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Will42805

Newby 2x72in. belt grinder

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Ok so i am posting this for suggestions, a little constructive criticism, and to avoid any costly mistakes. I purchased my grinder from thebeltgrinder. the grinder seemed to be built solid and easily adjustable and modifiable. I have 3 3hp 1700rpm 3 phase 240v motors i got that work was trashing due to a gearbox upgrade. I realize these are not the most idial for this application but they were free. I plan on running a 240 out to my garage. Once that is done i can use a vfd to power the motors. The motor will be mounted on the bottom deck and has a 32 tooth sprocket. The chain will come up through the table around a 15 tooth gear, 5/8 shaft with 2 saddle bearings. This will go to a 4in drive wheel. The saddle bearings will be raised up on blocks to afford the velt drive wheels some room. The gearing should about double the motor speed of 1700rpm to approx 3400rpm. There will also have a sheet of stainless or aluminum for both upper and lower table tops.

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Sounds like it should work well for you.  My first grinder was setup similarly, but with a little higher "gearing up" using a more conventional belt drive.  I'm not sure how the chain drive will hold up to those kind of rpm and how noisy it might be.  If at all possible I would recommend going direct drive with the system.  The grinders I've used, including my current one, that are direct drive are much quieter and have less sanding belt vibration.  Also, make sure that your motor is rated TEFC, at least, if not "washdown capable".

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I'm in the process of a build of the grinder on the DCknives. blogspot.  Since I have a 3450 (3600) rpm motor from an old air compressor that is what I'm using.  Had you considered running a 6 inch direct drive wheel to get your speed up around 2800 fpm?  Since you already have the bearing blocks and shaft, another option would be stepped pulleys like you find in a drill press to give yourself a variable speed grinder old school style.    I can see the appeal of using 3 ph as it allows the option of using a vfd in the future.  Im going to be wiring my motor for 220 single phase just to reduce the current draw.  I already have 220 in the garage where the grinder will reside. 

Please keep us in the loop.  Looks good.

 

 

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The motors i have are fully enclosed. I had not thought about vibration though, much less how fast that chain will be running. Time will tell. I would have preferred direct drive however i would have to buy a new motor. My budget is a bit tight. I liked this idia because i can gear it up or down as i wish. I had thought of getting a harbor freight 3600rpm compressor motor but they arent enclosed. Would just build a filtered vented enclosure for it and get the extra warranty. Lol

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If your motor is on the shelf down below, you could completely enclose the sides with furnace filters for maximum airflow. Just make sure you don't have anything flammable directly in the spark stream.

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If i switch to direct drive with a harbor freight motor it would go up top. Would enclose the motor on top with a filtered enclosure. I suppose it could be vented from the bottom too

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Well I'm not that familiar with the general rules of thumb for chain drives, so I've consulted my Mark's handbook.  Based on a "moderate shock" application (as you will be  turning it on and off regularly), 2 HP motor, 3620 RPM and the 15 tooth gear (smaller sprocket is critical one) they recommend a minimum ANSI #35 chain.  This has a 3/8" pitch (longitudinal space between rollers) and 3/16" roller width.

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Luckly that is the chain and sprocket size i have. Was worried it may be too small. The motor is 1700 rpm 3 hp. So hopefully that evens out

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You say you would have to buy a new motor to go direct drive, but haven't really explained why that is the case.  To me if you can find a way to use a 6 inch diameter direct drive wheel  there are a lot of potential headaches that disappear.  The only down side I can see is that at times you may want to run at lower rpm than will effectively cool the motor.

The first incarnation of my belt grinder had step pulleys, drive shaft, and pillow block bearings.   I have never regretted going to direct drive with a vfd.

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If i direct drive a 1700rpm 6in wheel i dont think ill have a very high fpm. Thats why i geared up the speed

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35 minutes ago, Will42805 said:

Luckly that is the chain and sprocket size i have. Was worried it may be too small. The motor is 1700 rpm 3 hp. So hopefully that evens out

Unfortunately for 3 HP it is off the charts I have for that kind of RPM, particularly with the 1.2 service factor modifier you get from Moderate shock (use 3.6 HP for evaluating).  Note that for heavy shock, which this may qualify for, the modifier is 1.4.  Personally I would be very leery of using this small a sprocket at this horsepower and RPM.  Per Marks the minimum recommended sprocket size is 18 teeth.

For reference: 1700 RPM and a 6" drive wheel works out to 2,670 FPM.  1700 RPM with an 8" wheel is 3,560 FPM.  I would go direct drive.

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If i direct drive a 1700rpm 6in wheel i dont think ill have a very high fpm. Thats why i geared up the speed

 

Ive noticed they have up to 8 in drive wheels on ebay. Perhapse that on the 1700 rpm motor would work

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Well, using a 6 inch diameter wheel you would have 1.5 times what you would have with a 4 inch diameter wheel.  With an 8 inch diameter wheel you could match the maximum fpm you would produce on a 3400 rpm motor with a 4 inch diameter wheel.  Since you have 3 hp motors I don't think you'll run into a power problem with the larger drive wheel(s).  For me it would boil down to which of the options is more expensive, time consuming, and difficult to try first.  I try to remind myself to try the easiest things first.  Regardless of which option you choose you can always modify it later if you aren't satisfied with the results.

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Thsts why i left myself room to play with the table. I think i am going to direct drive my 3hp motor behind the grinder. After i build the motor mount i just need to get a vfd. I think this option leaves less links in the chain to break so to speak...

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Let us know how it works out - good or bad.  You probably won't be the last person to be in a situation like this and it's always good to know the experience of someone who tried a similar setup.

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So if i put a 3hp 3400 rpm single phase motor and simply change drive wheel sizes to attain different speeds. It's certainly not as simple as turning down a dial but I would not get The loss of Power from using a rheostat.

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Honestly I think I'd rather use step pulleys and a belt rather than switching out drive wheels, but in theory what you're suggesting would work.  I still prefer a VFD and 3 phase motor with direct drive above either of those other options.  I use a cheap Chinese 2 hp motor and so far have not had any problems.

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Would anyone mind sending me a picture of a step pulley setup. I know what they are and I know basically how they work but I'm not entirely sure how you would hook up the tension system thanks

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Sorry I don't have any pictures from when I was set up that way.  However, I did not use a tension system per se.  The two identical step pulleys were mounted opposite each other so that the largest pulley diameter on one matched up with the smallest on the other.  That way the belt length required remained the same no matter which combination was used.  It was similar to the setup for changing speeds on some drill presses.

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5 hours ago, Buzzkill said:

Sorry I don't have any pictures from when I was set up that way.  However, I did not use a tension system per se.  The two identical step pulleys were mounted opposite each other so that the largest pulley diameter on one matched up with the smallest on the other.  That way the belt length required remained the same no matter which combination was used.  It was similar to the setup for changing speeds on some drill presses.

So you simply stretched the belt around to change speeds

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Image result for drill press step pulley

like this, from a drill press. You can move the belt to change the ratios and thus the final drive speed.

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Back when I used step pulleys I mounted the motor on a piece of plywood and then mounted the plywood to the base with a hinge.  The weight of the motor supplied the tension.

When you get a VFD you will be surprised how much quieter and smoother the grinder runs.

Let me know if I can help you. 

Wayne

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