Looking to Build a new grinder

M

Merino_Mat

Joined
May 30, 2012
Messages
9
All,
I'm look to invest into a grinder soon and think building my own is my best option. I don’t want to spend 1000+, but would like to build something I can expand off of.

I have been reading a lot and purchased a set of weldless plans. My questions are about motors. I was wonder if I can get some opinions on these two off of Ebay.

http://www.ebay.com/itm/Baldor-Moto...007?pt=LH_DefaultDomain_0&hash=item35be203eff

http://www.ebay.com/itm/Baldor-2-Hp...745?pt=LH_DefaultDomain_0&hash=item35be1bf451

These are both in my price range and seem like something I can expand off of.
The second link shows a Baldor but, it has a 10 shaft from the motor...is this something that would hurt me in the end?
Could I eventually connect a VFD to these?
Any opinions are great. thanks

Mathew
 
It's not that you could eventually connect a VFD, you would HAVE to use a VFD since these are both 3 Phase motors. If you don't have a VFD and want to use one right out of the box, you would have to find a single phase motor. It could then be run with step pullies to have variable speed.
 
These are both good motors in terms of quality and power, but as Jason said you will need a VFD to run them. I recommend using the VFD anyways, as it simplifies the construction somewhat (no step pulleys and no seperate shaft for the drive wheel) and opens a wide range of speeds.

The motors have other issues, however.

The first link is for a "washdown" rated motor, which might be useful if you wanted to make a wet grinder. It looks like it has both a face and bottom mount. The face-mount seems really large, and if it's not removable it seems like it would get in the way of most grinder designs I've seen. You might end up having to modify the grinder design if you wanted to use that motor. I'm really not sure if it is removable or not- I would ask the seller.

The extra-long shaft on the other would be a problem, since with a VFD setup you'll install the drive pulley right on the end of the motor shaft and you want the shaft as short as possible. The problem is that the keyway slot is only on the last 2" or so, so if you cut the shaft down you'd have no way to key the drivewheel to the shaft. The only way to use it would be to replace the shaft, and I'm not sure how feasible that is. It's not something I'd want to attempt, with how many motors are available on Ebay.
 
Both great replies thanks.
Can you expand a little more on 3phase (I admit, I know nothing about motors...)
I have to run a VFD? Is that because the speed of the motor is so great that step down pulleys wont help?
I want to eventually connect to a VFD. So, maybe saving more and buying both at the same time is ideal.

I see, so the motor will butt up SO close that the mount would get in the way. Thanks, I over looked that part.
 
Three phase is the type of power that it takes to run the motor. If I'm not mistaken, it is three 110v legs. This is fine with most industrial shops as they have 3ph hower but residential homes only have two legs of power coming in.

That is a very simplified version but unless you have 3phase power in your home (very few do), you should stick with single phase or go with vfd.

I use step pullies and they work great.
 
Residential grid power is 110v single phase. A phase is basically a supply of alternating current. So in 110v 1-phase you have one hot wire that alternates polarity (changes from positive to negative) 60 times per second. In a three phase system you have three hot wires that each alternate polarity at the same frequency, but the timing of when each phase switches polarity is staggered 120 degrees. This type of power lets you design a motor that has a rotating electromagnetic field. Most commercial/industrial buildings have 3 phase power for any motors over about 1 hp. That's why when you look for 2hp motors you will find mostly 3 phase.

The internal design of a 3 phase motor is different than for a single phase, so you cannot run one type of motor on the other's source of power. With three phase power you can use a VFD, which changes the frequency of the alternating current from 60 Hz to another speed you select, causing the motor to spin at a different speed. For example, a 1750 rpm motor will run at 1750 rpm at 60 Hz, but if you change the frequency to 30 Hz it will run at 875 rpm. You can run it very fast or very slow, and have a continous range of speeds in between.

Technically, you don't need a VFD to run a 3 phase motor on your single phase outlet, you just need a phase converter. This would transform 110v single phase @ 60 hertz into 230v or 460v 3 phase @ 60 hertz. You would not be able to adjust the output frequency and so you could not control the motor speed- it would always spin at its design rpm.

But VFDs that will convert 110v 1 phase into 230v 3 ph output are relatively cheap (mine was less than $200 IIRC, but I have to build an enclosure to keep metal dust out). To go with a single phase motor you need to buy a pair of step pulleys, plus an additional keyed shaft and a couple of bearings with bearing blocks for the drive shaft. The cost difference will not be so great, and the versatility of the VFD is much greater.
 
Merino_Mat said:
All,
I'm look to invest into a grinder soon and think building my own is my best option. I don’t want to spend 1000+, but would like to build something I can expand off of.

I have been reading a lot and purchased a set of weldless plans. My questions are about motors. I was wonder if I can get some opinions on these two off of Ebay.

http://www.ebay.com/itm/Baldor-Moto...007?pt=LH_DefaultDomain_0&hash=item35be203eff

http://www.ebay.com/itm/Baldor-2-Hp...745?pt=LH_DefaultDomain_0&hash=item35be1bf451

These are both in my price range and seem like something I can expand off of.
The second link shows a Baldor but, it has a 10 shaft from the motor...is this something that would hurt me in the end?
Could I eventually connect a VFD to these?
Any opinions are great. thanks

Mathew
Click to expand...

If you're building a good grinder, you will still spend $1k

I say go direct drive and VFD right away.


This motor with the long shaft only has a keyway at the end, so even if you cut it off, you need to mill a new keyway.
Forget that, not cheap enough for that.
Baldor 2 Hp 3Ph motor 5/8 bore 208-230/460 1740rpm [ U-4]


The huge flange, you could make that work
skip the step pulleys, make a plate or angle iron mount for the motor.


I would skip them both.
If they were $50 I'd make them work, for that price you can find exactly what you want new, with free shipping
Someone posted links within the last week, good deals.
 
Thanks guys.
I think going direct to VFD is the way to go.

thanks Robs92XJ for the detailed response.

12345678910 thanks, I think you are right. I will keep my eyes open for a better option. Building an enclosure wont be to bad, thats always an option.
I think I saw pictures once where someone used an old tool box and mounted it. Not a bad idea...
 
I have built my own KMG grinder for a grand total of about $400. $125 on the motor. Im a fabricator/welder so i didnt go with the weldless model, I welded the whole thing. The only cons to welding, in my opinion is if you aren't an experienced welder, your mistakes are libel to really hurt to undo. The blue print and cut list for the grinder are available for free online if you look for it. Many steel supply shops will cut to order for a reasonable fee. I bought all my hardware, tension and drive wheels, etc., through Beaumont.
That bring us to single or 3 phase. I went with a 3 horse single phase with step pulleys. Im a hobby bladesmith not a master. Obviously if the extra hundreds of dollars to go variable speed isnt going to hurt you, go for it. Variable speed has many advantages over stepped pulleys. But I have worked with both and For my purposes, I didnt need to spend the money to get the job done. With a 3hp motor, I never lose power, the thing would tear the blade from your hand before you could bog it down..
Shawn
 
Shawn,
Thanks, and No I'm not an experienced welder, but my dad is. I found some plans online also and am concidering both right now.
If I (we) owned a welder, I'm sure performing the job wouldnt be that bad. I guess it comes down to time.
We have a lot of good metal workers in town that are willing to cut anything down and take the time to make it right, so thats a plus.

thanks
 
Many commercial grinders use electric motors of the type TEFC (Totally Enclosed, Fan Cooled) and have a Frame 56 housing. This frame provides for mounting by securing the motor by screwing bolts into the face of the motor or by bolting an attached mounting bracket to a flat surface. the benefit of the totally enclosed motor is that it keeps grinding dust out of the internals and shorting the motor or ruining bearing surfaces. You should consider the rated RPM value also, typically 1725 or 3450, which will affect belt speeds as well. It should be rated for continuous duty, rather than intermittent duty to keep from overloading it when doing heavy grinding. I have gotten by quite well with a 1 HP motor on my Square Wheel. Besides of having the benefit of speed selection, you would also be able to change the direction of rotation which can come in handy. I would suggest you consider where you plan to go with your knife making and look to what you will need in the future. There are both AC and DC variable speed motors. The problem with the AC variety is the loss of torque at reduced speeds. A comparable DC motor does not have this problem, but would require 220 volts to be equivalent to a 120 V AC motor. Just my thoughts.
 
Last edited:
You must log in or register to reply here.
Back
Top