Fabricating Aluminum Sprockets
 

We're interested in possibly producing ANSI #25 pitch sprockets from aluminum. We have a plasma cutter, so cutting the tooth profile ought not to be too difficult.

I have vague notions of processes like heat treating, but no real experience with the craft; nor have I ever heard that sort of thing discussed with respect to aluminum.

Does anyone have any experience with the process of making your own sprockets from aluminum that might also have some tips to share?

Thanks.

Re: Fabricating Aluminum Sprockets
 

Talk to RAGE. Their 2005 bot had a massive #35 er that they did. I think they milled it though. As far as heat treat goes, I would suggest finding a sponsor to do it. That stuff can get difficult really fast.

Re: Fabricating Aluminum Sprockets
 

1114 has been machining our own aluminum sprockets for about a year now. We use a bench top CNC machine(like those found in many high schools) and a plain endmill. 1/8th for #25 and 3/16 for #35 sprockets.

We usually just use 6061 aluminum plate. Again 1/8th thick for #25 and 3/16's for #35 sprockets. We've never bothered heat treating them

After the milling is done, we put a slight chamfer on the teeth in the lathe. And a little deburing later and your done.

One of the really nice things of making your own sprockets is that you can put your own lightening pattern and bolt pattern in, and as long as it can all be completed without removing the piece, you don't need to worry about re-zeroing the machine. Everything comes out nice and concentric.

Due to the relatively small size of the milling machine we use, the biggest sprocket we can make is about 6.5" in diameter. That works out to something like 80 teeth for #25 or 53 teeth for #35.

We actually cut some out this afternoon for an off-season project we're working on. I've attached a jpeg of the inventor drawing. I don't have a descent camera with me, or I would post an actual photo of the finished product. It was 40 tooth #25.

Re: Fabricating Aluminum Sprockets
 

Unless your plasma cutter is CNC, I doubt it would work very well.

Re: Fabricating Aluminum Sprockets
 

It is.

Edited to add: We also have a CNC mill and CNC lathe, but we're interested in doing this only if we can do it quickly. Milling anything takes too long for my MTV-generation attention span. :)

Re: Fabricating Aluminum Sprockets
 

Hah I wish I got into plasma cutting. But I think it would be a really difficult job to remove all of the melted aluminum inside the teeth. I'd perfer CNC Machining something of that sort. Anyways if you do decide to CNC machine the sprockets thennn i'll be right there awaiting to help :) Good luck :D

Re: Fabricating Aluminum Sprockets
 

Well then, it seems to me that if you have the right tip and dry air, it should work just fine. What is the width of a typical cut? You might want to throw the thing into something like a vibratory polisher when you are done.

Re: Fabricating Aluminum Sprockets
 

Unfortunately, we've not had a chance to play with it yet. It was just installed in the lab last week and we're waiting for them to finish things up with a hood, shields and all of the other things we need to make it safe to operate.

We're just really excited about the potential to speed the process of cutting plate along. There are a lot of things we'd have like to have done last season, but we skimped on a lot because of how long it took to set up and run the mill.

Re: Fabricating Aluminum Sprockets
 

For aluminum, it's important to have a really good cutter on your table. I assume it's PlasmaCam, or a knockoff. Our lab got one last year, and I was very excited to be able to cut out parts in house. However, this was not the case because the cutter was not of excellent quality, and while cutting Al, it just melted out of the cut path. A shop in town actually uses a special gas or gas mixture to facilitate plasma cut on aluminum.

Re: Fabricating Aluminum Sprockets
 

You might want to check the temperature of the aluminum surrounding the cut. Aluminum usually comes heat treated or strain hardened (or a combination), but additional (especially prolonged) heat can affect those properties. Consider using an IR thermometer or a thermocouple to check that you're not exceeding 350°C in the surrounding metal for very long—this will tend to anneal the material, leaving it much softer and weaker. You need to consult a graph of temperature vs. time to see if what you're doing will remove the heat treatment.

Maybe this isn't a big deal; you could conceivably not need the extra strength from hardening. That depends on the loads on the sprocket. Also, the heat treatment could be restored, even if it was changed by the cutting. While it isn't difficult, you'd need an couple of temperature-controlled heat treating ovens to do it.

The ASM handbook will have all the necessary temperature and hardening data for any given grade of aluminum. Also, try the aerospace materials handbook.

Re: Fabricating Aluminum Sprockets
 

And of course you'll want your feedrates to be as fast and possible while still making a clean burn, but perhaps the machine/software has something in there to figure that out for you. If not, a little trial and error is all it takes. I recommend you check out www.cnczone.com if you haven't already.

Re: Fabricating Aluminum Sprockets
 

One of the fantastic things that our mentor from Microsoft Research, Mike, does is to determine feedrates and the like in advance for the most common materials. The lab we use is shared by a lot of people at MSR, not all of whom are versed in machine shop operation, so by providing as much information to them (and us) as possible, Mike really goes a long way toward making sure everything runs as efficiently and as safely as possible.

I'm reading CNCZone.com now. The more we can learn before the machine is up and running, the better we'll be. We have a lot of work we want to do.

Re: Fabricating Aluminum Sprockets
 

Unfortunately for sprocket work, a plasma cutter will heat a relatively large area around the cut, and especially the teeth. Almost definently the teeth will lose their original heat treated properties, and obviously the teeth faces will. One quick question though- does low heat like that (~350 degrees) really remove cold work properties?

Re: Fabricating Aluminum Sprockets
 

350°C isn't really that "low", is it? (Note that that's in degrees celsius, in keeping with the traditions of the civilized world!) But yes, it can remove cold work effects in most alloys.

Re: Fabricating Aluminum Sprockets
 

on 179 we had great success water cutting sprockets out of 1024 high strength aircraft grade aluminum. it took some finish work with a file and a sander but they work extremely well. this past year we bought a plasma cutter. and tried some sprockets. What a mess! the plasma cutter itself is extremely inconsistent and melts allot of material away leaving some tough nasty slag all around any contoured edge. the heat warps plate to the point that whatever you cut was moving while it was being cut so accuracy is not guaranteed. to cut something as small as Usable #25 teeth is nearly impossible with a plasma cutter unless you has a submerged table to dissipate the heat.