12 Replies Latest reply on Oct 18, 2016 12:57 PM by Don Cheke

    Rack and Pinion Self-Center Jig

    Don Cheke

      Hi All,

       

      I am trying to create a self-centering rack and pinion jig. I know nothing about gears so my trials have not been good. I think I have the basic concept worked out. Use two racks with a pinion at the center. I can probably maintain the rack in a parallel by using some nylon or other plastic material as spacer blocks and have other strapping (of a sort) to help create a channel for each rack to slide through. I can add a block on the end of each end to catch the sides of the extrusion I want to place a central hole in using the jig. I need to span extrusion lengths of about 48" up to about 84". I figured  that the rack segment would need to be about 48" long and the rack could be still longer without the gear travelling the full length at the ends. Hope that makes sense.

       

      Would someone be willing to design a gear and a rack about the size of the one attached and mate them so they travel in opposite directions when the pinion is turned. I would be very grateful. I can add all the other block and strapping afterwards.

       

      Screen-0024.jpg

        • Re: Rack and Pinion Self-Center Jig
          Alfred Jelinek

          Don,

           

          So the pinion(gear) turns and each rack goes the opposite direction...ie...clockwise = top moves right, bottom moves left?

           

          Just checking as this may be easy for me to get done for you....are you needing a complete design or a proof of concept?

           

          Thanks,

           

          Al

            • Re: Rack and Pinion Self-Center Jig
              Don Cheke

              Hi Alfred,

              Yes to your first question.

              I think I can work out everything but the rack and pinion itself. If I can get the concept to work in SolidWorks I think I will get the parts cut on a CNC laser in wood or metal. I was hoping that you or someone else might like to help without me needing to pay someone to do it. I am a new product designer, but I lack skill when it comes to gears and the like.

              • Re: Rack and Pinion Self-Center Jig
                Don Cheke

                Hi Shaidun,

                 

                That is what I am after. How did you get the mates to work? I do need the right gear ratio (which elude me) so that they would mesh properly with the rack. Can you help with that?

                  • Re: Rack and Pinion Self-Center Jig
                    Dennis Dohogne

                    Don, so long as the pinion and the rack have the same gear geometry they will mesh properly.  That geometry is mostly defined by Diametral Pitch (DP) and Pressure Angle (PA) for inch gears.  So long as the racks and pinion have the same DP and PA they will mesh.  There is no "ratio" between them that you need to work out except how far you want the rack to travel on a single revolution of the pinion.

                     

                    SolidWorks has advanced mates called Gear Mates that include the combination of a gear and a rack.  That is how those were done in the videos above.

                     

                    You should look online to consider off-the-shelf systems since manufacturing these will be very expensive unless you have your own machine shop.  Even then gears require special cutters and methods compared to conventional machining.  Laser cutting will work so long as you have an accurate SolidWorks model, but then the parts will typically be relatively thin if you are laser cutting sheet metal or wood.  Keeping the teeth engaged could be a problem.

                • Re: Rack and Pinion Self-Center Jig
                  Shaodun Lin

                  Hi Don:

                   

                  I used this Self-centering mechanism previously, in the real life it is not so accurate due to the backlash between rack and pinion.

                  If you are OK with the repeatability of 0.1~0.2mm , then it is OK.

                  • Re: Rack and Pinion Self-Center Jig
                    Dennis Dohogne

                    Don Cheke, check out these links:

                    1. Stock Drive Products:  Flexirack -  A 1M12MYHF202000  (Module 2, middle of first page), Guide Rail - A 1A12MHR201000 (Alum) or A 1M12MHR201000 (Nylon) page 2, Pinion - A 1M 2MYHF20024 (Module 2, 24 teeth, Pitch Dia = 48mm (1.89"), OD = 52mm (2.047"), bottom of second page)  http://www.sdp-si.com/PDFS/Flexirack-Flexirack-Clamps-Flexirack-Rails-and-Pinions.pdf

                    2. Stock Drive Products: Molded Spur Gears, Diametral Pitch, P = 16, 20 deg Pressure Angle, 34 Teeth, Pitch Dia = 2.125", OD = 2.25", Part No. A 1N 2-Y16034, PAGE 136:  http://www.sdp-si.com/PDFS/Spur-Gears-Inch.pdf   You'll need to supply your own racks, but these are easier to make than an accurate gear.

                     

                    And if you still need accurate geometry to send to a laser cutter here is a set of parts with P=16, 20 deg PA.  The parts are parametric so if you need a different number of teeth or a different P or PA they can be easily changed.  The gear has an accurate involute profile and it too is parametric by changing P, PA, N in the design table.

                      • Re: Rack and Pinion Self-Center Jig
                        Don Cheke

                        This is perfect Dennis!

                         

                        Thanks for sharing your knowledge and your skill to make the available. It is all and more than I had hoped for. If we go this route (and I hope we do) I will try and post a picture of it when completed. First I need to adapt my ideas to make it work as I envision (fingers crossed :-)).