue lies with THIS machine. As I mentioned, I'm going to run through it once again and make sure I didn't miss anything, then I'm starting on Plan A. :)
 
Larry,
Is it customary to store powders like that immediately behind your grinder? :D


Sorry, man, couldn't help it!




LARRYZ10 said:
It seems to me that the big problem with going to direct drive is the size of the drive wheel. If you use a 1725 RPM motor with a KMG the pulleys double the RPM before the 4 Inch drive wheel . You could double the RPM by using a 8 inch drive wheel but the SFM would still be less than the standard KMG setup. OK, you can set the VFD to double your speed but that is not preferable because of the loss of torque at lower speeds OR you could use a 3450 RPM motor and still lose lower speed torque. I have a KMG and love it. I also built a direct drive Polar Bear Grinder with a 2 hp 3450 RPM motor and it works ok but I really prefer the KMG. I would suggest you check the tension on you belt and use cast iron pulleys like Beaumont Metal Works supply. If you have to go direct drive consider buying a second grinder or sell yours and get another. Good luck. Larry Lehman

zYmxqSG.jpg

gpQo5ll.jpg
Click to expand...
 
I wish Rob would just make an adapter or something swappable (is that a word?). I still get vibration with a link belt. I'm more interested in tilting my grinder and direct drive would make that much easier to design something I think.
 
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