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  1. #1
    Hi All,
    I just finished squaring and making parallel etc my machine (again) and went to surface my UHMW/HDPE spoilboard. Have a look at the photo. I only took off 0.5mm using an 8mm 3-flute carbide endmill. This plastic tends to come off as a layer rather than being cut, when you're taking off so little, however my problem is certain areas of the spoilboard are absolutely perfect. Can't feel any undulations. But other areas are weird. After taking off the hairy bits left over with a chisel, its better, but still not nearly as smooth as other areas.

    Any idea why this would be happening?

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Nealieboyee; 28-04-2019 at 10:45 PM.

  2. #2
    I'd guess it's as a result of the fog/steam in your workshop.
    You think that's too expensive? You're not a Model Engineer are you? :D

  3. #3
    Quote Originally Posted by magicniner View Post
    I'd guess it's as a result of the fog/steam in your workshop.
    No but definitely the glare from the floodlight. Apologies, it was the best I could do at the time.

  4. #4
    Carbide endmill on plastic screams problems unless you have a particularly sharp edge, try a high speed steel cutter with a very sharp edge.
    You think that's too expensive? You're not a Model Engineer are you? :D

  5. #5
    Quote Originally Posted by magicniner View Post
    Carbide endmill on plastic screams problems unless you have a particularly sharp edge, try a high speed steel cutter with a very sharp edge.
    Ahh so that's why it was pushing the plastic instead of cutting. Very thin cut too so that wouldn't help.
    I don't have any hss bits yet but I'll put a wooden board in top of the plastic and surface that with the carbide bit and see the results. Just trying to check everything is square and true.

    Thanks very much

  6. #6
    Could give a single flute cutter a try as well, plastic melts when it gets hot, the less chip re-cutting the better, although that counts when your cutting deeper into the material i.e pockets and stuff like that it could help here to,.

    Keep an eye on your chip loads as well, when they get to low you start to see rubbing rather than cutting.
    .Me

  7. #7
    Hi Neal - have you managed to skim this spoilboard before with better results?

  8. #8
    Quote Originally Posted by Voicecoil View Post
    Hi Neal - have you managed to skim this spoilboard before with better results?
    This was the first time with this spoilboard. Why do you ask?

    Something else is wrong though. I have a feeling my x axis rails are bowed. I need to adjust them tonight. The cut is perfect on the left but not in the middle. Better on the right. That tells me the spindle isn't moving in a straight line and is climbing towards the middle of the gantry.

  9. #9
    Because if you hadn't had a good skimming before I was going to suggest a very similar prognosis to the one you've just come up with! Though it might be more than a matter of the rails being bowed - obviously they're less stiff in the middle than at the edges, so the spindle can move about more.

  10. #10
    Personally I thought at first that the spindle wasn't quite perpendicular to the bed and needs minute adjustment. It looks to be spot on when going in what ever the directions are to the left and right of the pic (top to bottom of pic), whereas you can see tiny lines/ridges on the cuts that go from left to right of the pic (the problem areas).
    .Me

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