5 Replies Latest reply on Feb 11, 2014 5:15 PM by Phillip Graham

    Mating notches with inside fillets

    Phillip Graham

      I have some parts of an assembly that fit together with a keyed notch in each part, held in place via gravity. The parts are perpendicular to each other, and there is an equal notch in each part.

       

      When I first draw them for an assembly, I use simple rectangular notches and coincident mate the bottom faces of the notches. This is fine for a schematic assembly. For the as-built parts cut via waterjet and mated, the notches must be slightly oversized and the inner corners of the notches must be filleted. The waterjet facility builds tool paths naively from exported DXFs, so the parts I send them must include the fillets and oversizing of the notches.

       

       

      When creating a revised assembly to reflect the as-built parts, I've been able to partially constrain the components with the "width" matebut I cannot figure out how to mate the fillets, which touch each other at four points. How can I mate these two filleted notches?


      Even further, I'd like to drive the notch depths to automatically account for the spacing needed from the fillet intersections. So I like to capture the separation distance between the mated fillets, and drive the overall notch depth based on this distance Any thoughts on how to do this?

       

      I've attached an assembly showing schematic parts as oversized, and as filleted, but with the original naive mates (a perpendicular and coincident mate).

       

      Apologies for the drive by post, and thanks in advance for any help.

       

      -Phil

        • Re: Mating notches with inside fillets
          Kirkwood Hines

          Hi Phil,

           

          If you make a reference plane in the part that is coincident with the upper edges of the fillet you can mate it together as coincedent within your assembly. If the depth of the slot changes or your fillets change size the position of the plane will update.

          Planes.PNG

           

          I'm not sure about the driven depth question. Do you want the thin edges of the struts to be on the same plane when the slot's sized properly?

           

          Hope this helps.

            • Re: Mating notches with inside fillets
              Phillip Graham

              Kirkwood,

               

              Thanks for the help! I think a reference plane will get me half way there. The plane that you draw above would be correct, were it not for the notch oversize. this causes the intersection point to lie along the arc of the fillet, and not at the start of the fillet.

               

              Let me explain about the depth driven question a little more. The goal, as you surmise, is to have the thin edges of the struts in the same plane.

               

              I have these parts cut by a metal working shop straight from exported DXFs, they don't don't do any CAM tweaking. Depending on the material stock, they are are either laser or waterjet cut. These two methods have different kerfs, different wall thickness variation during cutting, and different fillet requirements.

               

              So, it would be ideal to oversize the notch, add the fillet, calculate the resulting intersection plane of the fillet, and then use that reference plane to drive the final notch depth variation from the original notch depth.

               

              Hopefully that is clearer.

            • Re: Mating notches with inside fillets
              Mark Kaiser

              Here's an example using sketches for mating (as Jerry suggested).

               

              I'm not sure how you'd drive the notch depth based on the mate of the nothces.  Unless I'm understanding wrong, you mate the fillets first, then determine the depth of the slot?  How can you do this if the fillets are at the bottom of the slot?

                • Re: Mating notches with inside fillets
                  Phillip Graham

                  Mark,

                   

                  Thanks for the reply, and apologies for the substantial delay, its been a busy six weeks!

                   

                  Let me see if I can flesh this out this notch mating a little more:

                   

                  Simplest Case:

                  Both mating pieces are exactly the same width with the same fillet radius, and therefore both pieces touch at the start of the fillet.

                   

                  Harder Case:

                  The oversized notch. The square notch has a width of X + 2*(oversize offset). This notch narrows at the fillet by 2*(cos(theta)*(fillet radius)). The height offset of the plane where this intersect below the start of the fillets is sine(theta)*(fillet radius)

                   

                  So, if both notches are oversized by the same amount relative to the baseline width they'll both intersect the fillet at the same point. Combining the above shows that (oversize offset) = cos(theta)*(fillet radius) and solve for theta

                  theta = arccos(oversize/fillet radius)


                  The reference plane height offset is then sine(arccos(oversize/fillet radius))*fillet radius

                   

                  From this you should be able to define the reference plane offset from the notch. Then what remains is to define the entire notch depth relative to the nominal notch depth, at least to my mind.