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how to finish cutting edges?

Discussion in 'CNC Mills/Routers' started by mlowka, Nov 8, 2019 at 1:09 PM.

  1. mlowka

    mlowka New
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    Hi there!
    I’ve got a problem with the finishing of the carved edges in the mdf board- there’s always a visible rough stripe after the first pass. It doesn’t matter if the board is 10mm or 18mm thick. The rest of the passes is smooth and the problem doesn’t occur while cutting in plywood.

    Any ideas how to fix it? IMG_1984.jpeg
     
  2. Giarc

    Giarc Master
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    Do you do a roughing pass and leave stock for a full depth finishing path? That should clean it up. I usually leave about 0.20 mm (or a little more) for a finishing pass.
     
  3. mlowka

    mlowka New
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    unfortunatelly no. I'm using openbuilds cam or easel and not sure if I can do it there.
     
  4. Alex Chambers

    Alex Chambers Master
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    I don't know either of those two programmes, but if you lie about the size of the bit (tell your software it's 0.2mm bigger than it is), you will be able to create a second tool path with an accurate tool diameter for the finishing cut. Tip - measure the bit - they are rarely truly the diameter they claim to be.
    Alex.
     
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  5. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Valid tip that works with all (even the free) CAM softwares! All it does is move the offset a little further away
     
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  6. mlowka

    mlowka New
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    Great! Thank you! I've tried to lie about the size of the bit but figured it needs to be smaller :) I'll try with the bigger diameter :)
     
  7. jeffmorris

    jeffmorris Well-Known
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    In VCarve Pro, there is "Allowance Offset" in "Machine Vectors" in "2D Profile Toolpath". What is "Allowance Offset" for?
     
  8. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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  9. mlowka

    mlowka New
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    I've just tried it and it works only with the outside edge (cleans the offset) not the element which I wanted. I cut letters so I use path outside for the external cuts and path inside for the holes- your solution works here:)

    how can I adjust it to the path outside cuts o it clean the edge of the letter not the offset? I've tried to lie with smaller and bigger bit size and neither of them seems to work.
     
  10. Alex Chambers

    Alex Chambers Master
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    Not sure what you are doing in cam - as I said I don't use either of those bits of software - but your g-code created by your cam should define the path the centre of the bit travels, so if you tell your software the bit is (say) 0.2mm (radius) bigger than it really is that path will be 0.2 mm further from the finished workpiece than you want. Then define the toolpath again telling your software the real size of the bit and the resulting toolpath should be 0.2mm closer to the workpiece.
    Alex.
     
    #10 Alex Chambers, Nov 9, 2019 at 1:39 PM
    Last edited: Nov 9, 2019 at 2:52 PM
  11. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    0.2mm is really tiny (and remember 0.2mm diameter = 0.1mm offset difference as machine paths are offset by the radius of the bit) maybe you arent seeing the effect (I cannot see 0.1mm in wood grain) . Do some training cuts with an exaggerated offset like +1mm (+2mm on the diameter) and see it really does it. Its always Bigger (lying that its bigger) inside and outside cuts, same applied
     

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