Announcement

Collapse
No announcement yet.

Crowning sheaves

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Crowning sheaves

    I have volentered to make two flat sheaves of 4in. diameter. One to be 6in. wide and one 10in. wide. They are to run a 6in. wide sanding belt. I believe a crown is necessary to keep the belt on track. I looked in the mach. handbook but could find nothing. If anyone remembers a good " rule of thumb " in this regard I will appreciate seeing it.

    Thanks in advance.

    Jim
    Jim

  • #2
    I don't think you need a crown on one that size if running two wheels. On a 2x72 square wheel (3wheel) grinder the idler pulley is ever so slightly crowned and it's the tracking adjustment. I can tell you that too much crown makes it overly sensitive when adjusting. If I really wanted to find out I'd make the wheel flat and then build it up a little with electrical tape in the middle and see how it acted.

    On my 4x48 neither of the belts are crowned but one end has the tracking adjustment.

    Sounds like a macho grinder you're working on
    Last edited by Your Old Dog; 01-17-2009, 05:12 AM.
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

    It is true, there is nothing free about freedom, don't be so quick to give it away.

    Comment


    • #3
      The book recomends 1/16" on diameter per foot of face. That works out to 0.148 degrees from centerline to one side, or 0.296 degrees included angle
      Last edited by brian Rupnow; 01-17-2009, 08:44 AM.
      Brian Rupnow

      Comment


      • #4
        Sheaves

        Bringing in the Sheaves:
        http://au.youtube.com/watch?v=rPQsQI...eature=related

        Comment


        • #5
          YOD, I just finished my 2X72 grinder and made it to plan guidelines. It called for 2* crown from centerline both ways and that SOB is way too sensitive for tracking. I am going to remove some crown using Brian's posted formula and try again. I was wondering why it was so hard to track that thing.
          Thank you guys.

          Patrick

          Comment


          • #6
            Only the driven sheave needs a crown. If you crown both they tend to "argue", making centering unstable. Better to have less crown than too much - that causes instability too.

            The axes need to be well aligned since the crown only provides fine guidance.

            John

            Edit: http://www.visusa.com/belt_tracking01.htm
            Last edited by GadgetBuilder; 01-17-2009, 09:39 AM.
            Location: Newtown, CT USA

            Comment


            • #7
              Originally posted by GadgetBuilder
              Only the driven sheave needs a crown. If you crown both they tend to "argue", making centering unstable. Better to have less crown than too much - that causes instability too.

              The axes need to be well aligned since the crown only provides fine guidance.

              John

              Edit: http://www.visusa.com/belt_tracking01.htm
              According to the link, my tracking wheel is totally wrong cause it's an apex crown. Damnit. Take it apart and stick it back in the lathe.

              Comment


              • #8
                Originally posted by Your Old Dog
                ...
                On a 2x72 square wheel (3wheel) grinder the idler pulley is ever so slightly crowned ...
                Doesn't that square wheel make for a sort of bumpy grinder?
                Lynn (Huntsville, AL)

                Comment


                • #9
                  Never heard of "knocking the corners off" ??
                  You might not like what I say,but that doesn't mean I'm wrong.

                  Comment


                  • #10
                    Wheel crown

                    I was involved for several years in design of large bandsaws and maintenance equipment.

                    Most important is that the wheels not be low in the center of the tire.

                    Second is that you need to be careful that the structure not deflect when belt tension is appied. The belt, band or in this case sanding belt will tend to center up on the tight spot and if the frame deflects, will run off the wheels.

                    In setting this up, use the crown on the driving wheel and keep the rest of the wheels VERY slightly crowned.

                    Comment


                    • #11
                      I neglected to say what this is going to be used for. I am doing this for the local First Robotics competition group. High school kids. In my opinion it is a fine opertunity for the boys and girls.
                      The belt is part of the "play-ball " handling mechanism.

                      The 1/16th on dia. is what I have so far. The second sheave is being glued as I type this.

                      Some tape wound on might help to determine if more or less crown is needed.

                      Thanks all

                      Jim
                      Jim

                      Comment


                      • #12
                        I've heard that the R.O.T. is 1/8" per foot. Have used 1 degree on the compound and the pulleys have worked out well.

                        Comment


                        • #13
                          Shop wisdom

                          Thanks jdunmyer.

                          That's the "rule of thumb" that I've used - and was told to use over 55 years ago!! I could not find or confirm it in "Google" or else-where - still can't.

                          It seems to be a traditional "word of mouth" hand-me-down "shop/job wisdom" thing that just "works" - which it certainly seems to do.

                          I think it was a curve/crown with a rise of 1/8" per foot and a chord equal to the pulley/sheave width. I have done them with tapers instead of curves/arcs and they seemed to work OK but my "gut feeling" is to use the curve.

                          Comment


                          • #14
                            This seems like a good thing for Human Numerical Control. A graphing calculator or spreadsheet = easy, can use parabolic or what ever.

                            Comment


                            • #15
                              Originally posted by jdunmyer
                              I've heard that the R.O.T. is 1/8" per foot. Have used 1 degree on the compound and the pulleys have worked out well.
                              To state the obvious, that gives you a linear taper/crown. I was told that linear crowning (with a flat spot in the center) was recommended over a radius, but according to the article GadgetBuilder posted, the big-boys use a radius crown on most pulleys, and save the linear crown for wide, thin pulley like a conveyor pulley.

                              Lane once posted a cool picture of a radius jig that was a long bar on a pivot.
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                              Comment

                              Working...
                              X