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Easy way to make a plastic gear!
John Hill:
Hardly needs any words!
The set up.....
... and the result!
I think this plastic is ABS, I cut a disc of random size and mounted it in the lathe with spare change wheel mounted on an axle in the tool post.
The lathe was run at about 400rpm and the change gear pressed against it, of course the gear started to turn and I increased the pressure a little. After about a minute the sound changed somewhat which I assume indicated the plastic was getting hot and starting to soften, at that point I increased the pressure and in about 15 seconds or less the teeth were formed.
The blank does not have to be the same size as the gear and as far as I can see no matter what the size of the blank the teeth which are formed will always be shaped in true involute form. It should be possible to make gears with odd numbers of teeth (according to the diameter of the blank) and of course there is no need for any indexing devices.
BTW, this does not always work and it is easier with bigger diameters.
Now if I used a steel blank with an oxy/acet flame playing on the edge it might get hot enough to form the same way..... :scratch:
Stilldrillin:
--- Quote from: John Hill on August 16, 2010, 09:57:56 PM ---Hardly needs any words!
--- End quote ---
John,
Yer right! :thumbup:
:clap: :clap: :clap:
David D
cidrontmg:
Thatīs neat! I guess you still have to calculate (and machine) the plastic gear blank just the same as if you were milling/hobbing it from any other material, for the number of teeth that you want in it. Have you tried the method with small gears and small pitches?
Obviously it wouldnīt work too well with racks, but it just might work also for inside gears... The "tool" gear would need to be small enough to fit inside the blank... Hm. :scratch: I might need to experiment a bit about this. Inside gears Iīve never been able to machine satisfactorily :bang:
You might also be able to do the same with aluminium... The "tool" gear action would be more like that of a knurling wheel, instead of hot forming, though... But with a steel gear, not cast iron...
Food for thought and experiment. Thanks for a very good idea! :clap:
:wave:
John Hill:
Yes, you have to calculate the size of the blank if you want a praticular number of teeth but when just testing the process I used random sized blanks.
The bigger blanks are easier than the smaller ones as obviously the error from a random size is less in the bigger blank (due to the error being spread over more teeth). Something really small like a pinion would require carefule size of the blank but I think it would still work OK, I have not tried this.
Haha, I never thought of inside gears but now I must make one!
My original idea was not to make plastic gears but to make aluminium ones, I just made the plastic gear as a trial to ensure the teeth would be formed correctly as some people on another board argued it would not. My idea was to cut the aluminium gears with a hand ground single point tool and use this process to finish the gear shape. I have cut about 15 teeth on a 60 tooth aluminium gear at this time and when that is finished I will try this method to finish the gear shape.
RichardShute:
--- Quote from: John Hill on August 16, 2010, 09:57:56 PM ---
Now if I used a steel blank with an oxy/acet flame playing on the edge it might get hot enough to form the same way..... :scratch:
--- End quote ---
I have seen film of gears being made essentially just like that. I think it was from Ford's in the '60's but I may be wrong, it was a long while ago. A red hot blank was rotated with a pair of 'forming gears' one either side. The formers were sprayed with coolant to keep them cool and a finished gear popped out every 15 sec. or so. It was obviously auto fed etc, but well pre CNC.
Richard
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