Lasercutting Spur Gears?
 

Can spur gears be lasercut or waterjetted? I've seen a lot of both lasercut and waterjetted pieces and I really have no idea if gears are possible. Thanks.

Re: Lasercutting Spur Gears?
 

waterjets are able to cut anything...to a point.

a machine shop i used to work in just purchased a cnc waterjet, and i was there for the test cut after installation. the technician took a peice of 2-1/2" thick stainless steel, and cut a biohazard logo out of it. took 1 minute to do all the intricate details it had

amazing. so certainly, you could cut your gears with it.

ps... waterjets cut glass too ;)

Re: Lasercutting Spur Gears?
 

Something you should be aware of is precision in deep cuts. For gears, you don't have any room for slop in construction, because of the way that the teeth roll off one another.

Water jets are reasonably precise, don't get me wrong. I just got finished with a manufacturing class last semester, and one of the things you need to be aware of is that water jets tend to cut wider in thicker material, it sort of funnels out. If you're trying to make any sort of thick , fine pitch gears, you may want to make sure they'll hold your accuracy.

In addition, gears are often heat treated, surfaced hardened / coated to increase their lifespan. Typically, I think that gears used in FIRST robots take a lot of untraditional abuse to begin with, so you may want to think about your application.

Good luck!

Matt

Re: Lasercutting Spur Gears?
 

I was a little concerned about the surface finish of the cut with a laser or water machine. What I have seen doesn't seem nearly as smooth as a purchased gear. Will this be an issue? However, I know at least with the laser the quality of the cut depends on what type of gas and how much of it is used in the process. Also, I was wondering now if the laser machine would have a tendency to funnel out? The material would be 3/16" steel.

Re: Lasercutting Spur Gears?
 

Why, exactly, do you need these gears laser cut or water jetted? The processes entail considerable expense and as you've noted, might not give you an incredibly good surface finish. If you can find a source for your gear as a stock part, even if it must be lathed, or cut to length or some such, it would be vastly cheaper and easier. If delivery time is not a concern, you could even have a gear company custom machine your gears if they're some odd-ball tooth number or face width.

I think we could find a much cheaper source for you if you'd tell us in more detail what you're looking for.

Re: Lasercutting Spur Gears?
 

Lasercutting produces a tapered cut (funnels out as others have called it). I suggest using a wire EDM process for custom gears. Wire EDM can be extremely precise.

Re: Lasercutting Spur Gears?
 

Having worked with both laser and waterjet, I'll have to agree with Raul. Both laser and water jet cutters tend to have a kerf (the technical term for the material the saw removes) that gets wider with depth. With the water jet this can be mitigated to some extent by reducing the cutting speed, but it will always be there. Both waterjet and laser are best suited to relatively thin materials.

Wire EDM on the other hand can have a kerf as small as 0.0005" and while the speed of cut is dependent on thickness, the kerf width is not. So you can get some pretty straight polished looking cuts. It is also not terribly expensive and most EDM shops have software that allows you to just tell them the # of teeth, pitch and face width of a gear. They can do the program in a couple of minutes from there. There are a couple of good EDM houses out Sandrag's way but I'm not where I can dig up their names at the moment.

Re: Lasercutting Spur Gears?
 

The other problem with lazed or water jet cutting for such a piece is the surface finish will not be as good which could lead to F.O.D. Also the heat from laser cutting would change the material properties on the wear surface of the teeth. You have to consider a potential surface treatment to harden the gear afterward.

Re: Lasercutting Spur Gears?
 

Thanks for all the input. I was just curious since we have lasercutting companies as sponsors who are willing to make stuff for us. The gear I was referring too would be the PIC 0.7 module one that takes so long to get.

As for wire EDM, I know there's got to be a place within 20 miles (Sun Valley is like the industrial capital of the western United States). I just checked and there is a place in Chatsworth. I have know idea how much such a thing costs. I'm guessing the increased cost of a custom gear would not be favorable over the 4-7 week waiting period of the PIC gear. Has ever had a gear cut who could tell me how much? Thanks.

Re: Lasercutting Spur Gears?
 

I've never actually had a gear cut. A few years ago I did some research into who to go to and what it would take to get the work done. Then FIRST went and threw open the Parts List. So I never actually needed to use the information.

I seem to remember Dr Joe saying something about paying $60 for a custom aluminum sprocket when the off-the-shelf steel one was $40. But that was two or three years ago. The cost for EDM is driven by the material to be cut, its thickness, the kerf width (very small kerfs are more expensive, probably not an issue here), and the length of the cut. For a real small gear like that, the setup charge will probably be the biggest item. I would expect some premium over an off-the shelf item, but it shouldn't be more than twice a stock part and 150% would be reasonable.

I'm sure you know how to pull the "But we're just a poor high school robot team" thing to lower the cost. Be sure to point out that you are a future engineer (and therefore a potential customer). If you're willing to wait until they have some time the machine isn't scheduled for a paying job, then you might even get it free.

Re: Lasercutting Spur Gears?
 

Now another question: Can sprockets be lasercut out of the correct thickness of plate? Like how thick are #25 sprockets at the teeth anyhow? I don't remember if the thickness tapers off at the teath or not. Thanks.

Re: Lasercutting Spur Gears?
 

Laser cutting is used best on sheetmetal application like that. You could laser cut an aluminum sprocket but be careful with your material choice or you'll destroy the teeth pretty quick.

My $0.02
If I had free access to laser cutting I would design the entire frame structure out of monocoque aluminum to save weight. I would bend everything on a press brake, and use solid aluminum (aircraft style) rivets to assemble it. That is how I see the best application of that manufacturing method anyway.
-Pete

Re: Lasercutting Spur Gears?
 

quick note aobut water-jet cutting... the last time i had something water-cut, the jet spray expanded the further it went, so we ended up with a non-perpendicular edge (if only barely, but it was noticable, and it was only 1/4 inch thick.)

so i don't think water-jet cutting would be the best for sprockets, considering they have to mesh. laser might work, but water definitely won't.

Re: Lasercutting Spur Gears?
 

#25 sprockets typically have a thickness of 0.110", but the teeth are tapered slightly to the face of the tooth. I'm not sure what the face width at the very end of the tooth is. If you want to have your own #25 sprockets water/laser cut, (if I were qualified to make suggestions like this) I'd suggest getting plate the thickness of the end of the tooth and having that cut, but I'm not sure what function the taper performs (stabalizing the chain, I would imagine), so perhaps this is absolutely the wrong thing to do.

If you're dead set on making sprockets, you might consider getting cylinder stock of whatever material you're going to use, and turning it down to get the base structure of the sprocket (including a hub on each side, for this next step), and then tapering the circumference down, yourself, by hand. Then you'd laser/water cut the teeth into it. When you turn it down, you'll need to calculate the outer diameter from your intended tooth count, which just adds more complexity.

This all sounds like it could be a lot more trouble than it's worth, though. :)

Re: Lasercutting Spur Gears?
 

The taper exists as a pickup or lead-in. Its job is to keep the edges of the sproket from coming into contact with the edges of the chain. Idealy, the only contact you want between a chain and a sprocket is with the chain rollers.

The taper allows us to build robots with misaligned sprockets!

A lot goes into the design of a sprocket. You’re probably best off buying one (unless making one means you’ll get to play with an expensive cutting machine :) ). The taper should be easy to cut on a lath.

Greg