how tight should the flange be?
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  1. #1
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    Default how tight should the flange be?

    200 mm AO grinding wheels, 10 and 16mm thick
    60 mm center hole
    Clamping surface under the blotter is an annulus ID 80mm OD 100mm
    Flange clamped with 3 standard M6 cylindrical screws

    My question: what is the correct torque for the screws? I'm tired of "tight enough" and want a repeatable process. That's what my torque wrench is for.

    In principle a good designer would size/rate the screws appropriately. These are grade 8.8 M6 SHCS, normal tightening torque is 8 Nm = 6 ft-lbs, which generates about 2200 N of force. Since there are three screws, this would provide 6600N of force compressing the flange. That force is spread over an annulus of area 2,800 square mm. So the pressure compressing the grinding wheel would be about 2.3N per square mm. For comparison the compressive strength of glass is about 1000N per square mm.

    Is the answer just "look up the normal tightening torque for the flange screws"?

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    You did already look up the normal tightening torque
    What do you want more ?
    I do not own a torque wrench even
    Allen wrenches have a certain lenght to it (the short ones) that comes with the torque needed and the force a man can pull in normal conditions
    So keep that in mind when using a long one
    I know there is a big uncertainty in this but it does not matter that much otherwise you would only have torque wrenches in the toolbox
    (With a name like yours you should know all about allen wrenches)

    Peter

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    Quote Originally Posted by Peter from Holland View Post
    You did already look up the normal tightening torque. What do you want more ?
    I'm not sure if that's the correct torque for clamping the wheels. Am curious if others here can say for sure.

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    If it works, it works...?

    Is something happening different now?

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    Bruce, manufacturers of grinding wheels write on this topic: "always tighten with torque wrench".

    3M shows a table with tightening torques for their wheels (german; I didn't found the english page):
    Sicherheit beim Schleifen | Der Schleifprofi

    Cheers,
    Karl

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    Quote Originally Posted by CharlyDE View Post
    3M shows a table with tightening torques for their wheels.
    I'm happy to see that, but it doesn't go down to wheels as small as 200mm. Curious that the recommended torque does not depend on the screw size or thread pitch, since those set the clamping force.

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    Hi,

    for further tigthening torques see
    table 9-10 (Minimum dimensions for straight relieved flanges (machined))
    or
    table 9-13 (Dimensions for sleeve flanges (ISO type)):
    Grinding Wheel Use & Precautions Safe Handling and Preventing Accidents | Customer Support | KURE GRINDING WHEEL offers a wide range of grinding wheels and related products and materials

    The first table has values for grinding wheels around 200 mm diameter. It's easy to calculate the pressure compressing the grinding wheel to compare it the the values in the second table and recalculate the needed torques for your flange.

    Norton shows some general information, but hints to some standards and to ask manufacturers:
    https://www.nortonabrasives.com/sga-...quirements.pdf

    Cheers,
    Karl

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    Building crankshaft multi wheel arbors we would go around like the Norton advice but would tighten less and then go around again to spec. seems like it was 22 first round and 26 0r 28 ft lbs the second go around. Likely the arbor or machine manufacturer recommended numbers.
    Agree it makes sense to torque spec wheel mounts. Mostly I used a standard T Allen wrench and just tightened by feel making light tight/heavy and the go back around and make then very tight by hand for surface grinder wheel mounts...
    Nowadays with worry about one’s wrist the torque wrench is the better choice.

    The second go around is because the blotter gets crushed and so the second round makes the bolts more even. IMHO

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    Quote Originally Posted by CharlyDE View Post
    For further tigthening torques see table 9-10 (Minimum dimensions for straight relieved flanges (machined)) or table 9-13 (Dimensions for sleeve flanges (ISO type)):
    I'm not sure which table to refer to. Table 9-10 would give about 20 Nm of torque. Table 9-13 would give either 30 or 50 kg-cm, which is either 3 or 5 Nm. Do you think Table 9-10 is for flanges which are secured to a shaft with a single central nut, and 9-13 is for wheels that are attached to a removable hub?

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    The standard wrench for a single center nut is about 6 1/2- 7 inches long.
    Holding the wheel with one hand and the torque wrench at that length with your other hand see how much torque you can make.

    I would do that, tighten with a hand on thr wrench and one on the wheel as tight as I could do, and then with the wrench end on a block and two hands on the wheel make it just a little tighter. That was just enough to not have any wheel slip with a heavy grind.
    Yes, this was to the single spindle nut that was ½-13 and to the wheel mount single nut 1 ¼ -16.

    For the multi screw mounts I guess i would go to the mid or mid high range. Not to the highest like you are torquing down an engine head where you actually strech the bolts.

    Ot:

    My dad as an elevator mechanic had standard length wrenches for normal tightening, and long wrenches for torque tightening and loosening.

    It seems wrench length used to monitor how tight hand tightening would be.
    Pulling loose you might know how hard to pull the long wrench with not breaking the screw. Not coming you would think about it before something broke.

    I knew some old times who would put a little abrasive grit on thw mount to be sure the wheel would not turn..With my Two hands a little bit tighter I neve worry about too tight or not tight enough.


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