Lasercutting Spur Gears?

[sanddrag]

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.

[Greg Perkins]

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

[Matt Adams]

Originally Posted by Greg Perkins

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.

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

[sanddrag]

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.

[Kevin Sevcik]

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.

[Raul]

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.

[ChrisH]

Originally Posted by Raul

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.

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.

[Peter Matteson]

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.

[sanddrag]

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.

[ChrisH]

Originally Posted by sanddrag

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.

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.

[sanddrag]

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.

[Matt Adams]

Originally Posted by sanddrag

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.

Despite that the .7 module gears are such fine teeth, I would imagine that these could be laser cut. Per a slide on some non traditional machining methods, lasers can drill holes as small as .0002 inches in diameter and cut with depth to diameter ratios of 50:1. However, this will largely depend on the quality of the machines they have. In addition, the opperating cost for these machines is low ($1.50 / hour), so assuming that they'd be willing to spare the labor cost (the bigger part of the equation, $20-50 / hr) I'd bet you could make this happen.

Good luck!

Matt

[Bob Steele]

On our robot this year we used several water-jet machined gears.
Specifically we used a hard plastic 6" gear which was approximately 1" thick and was used to operate our arm. The small gear which was attached to the Van Door Motor was also cut on the water jet and was made of aluminum.

These gears performed flawlessly for us after we figured out that we could not use softer plastic gears because of the stress on the teeth. The cog is quite handsome. I would add a picture but I don't know how to attach it here.
The actual gears are skeletized with a webbing of titanium plate that holds the aluminum hub inside...very striking as the plastic is blue.

We were lucky enough to gain a waterjet cutting company as a terrific mentor this year. It opened doors for design that we didn't have before and we are very grateful that he chose to join with us.

By the way, the taper can be compensated for, one of the waterjets that is owned and operated by Rolls Royce has this compensation. The one we were able to use did not. We did not have any problems though with the gear.
I would expect that if you chose to drive a gear more stressfully (IE in a drive train...) that you might see some problems. For our application it worked admirably.

I will post a picture in the gallery if anyone is interested.
One of our mentors also designed omni-wheels which were entirely cut on the waterjet as well. The only additional machining that was necessary were some grooves for the small wheel axles (millwork) and tapping the holes for the screws used to hold the assembly together.

Like any piece of equipment, the waterjet is not a complete answer.
I only know that it opened doors for us this year that helped us immensely.
Thank you ... Mike Trapp and WaterJet Cutting of Indiana.

thanks
Bob