Yes, another grinder motor question?

C

couldbe

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Dec 7, 2012
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Hello, My name is Mike and I have been lurking around for several months now. I have looked at almost every thread related to grinder motors on this site an other. The opinions are all over the board.. I just ordered a GIB and need to puchase a motor. I will be using a VFD and not sure if a 1750 or 3450 rpm motor is the way to go. I would like to purchase the most flexible unit. I know the motor will be 240volt 3 ph in the 2 to 3 horsepower range. I think that a 3450 will be the best choice, but I'm just not sure. Would like the input from those that are currently using a 2x72 belt grinder.Tried to look for belt speed suggestions as that would help pin the rpm , but again they are all over the board as well.
This web site has been most helpful with information, there are a lot of very knowlegdeble knife maker located here.
Thanks in advance.
Mike
 
Thanks for the replies, just as I expected completely different then what I thought. My hope is the the experts will elaborate as I'm confused. I recently watched a video of a knife maker at work and he was grinding @ 7680sfm. I'm not sure they make a drive wheel large enough to get that speed out of a 1750 motor....
Mike
 
7680 is about an 8 .5 inch wheel at 3400 rpm



I started with a fixed speed 3400 repm motor and 6" drive wheel directly driven by the motor (like your gib)

That's 5338 SFPM

I just replaced the motor directly with a 3 phase of the same speed.

You will need a high speed to bet the best use out of the ceramic cubatron and blaze and Norton blue belts


and the VFD is there to reduce the speed

You may lose some torque at low speeds, but you run the slowest on the wooden handle materials not the steel.


There is discussion over 2 pole vs 4 pole motors (the kbac27d controller allows you to double the speed with an internal jumper setting
Some say one is better than another, I don't know about that.



You will see the 1740 rpm motors mentioned for the KMG and NWG grinders using the 3 speed pulleys,
but that's because the high speed is a 2:1 ratio that is the same as the direct drive motor at 3400 rpm.

2 HP is lots of power unless you are a full time maker doing work on large knives on the flat platen, racing the clock for production efficiency.
The jump to 3 HP will cost you in a larger motor and a larger VFD


The most versatile setup is a 1.5 HP motor in an KBAC-27D vfd by KB electronics.
That will allow you to plug into ANY normal 15 amp outlet and not be tied to a specific 220v installation.


http://www.bladeforums.com/forums/s...rn-how-to-make-knives?p=11612725#post11612725

See VFD Variable Speed made simple


Wayne Coe used to have the best prices, but you can shop around and find better.
Hookup is dead simple, however if you need help that may be a good way to go.
 
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couldbe said:
Thanks for the replies, just as I expected completely different then what I thought. My hope is the the experts will elaborate as I'm confused. I recently watched a video of a knife maker at work and he was grinding @ 7680sfm. I'm not sure they make a drive wheel large enough to get that speed out of a 1750 motor....
Mike
Click to expand...

~16". You'll need it custom made. ;)

Or a 1750 with a vfd running at 120hz with an 8" wheel.
 
If you are not doing a direct drive then you can get and speed you want by changing the motor and grinder pulley ratios.
 
I would use a 1750 RPM motor. They have four poles vs two in a 3450 RPM unit. this will be especially important with the VFD.
 
Thanks for the replies.
I guess, I should ask what the max sfm one would need. I'm thinking around 4600 would be good??The GIB I have purchased will be direct drive and a 6 inch drive would appear to be about the larger that would fit without mods. Don't have the kit yet, but clearance looks to be a problem if larger than 6 inch drive is needed. I'm just not sure that 1750 and a 6" drive will get to 4600. I would just like to make the best choice for all around use. I'm planning to order the motor today and I'm valuing feedback in that purchase.
What would be the problem going with a 3450 and then it would seam I would have no worries, right. Maybe not as much torque, but still workable.
Thanks,
Mike
 
couldbe said:
Thanks for the replies.
I guess, I should ask what the max sfm one would need. I'm thinking around 4600 would be good??The GIB I have purchased will be direct drive and a 6 inch drive would appear to be about the larger that would fit without mods. Don't have the kit yet, but clearance looks to be a problem if larger than 6 inch drive is needed. I'm just not sure that 1750 and a 6" drive will get to 4600. I would just like to make the best choice for all around use. I'm planning to order the motor today and I'm valuing feedback in that purchase.
What would be the problem going with a 3450 and then it would seam I would have no worries, right. Maybe not as much torque, but still workable.
Thanks,
Mike
Click to expand...

bladsmth said:
I would use a 1750 RPM motor. They have four poles vs two in a 3450 RPM unit. this will be especially important with the VFD.
Click to expand...

ernestrome said:
Or a 1750 with a vfd running at 120hz with an 8" wheel.
Click to expand...



I trust Stacy to understand the 2 pole vs 4 pole so based on that go 1700


If you use the KBAC-27D, you can change an internal jumper to run at double the frequency which gives you double the speed.
Some others may do this also you would have to read the manuals before you buy.

If you are buying new the 1700 rpm motors are cheaper and more plentiful on the used market also

When you buy the motor for the GIB look for a 56c frame motor
That will give you the right bolt pattern and shaft size.
 
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I have been told by two different manufactures that it isn't recommended to run a 1750 rpm 60hz motor above 90hz.
Mike
 
That depends on if they are taking about single phase or three phase motors.
A single phase motor run at 90 Hz would likely get very hot, and burn up. A three phase motor will handle it far easier. I don't recommend running them at 400Hz but 120 Hz should be fine.

There are also different types of 3ph motors. The ones rated as "Inverter Duty' will take whatever the VFD throws at them with a smile. A regular 3Ph motor will do OK, but I wouldn't run it at max RPM for hours on end. The bottom end is also a place where the two types of 3Ph motors differ. Inverter duty motors have better torque at low speed.
That said, thousands of regular 3Ph motors have been used on grinders worldwide, and seem to work fine for the needs of knifemakers.... but we aren't picky.
 
Trust me when they say 1700 rpm. I have a 3 ph 3600 rpm motor with variable on one of my grinders and it is about useless. Its good for doing handles and any fine tuning but thats about it. My mistake was not to do a search before I went out and purchased it. You are already ahead of the game. I am switching motor on it in the near future. The search engine is your best friend !

Mark
 
I run both a 2hp 3600rpm motor and a 2hp 1800rpm motor off the same KBAC-27D VFD. Whatever issues Mark is having with his 3600... I am not. In my experience (with my belt drive KMG), as long as the pulley ratio is dialed in, either works fine. I feel like the 1800rpm motor may have a bit more torque at low rpms -- probably due to the 4pole vs. 2pole configuration that Stacy mentioned (though it could also be that my 1800rpm motor is name brand vs. the 3600 that was purchased from Grizzly) -- but both motors work awesome on my KMG. I have no experience using either motor on a direct drive belt grinder, nor have I messed with the jumpers on my VFD to double the frequency... so no help there. My current configuration is running the 3600rpm motor on the KMG and the 1800rpm motor is on a direct-drive 9" disc (where the lower rpms are more useful to me).

My experience only... YMMV.
Best of luck.
Erin
 
My main grinder uses a 3hp 1725 Baldor motor. My Square Wheel uses a 2hp 1725 Leeson. I run both of them off of a TECO FM50 203 VFD. The TECO allows frequency parameters to be manually set, so I set mine at 90% max (although it will get to 120.) Using a 6.5" drive wheel on the 3hp grinder, I get good fast hogging speeds, but it's smoothly adjustable down to nothing. Raising the maximum frequency value increases the sensitivity of the speed pot, but that's fine with me. On the Square Wheel, I'm currently using the stock 10" drive wheel, which at 90 HZ generates insane ripping fast belt speeds that I never use.

I have a Pheer grinder with 2hp 1725 motor, using a smaller drive wheel- 4.5" or so. It's driven by a Vacon 10 VFD. I set the max frequency to 120 Hz, which I use a lot for rough grinding. I could handle a bit more speed yet with the small drive wheel.

I've been too lazy to do all the math to list the SFPMs involved here, just trying to give impressions of how these are working in my shop.s
 
I wonder if the hp has anything to do with my 3600 rpm motor Its a 3 phase 1 hp . I have a baldor 1 hp on my square wheel and that grinder has no vfd but flys.I can slow it down if I really lean into it.. But I just have to push just a bit and variable tanks. Electric motors for sure is not one of my strong points.
 
First off, Stacy isn't a mod without good reason so take his suggestions to heart. Second, maybe if you fill out your profile and let the guys know your previous knife making experience you may get other suggestions. The reason I say this is that, in my noob opinion, a fast belt speed shouldn't be your top priority. I am familiar with the video you mentioned in your original post and it will take you a long time to reach that level. If you are in fact new to knife making then slow is your friend.

I use a KMG, 1.5 hp Leeson 1750, 3 phase, with the KBAC-27d VFD and it goes plenty fast enough for me.
 
Marko,
A 1Hp motor is the bare minimum for a belt grinder. When you add to that a VFD, and the related power loss of converting the power to 3Ph, the motor will be pretty puny if any hard grinding is tried. A 2Hp should be the size for a full use VFD controlled grinder. 3Hp is a bit overkill, but I never heard a complaint from a maker who used 3Hp, either.
 
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