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Complex curves on a manual mill?

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  • Complex curves on a manual mill?

    How were complex curves and surfaces made precisely before CNC?

    I look at the complex shape of a S&W revolver sideplate and how it fits precisely into the far more complicated frame... or the flowing shapes of a Colt Single-Action Army and all the precise, irregular pieces inside... or the oddly graceful and hugely complex receiver of a M1 Garand.. and I am in awe of the design and manufacturing genius of people who did not have computer-aided design or manufacturing software to calculate the angles or precisely move the tools.

    How were the necessarily complex and precise parts of guns, automobiles and airplanes made before CNC? Rough forging/cutting/milling, then infinite amounts of filing to a line? How would that be possible in a production environment?

    Let's think of just a simple 2D example... a rectangle-ish shape with an irregular internal feature, like the drawing below (not a real part, just a quick example). Without CNC and only with manual tooling, how is this made to the tolerances shown? One-off or production, all are welcome to weigh in here.

    Click image for larger version

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    SE MI, USA

  • #2
    that part would be a pita, but I'm not sure there is anything that couldn't be be milled with a rotary table as they all appear to be radii vs transitions/spirals etc. Assuming those are inches, tolerances are large. I would rough it out then clamp (with the ability to leap frog the clamps) on a plate to which I'd placed tool makers buttons on the inside centres. It don't think it would be difficult, just long and tedious with lots of steps.

    there has also been various types of tracing machines for a long time, if the question is more production vs how to make one
    Last edited by Mcgyver; 12-16-2020, 08:04 AM.
    located in Toronto Ontario


    • #3
      I would stick it to a sacrificial plate with a small hole at the center of every radius to aid in the use of a rotary table with a face plate. Moving the part around could cut all the radius sections one after the other followed by the straight lines
      Helder Ferreira
      Setubal, Portugal


      • #4
        A Rotary table and Volstro head combination would take care of that.
        Bit of maths involved though


        • #5
          Pantograph mill.

          Punch and die, punch them out.



          • #6
            For production stuff id assume a tracer mill ? just a guess.


            • #7
              Stamping or pantograph are two that come to mind as Doozer mentioned.

              Stepping off the curves is another long forgotten method that isn't really used anymore. I've worked with many Patternmakers over the years, and CNC has long replaced that skill. The last guy I worked with that always wanted me to generate step off tables for him retired a few months ago. I just couldn't get through to him that by the time it took to generate the tables, or print out all the angles and info I could have programed and started cutting the block in the CNC mill. More than a few times I'd say sure, I'll get you your info after lunch, then after lunch just bring him the finished block. We didn't get along lol.

              George Britnell is a master craftsman still utilizing that skill in his model building. It's no doubt effective, just laborious.


              • #8
                I can now see how the circular arcs can be cut a rotary table and buttons/template to help set up for each arc.

                For a pantograph or tracer mill you still need at least one as a pattern, so we are back to how to make this with manual tools? Rough cut and file?

                Same question for punch/die... how are those made with manual tools?
                SE MI, USA


                • #9
                  +1 for mounting it on a sacrificial plate with all the radius centres reamed to fit a close fitting central pin on a rotary table. In this example, use a 3/4" diameter endmill. Tedious but accurate. Blending the straight lines would probably be the most awkward part.

                  All of the gear, no idea...


                  • #10
                    Probably made as any mass produced part, multiple machines (mills), each set up for cutting one of the critical features of the part repetitively. The semi-finished parts moved to the next machine and so on.


                    • #11
                      At the first shop I worked at out of college where we used to do this a lot, Almost all the 2d Feeler templates we used to make for checking fixtures used to be done that way. They generally had a tolerance of +/-0.006" - 0.01".

                      Essentially a 2d section was cut through the part with lots of lines, arcs and splines. From there I'd basically divide the spline/arcs into equal segments defined by the desired cusp to remain (we usually used 0.01-0.02"), then draw a circle with your cutter diameter tangent to each line segment. Move your cutter to each hole center, and plunge. The more circles you draw the less you need to file. The circles at long line segments were usually done first, and then pins inserted to butt against table slots to register the correct angle and to position of the piece to cut the lines. I'd also give a 1:1 so they could saw out most of waste if it was a big one that was all arcs/splines.

                      We used to have a custom lisp command for mechanical desktop that would do all the hard work of laying out the circles, and exporting the centers to a spread sheet. It made the Cad jockeys job (mine) much easier. Where I work now, we're essentially a refugee shop of that one, but none of that stuff moved over, hence my reluctance to go back down that route, but for a one off with no other option beside a manual mill, it would probably be your quickest path to victory. It honestly goes pretty quick once you get into it....I've done it more than I'd like to remember, but much prefer the way I do it now......It takes less time to just make the part in a CNC than it does to generate the step off tables now.

                      Just drew this up quick to explain it better. First you'd drill the green circles to establish the major intersections, and mill away the major straight sections, then come back and plunge out the magenta ones. We used to go down to about a 0.01" (0.25mm) spacing for most stuff. some guys would just skip every other hole if they felt like it. It was always great fun when you'd generate the table for a 1/2" endmill and the guy would come back and ask for another one because he wanted to use this nice 0.470" regrind that he had..... He even bring the nice shiny cutter to show you .


                      • #12
                        Accurate fixtures are made to hold the parts.
                        Several mills with rotary tables are set up, one for each operation and the fixtures are then moved from one mill to the next until complete, this may take 8 to 10 moves for the pictured part.

                        If only 1 machine is available then all parts are milled in steps, one operation at a time in a fixture, this is slow as only 1 part is being machined at any time.


                        • #13
                          A combination of an X Y platform on top of a rotary table. In some parts of the world this was referred to as a Rotary CrossSlide. Very common in the mold shops of old, back in the days before numerical control machines and circular interpolation. The cross slide took up quite a bit of vertical space, so was often used on a Bridgeport type machine with a riser block under the ram to provide the needed clearance. It's been a loooong time since I've used one. Takes a bit of planning and forethought, but once familiar with them a part like what's shown is a pretty simple task.


                          • #14
                            Originally posted by reggie_obe View Post
                            Probably made as any mass produced part, multiple machines (mills), each set up for cutting one of the critical features of the part repetitively. The semi-finished parts moved to the next machine and so on.
                            This hit the nail on the head for lots of stuff produced in large volume like firearms. Remember too that most stuff did not start from a block of metal, it was more likely a casting or forging.

                            A number of years back I toured the Smith and Wesson factory in Springfield MA. They had a huge production facility, a million+ square feet in total if I recall correctly, and at this point much of it was empty. They had an old photo of the rows upon rows of vertical milling machines all lined up, each set up with a fixture to do just one or two operations on a batch of frames, which were then sent along to the next machine for the next step.

                            They were showing off their new CNC machining centers that were making revolver frames that day, each frame was something like 90% machined in 3 setups. He told us that each of the CNC machines replaced 180 discrete machining operations.


                            • #15
                              Originally posted by alanganes View Post


                              They were showing off their new CNC machining centers that were making revolver frames that day, each frame was something like 90% machined in 3 setups. He told us that each of the CNC machines replaced 180 discrete machining operations.
                              But, I would offer a small bet that the 180 machines put out a total production many times larger per hour or day. CNC "can do" all the operations, but "can not" do them as fast. That line-up of mills could produce one finished part in the time of the slowest operation on the line. If that operation took 25 seconds "bin to bin" , then that's a part every 25 seconds off the end of the line. That CNC is in no way finishing a part that fast, especially if there are any tool changes. There is no part out of the CNC until all the operations have been completed.

                              And, at the moment, they do not NEED to do that. During WW2 they DID need to, and there is the difference between CNC and dedicated production. In many cases, it simply cannot keep up. The benefit of CNC is in flexibility, and as much as possible, single workstation part completion.
                              CNC machines only go through the motions.

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