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Thread: Boolean Cuts in FreeCAD

  1. #1
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    Default Boolean Cuts in FreeCAD

    In FreeCAD, when I Perform a Boolean "Cut" to difference two parts, the hidden mass of the part ends up as a ghost in the slice. This has actually caused the part to print a gap where it appears as a solid. Imagine a cylinder cut from a larger cylinder to create a cup. Then a rim created from a torus that has a radius of the thickness of the cup wall. Merge the torus to the cup so only half of the torus is visible. It appears to have made a rim around the cup. To be clear, It's more like a rib than a rim.But when it prints, it leaves a gap at the bottom where the two merge, and the walls of the inside of the cup try to print the shape of the torus, not the wall. When I lifted it from the bed it fell into three pieces. The cup, a torus and the rim.

    To fix this, I created a torus and merged it to a cylinder the same radius as the cup to create the shape it will be when attached to the cup. Then arranged it into place. Selected both and Make Compound. It seemed like a lot more work than it needed to be, but it printed correctly.

    Another one was a rectangle solid that needed a small square out of half of the bottom. Like a notch. After the cut it looked perfect. Slice and print, and the opposite side of the bottom has tiny gap where the top of the notch is. Pick it off the bed and it falls into two pieces. To make something that works, I had to create two Rectangles to compound together vertically. One the height of the original rectangle, the other the same height minus the notch. Arrange them and compound, slice print, perfect.

    In both cases, when you compare the failed part after slicing in preview with the part that worked, they look identical.

    I don't have enough experience to know if I'm just missing a step, but it's been frustrating coming up with an idea, having to print/fail, reprint/fail, recreate the part in a whole new fashion and print to get the part I need. By then, the idea in my ancient brain evaporates.

    Jeff
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  2. #2
    Join Date
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    Default Re: Boolean Cuts in FreeCAD

    For anyone who's interested, The thing I was doing wrong was I was using the "Make Compound" Boolean tool. All I needed to do was select both parts and use the Part, Join, Connect Objects tool. The former creates a mashup of both items. The way I was putting them together caused it to create something that made no sense to it. The simple connect objects create a solid from either part that has a solid. So the fact that the torus is half round is irrelevant as long as it resides inside another solid. I was sure it was something simple. I went back and retried the parts that I originally created, and using Connect Objects caused them to print correctly without having to create a half torus.

    Hey, if JPL can land rovers on Mars over and over again, the least I can do is learn to make a 3D plastic part that catches grease from a cheapo grill.

    Jeff
    Please consider becoming a Supporting Member of DIYC. Show your thanks to those who make this place possible.

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