25# Sprockets

[yarden.saa]

Originally Posted by nathan_hui

Is there a particular reason you want to make your own sprockets? Doing so requires either a CNC machine, rotary table, or indexing head.

Yes, we have a factory that can make it. The reason is that it will save us a lot of time and money. We are from Israel and we have to pay 40% more on everything from ths US (taxes, customs, shipment) and it takes about 2 weeks of shipment...

[DELurker]

I'd advise going to a bicycle shop instead. Or converting over to timing belts. Or buying Eagle V-Belting from Fenner Drive and using V-sheaves so that you can choose your custom lengths and make much simpler rotating parts.

However, if you want (or need) to make your own sprockets, I would recommend downloading the Martin catalog PDFs (http://www.martinsprocket.com/suppor...atalog-online). The materials and dimensions of the sprockets should all be in there. You should be able to fabricate your sprockets from there.

One recommendation would be to use a hardenable steel and flame-harden the teeth. A lot of sites abound on the web that can advise you how do do it properly. As always, safety first ...

[AdamHeard]

Originally Posted by DELurker

I'd advise going to a bicycle shop instead. Or converting over to timing belts. Or buying Eagle V-Belting from Fenner Drive and using V-sheaves so that you can choose your custom lengths and make much simpler rotating parts.

However, if you want (or need) to make your own sprockets, I would recommend downloading the Martin catalog PDFs (http://www.martinsprocket.com/suppor...atalog-online). The materials and dimensions of the sprockets should all be in there. You should be able to fabricate your sprockets from there.

One recommendation would be to use a hardenable steel and flame-harden the teeth. A lot of sites abound on the web that can advise you how do do it properly. As always, safety first ...

This is all true, but is way overkill.

Sprockets for FRC use can be cut by just about any 2d method (CNC router, mill, waterjet, laster) into 6061 Aluminum plate and be just fine. The cut time isn't crazy high to do so either.

[tim-tim]

I know of a few teams that make their own sprockets (for various reasons), and to ease the manufacturing process make the sprockets from .090 thick gears. By doing this the gears don't need the taper (chamfer) on the teeth.

Typical materials would include 6061-T6 and 7075-T6 for aluminum.

[DELurker]

Is aluminum strong enough for the shocks? I'm having a little trouble picturing one of our drivetrains using aluminum sprockets and steel chains surviving a season, especially since we're in a district (about 50 matches if you do well through district championships).

[AdamHeard]

Originally Posted by DELurker

Is aluminum strong enough for the shocks? I'm having a little trouble picturing one of our drivetrains using aluminum sprockets and steel chains surviving a season, especially since we're in a district (about 50 matches if you do well through district championships).

Yes, we had 16T #25 aluminum (7075) sprockets on 6" wheels this year, that's a very high tooth load.

Pretty much any plate sprocket (the smallest available from vex/andymark is 32T #25) will be strong enough unless the wheels are massive. As in 12"+.

[sanddrag]

We machined 22 tooth #25 sprockets from 7075-T6 bar stock due to the quantity we needed. Took probably 10 minutes apiece including hex broaching. Saved hundreds of dollars doing it ourselves. Had to play with cutter comp for chain fitment. Had trouble finding accurate CAD.

[R.C.]

Originally Posted by sanddrag

We machined 22 tooth #25 sprockets from 7075-T6 bar stock due to the quantity we needed. Took probably 10 minutes apiece including hex broaching. Saved hundreds of dollars doing it ourselves. Had to play with cutter comp for chain fitment. Had trouble finding accurate CAD.

Where did you try getting CAD from?

Solidworks or Inventor Built in generators?

-RC

[AdamHeard]

Originally Posted by sanddrag

We machined 22 tooth #25 sprockets from 7075-T6 bar stock due to the quantity we needed. Took probably 10 minutes apiece including hex broaching. Saved hundreds of dollars doing it ourselves. Had to play with cutter comp for chain fitment. Had trouble finding accurate CAD.

for $5 each, I'm surprised you did this! That's a crazy amount of work to avoid a $5 sprocket.

[yarden.saa]

Thanks!
We will probably make a few in order to learn how to do it, and then we will decide if it worth the time

[sanddrag]

Originally Posted by AdamHeard

for $5 each, I'm surprised you did this! That's a crazy amount of work to avoid a $5 sprocket.

More like $12 each. Hubbed sprockets. It's only probably $2 of bar stock so there's some savings. Not much trouble at all in a VMC. On a router I wouldn't bother.

[Cory]

Originally Posted by sanddrag

More like $12 each. Hubbed sprockets. It's only probably $2 of bar stock so there's some savings. Not much trouble at all in a VMC. On a router I wouldn't bother.

Are you unable to use the Vexpro sprockets?

[sanddrag]

Originally Posted by Cory

Are you unable to use the Vexpro sprockets?

Need 7/16" hex. If they made them in 7/16" hex, we'd be all over it.

[Redo91]

We had our sponsor laser cut some steel sprockets for us when I was a student. The only trouble we had was the chain would skip off. That was solved by beveling the teeth on a belt sander. We never had an issue with them after that.

[R.C.]

Originally Posted by sanddrag

Need 7/16" hex. If they made them in 7/16" hex, we'd be all over it.

Do you use 1/2" hex on the other side for the wheel?

We do the 7/16" step down as well (thanks adam!) and we love it. But the sprocket side is 1/2" hex.

I can see why its 7/16" on both sides as you can just buy precision 7075" (1/2" round) and just hex the portions you'd like vs machining everything down from a larger size. Is that the reasoning?

-RC