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IndustryArena Forum > WoodWorking Machines > Uncategorised WoodWorking Machines > Surface finish problems on pocket floors
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  1. #1
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    May 2018
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    Question Surface finish problems on pocket floors

    My parts involve making lots of small pockets, mostly all in hardwoods. I'm having difficulty getting a good finish on the bottoms--there are usually slight rows from the parallel finishing pass that don't appear to be bumps or cusps. (photo attached).

    CAM process:

    1. Rough the pocket with 0.03 stock left axially and radially.
    2. make parallel finishing passes with a .25 bullnose end mill (R=0.0615) with a step over of anywhere from .11 to 0.06 (makes no difference). 80IPM, ~14000 RPM.
    3. Contour inside with same .25 bullnose mill as above in two passes.

    Results:

    Pronounced "corn rows" that run in the same direction of the grain. Basically it looks like stripes of high-sheen area where a clean cut was made next to stripes that look dull, as if sanded. The final profile that finishes the walls and cuts to the same depth as the floor leaves a really nice, clean finish.

    Theories/Attempts

    I've used a flat .25 end mill to finish the bottom of the pocket and this doesn't leave the stripes--it leaves a uniformly dull finish, like what you'd see from sanding with 200 grit paper. Contrasts with the clean profile left by the bullnose. Zeroing the two tools exactly the same is also a challenge, sometimes there will be 0.001 or less that's visible.

    Tramming: I've trammed the machine using a 5" diameter tool to <0.001 about the y axis. I've had less success tramming about the x axis (the same axis as the wood grain) maybe 0.002 over that 5" span, but this error should go to nearly nothing when using a tool that's 1/20th the radius as the test tool.

    Scraping/sanding/planing inside the pockets isn't an option--besides being time consuming, they're often too small to work inside. The products are home goods where surface finish matters a lot.

  2. #2
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    Apr 2018
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    Re: Surface finish problems on pocket floors

    I can see two things happening here.

    You have programmed your tool to pocket it out in a zigzag pattern.

    On the "zig" the cutter will climb (down) cut, on the "zag" it will conventional (up) cut.

    In other words, in one direction the wood chip is starting in the uncut material , and on the return trip it's starting on the finished face.

    May I suggest not using parallel linear pocketing, but parallel spiral from the inside out, climb cutting, then the finish pass will skim the pocket walls and leave a beautiful finish

  3. #3
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    Mar 2008
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    548

    Re: Surface finish problems on pocket floors

    What CaistorAl said. Cut with grain climb cutting.

  4. #4
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    May 2018
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    Re: Surface finish problems on pocket floors

    Thanks for the suggestion. I've wondered if it has to do with alternating between climb and conventional, as if the cat gets its fur cut one way but then petted backwards by the mill on the next pass causing a rough texture.

    I chose to go with the parallel passes with the grain to disguise the finish as much as possible as spirals have always left faint spiral patterns on the surface. I will try doing spirals using an in-to-out climb pattern as you suggest--I may have been using conventional before.

    One other thing I haven't tried is parallel with-the-grain passes but programming it to only climb vs. both-ways finishing. Mostly wrote that off due to the added time.



    Quote Originally Posted by CaistorAl View Post
    I can see two things happening here.

    You have programmed your tool to pocket it out in a zigzag pattern.

    On the "zig" the cutter will climb (down) cut, on the "zag" it will conventional (up) cut.

    In other words, in one direction the wood chip is starting in the uncut material , and on the return trip it's starting on the finished face.

    May I suggest not using parallel linear pocketing, but parallel spiral from the inside out, climb cutting, then the finish pass will skim the pocket walls and leave a beautiful finish

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