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scale probs

Discussion in 'SketchUcam Help' started by matt james, Nov 10, 2018.

  1. matt james

    matt james New Member

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    Ok, So been learning sketchucam and seems ok, especially on osx and inside sketchup, dream coming true, nice. But am having some troubles getting exact drawing to reality scaling. the skp jpeg shows a test piece with 2.5mm bars with 2.5mm spacing, when tool path generated as shown it does show exactly the tool offset, in this case the bit measures 2.2mm (checked with quality calipers)so a 1.1 path distance, all good. but when cut as shown in photo jpeg the bars are measuring 2.2mm and a 2.8 gap, and this varies as you can see by eye the bar on the outside edge is 1.7mm! Ive looked through all options , played with G61 and G91.1, but cant seem to see anything else relating to scale or offsetting.. So whadda ya reckon?
     

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  2. swarfer

    swarfer Moderator Staff Member

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    The gcode is always correct, I know because I use it myself.

    You need to first calibrate your machine and make sure there is no backlash, belts are tight etc.
    https://openbuilds.com/projectresources/howto-calibrate-your-cnc-machine-for-mach3-or-grbl.145/

    note that the rotation of the bit will make it push to one side if there is any flex in the machine. try a cut with the 'overhead gantry' box checked and one without it checked. if you have flex or backlash then the 2 cuts will be different.

    to mitigate flex, set smaller multipass depths and make sure your tool is sharp (but depth must be larger than 0.002").
     
  3. matt james

    matt james New Member

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    ok, calibrated machine, ive had it for 3 yrs, never calibrated it! but came out spot on. so not there.
    tried overhead gantry, both same. not there.
    multipass is set to 1.5mm with 4 passes to make 6mm cut. 1000 feedrate.
    im cheating around problem by using 2mm bit but declaring it as a 2.2.
    the other thing is for years ive been cutting on this machine using sketchup-cambam or meshcam, and never had this prob. i cut multicopter parts so precision is important.
    i am using mach3.
    Thanks Swarfer for your time
     
  4. swarfer

    swarfer Moderator Staff Member

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    Please post your sketchup file (please saveas Make2016 file version if you are using a newer sketchup, Ionly have 2016) and also your generated Gcode.
     

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