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Thread: building a grinder station

  1. #1
    Join Date
    Nov 2009
    Location
    Bancroft area
    Posts
    233

    Default building a grinder station

    Hi:

    I am building a grinder stand with built in grinder. The reason I am building a grinder instead of just buying another 8 inch bench grinder is that I have pretty much all the bits and pieces in my copious pile of junk, I can have 2 output shafts spinning three stones (or felt wheels), and I can customize the output RPMs and thus surface FPMs. A secondary reason is that not just any old grinder has shafts long enough to take the Oneway balancing system. The incumbent doesnít. So I might have to buy a premium $$$ grinder instead of whatever is on sale for $70.

    grinder 010.jpg

    A photograph of what has ben done so far. The two shafts, and the motor are in their approximate positions so you can get an idea of the layout. The double ended mandrel will be set up in the usual position, with the third shaft ejecting through the left side at the back (as in photo). The motor will drive one mandrel, and the first mandrel will drive the second mandrel. I could in theory put two sheaves on the motor shaft and drive each mandrel directly from the motor, but then I lose considerable mechanical flexibility.

    A note on safety. All mandrels in the above proposed setup spin in the usual grinder direction and have right hand threads on the right side and left hand threads on the left ends. I see no difficulty shrouding the stones through the usual 270 or so degrees as done on bench grinders. A clear plastic cover will be installed across the stones to shield the operatorís eyes.

    This grinder will be the "fine" grinder for sharpening lathe tools and doing rough grinding of plane irons. I have another 8 inch 3600 RPM bench grinder up at the welding end of the shop for doing rough work. My plan is for the double ended mandrel to mount a 80x white Norton stone for plane irons in conjunction with the LV tool rest on one side, and the other side to mount a 80x blue Norton stone for lathe tools in conjunction with my old style Oneway wolverine tool rest system. The third output at the left back outside position I envision installing a 6 inch hard felt wheel and using it to hone irons and lathe tools. The whole unit is on wheels, so I will wheel it away from the wall to access the back of the unit to access the felt wheel.

    It is my understanding that a grinder for fine usage to sharpen turning tools and doing the rough grind on plane irons should optimally have a slower RPM than the standard bench grinder RPM of 3600 (or so). So with a separate motor and mandrels, I knew I could get a slower RPM, even if I start with a nominal 3600 RPM motor.

    As it turns out, I found a perfectly serviceable 1/4 HP 1750 RPM motor in said junk pile. So if I just install 2 inch diameter sheaves everywhere, my two shafts turn at 1750 RPM. My 8 inch stones on the double ended mandrel will provide about 2660 FPM, and my proposed 6 inch felt wheel on the single ended mandrel will provide 2750 FPM. Perhaps this is good to go with no further thought.

    All the sheave areas of the shafts with the exception of the motor are 5/8 inch. The motor is Ĺ inch and I have no sheave for it, so something must be purchased for it (presumably a 2 inch).

    In 5/8 bore sheaves, I have in stock, two 2 inch, a 2.5 inch, and a 4 inch. The mandrels need three sheaves in total, so with the proposed arrangement in the previous paragraph, I need to buy one more 5/8 bore 2 inch sheave.

    If I wanted to save myself $5 or it was useful, I could use the 2.5 inch sheave in three different ways:

    Mount it as the input sheave on the first mandrel and slow everything down to 1400 RPM with surface FPM of 2930 at 8 inches and 2200 at 6 inches.

    Mount it as the output sheave on the first mandrel to step up the RPM on the second shaft, leaving the first mandrel at 1750 RPM but spinning the second at 2190 RPM. This provides 4580 FPM at 8 inch diameter, or 3430 FPM at 6 inches on the second mandrel.

    Mount it as the input sheave on the second mandrel to step down the RPM on the second shaft to 1400 RPM, leaving the first mandrel at 1750 RPM. The resulting FPM on the second shaft at the two diameters will be 2930 (8) and 2200 (6).

    I donít think the 4 inch sheave gets me anything unless I want a second mandrel shaft RPM of either 875, or back up to 3500, what I started with on my other grinder. I donít think I want to spin the stones that slowly, but maybe the felt wheel should go fast. I know nothing of felt wheels and honing with same.

    I would enjoy comment from any interested parties, especially with respect to desired RPMs, but also issues of perhaps mandrel heights and positions.

    Regards,

    Boulter

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