I am designing a gear train to reduce from 170rpm to 6rpm and to drive a heavy load, estimated at approx 30kgs. I would be interested in your thoughts as to what material would be best suited for this application.
Thanks
Duncan
POM is probably a reasonable option if you have good enough venting to avoid formaldehyde poisoning. I wouldnāt use too small a module, but POM, nylon, and ABS all get used in gears plenty.
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It looks like injection-molded homopolymer POM (e.g. Delrin) gears are widely available in module 3, and also available in module 4. The thickness of a tooth is slightly less than half the reference pitch, depending on the pressure angle. The reference pitch is Ļ times the module; so a module 3 gear has a reference pitch of slightly less than 9.5, so each tooth is about 4mm thick (depending on the pressure angle). In order to support a larger weight, you just need to choose how thick to cut the gear. Glass-filled homopolymer POM is available, might also laser cut OK, and might improve strength, but itās very expensive.
For that much weight and plastic gears, I donāt think Iād want a smaller module than 3. And going with a larger module than 3 substantially reduces your options if you later decide that you want to replace some or more of your gear train with commercially-produced gears.
On the other hand, if you donāt care about compatibility very much, given the self-lubricating characteristics of POM, you might consider using a 14.5ā° pressure angle; itās still available but not as widely as 20ā° PA. It would give you a slightly thicker tooth.
You could consider a hybrid; you could use a brass gears at the loaded end of your chain, and cut plastic gears at the fast end of the chain with the right number of teeth to give you the exact reduction you are looking for.
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I have purchased some 12mm Acetal sheet and attempted to laser cut it but without success, I just melts. However, I am fortunate enough to have a small CNC router and using a long neck 2mm end mill I have successfully cut a rather superb test gear. So thanks for the material advice it was very good.
BTW Iām using a pressure angle of 20 deg and a circular pitch of 6 and Looking at this first gear I am sure it is going to be OK.
I used this website http://hessmer.org/gears/InvoluteSpurGearBuilder.html for the gear data.
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Circular pitch of 6 is module 6/Ļ so slightly smaller than module 2, so maybe I was too pessimistic. Glad it looks good! Long neck 2mm end mill sounds like it could be a nail biter to cut with, even in something as easy to machine as acetal. What DOC did you use?
Given that laser cuts are slightly conical, you wouldnāt have truly vertical edges, I would naively assume that CNC should be tremendously better for wear and longevity.
Just for the next person who is interested in this, FreeCAD has a good involute gear package in the FCGear Workbench and OpenSCADās MCAD also has a good involute gear package which also supports bevel gears.
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This is the cutter I used and at first I was a bit concerned, but I set the step down to 0.5mm and it cut beautifullyā¦
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