Building a 2x72 - what to look for in a motor? Edit: Done

GripnCOLDSTEEL

GripnCOLDSTEEL

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May 10, 2010
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Going to make a grinder out of scrap (mostly)

Ive been watching CL for a free treadmill for a while and nothing has come up. If I am going to buy one, I want to know what to look for.

Seems this is the cheapest way to get a motor and variable speed on a budget.

Any help would be appreciated.
 
Many tm motors are open framed, meaning there’s a high likely hood of failure due to grinding dust shorting them out.

I’d get a $100 Chinese vfd (also open framed, but easier to keep dust out of) and you could probably find a used 3 phase TEFC motor for $50 to $100 or just get an ironhorse brand for about $175-$200. You’ll was a 56 frame, c-face if building to mount directly to the grinder.
You’ll also need 220vac tonoiwer the vfd.
 
Some treadmills use TENV motors. Obviously better than a openframe design.
Also, alot of them are not reversible. Be sure it runs in the direction you want or is reversible.
 
There is a good reason you don't see treadmill grinders often … they are not all that good an idea.

If you build one, try and build it with the ability to change the motor out for a proper motor and VFD later on.

That said, I have seen pictures of grinders made out of 2X4's and a treadmill motor with skateboard wheels ... so as the old adage goes, necessity is the mother of invention.
 
My grinder is a 3.5hp treadmill motor from surplus center which are very reasonably priced. This is my first grinder. I've had no issues and it is very strong but I have filters to keep the dust out. My next build will be proper though. Consider this a learning exp.
 
I should mention that I have gone through two controllers though. I do plan on buying more motors for drill presses and my bandsaw. As a hobby on the cheap they're great but obviously not for professional use. If you can build a grinder you can swap motors later.
 
If you find the right skateboard wheels they work just fine. I like them MUCH better than a solid aluminum wheel. I started with solid metal wheels, and like the "give" of a poly wheel in the 70 to 80 duro hardness range. I found longboard wheels to be better suited for platen wheels. I use a 3" diameter X 2" wide wheel. They have been in use for over 5 yrs at least as a hobby maker.
 
Thx bros. Those surplus motors are pretty budget friendly. I may try the skateboard wheels as well.

Is there a "show your DIY 2x72" thread yet?
 
I think there theses a few but I used the plans from diy knife maker central as he has an awsome writeup. I ended up installing a pivoting tensioning arm though. I did do a detailed diy heat treating oven writeup. You'll be itching for one very soon.
 
Ken H> said:
Here is a good DIY thread on building a 2X72 grinder and it's a good result.
https://www.bladeforums.com/threads/2x72-grinder-build-2018.1577263/

The metal for the frame can be ordered total for <$200 I'm pretty sure.
Click to expand...

This is a great build. I built mine from tubing and the biggest problem is the seam inside the tube. You have to grind the seam and orientate the tube but you end up with slack between the tooling arms and frame so every time you switch arms you get a slightly different index and have to adjust the tracking. It's very slight but I think that a bolted design with flat plate would be much more accurate. Check out this video.
My grinder tilts but I love the way this grinder has the work rest isolated from the grinder frame but doesn't need adjustment when tilting. He does sell plans for this I think and you can see some of the problems he runs into building it. Welding will warp things if you're not careful.

Someone also recently posted a build that had a different clamping system. Essentially he cut a slot along the tooling arm receiver. He'd then had some tabs welded on with a threaded handle so the receiver pinched down on the arm. Seems like it would be way more solid.
https://www.bladeforums.com/threads...erful-2-x-72-sander-only-52-5-pounds.1631085/
 
If you're paying anywhere close to $75 you want to be sure it's a TEFC (Totally Enclosed Fan Cooled" motor so the metal dust can't get inside motor. An open frame motor will work a while, but is always subject to shorting out due to metal dust. Not sure what that "control box" is, unless it's the peckerhead on the motor for the wiring connections.

Short list, TEFC, 240 volt, 3 ph. Either 1800 or 3600 rpm will work just fine with VFD.

Remember, you can always purchase a brand newTEFC 3 ph, 2 hp 3600 rpm motor for $160 price range shipped.
 
Those pics are not great and there's really not much info provided. That motor control looks like it may just be a contactor or something, vs a VFD / speed control. I'm not sure what shaft size a 115T frame has, and a class B insulation is a little on the lighter side if you're gonna run on an inverter (VFD). It may be fine if you're not running the machine hard, but a class F insulation is usually preferred for inverter duty motors.

There's not much way of telling what condition the motor is in just from the pics, but it looks pretty well used. For $75, I'd probably keep looking, but that's me.
 
Understood, thanks for the replies. After looking at it, seems the box is just basically an on/off button.

What would you guys recommend new on the motor and VFD? (on the "cheap")
 
IronHorse motors are a good value for the money. You can get a 2HP for $158 to $214, depending on RPM. The 3600 is cheaper, but I prefer the 1800, as you'll get a little better torque on lower speeds.

For VFDs, eBay is full of the china made units.

Something like this would likely work, and it's less than $70. I have a huanyang that I've been running machines on for years without issues. They're normally about $100 to $130, but whether they're better than the one linked, I have no idea.
 
Drew, you forgot the link to the ebay VFD.

Correct, the 1800 rpm motor will have more torque at.... say 600 rpm than will the 3600 rpm motor turning 600 rpm. BUT, since you're only using a fraction of the torque available even with a 3600 rpm motor at 600 rpm it's sort of a moot point. I've always used 3600 rpm motors on both my 2X72 grinders because they have less weight and cost less.... Well, I do have an 1800 rpm motor on the disk grinder. Even running at 60% power (2500 rpm?) I've not been able to choke one down.
 
Ken H> said:
Drew, you forgot the link to the ebay VFD.

Correct, the 1800 rpm motor will have more torque at.... say 600 rpm than will the 3600 rpm motor turning 600 rpm. BUT, since you're only using a fraction of the torque available even with a 3600 rpm motor at 600 rpm it's sort of a moot point. I've always used 3600 rpm motors on both my 2X72 grinders because they have less weight and cost less.... Well, I do have an 1800 rpm motor on the disk grinder. Even running at 60% power (2500 rpm?) I've not been able to choke one down.
Click to expand...

Click the word "this". I used a hyper link. ;)

I also hyper linked the word IronHorse.
 
Darn Drew - you're right. I was on my house computer with a really crappy LCD monitor and the blue of the "here" didn't show to indicate a link (nor did the Iron Horse). On this computer it shows nicely. You're right, I do think IronHorse motors are about the best buy around, next to the cheap Chinese VFDs
 
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