Thinking of building a grinder

[Rusty Snuffers]

I'm hoping to step up to making my first blades this year.  I've found plans for a 2x72 "no-weld" grinder, including where to find the parts, wheels, etc.  I' fortunate that my brother-in-law owns and runs a welding and fabrication shop, so I'd likely weld the main frame together for strength and stability.

My question is regarding the motor.  Here at the office, we have an assortment of electric motors in a "retired inventory".  How big should I go?  Will it depend on the type of grinder?  I can post the link to the plans which shows pictures of the finished product and a good description (Or you can go to Amazon and search for "Plans Set for No Weld Grinder") if that helps to answer my question.

Thanks in advance for any assistance.
Rusty

[madness522]

1.5 would be the least I would go with.  I built an NWG several years ago and it was a decent grinder once I got all the wheels turning on the same plane.  I wouldn't weld it up until after you get it up and running and happy with it.  Much easier to adjust it with the bolts than breaking a weld.  If you have access to a 3 phase 2 or 3 HP motor use it and get a VFD. You will be much happier with the variable speed than the step pulleys.  I am still running the pulleys now and am going to upgrade to a VFD in the next couple weeks.

[Craig B]

I have a Coote 2x48 with step pulleys and a 1hp motor. You definitely want at least a 2hp motor. I can stall my motor without getting real rough with it.

[David Ricke]

Rusty, If you build this grinder Two horse would be fine make sure you get a 1750 motor and are able to slow it down. Things happen very fast at times. Good Hunting Knifemaker

[Lin Rhea]

 Rusty, If you build this grinder Two horse would be fine make sure you get a 1750 motor and are able to slow it down. Things happen very fast at times.

I second what knifemaker said. It's plenty fast and 2 HP is pretty good at that speed.

[Kevin Evans]

I agree with you guys, 2 Hp.
 I have 1.5 that I had, and put on KMG,sometimes and rarely I wish it had 2 HP .I usually put new belt on and things are fine.
There are so many variables its hard to say what would work best ,but better to be oversized than undersized.

[Rusty Snuffers]

Thanks for the input, guys.  One of our engineers is actually drawing up some plans for the grinder in our CAD program, based on the KMG and another homemade grinder.  I'll likely use wheels from Beaumont and scraps from our fab shop for the frame.  Unfortunately, the only motors we have left in our used inventory are 3ph 208-230/460 so I'll likely be looking for a single phase 2hp so I don't have to get an electrician out to rewire the house/shed.

Thanks again.  I hope to have this thing all put together some time in the next few months.  I'll post pics once I do.

[gables]

You might consider saving one of those 3ph motors for down the road. Many variable speed controllers convert single phase 220 input into 3ph 220 output. This way you could upgrade your grinder down the road and/or buy a KMG and use the 3ph motor and controller on it. I would encourage you to consider how you can use components from this grinder project for upgrades down the road.

[Rusty Snuffers]

Thanks again for the input guys.  I've got one of our engineers doing a model in his spare time.  

Another question about the motor: I have a 1.5hp 3450rpm single-phase motor.  Has anyone attempted to use a high-rpm motor, stepping it down with the right pulley setup?  I see Beaumont lists their belt speeds when using the dual-step pulley config.  I'm trying to figure out what I should shoot for with that in mind.  With the faster motor, the same pulley setup with a 4" drive wheel would produce speeds of 1750, 3500 and ~7000 feet per minute.  Should I try finding bigger pulleys so I can bring the speeds down closer to what Beaumont has?

Variable speed controllers and/or motors are a bit out of my budget for the time being.

Thanks in advance.
Rusty

[kbaknife]

If there's any way to do it, forget steps downs and rpms.
Since you're going from the ground up, listen to everyone above, and I'll put in my $.02 as well and 13 years of grinding:

2 hp.
Variable speed.
Variable speed.
Variable speed.

A decent VFD is not much over 100 bucks, and what you will save in safety, belts, control and making better knives will pay for it in only a short time.

[Lin Rhea]

I have a variable on one of my grinders and will keep it rather slow most of the time. The variable speed makes it a better tool.

To answer your question, I would never have mine going as fast as you mentioned. There is an element of danger that the higher speeds add that I dont want.

[Rusty Snuffers]

Thanks again, guys.

As to the speed reference, Lin, I was more thinking of getting the lowest speed number down to the 800 ft/min that Beaumont lists when using the step pulleys.  I'd certainly not want to have the belt moving too fast, for two reasons.  First reason being safety and the second to give the ability to slow down the removal rate so I'm not ruining my first blades.

Karl, can you point me in the direction of these $100 VFDs?  I can't seem to find them for less than twice that amount, particularly for 1.5-2hp motors.

Thanks again.