Building a 2x72 Belt Grinder

ToolAA · Jan 15, 2019

A few weeks ago I used a 15% off coupon to buy a 2x72 belt grinder kit from Ebay. The kit was $425 after the coupon. Today I repurposed a 20yr old treadmill motor and variable speed drive. The hardest part was that I had to power up the motor to grind down the shaft to fit the drive pulley, then make a reverse threaded custom retaining nut.

I still have to finish making the work table and knife jig. By this weekend I should be able to finish the control panel, with some other salvaged parts and I plan on 3D printing a vacuum shroud to attach below the work table.

Should be grinding some new knives soon.

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FrankOceanXray · Jan 15, 2019

Wicked.

The great length allows the media to cool? Or why so big?

dontpanic · Jan 15, 2019

Super cool. A 2x72 belt grinder has been on my list for awhile now.

About 2 weeks ag I was looking for a used KBAC speed controller. I happened upon a speed controller, motor and grinder frame. Scratch and dent. $430. Now I just need a tool arm and tension/tracking arm.

This is what I got.

ToolAA · Jan 15, 2019

dontpanic said:
Super cool. A 2x72 belt grinder has been on my list for awhile now.

About 2 weeks ag I was looking for a used KBAC speed controller. I happened upon a speed controller, motor and grinder frame. Scratch and dent. $430. Now I just need a tool arm and tension/tracking arm.

This is what I got.

That’s a nice score, it should work great.

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ToolAA · Jan 15, 2019

FrankOceanXray said:
Wicked.

The great length allows the media to cool? Or why so big?

2x72 seems to be a sort of knife makers standard size. The longer belt simple removes material more evenly, and faster at a slower machine speed vs. a 1x36 sander. The larger platen also allows you to position the work in more angles.

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dontpanic · Jan 15, 2019

ToolAA said:
That’s a nice score, it should work great.

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I hope so. I'm looking forward to seeing your machine work. Until I scored this, I was going to do a build almost identical to yours.

Best of luck

dontpanic · Jan 15, 2019

FrankOceanXray said:
Wicked.

The great length allows the media to cool? Or why so big?

ToolAA said:
2x72 seems to be a sort of knife makers standard size. The longer belt simple removes material more evenly, and faster at a slower machine speed vs. a 1x36 sander. The larger platen also allows you to position the work in more angles.

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As ToolAA stated above and it also has a lot of surface area so belts do not become loaded as fast. (More surface area means they last longer). Also there are many options in belt grit , abrasive type and belt material in this size. And its popularity keeps the prices down

I'm moving up from a 1x42, I can bog it down with with little effort. I'll be going from a 1/3hp to a 2hp motor.

smdub · Jan 16, 2019

As has been stated, the long belt doesn't wear as fast (lasts longer) since there is 2x as much grinding material to start vs a 36" belt.

I have one I built. Did a direct drive using a 3600rpm JM(?) long shaft 3hp pump motor. That avoided the typical pulleys and pillowblock bearings. It's a metal removal beast. I'll dig up a video I took when I first got it running.

AA, if you need help making a nut or anything send me a msg.

ToolAA · Jan 16, 2019

smdub said:
As has been stated, the long belt doesn't wear as fast (lasts longer) since there is 2x as much gringing material to start vs a 36" belt.

I have one I built. Did a direct drive using a 3600rpm JM(?) long shaft 2hp pump motor. That avoided the typical pulleys and pillowblock bearings. It's a metal removal beast. I'll dig up a video I took when I first got it running.

AA, if you need help making a nut or anything send me a msg.

Thanks for the offer. I actually purchased a reverse thread Hex Coupling. Then threaded it to to the shaft. Then with the motor on, proceeded to grind it to shape using a file and various sand papers. It ended up being .620-.623 dia. I was quite proud of my poor-mans mini lathe.

smdub · Jan 16, 2019

Here is the video I took of it when I was first able to power on. Got the platten and wheels from Beaumont/KMG.

FrankOceanXray · Jan 16, 2019

ToolAA said:
Thanks for the offer. I actually purchased a reverse thread Hex Coupling. Then threaded it to to the shaft. Then with the motor on, proceeded to grind it to shape using a file and various sand papers. It ended up being .620-.623 dia. I was quite proud of my poor-mans mini lathe.

smdub said:
As has been stated, the long belt doesn't wear as fast (lasts longer) since there is 2x as much gringing material to start vs a 36" belt.

I have one I built. Did a direct drive using a 3600rpm JM(?) long shaft 2hp pump motor. That avoided the typical pulleys and pillowblock bearings. It's a metal removal beast. I'll dig up a video I took when I first got it running.

AA, if you need help making a nut or anything send me a msg.

I like you guys.

bigcountry · Jan 16, 2019

I have a 1HP baldor and pulley setup on my oregon blademaker. I am upgrading right now to a Kbac 27d VFD and Baldor 2HP. So if you ever need another motor setup, let me know.

bigcountry · Jan 16, 2019

FrankOceanXray said:
Wicked.

The great length allows the media to cool? Or why so big?

if you had a 1" X 30", belts wouldn't last long. Right now for me to make a knife, I go thru 4 belts, and for ceramic, thats $10 a piece. Longer the better.

I learned the hard way not to use worn belts to make a bevel. Kinda the same concept that a sharp knife is a safe knife. You have more control.

Bertfish · Jan 16, 2019

I cheated and just bought a Grzzily for dad for Christmas. With coupon on Ebay it was 525 before shipping.

smdub · Jan 16, 2019

Bertfish said:
I cheated and just bought a Grzzily for dad for Christmas. With coupon on Ebay it was 525 before shipping.

The major problem w/ the Grizzly is that its only 3600 sfm and can't be changed due to the single phase motor. Belt grinding metal really needs to get to 5000-8000 sfm. Wood needs to be much slower. But it works *WAY* better than no grinder at all and the price is good for new. :thumbsup:

A three wheel type grinder also allows you to independently change platten type, wheel diameter (for hollow grinds), and wheel cut pattern w/o changing the drive wheel (which needs to be domed for self tracking) or affecting belt speed. Two wheel grinders have compromises.

FWIW, Here is info from Norton: Page 13 gets into belt speeds. (1m/s = 197 sfpm) It has lots of other useful belt info too.
https://www.nortonabrasives.com/sga...Industrial_technical_data_health_safety_8.pdf

bigcountry · Jan 16, 2019

Yea, but 95% of knife makers will never graduate to hollow grinds and the rest. I have over $2000 invested in my grinder. I am lucky to have the opportunity to have the bells and whistles. But I can do 90% of my work on a grizzly. I have seen a bunch of knives screwed up on 3600 sfm with 50grit belts.

smdub said:
The major problem w/ the Grizzly is that its only 3600 sfm and can't be changed due to the single phase motor. Belt grinding metal really needs to get to 5000-8000 sfm. Wood needs to be much slower. But it works *WAY* better than no grinder at all and the price is good for new.

A three wheel type grinder also allows you to independently change platten type, wheel diameter (for hollow grinds), and wheel cut pattern w/o changing the drive wheel (which needs to be domed for self tracking) or affecting belt speed. Two wheel grinders have compromises.

FWIW, Here is info from Norton: Page 13 gets into belt speeds. (1m/s = 197 sfpm) It has lots of other useful belt info too.
https://www.nortonabrasives.com/sga...Industrial_technical_data_health_safety_8.pdf

smdub · Jan 16, 2019

Understood, but AA is building and not buying. I was pointing out the advantages of the 3-wheel he's building. I have $621 in the mechanicals (incl flat platten, $213 small wheel grinding attachment w/ 2 small wheels, + 1 large wheel) and $281 in the electronics. So I have a 3hp 3-wheel w/ several attachments (unnecessary for knives) for $902 (All in 2010 dollars.) It will save time, get finer finish, make belts last longer, and do other materials easier. As I said the Grizzly is a good machine for the money. You can do a lot with it. You can see where building one like AA can get a nicer machine for similar/less money.
FWIW, I don't make knifes. I sometimes lament the fact that my two biggest grinders are currently hidden behind a large machine in the garage.

They are huge time savers and I wouldn't want to be without one. For general metal working its one of those 'how did I go so long without it' type of tools.

ToolAA · Jan 16, 2019

smdub said:
Understood, but AA is building and not buying. I was pointing out the advantages of the 3-wheel he's building. I have $621 in the mechanicals (incl flat platten, $213 small wheel grinding attachment w/ 2 small wheels, + 1 large wheel) and $281 in the electronics. So I have a 3hp 3-wheel w/ several attachments (unnecessary for knives) for $902 (All in 2010 dollars.)

For now I’m about $540 in parts total considering the salvaged motor. However I do think I’m going to get a 10” rubber wheel eventually.

What do you use the grinding attachment with the 2 small wheels for? I’ve seem them on ebay.

Also my salvage project box is too small for the power supply so I had to put that part on hold tonight. I decided to design a dust collector which will attach to the bottom of the work platen and wrap around the bottom pulley. Hopefully it will capture most of the dust.

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smdub · Jan 16, 2019

Small wheel adapter was to fishmouth tubing for roll cages and bicycle frames. I have never actually used that adapter as my building more of those has been few/far between since I built the grinder.

You 3D printing that collector? I think anything plastic will be a serious fire hazard. See my video as to the sheer volume of sparks generated. It'll burn through non leather shoes if you aren't careful. W/ dust collection, also be careful mixing and aluminum and steel too. Thermite will build up in the system and can be set off by grinding sparks.

ToolAA · Jan 16, 2019

smdub said:
Small wheel adapter was to fishmouth tubing for roll cages and bicycle frames. I have never actually used that adapter as my building more of those has been few/far between since I built the grinder.

You 3D printing that collector? I think anything plastic will be a serious fire hazard. See my video as to the sheer volume of sparks generated. It'll burn through non leather shoes if you aren't careful. W/ dust collection, also be careful mixing and aluminum and steel too. Thermite will build up in the system and can be set off by grinding sparks.

I was planning on 3d printing it. However now it looks like I should just bend a cover out of sheet metal.

I have a small cyclone can before my actual shop vac but after your remarks I may need to rethink how I’m going to be able to catch some of the dust without creating a fire hazard.

Thanks for posting that warning!

Building a 2x72 Belt Grinder

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