Announcement

Collapse
No announcement yet.

Cutting plastic gears..

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Cutting plastic gears..

    I have a task ahead to cut a dozen or so small plastic gears (25 and 60mm diameter modul 2) and the material I have is nylon and acetal spur gears.

    Now the question is how to minimise the hairy edges?

    I am thinking I need to drill the rod stock for the centre boss then part off the individual gear blanks and bolt them all together through their centre holes, perhaps an MDF blank on the ends.

    I will cut the gears all at once using a dividing head, vertical mill and the appropriate gear cutters.

    Will the process avoid most of the hairiness?

    Thanks

  • #2
    I've done similar with good success, but I used 3/4" thick aluminum as the ends for capping material. One cap was threaded with a blind hole on one face, and a centering hole for a tail stock center on the other face. The other cap had a boss turned to allow rigid clamping in a lathe collet, and in the dividing head chuck, with a through hole for the threaded end of the tie rod. The center tie rod was ground stock that slip fit on the id of the blanks. Not much for burrs, but there were sharp edges that fortunately didn't mater in the prototype application.

    Comment


    • #3
      Thanks Tom.

      Comment


      • #4
        I would be inclined to cut the gear in one long length, then cut them apart. You could try gently using a propane torch to minimize the "hairs" . Bob.

        Comment


        • #5
          That would seem the obvious way Bob but when I have a 'stick' of all gears I expect it would be a challenge to 'part' them off being too big for the lathe spindle.

          Comment


          • #6
            I hand-deburr them then get rid if the very fine whiskers with a heat gun.
            Peter - novice home machinist, modern motorcycle enthusiast.

            Denford Viceroy 280 Synchro (11 x 24)
            Herbert 0V adapted to R8 by 'Sir John'.
            Monarch 10EE 1942

            Comment


            • #7
              If deburring with a heat gun is practical that does open the choices for the machining process.

              Comment


              • #8
                Use a heat gun with precise and independent programmable flow and temperature. I have one for Bosch and use it for all type of things, including plastic welding and melting solder. Mine is 150F to 1300F

                Acetal is easy to de-whisker with the correct heat. I've not had as much luck with nylon.
                Last edited by lakeside53; 04-21-2018, 08:24 PM.

                Comment


                • #9
                  The nylon will have all kinds of stringy hairs. The heat gun is probably the best choice for deburring them. If you try to use a burr knife it just creates more strings.
                  The acetal will machine cleanly with minimum burrs, especially with a sharp cutter. The heat gun may be the best for that one too.

                  Comment


                  • #10
                    I prefer a propane torch. The whiskers don’t melt they vaporize.

                    Comment


                    • #11
                      I can say with some certainty that I likely have more experience with this than anyone else on this forum, having done it once or twice now. I've tried many, many methods. Some logical, some not so logical, some were even hair brained. But I tried them. By far, the best way was sending them out for dry ice blasting. Fast, cheap, painless. However, a decidedly pay-for option. Second best I found was freezing the gears, dawning an Optivisor, and dragging a scalpel or razor knife. Heat never works out well, it seems. You get one or two that work as desired and then whoops, so much for that one...




                      Comment


                      • #12
                        so how do you work around the fact, that nylon (and probably all other plastics) changes size when machined. i find i have to let parts sit ovenight to stabilize.

                        Comment


                        • #13
                          Originally posted by dian View Post
                          so how do you work around the fact, that nylon (and probably all other plastics) changes size when machined. i find i have to let parts sit ovenight to stabilize.
                          Was this meant for me? Speaking only for myself, it is not very much different than dealing with Metals. One accepts that there are certain accommodations that need to be accounted for, and works around them. And yes, allowing for stabilization is one of those accommodations. It varies from material to material, but in my experience it is not much different than making an Aluminum part in a 20°C/68°F @ 30% - 40% RH and then having the end used inspect them for use across the continent at 32°C/90°F @ 70% - 80% RH. There ARE going to be differences in the results. No difference with plastic gears. So, one does what one can, and let the other things fall where they may.

                          That said, some are relatively easy to work with, while others can be a real pain in the buttockal unit. I've 6/6-60 found Glass Filled Nylon to be relatively easy to deal with, while fresh regular Nylon will walk for days. Ultem was an interesting experience, too.

                          Comment


                          • #14
                            "Nylon will walk for days": thats what i was talking about. why does it? (aluminum will stabize after 20 min.) and how does the glass filled stuff machine? would you recommend making parts (bushings, spacers) out of that?
                            Last edited by dian; 04-24-2018, 02:33 AM.

                            Comment


                            • #15
                              The main reason nylon "walks for days" is moisture absorption. Neat (no glass or other filler) nylon is a great choice for gears but you have to account for dimensional changes in service.

                              I have not only designed many plastic parts including gears but also made lots of prototypes so I have some experience with this subject.

                              a sharp knife is what I've always used. But then I don't think I've ever made more than a dozen gears at once so deburring manually was ok.
                              Last edited by strokersix; 04-24-2018, 04:53 AM.

                              Comment

                              Working...
                              X