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I Got That Wood Grain Pattern Again..............

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  • I Got That Wood Grain Pattern Again..............

    A couple weeks ago I replied to a thread that someone started about tramming in the head of the mill. Someone mentioned that if your getting this Moire pattern it's an indication that the head is properly trammed in.
    Someone else mentioned that it's caused by an interrupted cut. I say it's caused by vibration, which can also be caused by an interrupted cut.
    However........ I was milling some soft cast iron the other day and noticed the patter again. I was only taking .0005 per pass, hardly enough DOC to cause enough vibration from an interrupted cut. I was using my 2" dia. shell mill with 3 dead sharp inserts.
    The part is 1 3/4" wide and I had the part centered under the shell mill. There is some slight vibration in the variable speed head of the mill and my guess is that is what causes the pattern. I should have played around with the RPM's to see if the paattern changes in design or goes away, next time I will.

    You know........ if I wanted to put this pattern on something I wouldn't be able to!!!!! Life sucks and then you die!!!

    JL......................



  • #2
    There's something in relation to the crescent - if you look it's where the pattern line starts and stops on the other side,,,
    it's actually quite beautiful - we'll take 4,000 of them by next tuesday....

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    • #3
      Spirograph!

      You can get patterns like that, down to the microscopic level, when waxing a car. They can be fine enough to form a diffraction grating, and then it really becomes noticeable. That's why they say to wax using straight strokes and not circular.

      So with that as an example, you can't expect a very light cut to eliminate the problem. I see similar effects when taking fine cuts on aluminum. In some ways it seems the finer cuts produce more diffraction.

      If you were uh, bored you could measure the distance between the grooves and try and relate it to your rpm, feedrate and number of cutter teeth.

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      • #4
        So does this effect mean your mill is trammed in correctly? I get this all the time on parts I make, even when using a fly cutter.
        Please advise.

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        • #5
          It looks to be a pattern in the cast?? If you look close you can see the cut going across the pattern?
          Just saying?

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          • #6
            That's really interesting. Like AK says, it's actually really beautiful. You need to come up with some kitchen gadget or coffee table knick knack that highlights that pattern!

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            • #7
              I get that often on a light finish cut.
              My theory is that with the head in perfect tram, the leading side of the cutter does all the material removal, and the trailing side scratches whatever has sprung back.
              Mike

              My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

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              • #8
                The irregular shape leads me to believe that maybe the work piece was rocking as it was being cut.

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                • #9
                  Originally posted by ranger302 View Post
                  So does this effect mean your mill is trammed in correctly? I get this all the time on parts I make, even when using a fly cutter.
                  Please advise.
                  I don't know if this effect means that your mill is trammed perfectly or not, I think it's more vibration related. I suppose I could knock the head slightly out of tram and see what happens!!!
                  The pattern isn't in the cast, what you see at the right hand edge of the part is the original mill marks. The part was slightly out of square and I needed to square it up.

                  JL.........................

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                  • #10
                    Here is the picture I posted a few weeks ago in the other thread. This is a piece of 6061 alum. 3/4" in width.
                    It has the same pattern, I was also using the same shell mill. So this proves it's not in the cast.

                    JL......................

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                    • #11
                      + one on it not being the cast. If you can do that down a knife blade you would have a seller.

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                      • #12
                        Joe lee, Bob S brought up something along the lines of what I gave thought to earlier,,, except im not thinking the piece was actually rocking but being held tighter on one end than the other - this would set up different frequency patterns which would in turn show in the work, for me im actually trying to figure out why the pattern is progressive from one side to the other...

                        the bigger picture of why any of it exist could be anything from a loose quill to a multitude of other reasons...

                        checking a vise for stable clamping is easy - just lightly put the piece in and see if both sides hold the same - if one side is drastically engaged whilst the other is loose you may have a tweaked vise, this can happen from someone putting something in on just one side then clamping down hard on it, can also be the corrective measure although you can break something in the process...
                        Last edited by A.K. Boomer; 05-23-2013, 04:25 PM.

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                        • #13
                          I think your pattern comes from vibration introduced by the interrupted cut. It would have been interesting to see what would happen with changes in rpm or feed rate, or a change of cutter. I'd bet that if the work piece were taller or shorter the pattern would be different.

                          I run into a similar effect frequently when I make hard maple rolling pins on a metal lathe. A difference in grain density will set up a vibration in the wood cylinder that then creates a texture pattern on the cut surface. Usually the pattern will be a series of closely spaced helices. Sometimes slowing down the rpm will stop it, other times it works better to run it faster. Sometimes the only cure is to put on leather gloves and put some hand pressure on the spinning workpiece to damp the vibration. I haven't yet tried a follow rest.

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                          • #14
                            Originally posted by JoeLee View Post
                            Here is the picture I posted a few weeks ago in the other thread. This is a piece of 6061 alum. 3/4" in width.
                            It has the same pattern, I was also using the same shell mill. So this proves it's not in the cast.

                            JL......................


                            I have to tell you when you figure it out you need to let us know, there are items that something like that would look really neat on and now you have me wondering what anodizing would look like on that aluminum...

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                            • #15
                              I'd sell it on ebay as Old-Growth Aluminum recovered from Lake Erie.

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