grinder motor question

jspake

jspake

Well-Known Member
hi guys, its been quite a week.

i've been running a KMG grinder for the past 3 years or so and liking it very much. for a few different reasons, bench space being a big one, i've decided to convert it into a direct drive machine. conceptually its not that complicated, but i have fit a few bumps. one i need some help with. the first thing i noticed was that my drive wheel had a 3/4 ID for the shaft, and my motor has a 5/8 shaft. obviously the pulley system made that fine. so i bought a drive wheel with a 5/8 ID only to find that the shaft for the motor isn't quite long enough to get the drive wheel far enough away (to the right of the motor) to align properly with the idler wheel and tool arms... frustrating. i really only need it to be about an inch longer.
my question... is there a way that i can extend the motor shaft about an inch or so? i've thought of making some sort of dummy plug with a keyway slot milled that can just fill in the space inside the drive wheel so that the key can be tightened down and secure to the motor shaft and the plug equally... would that be safe? the other thought i had would be to make some soft of a bushing or collar to go around the 5/8 shaft and fit into the original 3/4 ID drive wheel. this seems like probably a worse idea. what do you think?
 
a Lovejoy coupling with the appropriate shaft size on each side might work. I don't think it would work any better than what you have now. I did see a YouTube vid where someone mounted the motor on a home made bracket directly above the pillow block bearings and that way the pulleys were vertical, drive over driven, and used the same v-belt. That's probably the most elegant solution and doesn't require any re-engineering, only a bracket/motor mount.
 
thanks john. i've already got a plate mounted to the "right" spot at the back of the grinder. there's pics somewhere of KMG that david sharp of sharpwerks modified, and i made a similar mod. removed a piece from the back support and welded on a plate behind it. so THAT part i think is okay. its just the motor shaft length (or lack thereof) situation that i need to solve. hopefully after that is settled i hope it will be smooth sailing.
 
a shaft extension with a broached keyway wouldn't be hard to make, but getting it aligned perfectly so that this doesn't become a big, shaking mess might be a challenge.
 
The shafts on 56C motors is a standard (they are all the same diameter and length. If you got your replacement wheel from www.USAKnifemaker.com I think that you may have mounted it to the motor with the milled indention mounted toward the motor. If you turn it around it should work fine. If you roll a bushing from sheet metal 1/16" thick, leaving space for the keyway that should be fine. Be sure and square the motor to the grinder frame. I use a carpenter's square and lay the long leg along the grinder frame and the short leg along the feet of the motor. If it doesn't track well you may have to loosen the mount bolts and wiggle the motor back and forth.

Let me know if I can help you.
 
The cheapest and simpliest solution would be to just purchase and install it with a Lovejoy coupler. One side of the lovejoy with a 3/4" ID, and the other side with a 5/8" ID. If its bench space your lookng to save, why not place the motor on a "cradle" under the bench, cut a slot in the bench for the belt to pass through?....... setting the motor/drive up such as the way most table saws are setup. My KMG has been set up like that ever since it arrived in the shop.

I've setup a few grinders like your trying to (direct drive), and its very often creates more problem then it solves. The most troublesome area being that of vibration and noise. Even if using a lovejoy coupler, you have to be pretty much "dead on", otherwise you get excessive vibration and noise.
 
If wanted to go cheaper than the lovejoy there are many of 5/8" ID x 3/4" OD shaft adaptor sleeves available from mechanical supply houses and ebay for around $25. I did bigger version of this on my big grinder with a 7/8" ID x 1 5/8" OD adaptor so could run a sleeved 8" x 3" steel drive wheel on a 2hp DC motor and it runs very true. If a sleeve adapter does not give the length and can't lock it on the motor shaft, you will have to do the lovejoy or other similar shaft adaptor route.
 
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thanks a lot for all of the tips. i did not realize that all 56C motor shafts were the same size. this makes it even weirder that i'm having the trouble that i am.

i'm not sure what a lovejoy coupling is. i've looked it up online, and i'm not really clear how this would help me.

the 3/4 ID drive wheel that i have is offset in the way that you describe, wayne. unfortunately, the screw is impossible to adjust (at an angle) because the motor is in the way when the wheel is facing the correct direction for what i want to do. this pretty much makes that wheel unusable for my purposes on this build.

i think the 5/8 ID drive wheel that i just picked up is going to work out in the long run. i think it just boils down to the wheel not being as tight to the motor as i was expecting. i did a rough assembly tonight and things are more or less going to work out as-is. if i make a couple of adjustments i think i will be in a better spot than i was when it was belt driven. its already quite a bit quieter. also i think i need to take the idler/tracking wheel off and face the spacer nut. it seems like that wheel is just completely not lining up with either the drive wheel OR the tooling arm wheels because it "sticks too far out", if you know what i mean.

this is the first time i have really taken a hard look at how all of the little components of this grinder work together. its been a pain in the butt, but i feel like i'm learning a lot. thanks to all of you for the input and ideas!

-jeremy
 
If your looking for the cheapest route, and saving bench space, here's what I was talking about mounting the motor like a table saw motor is usually mounted. All it will cost you is likely a new, longer belt:





The toughest part for me was horsing that big 3hp motor down there and mounting it to the swing plate.
 
Yes, the weight of the motor works as the belt tensioner..... in fact that particular motor is actually too much weight...notice the chain with the spring? That attches to a turnbuckle to take some of the motor weight off the drive belt.

I keep waiting for that motor to burn out (its an old 3hp/180Volt DC motor.... thats what we had to use for variable speed before VFDs came out) but it just keeps going.) :)
 
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