Variable Speed KMG on a "shoestring" budget

Very nice set up, Dan! Your making me very jelous! Do you ever sleep, with everything you've got your fingers in, I'm guessing about 2 hours a night is all you could manage! I'm going to have to upgrade now, for sure.

Clint

www.chisanknives.com
 
RE Reversing motors and breaks.

I'm no expert, but do know what's in the manual for my controller board.

Breaking is done by disconnecting the motor from the controller and connecting it to a resistor. The resistor size (ohms and watts) is based on a number of factors: HP and the momentum of the machine it is running. I checked into it for mine, but I can't remember. Something in the range of 50 ohm and 100 watts. Or what is 1000 ohms and 10 watts - told you I can't remember. Since grinders don't have alot of momentum (like a 100lb fly wheel!) and you are not stopping constantly it doesn't take a lot of watts.

Reversing (on my board) requires a reset of the controller. Not that it cares what direction the motor is running, but it does keep track of the speed, load, volts, .... stuff. There are two ways (on my board) to reset. One is to turn it off. The other is to short out the reset leads.

To add forward/break/reverse, you need a 3P3T switch. You wire it up just like Dan drew. Except that in the center position you disconnect the motor from the controller and run the motor leads thru the resistor. Also in that position you reset the controller (that's why it takes 3 poles).


I've finally found such a switch, but haven't finished wiring it up. So for now I power off and wait for the motor to stop.

Gee, I don't know if anyone really cares about that information.... I just got to blabbing.

Sorry,

Steve
 
Just FYI...

The dynamic brake on my board calls for a 500 Watt, 20 Ohm power resistor stop switch. That was all I needed to hear to just leave it alone...:D

If only my high school electronics teacher could see me now...he'd say "duck!"...:eek:

Actually, he's dead. :(

(R.I.P.)

:footinmou :footinmou
 
Nice setup! You don't need that reverse setup. Just turn your machine upside-down. :D
 
Originally posted by Burchtree
Just turn your machine upside-down.
Click to expand...
Doh! I shoulda known better...all that time I spent hanging upside down instead..."just turn the machine, doh!"

:p :p
 
As promised, I'll continue to update this thread with diagrams and information the best I can.

Here's a diagram of how I did the motor mount:

motormount2.gif



The motor did not come with a mount - just 2 holes in the bottom. After some fiddlin' around I determined these to be 5/16" diameter holes with "fine" threads. I got 2 bolts and 4 lock washers at Home Depot.

I wanted to be able to have some play with the mount in case I couldn't get the belt do sit tightly. So what you see above is what I came up with.

2 mounts, really. One mounts to the motor, and then that mounts to the table.

The 2 smaller pieces help brace against the motor "bucking" when I need to reverse directions (which it does, even when completely wound down).

The shim allows the motor to sit up off the mount and air to flow around it freely. Since it's a softer wood, I can really crank down hard on the motor mount screws and make sure the lock washers set in good.

The counterbore is to make room for the head of the screw and to give me a flat bottom. The main reason for this was to allow for adjusting - in case I screwed up putting in the mount holes, etc. or the belt doesn't fit, etc.

The tabletop mount bolts go all the way through to a brace piece below the table. If I needed to, I could have cut a wider (or elongated) hole in the tabletop for adjustment purposes, without having to worry about damaging the tabletop.


This was tough at first to visualize and come up with the right idea, and even more mind boggling when I had to figure out what order to assemble everything in...


Overall, though, it serves my purposes well and raised the motor up a little bit - something I wanted anyway since I'll be putting a buffing wheel on it.

Thanks for all the comments and feedback so far. To those who are debating on whether or not to get a KMG...

...here's some fuel on the fire. :D


Dan
 
Dan, real attention to detail and a proof of no lack of patience on your part. I did not go to such lengths on my mount but am glad for your sharing because it may help me to improve my own.

RL
 
Thanks a lot Dan,

Here I was all set to get the Craftsman 2" x 42" grinder and I found your post. Had I not known it was this simple I would have been content with the Craftsman. Now I have to rethink my whole plan!

I hope you're happy, :D

Eric

PS, Very cool job on the set-up.
 
Thanks, Eric. I cannot take credit for the idea, only for posting the specifics online. Sando and rlinger were very helpful.

One caution, though. It seems that some folks have had problems with the specific motor and controller I have listed in this thread. So, I'd say keep your options open on those 2 things and if you can afford a step up, get it. (but still look at surplus center for the parts - great prices).

Dan
 
Hey Mer Dude,

I discovered something when I was all done:

I had the Sear 1hp 3wheel 2x42 grinder.

Then I ordered the KMG and that motor setup like Dan's.

Then I found out the DC motor fit the Sears Grinder!!! Same motor size, shaft size, everything. I could have had a variable speed grinder all along - not that I don't like my KMG, but it would have been a nice step up.

Steve

PS I don't know if sears still has the 3 wheel grinder. I don't know if this is true for their 2 wheel model
 
Hi all, I was one of the guys who had some problems with the setup thats posted here, but just to let everyone know i have absolutly so regrets, and i would do it over again, hey, where else can you get a DC motor, controller, switches, and a box to put them in for under a hundred dollars including shipping!!, I have not put in the resistor for the dynamic braking yet, i just slow it down carefully and it works fine. thanks to all who took the time out to help with this project. Tom
 
Why would you want to reverse the rotation and grind with the belt spinning the other way? I'm probably missing something pretty obvious here but don't you want the sparks / shavings flowing away from you?

Curious,

Eric
 
Hey Eric,

Nope - not the same that's the 2 wheel. I don't know the motor size on that one. Maybe you can swap it?

I like 3 wheel model, very sturdy cast iron deal.

RE going backwards - almost no value.

I only use it with the platen horizontal. That's for sharpening and some flatten work - real slow.

Steve
 
Motor reversed - serves 2 purposes for me.

1 - allows me to slack belt grind on the top of the belt (behind the 2" wheel) and the sparks/etc. goes away from me, plus I can stand right in front of the belt. I don't do heavy grinding that way, but it helps when I'm trying to put on a satin finish or polishing or sharpening, etc.

2 - I have a buffing wheel attached to the other shaft. Most of the time I work with the wheel spinning top-toward-me. Again, every once in a while I get a big knife (such as a khukuri) that I'm polishing and I don't like lettin' it hang down so low, so I reverse the direction and buff/clean/etc. with the top-moving-away on the buffing wheel. I'm buffing lengthwise, by the way, not across the blade. Works better for me.

If you don't ever see yourself needing to do that, then don't bother with the switch. Even though I reverse only maybe 5% of the time, that 5% is definitely worth it for me.
 
Can someone tell me if this setup will work with 110AC power? That's all I'm wired for. It looks like in the PDF controller manual that you have to be running 220AC in order to support a 1.5 HP motor. What are you guys using? Thanks -chris
 
I've got this one running on 110V household outlet. Works pretty good for a "first motor". In fact....

It's paid for itself already...and because of that, I now have an AC VFD system on order. When I get it, I'll post the results here.

It's a pretty neat setup. The lil' box has both a step-up transformer (110V,15A to 220V,7.5A) and Variable Frequency Drive (also changes single AC to 3 phase) inside. This then powers a low-amp, 1.5 HP, 3 phase, 1750 rpm, AC motor which can be quadrupled (240 Hz max) to 7000 rpm. All for $440 - trans/invert/motor (including 1 yr. warranty). And it runs on 110V. ;)
 
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