Assorted ginder questions

artificialj

artificialj

Joined
Dec 9, 2010
Messages
153
So I have a couple of questions relating to grinders/motors/VFDs that I couldn't find really clear answers to through searching. Any input would be great!

I have a couple of these motors: http://www.baldor.com/products/deta...ralPurpose&winding=35WGR986&rating=40CMB-CONT , and am going to probably be getting a VFD like this: http://dealerselectric.com/item.asp?PID=620 . I am planning on hooking one up to a KMG, and was thinking of building a disc grinder with the other.

Questions (sorry, I know some of these are fairly basic):

1) I know that everyone says that the 3450 rpm motors are too fast, and that 1725 is a better baseline. Do I need to slow this down between motor shaft pulley and drive shaft pulley (by getting different diameter pulleys), or is it going to be ok to just use the VFD for all of my speed control?

2) I want to reduce the motor shaft on one of the motors from 7/8" to 5/8" to use my 9" disc sander mounts. Any reason not to just get an inline shaft reducing adapter from Mcmaster? Is there some benefit to building a pulley system to drive a 5/8' shaft instead?

3) On the disc grinder I want to have a reverse switch. Is this just as simple as wiring an appropriate switch between the VFD and the disc grinder motor? Or is there some option on the VFD for reverse?

Umm, I can't think of what else I wanted to ask, but will update when I remember.

Thanks,
Jay
 
Those are some good questions. I think Rob at KMG could give you the best answers. What I think I know - is I am concerned the motors are not sealed-but maybe I just don't know that abbreviation. I guess the cooling and torque are affected also by the 3450 vs 1725 - but w/ 3 hp power is no problem. The VFD I believe is very popular and should be fine along w/ the popular line supplied as option with KMG's. There might be a reverse switch on the VFD or optional. Will you be wiring the VFD to handle both motors through a rotary cam switch? It seems like lots of people use 3450rpm motor. 3/4hp is popular for disc grinders but then you need a second VFD.

D
 
That's the same VFD I have. I run a 3 hp Baldor with it. On the VFD is a row of auxiliary terminals for things like motor braking, a speed pot, run/stop, and fwd/rev. There is a 12V hot terminal in this row, it supplies 12V to whatever switches you want to use, you then run a wire from the switch back to the appropriate terminal, such as fwd/rev. The manual explains this well.

I'd not thought about installing a switch in the power line from VFD to grinder. If it was installed so that it swapped any 2 of the three hot wires, I suppose that would work as well. Probably not a good idea to flip a switch installed this way with the motor running. If fwd/rev is wired as per the VFD instructions, this is no problem. The VFD decelerates the motor, changes direction, accelerates. If you don't plan to run external controls, fwd/rev is easy to use with simple data entry right on the VFD face buttons. No switch anywhere is really necessary.
 
Those are open motors.
Not ones you would chose to buy in this instance, but if they were free...

I'll leave most of your questions alone, but answer the one I know.
There is a reverse option in that VFD.
You have to add an external switch, but the option is there.

For those kinds of dollars, buy a KBAC 27D from Wayne Coe.
$375 shipped if I remember correctly.

I have both, and much prefer the KBAC.

It has a real knob for speed control, and 2 blank holes for adding switches.
I add a switch for forward/reverse, and a 3PDT to send the output to 2 different machines.
I have 2 configured this way to run 4 grinders.
It's very clean, and very convenient.

The FM50 powers my surface grinder.

You're should be OK on 3hp @ 3450, just configure your pulleys so that you get your max sfm that you want at 100% power.
You will get the most sensitivity out of your speed pot that way.

I personally would build a couple of pillow blocks, and pulley the disk, but that's just because it seems stronger that way to me.
I could be full of beans.
But it seems like you could really lean into it without stressing your motor bearings, and again, you can configure the pulleys to get the RPM you want.
You can get a lot of extra leverage/stress when you extend a shaft like that...
My disk maxes out at 1750, but it's also the least used tool in my shop, so I can't speak too much about it...
A coupler and a pillow block would work too.

You'll probably kill those open motors before too long anyhow, and by then, you'll know what you really want/need...

EDIT: Damn, apparently I was typing a long time.
Salems post was not there when I started...
 
Cool, thanks for all the answers guys. As to the motors, yeah, not the best enclosure, but at the price I couldn't pass on them. Hopefully some pantyhose or homemade filtered enclosure will keep them alive for a bit.

I thought that the KBAC 27D was only rated to 2hp, and Wayne Coe doesn't sell the KBAC 29. Would you go with the KBAC 29 from kb electronics instead of the TECO?

Also, yeah, was going to use a rotary cam switch for using the VFD for both motors.
 
My bad, the 27 is indeed only rated for 2hp.

The 29 is 3hp, and appears to be the same control configuration.
Inexpensive HERE too.

If you buy a KBAC, I suggest buying a FWD/REV Switch, and a POWER ON/OFF switch, as they only come with RUN/STOP

I prefer the KBAC because it has "real" switches and knobs.
Twist a knob for speed, flip a switch for whatever else.
The Teco can do that too, but the KBAC is that way by default, and it's all in the enclosure.
Very clean, very tidy.

Salem got me again.
posted while I was editing to add the reasons I prefer the KBAC.
For a remote setup, the controller just doesn't make a difference, my particular setup has the controller between the 2 machines, within easy reach of either.
 
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Brian has both, so I'll bow to his experience, but FWIW I'm happy with my TECO. I mean, I added a remote control switch box for everything, so it matters not to me whether the VFD comes with a speed pot or room for switches. Other than that, it does everything I want it to just fine...
 
Haha, it's like a chatroom in here.

Thanks for the link to the -29 at cheaper price, that makes it about the same cost as the TECO.

Ok, so now about the disc sander drive. The main reason I was looking at the step down coupling for the shaft was that it would accomplish the entire thing with just one part, where as once I get into pulleys I have 6 parts (pulley x2, 5/8" shaft, pillow bearing x2, belt) plus needing to build a structure to properly mount and align them. Seems overly complicated, and, judging by my fabrication skills, fraught with disaster.

The step down shaft adapter I was looking at is only 3 3/4" long total, with 3/4" of that being around the 7/8" shaft. I have little experience using a disc grinder, but do you guys really think I will be applying enough force to the disc for it to be a problem?

If the answer is "go with the pulley system," any advice on sources for parts? I've been looking at mcmaster-carr, and, although they have all the parts I would need, I have no idea on how to choose the right ones amongst all the varied options. Endless choices on belt dimensions, etc. Is there a right choice here, or do I just choose one set of dimensions, and make sure everything else matches up?
 
Time for a disk guy to step in.

I own one, and it gets next to zero force, as all I do with it is dovetail bolsters.

They are a real workhorse for some other guys.

I look at things from a different angle than a lot of folks, and real world experience trumps theory most of the time!
 
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