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Help with reverse engineering

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  • Help with reverse engineering

    I have purchased a saw blade to build a sawmill for lumber. It will be a swing blade sawmill. The blade has a 30mm center hole to center the blade on a hub. As a design feature nothing protrudes through the blade so that it is flush on the side opposite the shaft. The blade is fastened to the hub with 5 counter sunk bolts spaced at 72 degrees. The blade is also driven by 5 hardened pins spaced at 72 degrees and offset from the bolt holes by 36 degrees. The drive pins are on a larger radius than the bolts. Through careful measurement with a caliper I have determined a few of the holes are off by as much a .010 inch. I have turned a close fitting transfer punch to mark the drive pin holes on the hub while the blade is bolted to the hub. This is ok for this blade as I know I can make it fit. But what about the next blade I install. Without knowing manufacturing tolerances on the blades I am at somewhat of a loss and don't think the next blade will fit. I have a vertical mill and a rotary table so I can space my holes that way instead of using a transfer punch. Then I will have to undersize the pins by say .005 inch to account for blade varriation. The bolt holes are tapped into the hub at this time but they can be drilled out to a clearance hole and a nut used on the back side on the hub. How would you go about this blade to hub fit?

  • #2
    If the blade is a "consumable" item, and will be replaced on a regular basis, don't make an odd hole pattern to perfectly match the blade. Make the holes at exact 36 or 72 degree increments and use the most accurate pattern that you can achieve. Use undersize drive pins where you have to. There is nothing worse than making a drive hub to fit a "bastard" size, and then finding out it never matches anything again after the first blade is used up.
    Brian Rupnow


    • #3
      Get another blade, might be easier


      • #4
        I would leave the bolt holes alone if they are accurately placed and modify the saw blade to fit on accurately spaced drive pin holes. AFAIK saw blades for wood are very good material but aren't hardened (please correct me if I am mistaken) and if so I would bolt it to the hub and then create 5 new accurately placed holes for the drive pins simultaneously through both blade and hub offsetting them from the existing holes by a tad.
        Location: Saskatoon, Saskatchewan, Canada