5 Replies Latest reply on Nov 18, 2014 12:10 PM by Brian McEwen

    Proper dimensioning of curves

    Chris Beckman

      Im attempting to dimension a part that has multiple arcs and tangent lines connecting them as seen below.  These drawings are to be sent out to be CNC'ed (part files included also), but the only contact I have with the company is through a middle man who knows very little of solidworks/CNC/etc.  Wouldn't a company that does CNC'ing have software like SolidCAM or DelCAM that they simply use the solid model to create the CNC program/code?




      Whats the proper way to do this?  Ordinate dimensioning of the center marks?




      Perhaps a chart with x/y coords and radii?

        • Re: Proper dimensioning of curves
          Daniel Andersson

          They may need different dimensioning depending on what system they have in the machine... IF they code manually. There might be different options/techniques depending on the software used in the machines.


          I recommend that you ask to speak directly to the person making the cnc program. Perhaps they might do with a dwg or step file. If so, you could reference on your drawing to the CAD data for non - specified dimensions and just add some control dimensions to the drawing.

          • Re: Proper dimensioning of curves
            Denzil Searle

            Personally I'd dimension to the centre marks as per your example. Having said that, I can't imagine many subcontract machining companies these days are spending time doing manual programming. It takes longer and there is more risk of mistakes. What would they do if your feature was based on a spline rather than circular arcs? As above, ask to talk to the person who does know the details.

            • Re: Proper dimensioning of curves
              Cody Zorn



              - If you send a DXF or DWG, they can pick dimensions off the drawing as they require.

              - Bypass the middle man that doesn't know much about CNC.


              Hope this helps,


              • Re: Proper dimensioning of curves
                Brian McEwen

                The other guys may be right about how it should work (the shop must at least be able to read a .dwg as mentioned), but I can tell you what our R&D machinist would want.


                To program from the drawing he would want arc radius, and the end points and center points of each arc or straight. And he likes ordinate dims. So to your example above I would add dimensions to the end of each segment.


                I can't tell if that is a single groove cut or a positive feature, like a ridge of material. If it is machined on both sides he would want both sides fully dimensioned so he didn't have to do the math. Basically just give them all points so they can do it how they want.  Detail view perhaps.  If you want a correct drawing you could set the over-defining dimensions to reference. We sometimes do a whole view that is "Machining Reference Only".


                On the other hand when it is definitely CNC we sometimes use a cop-out note for complex geometry: ""PART GEOMETRY NOT DETAILED ON THIS DRAWING IS DEFINED ON THE ELECTRONIC CAD FILE OF THE SAME REVISION.""  So we don't have to dimension everything, just stuff we really care about or want to tolerance.