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Unread 10-09-2006, 15:06
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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.

Last edited by Tristan Lall : 10-09-2006 at 15:08.
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Unread 10-09-2006, 15:12
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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.
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Unread 10-09-2006, 15:35
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Re: Fabricating Aluminum Sprockets

Quote:
Originally Posted by sanddrag
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.
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.
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Unread 10-09-2006, 16:54
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Re: Fabricating Aluminum Sprockets

Quote:
Originally Posted by Tristan Lall
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.
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?
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Unread 12-09-2006, 08:27
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Re: Fabricating Aluminum Sprockets

Quote:
Originally Posted by Andrew Blair
One quick question though- does low heat like that (~350 degrees) really remove cold work properties?
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.
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Unread 12-09-2006, 08:45
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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.
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Unread 13-09-2006, 11:25
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Re: Fabricating Aluminum Sprockets

I would not recommend plasma cutting because it will affect any heat treating and it will laso not leave a smooth surface for the sprocket teeth.
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Unread 17-09-2006, 22:04
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Re: Fabricating Aluminum Sprockets

We've done custom sprockets on a CNC router with great success, so I'd say just do it on a CNC mill or router and find another project to mess around with your new plasma cutter.
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