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Roller Chain sprocket design

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  • Roller Chain sprocket design

    Need a sprocket for a non-standard roller chain, may have to make it myself. Need guide lines on laying out the tooth pattern. The chain is .475 pitch with a roller diameter of .305 and roller width of .120. Tooth count of at least 24 but can be more if needed to clear the hub which will be for a 1" shaft. The chain is from a Genie garage door opener and does not seem to be a standard size..
    North Central Arkansas

  • #2
    See if this article is any help. It appeared in Machinist Workshop magazine a few years ago. Sprocket math is at the bottom.

    For just a little more, you can do it yourself!


    • #3
      That looks like a good start. I can probably use the drive sprocket to approximate the outer half of the tooth shape since it is a low speed application.

      Last edited by ulav8r; 02-19-2020, 12:51 AM. Reason: typo correction
      North Central Arkansas


      • #4
        If your point is to learn how to make the sprocket, good for you. If your intent is just to get a replacement sprocket for a Genie garage door opener the more practical route is to just order one from Genie.


        • #5
          This tutorial by Lars Christensen may help.


          • #6
            If you decide on making it I can get you a DXF file of the geometry.



            • #7
              Could it be a metric chain?


              • #8
                Rummaging on google shows no evidence of any standard roller chain (inch or metric) with 0.475 pitch. Since this is close to the
                universal standard of 0.50" it seems it would be easier to just spend $10-15 for a 5spd bicycle chain and use readily available
                chainwheels for the sprocket. I suppose Genie could be making non-standard chain but seems like a silly thing to do considering
                the replacement market is almost nil and new install is only usage. It is not like razor handles and blades.

                When I adapted a used chain drive (Genie) GDO for a z axis drive on my 3n1 15yrs ago I used bicycle chain and sprockets for
                this purpose.

                For grins measure pin to pin distance for 24 links and see what you get. If 0.475 pitch it should be about 11.4"
                Last edited by sch; 02-19-2020, 04:10 PM.


                • #9
                  Wife wanted me to take her grocery shopping this morning(needed me because of a bum knee. On the way back I decided to stop by a door place to see if they would have a source for the sprockets. They had a used one on hand, 48 tooth mounted on a 3/4" stub shaft($10). I can use bushings to mount it into the shaft that holds the torsion springs and cable drums. I will then mount the opener to the wall to open the 10 foot door into my workshop.

                  Genie uses a 12 tooth sprocket to drive the chain that raises/lowers the door. Converting to wall mount and putting a sprocket on the spring/drum shaft will have the motor out of the way when I install a hoist rail centered on the door opening while also avoid having to purchase lift extensions to get a 10 foot lift.If the large sprocket slows the lift too much, I can use the sprocket purchased today as a blank to make a smaller sprocket.

                  Thanks for all the replies.
                  North Central Arkansas


                  • #10
                    Originally posted by old mart View Post
                    Could it be a metric chain?
                    No, metric roller chain, with the exception of the 5,6&8 mm pitches, is actually inch dimension British roller chain with metric units applied-

                    I just need one more tool,just one!


                    • #11
                      I remember back in the 60's, my first motorcycle, a Norton Jubilee 250 used a 1/2" X 0.305 chain, the common size for bikes of up to 250cc those days.
                      To get a decent measurement of the pitch, as long as the chain is in reasonable condition is to use a ruler on about 20 pitches, if it is 1/2" then it will be a bit more than 10 inches long.
                      Last edited by old mart; 02-20-2020, 10:57 AM.


                      • #12
                        If you have a cad program that will accept DXF files go here

                        Enter the parameters and download the DXF file and take the dimensions from that.

                        Barring that Machinery's Handbook has the data on generating the tooth profile


                        • #13
                          I will find out next Tuesday how well the sprocket I bought will fit the chain I have. Realized yesterday that if I did not find a sprocket that fit I could use a 1/2" pitch sprocket and just cut the teeth a little deeper. As the root of the teeth were cut deeper the pitch would decrease. Won't bother to figure out how much deeper they would need to be unless I really decide I need a different sprocket.

                          Bented, sprocketeer looks like just what I needed to design the complete sprocket. Thanks.
                          North Central Arkansas


                          • #14
                            The chain fit, 👍 The shaft the sprocket is on is 3/4", the id of the drum shaft measured .850. Got a 3/4 x 1 x2" "spacer" from Tractor Supply. My only lathe that runs has been in storage in my Dad's garage. Moved it to where I could use it. No chuck key handy(in a box somewhere), only one tool holder and HSS tool bit(others hopefully in the same box). Ground and filed the end of a bolt to reverse the jaws of the four jaw chuck and then tighten them onto the spacer. No indicator here so moved the tool bit close to the spacer and used that to indicate the part, got it within 3-4 thousandths based on eyecrometer measurement. Left hand tool holder would not get closer than 1/2 inch plus of the chuck jaws with 1 inch of spacer in jaws and 1 inch sticking out.

                            Picked up a file and started working on filing it down. It would have taken 6-8 hours or more to cut it down enough so I looked at my tool bit again and decided to try to use it. To get it to cut close enough to the chuck I cut with the back side of the bit, to keep it from rubbing I set it about 1/8" below center. It gave a very rough cut but it did take it down quickly. After 4 passes I filed it smooth, measured with calipers and repeated till I got it to desired size. That had 1/2 the length to size, turned it around and made one cut that pulled it out of the chuck as I backed off(It was cutting in both directions). Quit to eat supper then went back to it. Put it back in the chuck and re-indicated it again with the tool tip inside the bore. Cutting the first end took about an hour and a half, not including the time it took to grind the bolt down to use a s a chuck wrench. The second half was finished in about 20 minutes, including the spacer in half and mounting it on the sprocket shaft. First was put on the shaft and slid up against the sprocket. The shaft had a 1/4" hole 3/8" from the end so the second spacer was installed flush with the end, then a center punch was used to drive material into the hole on each side to secure it to the shaft.

                            After driving the shaft into the drum shaft I will drill through both to lock the sprocket to the drum shaft. I will then be able to install the opener and have easier access to the shop.

                            The sprocket is a 48 tooth so the opener will have plenty of power but will be very slow. I expect that I will end up cutting it down to 24 teeth, but that will be a year or more away, after the house is completed and we are moved in. My wife and I are doing most of the work. After we finish the wiring and plumbing we will have drywall hung and finished by someone else, then all the rest of the work will be by us so it is going to take a while.
                            North Central Arkansas