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Thread: Sprocket cutters
03-31-2010, 11:27 AM #1
Here's some questions for the gear/sprocket experts -
I'm looking at chain and sprocket data for the size chain I use on our vintage race motorcycles - #219 cam chain in this case. Finding data on #219 chain is not as easy as more standard chain like #35. In fact it's been downright frustrating at times, but I think I may have figured something out.
I have found the sprocket charts and data at the Azuza website , as well as looking at sprocket cutter data on the Ash Gear website.
It looks to me like #219 chain might use the same involute sprocket cutter as #35 chain as the roller diameter is exactly the same at .200" but on a smaller sprocket pitch diameter and smaller pitch distance of .306" vs .315". Am I right in that? I've looked a lot and <never> found a 219 sprocket cutter - if I'm right that would explain it.
It appears that 428 vs 420 (and 415) chain might also use standard roller chain cutters but with adjustments as well - the 428 chain that is stock on our racers has a 1/2" pitch and roller diameter of .335", while 415 and 420 chains have 1/2" pitch and roller diameters of .306", with 415 being just narrower between the sideplates. Those would appear to use cutters for #42 british (.335" roller diameter) and #41 american (.306" roller diameter) on appropriate pitch diameters and pitch distances.
Any thoughts from the actual experts?
03-31-2010, 01:27 PM #2
One other thing I didn't mention above (if I'm right anyway) would be that the cutter numbers would be somewhat different too - cutter for 12-17T sprockets in #35 would be for a different number of teeth when used for cutting #219 sprockets - like 15-22T for instance (just throwing out ballpark numbers without doing any math) as the arc described by the roller as it meshes/unmeshes with the sprocket is on a different radius due to the different pitch distance.
03-31-2010, 01:30 PM #3
I don't quite understand this. The only places that I'm aware of that use sprocket cutters are those that hob the sprockets. I've made several sprockets that we just use an end mill to cut the roller diameter. I've done this with a dividing head turned up and feed the end mill down. We've done several "special" #100 sprockets where we've just had the sprocket done on a waterjet and the chamfer was added afterwards.
03-31-2010, 02:05 PM #4
Sprockets can be cut with hobs and would be for those in a production environment or with hobbing machines. For those of use using horizontal mills and dividing heads you use a sprocket cutter - looks just like a gear cutter but generates the space between the sprocket teeth for the roller to sit in, including the flanks of the teeth.
Roller chain sprocket teeth are not simple curves - at least from the pitch circle outward (the addendum). It's a form of involute curve. The bottom of lower half of the space (the dedendum portion of the tooth) is a simple radius, but not the addendum portion. Sprocket cutters are just like gear cutters in that they are approximations, and you need a range of cutters to cut all tooth numbers. Usually something like 7 cutters in a set if you want to have them all. Hobbs do cut perfect sprockets without approximation.
Those of you with CNC capabilities can of course ignore all this claptrap and just draw the sucker you want.
03-31-2010, 02:14 PM #5
03-31-2010, 02:15 PM #6
Personaly i never get bored spitting these odd balls out with 2 axis cnc on the bridgeport. Its a ideal job for a machine with no toy changer too! The first ones i done i spent ages in cad working out the geometry. Its pritty simple in practice and I came to the conclusion that on larger sizes the teeth can be just simple curves.
04-02-2010, 11:33 AM #7
There's got to be someone on here with involute gear and sprocket data rolling around in their head...
Or has everyone been working on CNC machines so long they've forgotten all these antique methods?