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Easy way to make a plastic gear!

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Lew_Merrick_PE:

--- Quote from: John Hill on August 17, 2010, 06:08:13 PM ---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.
--- End quote ---

One of the tricks I have used over the years when making a gear train with homemade tooling is finish the gears with .004/.001 excess in my over-pins measurement.  I then set up a dummy of the gear train such that I can "drive" each gear the last couple of thou to center distance, fill my dummy gearbox with fine lapping compound, and "run them in" the last couple of thou.  I start the gears being driven (usually with whatever electric motor was lying about my shop) at center-distances that allow it to run and then tighten each of the "adjustments" a bit as the motion smooths out -- this having been done in the days when 600 grit Clover lapping compound sold for $0.75/pint.  The AGMA frowns on such a practice, but it works better than you might think.

jim:
would delrin work?

John Hill:

--- Quote from: jim on August 21, 2010, 12:37:46 PM ---would delrin work?

--- End quote ---

Someone on another forum saw my post and tried delrin (acatel, I think it is the same stuff) but he was unable to get enough friction in the early stages to heat and soften the blank.  He played a gas flame on the acatel but it was not a success.  Mind you, not all mine were successes either and it must have been incredible luck that the first one I tried came out so well! :med:

I would not give up on delrin.

John Hill:
Further to my original idea, I make a 60 tooth aluminium gear with a hand ground single point cutter and as would be expected the tooth shape is not perfect.

I ran that gear against a steel one for about an hour with as much pressure as I felt my lathe was comfortable with and at the end of it the aluminium gear appeared unchanged! :scratch:

cidrontmg:

--- Quote from: John Hill on August 22, 2010, 04:58:49 PM ---Further to my original idea, I make a 60 tooth aluminium gear with a hand ground single point cutter and as would be expected the tooth shape is not perfect.

I ran that gear against a steel one for about an hour with as much pressure as I felt my lathe was comfortable with and at the end of it the aluminium gear appeared unchanged! :scratch:

--- End quote ---

Hm. And if you would use something like valve grinding carborundum paste, it probably would embed itself to the aluminium gear, and just grind/polish the steel gear. Rats.
Then, a plastic gear would be even softer than the ali gear, so running those together would grind the ali...  But the ali gear might also wear in the wrong places, destroying the gear profile... Rats.   :scratch:

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