New here. Belt grinder questions/suggestions

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Dcbruton

Joined
Jul 12, 2023
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22
Hello friends, knife making newb, here.

Just starting my knife making journey and want to build a 2x72 grinder. I’ll mainly be building Japanese style chef knives.

Everything will be as budget conscious as possible and I’ll be doing all the work myself.

I have a free 2hp 3phase motor I plan to use. It’s only 1150 rpm though, I worry that’ll be too slow. And it’s got a 1 1/8” arbor. But hoping I can run a 7-7.8” drive wheel, and get speeds fast enough a newb could learn on?

Going to be running Amazon vfd for speed control.

I have a friend that runs a massive fab shop, so I can get my chassis tubing or laser cut parts from him for a friendly price. Wondering how you guys determine the geometry for the wheel placement on these builds?
 
Welcome Dcbruton. Fill out your profile so we know where you live and something about you.

The custom search engine is in the stickys. It will help you find many threads on building grinders.
There are plans with CAD files available online.

Most all grinders follow the same basic pattern - two tool arm sockets, 1.5" or 1.25" square tool arms, various flat platen and contact wheel setups, tool rests, etc. Being able to flip from vertical to horizontal is nice, but not an absolute necessity. Tracking is important, so build it rock solid and as precise as possible. Don't scrimp on metal thickness for the frame parts, as it will, affect rigidity of the whole machine.

Your 1150RPM motor will be fine. The VFD will be able to run it at 2300RPM and with a 7" drive wheel it will be plenty fast at 4200fps max speed. It is the slower speeds that most of us use anyway.
 
As Stacey said your motor will be just fine with a 7 inch drive wheel. I would recommend a direct drive setup as that is much easier to get the motor mounted square to your frame with a lot less pieces.

Build it as solid and square as possible. That plays into how well it will track and how hard you can push on it.

I like the bottom of the drive wheel to be the lowest point. Look through as many plans as you can find and study them close.
 
I have built a couple (3?) 2X72 grinders of the KMG clone type. Where I to build another here's a set of plans I'd use. I like aluminum as a build material and is about the least expensive. The thread does a good job of explaining. https://www.bladeforums.com/threads/free-2-x-72-belt-grinder-plans-2020-version.1705344

Here's an earlier thread with step by step build of an earlier version of same grinder. bjansen does a really good job with his plans and step by step WIP of the grinder.

2x72 Grinder Build - 2018

I spent some time putting together a grinder build along. I have built 9 grinders over the past 5 years and I have revised my plans a bit each time – I think I now have what I think is a very good 2x72 grinder. I put together this build along so that others who may want a nice grinder could...
www.bladeforums.com www.bladeforums.com

Good luck and have fun.
 
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I built a 2x72 and used it for a couple years before buying a Reeder.

Definitely go for a direct drive. I used heavy walled steel tubing to do my build, because I was able to get it for free.
I welded it together, and despite my horrible welding skills and my crappy welder I was able to get things fairly square.
My biggest problem was with the difference between the interior size of the pipe and the standard size 1.5 inch aluminum I used for the tool arms.
It added quite a bit of slop into the system and made it hard to get the tracking repeatable. I was able to figure it out eventually, but eliminating that variable would have made it a lot better.

As they say, if you can't make it accurate, make it adjustable!
 
I tried running a 6-pole (1150 rpm) motor on a VFD. They do not work. According to KBAC VFD's are not designed to run 6 pole motors. It had speed, but no torque. Even a slight amount of pressure and the motor stalled. I recommend a 1750 RPM 4-pole motor.
 
J. Hoffman said:
I tried running a 6-pole (1150 rpm) motor on a VFD. They do not work. According to KBAC VFD's are not designed to run 6 pole motors. It had speed, but no torque. Even a slight amount of pressure and the motor stalled. I recommend a 1750 RPM 4-pole motor.
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This is interesting because a 6 pole motor should have more torque than a 4 pole motor. I wonder if the correct vfd was acquired if it would work ok??
 
J. Hoffman said:
I tried running a 6-pole (1150 rpm) motor on a VFD. They do not work. According to KBAC VFD's are not designed to run 6 pole motors. It had speed, but no torque. Even a slight amount of pressure and the motor stalled. I recommend a 1750 RPM 4-pole motor.
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Bummer. I was starting to get excited reading all of the comments, until I got to this one. I thought it was a very odd rpm compared to all of the other motors I had seen
 
Not a problem. I might have a motor for you. Send me an email at spely@cox.net

Where in NC are you. You might be able to come up for a visit and get a bunch of stuff.
 
Mt. Gilead. Middle of nowhere. But an hour from everything. Haha. 60mi east of Charlotte. 60mi south of gboro
 
Contender Machine said:
This is interesting because a 6 pole motor should have more torque than a 4 pole motor. I wonder if the correct vfd was acquired if it would work ok??
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That is exactly what I figured. It ran ok if you had the setting at 60hz (1150rpm) but if you switched it to 120 Hz to get the 2300 rpm that was when it lost torque. I sold it to a guy that used it for a disc grinder because he wasn't going to run it over 1150 anyway.
 
Stacy E. Apelt - Bladesmith said:
Not a problem. I might have a motor for you. Send me an email at spely@cox.net

Where in NC are you. You might be able to come up for a visit and get a bunch of stuff.
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Clicked the email link and sent you an email. Got an error message in return saying “address not found.”

Dcbruton891@gmail.com is mine if you’d like to reach out to me there, if not, maybe we can figure out how to get in touch. My brothers family is in Gainesville, va area so maybe we could make it a family/knife making trip
 
J. Hoffman said:
That is exactly what I figured. It ran ok if you had the setting at 60hz (1150rpm) but if you switched it to 120 Hz to get the 2300 rpm that was when it lost torque. I sold it to a guy that used it for a disc grinder because he wasn't going to run it over 1150 anyway.
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Yeah that is very interesting and good to know! You would need a rather large drive pulley if you were limited to 1150 rpm
 
Back to the shopping for a motor since the 6 pole is a no go. What are the pros/cons to 1750 vs 3450 rpm? Seems like most recommendations are for 1750 but I see a lot of YouTube builds with 3450

Also if I land on 1.5hp instead of 2. Will that be a noticeable difference?
 
House Handmade has plans for a really nice grinder that I've heard only good feedback on. If I were building one myself I'd go that route.
 
Michael Black said:
House Handmade has plans for a really nice grinder that I've heard only good feedback on. If I were building one myself I'd go that route.
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I’ve watched a lot of videos on his revolution. Want to try to take that basic idea and simplify it a bit, in a perfect world. And if I end up with a motor that isn’t 56c frame, I’ll prolly just attach it to floor and make it to where it just doesn’t rotate, like his does.
 
The 1750 rpm motor will have more torque than the 3450. Most people get along fine with a 1750 rpm motor with a 6 inch drive wheel because most people don’t grind that fast. With a 1750 rpm motor with a vfd you can always double speed it. I have my grinder setup that way and run it around 2000 rpm a lot.

You can get a lot done with 1.5 hp but having more is better of course.
 
I just read through the posts here real quick but what sticks out in your first post is that the arbor on the motor you have is 1 1/8".

Most drive wheels that you can buy for belt grinders are intended for motors with a 5/8" arbor. Yours is almost double the that.

Where do you plan on getting your 7" drive wheel that has a 1 1/8" arbor hole? Do you plan on taking a drive wheel with a 5/8" arbor hole and machining it out on a lathe to 1.25", and with a keyway?

And is your motor 56C face?
 
oceanrider said:
I just read through the posts here real quick but what sticks out in your first post is that the arbor on the motor you have is 1 1/8".

Most drive wheels that you can buy for belt grinders are intended for motors with a 5/8" arbor. Yours is almost double the that.

Where do you plan on getting your 7" drive wheel that has a 1 1/8" arbor hole? Do you plan on taking a drive wheel with a 5/8" arbor hole and machining it out on a lathe to 1.25", and with a keyway?

And is your motor 56C face?
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Motor is not a 56c face. But I was planning on mounting it to base of machine instead of face mounting it. I’ve found some 7” 1 1/8” shaft drive wheels on eBay. But it has also been pointed out that, that motor is a 6 pole and will not work with a vfd. So I’m in search of plan B motor as we speak.
 
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