single Phase 2hp motor, can i make this variable speed?

M

mikereineman

Active Member
Hi guys, I am new to the game, I am currently making a eerf grinder, I am on a limited budget as we all are. I was given a
single phase 2 hp industrial motor, my guys at my work wired it for me so it plugs into 110 and has a on off switch, I want to direct mount it and install my drive wheel directly to the shaft. But as I am learning , it runs at over 3000 rpm and that is not the best for grinding knives, so is there any way at all to make this a variable speed set up with out going to pulleys and would pulleys even slow it to speeds I would need? Thanks guys
 
No, there's no way to make the speed of a single phase motor variable in a way that'll work well on a grinder.

RPM isn't really an issue in itself. Belt speed is. If you fit a 3" drive wheel to a 3500 RPM motor, you'll get the same belt speed as a 6" drive wheel on a 1750 RPM motor.

A VFD setup doesn't cost all that much more than a fixed speed motor and step pulleys once you cost in the extra shaft, bearings, pulleys and belt.

How about building a fixed speed grinder with a motor-mounted drive wheel, then upgrading to a 3-phase motor and VFD when funds allow?
 
thank you for your input, my research was pointing me in that direction but wanted to make sure, so if i understand you correctly i can use this motor and use a three step pulley to slow it down, kind of like the set up on a kmg or no weld?
 
They also make 4 step pulleys.
When I started out with my first Coote Grinder I had been given a 1 1/2" Hp 3600 RPM motor.
I went to the local hardware store a purchased Chicago Brand Airconditioning/Fan four-step pulleys. the shaft sizes were different on my Grinder & Motor. so I got two diff arbor sizes.
That and some link belt and hinges with a plywood board for the motor and I was in biz!

You really want to be able to slow down the machine for the finer belts of 400 Grit and up!

Let us know how it works out?

Laurence

www.rhinoknives.com/
 
thanks guys, so is there a chart or a way to calculate the rpm, i know i have a 2 hp motor that runs 3600 rpm, if i use the step pulleys what are the speeds reduced too? Thanks again for helping out the new guy.
 
Your belt speed will be;

motor speed (RPM) * motor pulley diameter (") / shaft pulley diameter (") * belt wheel diameter(") * Pi / 12

So for a pair of 432 pulleys and a 4" belt drive wheel, you'd get:

High speed: 3600 * 4 / 2 * 4 * 3.14 / 12 = 7536 SFM

Mid Speed: 3600 * 3 / 3 * 4 * 3.14 / 12 = 3768 SFM

Low speed: 3600 * 2 / 4 * 4 * 3.14 / 12 = 1884 SFM
 
mikereineman ,Tim's comments are right on! Because you already have the motor go ahead and use it. When you can afford the 3 phase motor and VFD you can change. You will then really know the difference. the main thing is go get going now with what you can afford. If you think that you will be upgrading to a VFD within the next year or two save the $100.00 or so that you will spend on pulleys, shaft, belt and pillow blocks and put that in the account for your new setup.
 
I am making one of Tracys NWG grinders although I have done a bit of welding on it. I am using a 2 hp/1760 motor wired for 220 with a three step pulley on the motor shaft and one on the eqipment shaft and am pleased with the speeds. I do not pay a lot of attention to specific speeds, rather I am more interested in slowing the speed down in order to gain considerable control and keeping the steel cooler. Like Tracy I started with a Grizz machine and ruined a lot of blades with the too fast motor...3400 rpm. Currently making tool arm with the small wheel attachment for making finger grooves and ricasso work. While the VFD is a good idea, I think for most of us a step pulley is fine and I can change speeds fairly quickly. I do recommend the link belt for durability and noise control. Make friends with your local motor rebuilder....good guys to know and they frequently have good rebuilds available much less than a new motor. I picked up this motor for $150. The shop owner stands behind his motors, so no worries. No offence to you VFD guys! Slower speeds rock!
 
The first grinder I built was a NWG (welded). I was so amazed at how well it worked and how easy it was to build I contacted Tracy and got permission to start conducting "Build a Belt Grinder" workshops and selling motors. I kept seeing folks requesting VFDs. I said, "You've got 4 speeds why do you want a VFD?" I still kept seeing the requests for VFDs so I got a distributorship to sell the KBACs. So I thought, If I am going to be selling these things I guess that I had better build a grinder with a direct drive and a VFD so that I can intelligently discuss them. I was amazed at how much smoother and quieter the grinder ran and the added power.

I still believe that a step-pulley set-up is good and will serve many maker's needs, but, once you can afford it and can justify the expense you will want a variable speed grinder with a VFD. I still have one set of step pulleys, pillow blocks, shaft and belt that I need to sell but when I get calls I invariably sell another VFD rather than the step-pulley set-up. After all it is about helping other makers, not just making a sale.
 
timgunn said:
Your belt speed will be;

motor speed (RPM) * motor pulley diameter (") / shaft pulley diameter (") * belt wheel diameter(") * Pi / 12

So for a pair of 432 pulleys and a 4" belt drive wheel, you'd get:

High speed: 3600 * 4 / 2 * 4 * 3.14 / 12 = 7536 SFM

Mid Speed: 3600 * 3 / 3 * 4 * 3.14 / 12 = 3768 SFM

Low speed: 3600 * 2 / 4 * 4 * 3.14 / 12 = 1884 SFM
Click to expand...

Just so I can make sure I understand the formula, would you mind writing it out, instead of the symbols? I'm pretty sure this algebra, but putting RPM in ( ) kinda confrused me, which is no feat in itself. I have been wanting to know this information for so long. Thanks for sharing, Rex
 
McClellan Made Blades said:
Just so I can make sure I understand the formula, would you mind writing it out, instead of the symbols? I'm pretty sure this algebra, but putting RPM in ( ) kinda confrused me, which is no feat in itself. I have been wanting to know this information for so long. Thanks for sharing, Rex
Click to expand...

Sorry, I missed your question the first time around.

The formula and numbers are what you want. The values in brackets are just the units you need to be using for the input data. I put them in for clarity :lol: as not everybody thinks in feet, inches and RPM (I'm in the UK and old enough to think in a strange combination of Imperial and Metric units; in my head, distances are in miles, small stuff is in thousandths of an inch, most other stuff is in metric. Temperatures are in degrees C; basically it's all just a horrible mess and I just tend to assume everyone else's head is the same)

Longhand, it's:

motor RPM, times motor pulley diameter in inches, divided by shaft pulley diameter in inches, times belt wheel diameter in inches, times Pi, divided by 12, equals belt speed in surface feet per minute.
 
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