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Thread: Slippery problem with full circumference rotary lithopanes

  1. #11
    Join Date
    May 2011
    Location
    Mount Juliet, TN
    Posts
    111

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    0 Not allowed!
    Well you saved me some time. The thin rail I was going to use was a 3/32" oak lath which would have flexed like crazy compared to your 6mm/1/4" acrylic which apparently already flexed too much.

    I downloaded the .MPC files for your rotary jig Mark II but I see in some of the posts there is a Mark III. I did an extensive search and found some photos but never could find any .MPC files on that version. It looks radically different but that may be just the acrylic top. How much did the Mark II change to make the Mark III? If it is significant can you direct me to the mpc files? (assuming you posted them)

    I bought your UCB project plans and will be going to Lowe's to pick up the hardware today. I will probably make the ACB version since I have plenty of knobs and threaded rod on hand from other projects.

    Thanks.

  2. #12
    Join Date
    Nov 2008
    Location
    Vancouver Island
    Posts
    8,157

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    Well I have some interesting results.

    I used a 1/2" thick rail under the jig and got the same results. Tracking sensitive to head pressure. This seems to eliminate distortion of the rubber belts as the cause. I wondered if it might be simply all the pressure on the end of the belts which was the problem. To test this, I tried it with my own rotary jig which has a 3/4" wide drive rail and so causes the same pressure. (I usually use it on my sandpaper machine because of a different DC system on the rubber belt machine.) Tracking had no issues and did not depend on head pressure.

    I am left to conclude that the tracking problems must have to do with the timing belt. I think I may have an explanation. See what you guys think of this:

    The timing belt has teeth but the two rollers are smooth. When the belt gets pressed into the rollers, only the tops of the teeth are against the rollers. The gaps between the teeth have no support and these thinner parts of the belt can be pushed in and distort causing the belt to shorten. This distortion must cause stresses between the rubber belts and the timing belt as they roll. I do not know how exactly, but this causes the timing belt to lag behind. More head pressure, more lag.

    This would be easy to test. LHR could try using proper sprockets for the idlers instead of the smooth pulleys.

  3. #13
    Join Date
    Nov 2008
    Location
    Vancouver Island
    Posts
    8,157

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    0 Not allowed!
    Quote Originally Posted by 200k View Post
    I downloaded the .MPC files for your rotary jig Mark II but I see in some of the posts there is a Mark III. I did an extensive search and found some photos but never could find any .MPC files on that version. It looks radically different but that may be just the acrylic top. How much did the Mark II change to make the Mark III? If it is significant can you direct me to the mpc files? (assuming you posted them)
    I have not posted my rotary jig files here on the open forum. Being a beta tester with early, inside knowledge of the CW rotary jig, I did not think it would be ethical. After a year, however, I posted them on the senior members forum because some senior members wanted to experiment with it. I will send you the files if you PM me your email.

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