Will this motor work for a 2”x72” grinder?

S

seanystrangle

Joined
Oct 1, 2009
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374
I have this motor from work, I’ve been think about building a grinder for a long time, if this one would work I think I’ll go for it.
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Looks like an ok Motor. I personally like to start with a 1740 rpm motor. Thy usually handle around double the HZ easily. My issue with a 3450 motor is if you turn it down with a VFD to 1750 you have lost a good bit of your HP. So starting at 1740 works good for me as I can go to 120hz or drop to around 30 or HZ with out any issue. The faster motors will work to but I don’t think thy are as stable when over driving them up to double the HZ as I don’t think thy are rated for that kind of speed. I have a VFD rated motor that’s rated for crazy speeds but it’s unique. But like I was saying that motor will work and get you going.

VFD-tourque-HP.jpg
 
Agreed, it will work. Not what I consider ideal, but others will disagree.

Lots of folks like a screaming fast motor, and I can't fault their reasoning, but I just don't have the skills to grind that fast!
 
It will work .. with a VFD ... on 240VAC.
As said by the others, I prefer a 1750RPM motor. But, free is free.
You can always change it out later for a 1.5 or 2HP 1750RPM if one comes along.
 
Keep in mind that the shaft diameter on a 145 framed motor is 7/8", so make sure you order your drive wheel accordingly. IIRC, the face mounting dimensions should be the same, so that shouldn't be an issue. Given that it's already at 3450 RPM, I'd recommend starting with a 4" diameter drive wheel. That will still give you more than enough top end speed (especially if you double your frequency), but the low end will be a bit more manageable as well.
 
If it was me I would try a 5” wheel at 60hz gives you around 4500sfpm where I consider the sweet spot for the type of grinding/roughing we do. Yes you can grind faster and I use to be one of them. My grinder use to top out at about 10,000sfpm. But power in the low end sucked. Anymore I seam to be in the 2-3k range for what I do. Your highest load is going to be roughing so design your grinder to be running at 60hz at that sfpm abd you will have all the power you need. I WOULD not over drive a 3450rpm motor.
 
We have motors with lower rpm but there is another problem with them, hey maybe with enough effort I could make them work?
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oagTBJy.jpg

this one is a little better
HNXoJRi.jpg
HNXoJRi.jpg
 
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JTknives said:
Looks like an ok Motor. I personally like to start with a 1740 rpm motor. Thy usually handle around double the HZ easily. My issue with a 3450 motor is if you turn it down with a VFD to 1750 you have lost a good bit of your HP. So starting at 1740 works good for me as I can go to 120hz or drop to around 30 or HZ with out any issue. The faster motors will work to but I don’t think thy are as stable when over driving them up to double the HZ as I don’t think thy are rated for that kind of speed. I have a VFD rated motor that’s rated for crazy speeds but it’s unique. But like I was saying that motor will work and get you going.

VFD-tourque-HP.jpg
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I’m not too worried about the power for now, I don’t plan on hogging off material too much, I forge the basic shape and use a bench grinder to clean up what I messed up so this will be for mostly beveling and cleaning things up.
A.McPherson said:
Agreed, it will work. Not what I consider ideal, but others will disagree.

Lots of folks like a screaming fast motor, and I can't fault their reasoning, but I just don't have the skills to grind that fast!
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I’m positive I don’t have the skills either haha I’m sure I’ll mess up more than I don’t but that’s just part of learning

Stacy E. Apelt - Bladesmith said:
It will work .. with a VFD ... on 240VAC.
As said by the others, I prefer a 1750RPM motor. But, free is free.
You can always change it out later for a 1.5 or 2HP 1750RPM if one comes along.
Click to expand...
I have more than enough power at my house for it I’m not too worried and I’m going to be having a shop built soon and a whole new line of 200 amps ran to it so I should be good there and I’ll just have a VFD built at work with old parts so I won’t have much cost there.
Drew Riley said:
Keep in mind that the shaft diameter on a 145 framed motor is 7/8", so make sure you order your drive wheel accordingly. IIRC, the face mounting dimensions should be the same, so that shouldn't be an issue. Given that it's already at 3450 RPM, I'd recommend starting with a 4" diameter drive wheel. That will still give you more than enough top end speed (especially if you double your frequency), but the low end will be a bit more manageable as well.
Click to expand...
I have access to a machine shop and a passable amount of knowledge to work everything there I’m just planning on making all the wheels my self so shaft size won’t be too big of an issue. But I will take your recommendation for the wheel size into consideration. I really have a lot more research to do on this it’s really only ever been a passing thought before yesterday.

JTknives said:
If it was me I would try a 5” wheel at 60hz gives you around 4500sfpm where I consider the sweet spot for the type of grinding/roughing we do. Yes you can grind faster and I use to be one of them. My grinder use to top out at about 10,000sfpm. But power in the low end sucked. Anymore I seam to be in the 2-3k range for what I do. Your highest load is going to be roughing so design your grinder to be running at 60hz at that sfpm abd you will have all the power you need. I WOULD not over drive a 3450rpm motor.
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Maybe I’ll mess around with that too. I might make a bunch of wheels to try out and see what works best.
12345678910 said:
Yes, use a vfd.

If your worried about speed being too high or losing torque at lower rpm.s use a smaller wheel.
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I plan on just having a VFD built at work, I figured there is no point in having a 3 phase motor without one. I will definitely look into the ratios for smaller wheels too.


Thank you everyone for the advice, I never really put much thought into building a grinder until I ran across this little motor. I have a lot more planning and research to do on the entire subject. Thank you again everyone and I will keep an eye out for small lower rpm motors as recommended.
 
Stacy E. Apelt - Bladesmith said:
Oops! I glanced and saw 1.5HP. Yes, that's a big big.
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Haha sorry it was meant to be a joke, I work at a large motor repair/ new manufacture shop as a DC Winder, it’s really really rare we get anything lower than 15 hp and honestly anything under 100 hp we usually just buy a replacement from the original manufacturer. It was kinda a miracle I found that 2 hp motor.
 
Once I get this lathe I have sold (make room for the new one) I will have a real nice 7hp Baldor 1170rpm TEFC with VFD that I want to move to the grinder. I think for your application the 3500-4500 max top end would be good. Still give you good torque on the bottom end. But generally I find as I slow the grinder down I’m going to finer and finer grits which require less and less pressure so it works out good.
 
Knifemaking legend William Scagel did something similar. He refused to let the power company put power poles through his property, so he never had power. He bought a Cadillac and managed to drive it to his home/shop. He took the engine out and used it to power his shop. He never drove again his whole life.
 
JTknives said:
But generally I find as I slow the grinder down I’m going to finer and finer grits which require less and less pressure so it works out good.
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That's exactly the case with a 3450 rpm motor. I've been using a 3450 rpm motor for several yrs and never notice any lack of power at lower RPMs because as JT says with the finer grits used at lower RPMs full power isn't required. I use a 4" drive wheel with motor max'd around around 3800 rpm for a max belt speed of 4,000 SFPM. I doubt seriously anybody would ever notice the difference between a 1750 and 3450 rpm motor while using.
 
"Will this motor work for a 2”x72” grinder?"

I've read this literally hundreds of time on forums and groups.
95 times out of a hundred it's some shitty open framed, no mounting options, DC no controller, treadmill motor with an impossibly small shaft.

It gives me great surprise and joy when like this one it's damned near perfectly fit for the use.
 
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