25# Sprockets
 

Hi,
Are there teams that make their own sprockets?
if so;
What type of metal and width?
Do you have any CAD to show examples?
do you have any tips?

Re: 25# Sprockets
 

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

Re: 25# Sprockets
 

We've cut a few in a pinch on our router in a pinch. They're pretty quick to cut, and we've always just used the largest cutter that fits in the tooth. We've cut both #25 and #35.

With how cheap they are from AndyMark and Vex, we prefer to buy them whenever possible.

Re: 25# Sprockets
 

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...

Re: 25# Sprockets
 

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 ... ::ouch::

Re: 25# Sprockets
 

As mentioned above, most teams don't do it due to the fact that AM (and similar) sprockets are so readily available and cheap. I am sure, however, that there are a few teams out there that do it just for giggles.

It is relatively light on the design process. Drawings for the sprockets are readily available online from various sources. Drawings can also be done easily with a tool in inventor (don't ask me how, but I've seen it done).

Once you have your design, you have to choose your manufacturing process. A popular method is to use a waterjet to cut them out of a sheet of 6061 aluminum that is .125 of an inch thick. I prefer the waterjet idea as it allows you to make a lot of them at one time and minimizes machine time.

Re: 25# Sprockets
 

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.

Re: 25# Sprockets
 

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.

Re: 25# Sprockets
 

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). :yikes:

Re: 25# Sprockets
 

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"+.

Re: 25# Sprockets
 

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.

Re: 25# Sprockets
 

Where did you try getting CAD from?

Solidworks or Inventor Built in generators?

-RC

Re: 25# Sprockets
 

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

Re: 25# Sprockets
 

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

Re: 25# Sprockets
 

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.

Re: 25# Sprockets
 

Are you unable to use the Vexpro sprockets?

Re: 25# Sprockets
 

I've been meaning to run plate sprockets and gears on a sponsor's laser, do you have experience with any pros/cons of having them waterjetted vs laser cut?

Thanks,
Akash

Re: 25# Sprockets
 

It really depends on the specific machine, and the knowledge of the person operating it.

First I'd say get some samples cut, and see for yourself. That trumps all advice I'm about to give.

We've had gearing water and laser cut on multiple different machines and different sponsors.

Most waterjets take a real quality hit on curved teeth as the cut is slowed down and excessive blowout seems to happen. The lower the toothcount, the more the teeth are curved. Even with this, pretty much every gear we've cut at 16DP or larger (including a 9T pinion) has run fine after some wear in. Our swerve also ran a 50T 20DP gear that ran fine.

When you get into huge gears, like the 300ish toothcount 24DP turret gear for Encore, the teeth are essentially straight and the smaller toothsize isn't really an issue.

Every waterjet gear we've cut has required some run/wear in, but has performed fine and lasted the season.

For Lasered gears, if they know how to run their machine right, you should get far better results that allow much more freedom in terms of small teeth and small toothcount. I did have one laser run that was just too gummed around the edges and was a total failure; this however was from a company that primarily worked in steel, and never worked on parts with fine detail.

As for sprockets, pretty much everything should work. For some waterjets you may want to artificially shrink the sprocket a few thou. Wear in will also be necessary (but can be done on the final vehicle of course) unless they are nicely tumbled or something. Laser should make beautiful sprockets.

In summary, we love it as a process. It's not the greatest method for small gears, and small teeth; but these are the easiest gears to cheaply get premade, so it isn't really an issue.

Re: 25# Sprockets
 

We routinely make our own #25 sprockets from 0.09" plate aluminum on the waterjet. 6061 works fine.

We also used custom sprockets in our drivetrain this season using the same process....no maintenance and no failures.

Re: 25# Sprockets
 

Thanks for all the input and feedback!

One more item: Would the heat from the laser make the teeth brittle or anything?

Re: 25# Sprockets
 

If anything, should anneal the metal, unless you quench the part after fabrication.

Re: 25# Sprockets
 

Don't take this as fact. I would wager it anneals the material, but I've heard that if the settings are correct it can locally harden.

I'd ask the shop to be sure.

Re: 25# Sprockets
 

Will do!

Thanks,
Akash

Re: 25# Sprockets
 

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

Re: 25# Sprockets
 

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.

Re: 25# Sprockets
 

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

Re: 25# Sprockets
 

That's why 254 does it.

254 is still forced to use 1/2" hex on the gearbox though.

Re: 25# Sprockets
 

Exactly. .500 PG 7075 round. Mill the hexes, done deal.