Announcement

Collapse
No announcement yet.

Flat belts

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

  • #46
    Originally posted by Jonesy View Post
    Something like this..... with a quick tensioning method for the belt at the top and a sprung tensioner (off one of my scrapped cars) on the slack side of the motor belt.
    it's really advantageous to have a two speed 1st stage so you want a way to easily loosed both belts. If you put the pivot up at the top so the counter shaft moves at an arc more or less at an angle bisecting the lines between the drive stages, your tensioning device loosens both belts. Here's one I made for an underbench drive for a Schaublin 70 but the same principles apply. It has T slots to set each belt's position, then a toggle that loosens both

    in Toronto Ontario - where are you?

    Comment


    • #47
      That's very nice MG. I bit beyond my capabilities though.

      Comment


      • #48
        Thought I'd give an update...

        I FAILED.

        My home made flat belt pulleys were fine, but my home made flat belts were not up to the mark.

        Although they worked, and I was well pleased with the grip and power transfer, the joins were letting me down.

        No problem with strength. They are not coming apart. And they're flexible at the joint.... but maybe not quite flexible enough

        The issue seems to be related to the wire mesh reinforcement that runs between the 2 rubber layers.

        When the joint is flexed the mesh binds up and gives an audible click that can be felt with my fingers.

        Under tension, when coming off the pulley, so the belt is straightening, this click is quite severe and the jolt in the belt can be felt through the drive.

        It was most severe on the small motor pulley. I doubled its size and it was better, but still no way good enough.

        With the step pulley belt on the countershaft doing the exact same thing, it was horrible.

        So I accepted all your advise and bought a serpentine belt for the step pulley, and ran it on the flat side.

        I also re-cut the motor and main pulleys for a V belt.

        It's now as sweet as I could possibly have hoped for.


        Thanks again.





        Comment


        • #49
          That the belt's stretch is needed for the crown to function is completely true. If you examine the way the crown "steers" the belt, you see that it must stretch a bit for that to happen. A belt that does not stretch will not work well on a crowned pulley.

          But sanding belts do have a bit of stretch. Just not as much as one made of rubber, leather, or similar materials.

          A further illustration of this is my use of a serpentine belt on my lathe. The counter shaft of my lathe is mounted on the welded steel table and the previous owner did not do a very good job of aligning it with the lathe's pulley. So tracking, via the crowned pulleys is what keeps the belt running on them. I had corrected this alignment as best as I could but when I switched to the serpentine belt, which is a lot stiffer than the leather ones, I found that I had to increase the tension to have it track. In other words, I had to stretch the serpentine belt to have the steering mechanism of the crowned pulleys function properly. With the slight, remaining misalignment, at lower tensions the serpentine belt just jumps off the pulleys.



          Originally posted by J Tiers View Post
          That is the exact physical setup of the Logan, and most older Southbend. A V-flat combo for motor (like SB also) and a flat belt with both crowned, for the short belt to the spindle.

          Belt length should not be a factor... but belt type probably is. Sanding belts do not typically have much stretch, especially the ones on hand held belt sanders. Leather and rubber drive belts do. Crowning may work better with a belt that has some stretch.
          Paul A.
          SE Texas

          And if you look REAL close at an analog signal,
          You will find that it has discrete steps.

          Comment


          • #50
            This gets back to my previous comment about a belt needing some "give" in order for the crown to function. Obviously the designers of this sander had it working before it went into production. Or, at least, one would hope so. Since it is a Craftsman, that was probably with Sears/Craftsman brand sanding belts. But with so much being made in China, perhaps not.

            I do not know if you can still buy Sears/Craftsman sanding belts. If you can, perhaps try them. If not, then I would suggest trying some different brand belts to see if any of them will track better.


            Just thinking here, but in the case of belt sanders, in order for the tracking adjustment to work, it seems to me that the stationary roller (drive roller?) would be crowned in order to keep the belt running in the location where the adjustment has set it to track. And the adjustable roller would be straight so that it is pulling the belt to one side or the other. By having the crown on the one roller and none on the adjustable roller, it should be possible to steer the belt from side to side while retaining the steering mechanism of a crowned roller. Thinking about this a bit more, I would think that the crown would be very small so that the belt would also move from side to side on that, crowned roller as well as on the flat one. But a small crown would be needed in order to keep the belt from continue moving to the side and ultimately hitting the sander's housing or just jumping off completely. In addition to being very slight, this crown could be flat in the middle and only sloping down on the two ends, providing ever increasing centering action as the belt is moved toward one side or the other while it is still held perpendicular to the roller's axis by that central flat area. If this is so, then some tinkering would be needed to find the best shape for that powered roller and the results would be dependent upon the properties of the sanding belt used. Hence, my suggestion to try other brands of sanding belts. But I am just trying to work out how a belt sander works here and I could be completely wrong. Anyone else have any thoughts or contributions on this?



            Originally posted by MrWhoopee View Post

            I've been dealing with tracking problems on my Craftsman 6x48 combo sander. The tracking adjustment is crude and touchy. Once I do get it tracking properly, pressure on either side of the belt will cause the belt to creep (iirc towards the opposite side) and the belt will not come back to center without applying pressure to the opposite side or readjusting tracking. I've tried wrapping tape on the center of the upper roller to increase the crown, but it did not seem to help. I haven't looked at the drive roller to see if it is crowned. Suggestions welcomed.
            Paul A.
            SE Texas

            And if you look REAL close at an analog signal,
            You will find that it has discrete steps.

            Comment


            • #51
              That sounds exactly like the present set up on my SB-9 lathe. I did fail to mention that one of the reasons that I switched to the serpentine belt was that constant click, click, click the metal staple joint in the original leather belt made as it hit the pulleys. I hated that sound and even though I was advised that the metal staple did no harm to the pulleys, somewhere in the back of my mind I just did not completely believe that.

              Anyway, I am glad you are up and running now. Enjoy!



              Originally posted by Jonesy View Post
              Thought I'd give an update...

              I FAILED.

              My home made flat belt pulleys were fine, but my home made flat belts were not up to the mark.

              Although they worked, and I was well pleased with the grip and power transfer, the joins were letting me down.

              No problem with strength. They are not coming apart. And they're flexible at the joint.... but maybe not quite flexible enough

              The issue seems to be related to the wire mesh reinforcement that runs between the 2 rubber layers.

              When the joint is flexed the mesh binds up and gives an audible click that can be felt with my fingers.

              Under tension, when coming off the pulley, so the belt is straightening, this click is quite severe and the jolt in the belt can be felt through the drive.

              It was most severe on the small motor pulley. I doubled its size and it was better, but still no way good enough.

              With the step pulley belt on the countershaft doing the exact same thing, it was horrible.

              So I accepted all your advise and bought a serpentine belt for the step pulley, and ran it on the flat side.

              I also re-cut the motor and main pulleys for a V belt.

              It's now as sweet as I could possibly have hoped for.


              Thanks again.




              Paul A.
              SE Texas

              And if you look REAL close at an analog signal,
              You will find that it has discrete steps.

              Comment

              Working...
              X