how to design sprockets

[Cory]

I seem to remember Team 173 saying that they made sprockets on their CNC machine, either for themselves, or to sell for a profit. Perhaps one of them could elaborate.

I also seem to recall reading/seeing/hearing that the i-part models of gears and sprockets are not good enough to use to cut sprockets or gears.

[Swampdude]

Last year I used http://www.cadregister.com/ and searched for "sprocket" then you'll see Madison sprocket in the list, then I used type A plate, 3/8 pitch. Then pick the tooth quantity you need from their list and download the CAD file. This file will only have 1 tooth showing so you need to array that tooth around the number of teeth you picked, they should all match perfectly. We had these patterns blown out by waterjet, and then had to bevel the outside edges of the teeth to get them to fit in the chain right. If you just stick the sprocket in the chain without the beveling you'll find the chain will only mesh with 1/2 the teeth then ride out on top of the rest. So that last step is important.
I also made a point to make a variety of sizes in the event I needed to change any ratios after the fact.

[JulieB]

i would just use a ruler and design on the cnc mill it would take that long.

[coreyjon]

I'm just curious why it is you need to machine your own sprockets. As it was said above, sprockets are so innexpensive, that I can not see the need to spend the time making them in the shop. (other than to say that you made the sprockets yourself - Something I might do - even though it is impractical).

[Cory]

Originally Posted by coreyjon

I'm just curious why it is you need to machine your own sprockets. As it was said above, sprockets are so innexpensive, that I can not see the need to spend the time making them in the shop. (other than to say that you made the sprockets yourself - Something I might do - even though it is impractical).

If you've got the CNC machine, the only cost to you is the cost of the raw materials.

[Swampdude]

For us last year, we had 2 very good reasons. The weight - since light weight sprockets in 3/8 pitch are going to be hard to find and not necessarily have the interior (shaft) shape we need.
The mounting configuration we needed was unique. So we ended up with an extremely light and strong, custom made sprocket that fit the design perfectly in the end.
As long as we have the waterjet as a resource, I plan to make sprockets. Sprockets are a great place to save weight. For example, we had (4) 60 tooth sprockets that would have weighed 2.8 lbs ea. (in steel) x 4 = 11.2 lbs
but the custom high strength aluminum ones weighed around .7lbs x 4 = 2.8 lbs - 8.4lb savings!

[team222badbrad]

This is what we did on our CNC this year.

We choose the chain size.
Measured the chain spacings and such
Calculated how many teeth we wanted on the sprockets.
Got some plate aluminum.
We then figured out how far the teeth/holes needed to be apart. Calculus....
Made a G code program.
Once we got the code ready we took a drill bit slightly bigger than the chain "hooks" or whatever you call them. The machine then drilled a series of spaced holes all the way around the plate of aluminum. We then placed a mill bit in the machine and machined half of the holes away.

Here are some pics of our arm's gears:

http://www.tigertrons.com/Pictures/2...n/100_0596.JPG
http://www.tigertrons.com/Pictures/2...n/100_0710.JPG
http://www.tigertrons.com/Pictures/2...n/100_0716.JPG

These worked great for us. We also made some 50 tooth sprockets for #35 chain in our drive train

[SpaceOsc]

Originally Posted by team222badbrad

This is what we did on our CNC this year.

We choose the chain size.
Measured the chain spacings and such
Calculated how many teeth we wanted on the sprockets.
Got some plate aluminum.
We then figured out how far the teeth/holes needed to be apart. Calculus....
Made a G code program.
Once we got the code ready we took a drill bit slightly bigger than the chain "hooks" or whatever you call them. The machine then drilled a series of spaced holes all the way around the plate of aluminum. We then placed a mill bit in the machine and machined half of the holes away.

Here are some pics of our arm's gears:

http://www.tigertrons.com/Pictures/2...n/100_0596.JPG
http://www.tigertrons.com/Pictures/2...n/100_0710.JPG
http://www.tigertrons.com/Pictures/2...n/100_0716.JPG

These worked great for us. We also made some 50 tooth sprockets for #35 chain in our drive train

how well did they do with the chain? did it slip any? was there a harsh destruction of metal noise? and how much did it weight?

[team222badbrad]

They did great with chain. No slipping or anything. We did have a little side wear on the drivetrain due to misaligned sprockets/chain. We have been through 10 competitions with these sprockets and they are still working.

I do not have an exact weight, but I think they weighed half as much as the steel sprockets!

You do not need any fancy programing to make a sprocket work.
Just a simple program, CNC mill, mill bit, and a drill bit!

[KathieK]

[quote=Cory]I seem to remember Team 173 saying that they made sprockets on their CNC machine, either for themselves, or to sell for a profit. Perhaps one of them could elaborate.[quote]

I'm sure that one of our CNC Committee members can elaborate. But yes, we make our own aluminum sprockets - CNC Software (producers of MasterCam Software) is one of our sponsors!

You are not that far from us - perhaps a field trip is in order?

[Travis Covington]

The machinerys handbook has all the ANSI Sprocket Tooth Forms for roller chain sprockets. It also has all the neccesary information for flange thickness and tooth section profile dimensions.

It is not super complicated to create a sprocket. Sit down with the tooth form and profile information and you should be able to make a CAD/CAM drawing fairly quickly.

[Tom Bottiglieri]

RAGE cnc'd us some sprockets out of delrin for testing purposes in our drive train... which reminds me we should test them lol. Compared to steel, these things were as light as air and seemed to be pretty strong. I'm not sure if it will hold up through the bashings of our transmission though

[Dick Linn]

Since we don't have access to a milling machine, I've been trying to find a source of reasonably priced aluminum sprockets. This may be a good source

http://www.jackssmallengines.com/gok...msprkt_35f.cfm

19 to 94 teeth, prices from $14 to $36. Looks like they will custom drill them, though they don't list the cost for that.

Now all I need is a reasonably light flange with a keyway to attach them to a 1/2" or 5/8" shaft.