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Freecad - Joining solids to print

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  • Freecad - Joining solids to print

    I am hooked on learning Freecad. I haven't purchased a printer yet, but thought I should learn the design tools a bit to know if i will do much customer designing before a purchase. It could influence my decision on what printer to start with. The videos have been a huge help and my best resource. I am trying to understand how to add solids to design to build a small miter fence for and bandsaw (It did not come with one - yes I could build it from wood more quickly, but this is my way of learning).

    The fence has two parts to print. The bar itself and the fence fixture. I wanted a simple key to align the two pieces so I can glue or screw them together. I started with the bar since it was easiest. I modeled and padded a simple rectangle as the first body. Then I selected the top face and sketched the key on top and padded it. So far so good. Here is what i am not clear about.

    Is the key part of the bar as a single solid that can be printed?
    Or
    Do I need to do a Boolean operation to join the two pieces into a solid?

    I did the latter and I guess it worked, but since their are lines at the seams of the pieces, I am unclear on this. Here is a screen shot that might help:

    Thanks for any education you can provide me.

    Click image for larger version

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  • #2
    My experience is that, as long as the pieces are touching, they will print as a solid. 1 way you can check this is to install a slicer such as Cura. Configure Cura for some printer. It doesn't really matter which 1, as long as it has a big enough printbed. Load in your model into Cura & slice it. Go to the Preview window & use the vertical layer view slider on the right side of the screen to move up & down through your model. If the layers flow smoothly from top to bottom you're good to go.

    That said, for a model like you're doing, I would draw & pad the main bar as you've done. Then, I would create a sketch on the face of the bar, then pad out that sketch. Since the 2nd sketch is built right on the padded 1st sketch, it really has no choice but to be joined.

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    • #3
      As long as both pads are touching each other, the result is one object.

      In fact FreeCAD does not support two objects within one body.

      However your workflow is wrong. Usually you only need one body and when using two they are not nested. A body in FreeCAD is one component. So if you want to create a Nut and a Bolt you would have two trees of pad and pocket operations. Each one starting with a body group.

      When dealing with the Part workbench you usually don’t need any boolean operation. These are mainly required, when you use the menu item to create a cube and a circle as base and want to continue from there using sketches. Honestly this makes not much sense and only helps to migrate from e.g. tinkercad.

      With the next iterations of FreeCAD the will be the split tool, which allows to create e.g. a case and then extrude lines to use the resulting surface as a split section. Boolean operations are used here to combine multiple surfaces before using the result as the split surface.

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      • #4
        Thanks for the feedback. I was a bit confused on when to use boolean operations. I saw it in the Dr. Vax video designing the pawn where he joined the sphere, I will redo it and load it to the Cura slicer to see what it looks like. I don’t have a printer yet, so I can’t take it to a conclusion.

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        • #5
          Yeah, it is a little confusing when you look into FreeCAD for the first time. Here is a look onto one of my current projects. Check the tree on the left side.

          I usually create a part and then a body, before I even start. As you can see the project is separated into three bodies (the one named B_Socket is collapsed to fit the screen.). The part section is not required when using part design, but I figured it does not hurt and probably give future compatibility.

          Click image for larger version

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          As you also can see the spreadsheet is located inside the part section as well. Unfortunately you cannot drag it around for no reason and I did create the spreadsheet after creating the first body. Not a real problem, but I would have liked it at the top of the body list, as they all reference the data in it and it would be easier to find.

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          • #6
            Is the ring printed separately from the sprocket? I figured it was better to print the miter bar separately from the fence, then glue them together. But i am doing the two pieces in two separate files. Not a big deal to have two files, but there should be a way to create a file as an assembly of the two parts, but print them separately. I am sure there is a way, but small steps for me as i figure this out.

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            • #7
              The ring is a part, the stand and the lid of the stand. You could select all three and use boolean or multiselect and export to store them as one STL.

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              • #8
                Originally posted by rmazzi View Post
                Is the ring printed separately from the sprocket? I figured it was better to print the miter bar separately from the fence, then glue them together. But i am doing the two pieces in two separate files. Not a big deal to have two files, but there should be a way to create a file as an assembly of the two parts, but print them separately. I am sure there is a way, but small steps for me as i figure this out.
                Believe it or not, you could design them separately (into 2 individual STL files) and then actually combine them into 1 object in Cura. You use the move command in Cura to place the objects adjacent to each other, then slice. Then, use the Preview window to slide up & down through the layers, checking that the layers are joined. It works.

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                • #9
                  Originally posted by rmazzi View Post
                  Is the ring printed separately from the sprocket? I figured it was better to print the miter bar separately from the fence, then glue them together. But i am doing the two pieces in two separate files. Not a big deal to have two files, but there should be a way to create a file as an assembly of the two parts, but print them separately. I am sure there is a way, but small steps for me as i figure this out.
                  Yep there is a way to make them an assembly of two parts, and have easily exportable as separate STLs. They can just be two separate bodies in one file, and even if they touch, they're still considered separate to freecad. You can export one, then export the other. You can design the two parts in relation to each other, or you can design the two parts in relation to the origin and simply move one of the parts in place. There's a lot of flexibility in how you want to approach it.

                  In more advanced assemblies, you could use one of the assembly workbenches to put the parts together and even animate them to see how they move together, but that should be for later when you're ready to learn that.

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