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Thread: Homebuilt Belt Grinder Questions.

  1. #1
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    Homebuilt Belt Grinder Questions.

    I am in the process of making a home made belt grinder. This will be used initially so that my venture company can do some knife making. I have a few question for you guys. Firstly how large of a diameter of shaft is needed for the pulleys. Secondly I am thinking of making all three of the flat pulleys with plywood, either key waying or set screwing the drive pulley to the drive shaft. The drive pulley will be supported by two bearings, though I'm not sure what kind, one on each side. For the idler pulley and work pulley I am thinking of just turning the pulleys on the shaft without any bearings. My rational for this is that it is cheap, and i don't plan on using the grinder for a lot of work, and making a new set of pulleys takes less than half an hour to make on the table saw/ disk sander. Do you guys see any problems with this, specifically safety issues as there will be other people other than me using the machine.

    Mitch

  2. #2
    Administrator Site Admin Anon's Avatar
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    Safety issues: For any machine that employees will be using, you have to have a guard on it so people can't stick their fingers into the wrong parts.

    Plywood pulleys might work, depending on the strength of your plywood, torque requirement, and what speed they spin at (if they spin at high speed, they could present a danger of flying apart catastrophically). My concern would be that the wood would wear where it spins on the shaft (if you don't have any kind of bearing or bushing there) and make a sloppy fit that might cause the belt to fall off at speed, or even walk the pulley off the end of the shaft. Bearings are pretty cheap and pretty easy to come by, so I'm not sure what the motivation is for skipping them. If you don't have a lathe and think it'll be difficult to get concentric bearing bores in a plywood pulley (not unlikely that you'll have difficulty holding any kind of tolerance with plywood) you can mount the pulley rigidly to the shaft and set the shaft up on a pair of pillow blocks.

    I'm not sure if conventional setscrews or keyways will be that compatible with plywood. Not knowing what size machine you're making, I'd be concerned about the plywood mushing up and allowing the attachment mechanism to slip. Of course, if you cast aluminum pulleys instead, they'll last forever--but another potential option is machinable plastic stock, which can do most of the things metal can (not with as much strength, obviously, but you can tap machine screw threads in it and stuff, which you really can't with wood) and is typically cheaper if you're buying stock.

    For shaft diameter: Big enough not to wobble at speed, and big enough to transmit all the torque you need to transmit. If you don't want to do the actual calculations, you can get a ballpark by looking at how commercial machines are made. Materials are generally cheaper than design effort for a one-off, so it's okay to over-build things a little.
    The process of turning stumbling blocks into stepping stones can at times require the use of a large sledgehammer.

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  3. #3
    I agree with Anon.
    plywood might work ok for a bit but if you are going to the effort of making a machine you are better over building rather than using something that you know will fail.
    If you go for a design without bearings then the wheel center is going to get hot quickly and fail quickly.

    Donk
    Needs must while the devil rides.

  4. #4
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    Have a look at this site if you have'nt already, plenty of info and ideas here.
    http://www.homemadetools.net

    I remember one horror story from my childhood, this fellow decided to build himself a grinder using a vw engine , anyway the wheel shattered , blew right through his chest and killed both his kids who were standing nearby watching. One of those things you never quite forget!
    Last edited by somyunguy; 01-14-2014 at 08:55 PM.
    Dazed and confused, too many projects!!

    Hamish.

  5. #5
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    Check out Grantham's Crowned Pulley thread. I've embedded the video he links to below. I think this grinder is at least as nice as any that you could buy.


  6. #6
    Senior Member Bob S's Avatar
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    Back a year ago this subject was brought up and here's what was said. Bob

    http://www.alloyavenue.com/vb/showth...t-sander-build
    I used to spend my time to save money but now I'm willing to spend my money to save time.

  7. #7
    I'm building a grinder using some ideas from Grantham's video but cut the crown on the tracking wheel a different way. The compound would cut a taper, but the tracking wheel needs to have a radius.
    I mounted the wheel with bearings installed on the mandrel. Then starting at the center with .125" feed increments I plunged to a depth calculated from the radius needed using the right triangle hypotenuse to create steps. Then the entire surface is blued and a file used to blend the steps together. Here the surface is partially blended. I cast the contact pulley but machined the drive pulley and adapted it to a treadmill variable speed motor.

    DSC00899.jpgDSC00896.jpgDSC00890 (1).jpgDSC00895.jpg
    If you think you can't do it, you're right!

  8. #8
    I am engaged in some knifemaking currently- and had the fortune to find an industrial grinder for sale in my area cheap with a VFD- but you can lurk on the "Blade Forum" to find a number of 2x72 grinder builds.

    Detailed plans can be found along the way- one that appeals to a number of folks and was on my shop list was the EERF ("Free" backwards) plans outlined on http://www.wilmontgrinders.com/Pages/EERFGrinder.aspx

    My bearings are skateboard bearings that I recessed into the Al wheel- reason is these wheels are exposed to grinding dusts and even the "sealed" ones will develop grit wear. The skateboard bearings are cheap and come in a 5 or 10 pack and are an easy replacement (7.00 for 5 skate bearings versus 2.80 each for Timken last time I shopped local- a long time ago...)

    Google the "No Weld" grinder as well.

    A word of caution- a lot of guys use aluminum 1.5 inch square stock for the tooling arms- and in some cases the total weight of the machine is a bit "Flimsy" under stress- I switched to mild-steel 1018 1.5 inch solid stock and the vibration dampening was WELL worth it. I use 10" wheels down to the 3/4 inch profile wheels.

    Just a few thoughts- hope it helps
    Discipline in any art is directly attributed to the disciple you are of that art's teachings, its collected body of knowledge... and your own ability to share it openly. -George Cloyed

  9. #9
    Quote Originally Posted by somyunguy View Post
    Have a look at this site if you have'nt already, plenty of info and ideas here.
    http://www.homemadetools.net
    Thanks for the link! We have a new ebook out: How to Make a Belt Sander. 100% free of course. Click the graphic below to check it out:


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