# Thoughts on the 2"x72" Belt Grinder



## randyjaco (Jan 16, 2021)

There are a lot of posts on 2x72" belt grinders on this forum. These grinders are extremely useful in the shop, and I find mine, the most used machine in my shop. Just about anything I cut ends up with a pass or two on mine. I have found additional unanticipated uses, such as turning down rubber cylinders, grinding lathe bits, and other things I used to do on my pedestal grinder.

 I am not trying to minimize the efforts of others, but it really doesn't require great design skills or big outlays of cash. You don't have to own a welder, but it helps to have access to one. If I were a professional knifemaker, I might opt for one of those high dollar units, but I am just a retired garage shop hacker and this serves all my needs at a minimal cost. 2x72 belts last a surprisingly long time as long as you don't poke through your belt. You learn quickly how to prevent that.

I was able to put this one together for @$200, a street find, and stuff from my scrap pile. My biggest expense was the 10" wheel that I bought off eBay for @$150. The street find was a treadmill with a 1.5hp DC motor and attendant electronics. I have minimal electrical skills, but there is a host of information on the Net to convert a scrap treadmill motor into a useful power source. Those motors run of 120vac power and you have variable speed capability. There is no need for 220 power, 3 phase motors, VFDs, multi-pully sheaves, etc. That brings the cost and complexity way down. So what I am trying to say is just about anyone with a small shop can build a 2x72 belt grinder. Just do a little research, go take a look at as many versions as you can (in person or on the net.) Just about anyone who has one loves to show his/hers off. Go visit a knifemaker or anyone who might have one. Then start collecting parts that might work. The biggie is the treadmill. I find that one shows up in my neighborhood about every 6 months. I now have a spare for future projects.   Other junked sports equipment can provide many of your structural parts. If you have a local scrap yard that will let you scavenge, you will have a gold mine for this and future projects. Craigslist, Freesale, 5miles, etc have free pick up categories that can provide additional opportunities. As you start accumulating parts, your design will change accordingly. Just be flexible, these machines can be pretty low tech.

I made the one pictured below within 3 weeks of finding the treadmill. Your design does not require heavy-duty structural components. Most of my components are thin wall tubing, pretty much tacked together. After 2-3 years of use, nothing has cracked or broken. The 1.5hp motor is adequate for the job. 2hp would be better, but the 1.5 was free.   The variable speed electronics does the job to get the belt speeds I need. Just do the proper calculations so you get close to the midrange of belt speed with the pulleys you use. The belt tracking mechanism, which I thought would be difficult, was pretty simple in the end. The DC motors are not sealed and there is potential for grit/etc. to get inside, but I found that a simple metal shield over the motor has so far solved that problem. Cheap electronic project boxes adequately protect the electrical components. I have had no cooling issues. As you can probably judge from the pictures, space is a problem in my shop, so compactness was crucial to my design. The dimensions of my grinder are 41"x19"x22". That could be reduced some.

So stop procrastinating, start gathering some materials, design and build one. If you run into difficulties, there are people on this forum and others that will help you solve your problems. That is why you joined, right? In the end, the project will be very gratifying, and you will wonder why you waited so long. Besides, isn't something like this the reason you bought all those tools in the first place?


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## Ed ke6bnl (Jan 16, 2021)

I made one with many parts laying around, I did choose to by the wheels rather than make them and I purchase 2 in. receiver hitch material without any weld seem in the length of the material. I went with a belt and pulley to the dimension I need for sfm. they can be changed. 1 HP motor and that could be upped. I have a couple of the tread mill motors and was curious how they are working out for you? I built this during the very first covid lockdown, I had been gathering the parts prior to this event. I also added a long handle with a steel cable to quickly remove tension to change the belts. I need to make a 10 in wheel like you did for mine.


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## randyjaco (Jan 16, 2021)

You look like you have a good start on your grinder. I have never had any problems with that DC motor. I wasn't so sure at first, but it has been seamless. Unless you are planning to cast that 10" wheel, it is probably cheaper to buy one than make one   I also prefer having the rubber tread on that wheel. Putting the rubber tread on the two flat platen wheels wasn't much fun. It took a couple of tries to get that right.


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## Tmate (Jan 23, 2021)

There must be an infinite number of ways to configure these things.


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## randyjaco (Jan 25, 2021)

Maybe not infinite, but there are definitely a lot. A knife maker friend of mine adapted one of his to a surface grinder. It seemed like a blasphemy to me, but he is very happy with the setup. He is able to grind down pieces of metal at rates like a shell end mill. A 30 grit belt will remove  very hard metal at amazing rates.


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## mf294-4 (Feb 20, 2021)

Why only 2” wide? Why 72” long? I am using a cheap delta wood sander with a 4x36 belt and I think it works good but would like to build a heavier duty one. Will not be using for knives. Use it for anything I can get up to it.


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## Tmate (Feb 20, 2021)

mf294-4 said:


> Why only 2” wide? Why 72” long? I am using a cheap delta wood sander with a 4x36 belt and I think it works good but would like to build a heavier duty one. Will not be using for knives. Use it for anything I can get up to it.



The rule of thumb for a belt grinder is one H.P. for every inch of belt width.  The 72" length gives the belt more time to cool per revolution, and only requires a 2 H.P. motor.  You can also use a large or small contact wheel and vary the size of the drive wheel to adjust your speed range.


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## Hawkeye (Feb 20, 2021)

When I built my 2" grinder, I was planning on a 72" belt, but the local outlet only had 48". I made the machine to take the 48", but planned it so I could add 72" later. I can change belts without tools in less than 30 seconds, 48" or 72". Very handy.

It runs on a treadmill motor, so I also have variable speeds - good to slow down to finish an edge without overheating. I also have a larger table I can bolt on for grinding knife blades with an angle jig.


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## Yester5 (Feb 21, 2021)

“Local outlet”? I buy my 2x72 belts in bulk on line. The choices are amazing. I’m all for supporting local business, but small USA vendors like Pop’s knife supply are awesome too 


Sent from my iPhone using Tapatalk Pro


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## Dabbler (Feb 21, 2021)

Tmate said:


> The 72" length gives the belt more time to cool per revolution


    Very good point, that allows you to push the belt sander harder



Tmate said:


> The rule of thumb for a belt grinder is one H.P. for every inch of belt width.


I hear this a lot.  it just isn't true.

It is useful to describe what you need to push the belt to its limits, where the motor bogging down and the belt tearing in half are approaching each other, but

The HP demand is based on how you use it.   The motor torque is of course related to the RPM of the motor (and thus the SFPM of the belt), the voltage of the motor, and the inefficiencies of the drive.  Variable speed DC drives need more horsepower to do the same work.

If I was using the machine as a hogger, then I would go 3HP (4 would be better) , 220V 3phase 1725 motor driving a 4" drum directly for 1700SFPM on a 3X79 belt.

I use my for shaping contouring deburring and finishing:   1HP 3/4 HP and 1/2 HP work well for me - all on 4X36 grinder/sanders - I don't need a 4HP machine to do the work. In fact the 2x72 I really want is a 1HP 3PH version.


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## Tmate (Feb 21, 2021)

Dabbler:

As you have  stated, a grinder's h.p. requirements depend on what you are going to use it for.  Evidently a lot of people think they need 1 h.p. per inch of belt, hence the "rule of thumb" we have all heard over the years.


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## Dabbler (Feb 21, 2021)

I had a complete brain fart!  all my sanders are 6X48.  sheesh I'm not firing on all cylinders!!!!  I couldn't imagine a 6HP sander for them!


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## tweinke (Feb 21, 2021)

My 2x72 is 1hp. probably cant hog like the big boys but it is absolutely adequate.


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## Hawkeye (Feb 21, 2021)

Yester5 said:


> “Local outlet”? I buy my 2x72 belts in bulk on line. The choices are amazing. I’m all for supporting local business, but small USA vendors like Pop’s knife supply are awesome too


The locals still don't carry 72". I got mine on-line too.

Local stores carry less and less stuff all the time. People buy on-line, so the stores stock less. The stores stock less, so people have to buy on-line. Vicious circle.


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## Tmate (Feb 22, 2021)

Local stores are booming like seven-elevens - slim inventory, more convenience.


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## hman (Feb 22, 2021)

Last night I learned something about the disadvantage of a 2x36" belt sander.  I was rounding over the corners of a piece of UHMW (or some kind of similar plastic) that I'd milled and bandsawed to rough shape.  The belt on my machine is vertical, with a ~5" drive wheel at the bottom and a ~3" return wheel at the top.  Being as short as it is, the belt was holding on to the staticky swarf long enough for it to fly off the upper wheel and right into my hair, face, shirt, etc.  

I'd be willing to bet that a 2x72" belt would do a better job of letting go of the swarf/dust/debris.


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