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CAD dimensional hole changes for printed parts

Discussion in 'Software' started by WADZOQUADZ, Mar 29, 2016.

  1. WADZOQUADZ

    WADZOQUADZ Member

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    Iv been doing a lot of Cad designs in Solidworks for printing and have been trying to get the hole dimensions to exactly what they need to be . When 3d printing holes are always undersized from the actual Cad dimension so you must compensate by making the holes larger so they come out the right diameter .

    I have been just oversizing all holes by .2mm and it works but its not perfect .

    I am trying to get the tolerences as good as possible and found some equations that work pretty well. Some times this equation gives me slightly oversized holes.

    "Two formulas have been identified for modifying the dimensions of hole diameters. To use these formulas, the x value is your desired diameter (for example 4 mm) and the y value is the adjusted diameter for your CAD model (in this case 4.34 mm). Use the vertical hole formula if the axis of the hole is parallel with the Z axis of the build plate and the horizontal hole formula if the axis of the hole is parallel with the X or Y axes. Both of these formulas are in millimeters."

    If your part requires dimensionally accurate holes, use these equations.

    • y = 1.0155x + 0.2795 vertical
    • y = 0.9927x + 0.3602 horizontal
    https://innovationstation.utexas.edu/tip-design

    How do you guys compensate for this ? Any better equations i can use / or specific for our Robos. Obviously there are a lot of other variables too like filament type, slicer settings etc.
     
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  2. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Two other things you can do to increase accuracy, If you are using S3D check the box that says "Outline Direction: Outside-In" on the Layer tab. On the Other tab use Horizontal size compensation. If you use Slic3r you can set XY Size Compensation which is in the Print Setting >> Advanced tab as well as the checkbox to do External perimeters first on the layers and perimeters tab.
     
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  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    @WheresWaldo Waldo has nailed it. There is more too it (ugh...) that even just the material properties. HOW you print it can matter :)
     
  4. danzca6

    danzca6 Well-Known Member

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    Being able to compensate in the slicer is far better than having to dink with the actual model. It's nice to be able to keep the model dimensionally clean. I'm going to have to install Slic3r and play with that because it is something that has bothered me for awhile. I just make sure to clean out holes with the proper drill sizes, but this might save me that post processing work. Thanks for reminding me of this Waldo.
     
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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  6. WADZOQUADZ

    WADZOQUADZ Member

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    I always keep horizontal size comp on .15 in S3d. What do you have this set at? This is only for external outline though ,correct? I didnt know about changing the setting to outside in .Iv never played with that before and always had it on inside out. What exactly does this help with?
     
  7. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Better placement of the outer perimeter. Going inside out will nudge the outer layers further out than you would expect. Setting this nudges them further inward. I am in the same mindset as @danzca6 alway make the model dimensionally accurate, then make all the compensations in the slicer. That way the model is the model and could be used regardless of the manufacturing method.
     
  8. WADZOQUADZ

    WADZOQUADZ Member

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    I would love to keep the cad model accurate . I have a cnc background . Iv never needed to change the dimensions of the model except for the holes only. I have always create two cad files .One with accurate dimensions for reference or other manufacturing and another file with enlarged holes for 3d printing using a global variable in solidworks. I guess what im confused on is what can change the hole dimensions in S3d without affecting other features like external dimensions. Iv also found that vertical holes need a different amount of compensations then horizontal holes.

    I also keep the resolution as fine as possible when saving as STL
     
  9. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Because of the way FDM printers lay down the filament. The slicer patterns affect how the model will end up. Nozzle sizes can affect this too...

    DLP does not have this issue (granted, it has other issues...many, many other issues).
     
  10. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    The problem with additive manufacturing is that you have a lot less control of the output than you think. Also depending on the material used you have to account for swelling and or shrinkage of the material. There is almost no way to apply a universal formula to your prints to get them perfect in all dimensions, so we all do the best we can. I play with things like extrusion multipliers, XY compensation, perimeter layouts to get as accurate as I can, but I still have to drill out some holes to get to the correct dimensions. I occasionally have to sand off a high spot on the side where my extrusion multiplier was too high. Every filament I print with has different requirements, that is why I don't mess with the model, ever. I make as many of those adjustments in the slicer, and the rest as video people are fond of saying is "fix it in post."
     
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  11. Ryan TeGantvoort

    Ryan TeGantvoort Active Member

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    Sorry for bringing up a slightly old Thread but .......

    Wow, I would have never thought this would be a good thing. But it has actually made my walls smoother, and I actually just printed a 15mm Cylinder with a 5mm Hole in the center and a Dowel Pin with 5mm diameter and I could actually fit them together! If I switch it back to Inside-Out, they will not fit together. :confused:

    My first layer was slightly affected by this change though as it added a little blob right where it starts. Nothing major but would be cool to have a setting to swap to Inside-Out for just the First Layer.

    I don't think this would be a good setting for anything with an overhang though. I am going to try and adjust the Horizontal Offset with Inside-Out and see what happens!
     
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  12. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Amazing isn't it what non-obvious tweaks can do to the slicer :)
     
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  13. Ryan TeGantvoort

    Ryan TeGantvoort Active Member

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    -0.07mm was the magic number for the Horizontal Size Compensation in order to keep the Inside-Out setting
     
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  14. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    You see @Ryan TeGantvoort patience and a bit of setting tweaks can usually get us where we want to be. Our machines are precise manufacturing instruments and it does take some work and some trial and error but we can make them accurate too. Could you imagine having a model that compensates for inaccuracies in your particular printer and then sharing it with others only to find that it doesn't fit for anybody else! That is why we don't mess with the model.

    From now on before I use any of @KTMDirtFace's models I am going to have to ask him if he tweaked the dimensions to "make it work." :D
     

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