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

Re: Lasercutting Spur Gears?
 

watterjets can do prety much anything , but only one axis at a time, these sprockets had to be file'ed in between the teeth because the tolerances weren't perfect, but never the less its an awesome machine , i wish i had one in my room. prety much anything is possible its completely indiscrimnate with materials you can cut thru anything

Re: Lasercutting Spur Gears?
 

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

Re: Lasercutting Spur Gears?
 

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

Re: Lasercutting Spur Gears?
 

We have two waterjet machines at NASA Langley, one is 2' X 4' capacity and the other is a 4' X 8' machine. The diameter of the jet stream and resulting minimum corner radius is .020" (when machine is properly maintained). So if you can live with that much radius for accepable clearance in your gear design you are o.k. with a waterjet...something the size of that small gear on the drill motor...forget it.

As for the "funneling" that will angle the sides, we have an articulating head on the big waterjet that completely eliminates that! The machines internal software looks ahead at the part geometry and compensates for stream cone/funneling and lag. So if you send this work out you can specify that type of machine. Ours is a Flow Bengal 4X8.

I have used gears made of 3/8 inch aluminum plate that were waterjetted on the older machine and the fit was great as long as you reverse one so the angled sides compliment one another! (Relativley low rpm use)

The maintainence issue stems from the orifice that the high pressure water (50,000 PSI) and abrasive sand passes through, it is made of ruby but will wear over time and the stream diameter gets larger.

Re: Lasercutting Spur Gears?
 

I talked to our laser guy and he said if I can draw it he can cut it. He said the finish will not be as good as something you could buy but it should be acceptable for the use. Now I'm just wondering how to draw it? I have no idea how. Also, I was wondering if the gear can be machined on something like a 4 axis CNC. If we put round stock of the proper OD in the 4th axis the machine can index it for cutting the groove between each tooth. However, I have no clue as to what tool (or if one even exists) to cut the teeth in size of gear. Any insight?

Last, I have one more question. Is 3/16 wide steel gear witrh a 2mm keyway (8 mm bore for the Chia shaft) enough to hold the torque it will have on it. Will the keyway strip out or enlarge or should it be okay since it is steel. Now, we could always go to a titanium gear. No joke. The laser cuts it very nice.

Anyway, my end goal in all this is to get another source for these gears besides PIC. If we make them, it would not be much harder to make 20 than it would be to make 2 so we could make it easier for everyone.

Re: Lasercutting Spur Gears?
 

With good equipment, waterjetting's funneling shape can be removed. Our team used WireEDM (as Raul suggested) for our purposes.

We drove our treads this year with this custom cut gear:
http://www.chiefdelphi.com/forums/at...achmentid=1992

Which you can see on the robot:
http://www.chiefdelphi.com/forums/pi...&quiet=Verbose

We also used it for a veeery nice gear in our gearbox that I don't have a picture of at the moment. Regardless, WireEDM is the most precise way to do it. It's just painstakingly slow.

Re: Lasercutting Spur Gears?
 

I was actually able to redraw the one on firstcadlibrary with very little difficulty. So, I will be trying to make the 54 tooth one. Now, simple logic tells me that the actual height of each tooth should be the same between different sizes of the gears. The outside diameter of the 60 tooth gear is 43.4 mm. The root diameter of the 60 tooth gear is 40.25 mm. This is a difference of 3.15 mm. Is this difference number going to be exactly the same no matter what tooth count the gear is? PIC lists the difference between outside diameter and pitch diameter to be 1.4mm. So assuming all this is correct, the pitch diamter of a 54 tooth 0.7 module gear would be 54 x 0.7 = 37.8mm and the outside diameter would be 39.2mm. If we subtract the OD-root difference of 3.15 mm, the root diameter should be 36.05 mm. Is this correct?

Also, I assume the shape and dimensions of each tooth remain constant across the various tooth counts of a particular gear. Is this true?

Thanks.

EDIT: I called an EDM place and they said it would be something like $35-50 per piece and they could do it in a day. I forgot to ask if there is a setup charge. Would anyone here know? Because I don't want to call back because the guy was very hard to understand and he went on and on forever.

Re: Lasercutting Spur Gears?
 

Sanddrag,

With this web utility you will be able to generate accurate DXF drawings of ANY gear you will need. The laser should be able to directly import the DXF file you create and go to town on your new gears. There is also a provision for "offset" that would be the value of the laser diameter of cut.

I have used this, you will like it, and learn gear terminology too!

http://sinfor.lcs.mit.edu:8180/pcbmill/gears

df

Re: Lasercutting Spur Gears?
 

Whether or not there is a set up charge is a business by business (and sometimes job by job) thing. But since he was quoting by the piece and didn't mention it, then there probably isn't one. Though it wouldn't hurt to check.

The shape of the involute surface of the gear tooth does vary with changing diameters, but the other parameters (tooth height, addendun, dedendum, etc) remain the same. So you wouldn't want to design a 10 tooth gear and then just copy that tooth for a 60 tooth gear.

The interesting thing is that for conventionally made gears, you only need one hobb per pitch. All gears of a given pitch can be made from a single hobb, which is fairly straight forward to design. One instance where the old way might really be easier.

If your laser guy says he can cut it, and he isn't charging you, then I'd have him do it first. If he really can't produce what you need, what have you lost? But you're sure to learn something in the process.

ChrisH

Re: Lasercutting Spur Gears?
 

Could you please explain to me (or show a picture) of what the involute surface and hobb is? Thanks.

Re: Lasercutting Spur Gears?
 

It's convienient, but watch out if you want to cut those on a laser (or a waterjet or an EDM). The .dxf generated by this utility is only approximate--it doesn't contain a proper involute curve, instead relying on straight lines of just about the right proportion. For a large-pitch gear (over 20 or so), this might work, albeit with a lot of wearing-in necessary. For anything finer, I'd avoid it outright, except in an emergency (i.e. you need the 0.7 module gears yesterday, and PIC is out of the question because they take too long!).

Watch out for the potential for roundoff error when using this to create metric gears (by inverting the module and multiplying by 25.4)--it reports that my 84 tooth 0.7 module gear has 83.55 teeth (that's measuring at the intersection of the two straight lines on the tooth face--these should be a curve--and taking that to be the pitch diameter, then dividing in the module). Maybe this isn't intended to be the pitch diameter, but since there's nothing else specified....

This is a nice approximation for importing into a CAD system, if you feel the need to jazz up your drawings with actual teeth; bear in mind that I usually just draw cylinders in Pro/E, and mate them at the pitch diameter, or specify a few thousandths open centres (0.005" or so, depending on various factors).

So use it, just be warned that it might not produce "real" gears! (I've been searching for something like this that can put a real involute on the teeth, for exactly this reason--putting it on an EDM would simplify the supply chain for those stupid metric gears infinitely!)

P.S. Now that I look at the 20 pitch gear that it generates, there is more than one segment making up the "involute" surface--and there is no clearly defined pitch diameter--so maybe there is no roundoff error to speak of, and the intersection of those two segments on the gear face just happened to occur near where the pitch diameter was supposed to be. (So don't assume what I just did--that if there are two segments on a tooth face, that their intersection falls on the pitch diameter!) Also, finding several segments on the tooth face reinforces my thought that the accuracy of this tool diminishes with the decreasing pitch of the gear--big gears will have lots of segments, and therefore be better approximations (relative to their size) and small gears will be badly modelled.

P.P.S. So what? Maybe you could design a gear with 7 module, and scale it down by a factor of 10, and get a much improved approximation. Or 700 module, and scale by 1000. In fact, I think that I'll try that! (But careful: I know that CNC plasma and flame cutters don't always like lots of little segments on a toolpath--though they aren't accurate enough for gears anyway--but maybe EDM, laser and waterjet don't want small segments either?)

Re: Lasercutting Spur Gears?
 

I think I might know what the involute surface is. Is it the front or rear of the tooth? In the firstcadlibrary model it is curved a bit. So this curve changes with tooth count? Is there some sort of formula to determine what radius this curve is based on the number of teeth in the gear? Also, I'm still clueless as to what the hobb is.

Thanks for your help everyone. I am learning a lot.

Re: Lasercutting Spur Gears?
 

Let's start with the easy one first. A hobb looks a lot like a rack from a rack and pinion. I've only seen them in pictures but I'll try and explain them. The teeth on the hobb are trapezoids with the angle on the trapezoid being the pressure angle of the gear. When making a gear, a blank is placed on a rotating shaft and moved up and down in relation to the hobb. The hobb scrapes out one gap, then they rotate the gear one tooth and do it again. They keep it up until the gear is done. Or something like that.

The involute is a particular kind of curve. The easy way to picture it is to place a string on a round object like a can. Put a pencil in the string and unwrap the string while keeping the string tight, The shape you get is an involute. There is mathematical equation for it, but it is ugly. This year I generated a 30 degree pressure angle gear. It was a royal pain and took me several tries to get it right. Even then it was an approximation. I generated several points and then used a spline to connect them. The method I used to generate the points would take me at least a couple of pages to explain. If you do a google seach on Involute you will find tons of info including instructions on how to do a gear in CAD.

If there seems to be a heavy demand I'll do a paper on the creation of involute gears, but not until after Atlanta.

Chris

Re: Lasercutting Spur Gears?
 

So I tried it, and here's the result:

Here's the 0.7 module metric gear (84 teeth, 6 mm bore) that we used on our current gearboxes (you know, the 3-motor, 2-speed, shift-on-the-fly ones... :yikes: ). It's in AutoCAD 2000 .dxf format (zipped for fun),

Sure enough, the teeth are composed of little surfaces (0.001" long, or so), which approximate an involute. Does anyone have any experience feeding this sort of shape to an EDM, waterjet or laser, and if so, would it work without choking on the tiny little segments?

Re: Lasercutting Spur Gears?
 

I'm still a little unclear on exactly what the involute curve is on a gear but I think I am getting closer.

It is this:


Or this:


BTW this is the 60 tooth 0.7 module gear from firstcadlibrary.

Re: Lasercutting Spur Gears?
 

How does Ed Sparks draw those on firstcadlibrary? Is that a real involute, or is it a closely approximated constant-radius curve (i.e. segment of a circle)?

Here's how to calculate and draw an involute curve in Pro/E, and put it on a part--I didn't want to go through all of this, but maybe it's a better thing in the end. If you wanted to try it, maybe Inventor can do this too. (Then again, probably not.... :p )

Re: Lasercutting Spur Gears?
 

It's the top picture. Sometimes an involute is approximated with a radius, which is apparently what was done there. But a real gear has an involute.

ChrisH

Re: Lasercutting Spur Gears?
 

I believe Ed Sparks' model is a closely approximated constant-radius curve (i.e. segment of a circle). Now understanding what an involute curve is, I have a new question. Will gears work with either an approximated constant-radius curve or a straight face tooth?

Re: Lasercutting Spur Gears?
 

For those that are interested:
http://www.metalworking.com/DropBox/GearHobb1.JPG

And I have a question. What radius circle is used to generate the involute curve? Does it change from gear to gear? I'm assuming the circle shares it's center with the gear, but it seems like it should have a smaller radius as the tooth face is not perpendicular to the face it intersects on the gear.

Greg

Re: Lasercutting Spur Gears?
 

The involute , or ever increasing radius surface, maintains the proper angular contact of the two mating gears as they mesh with each other to drive your robot. As the one gear tooth drives the other, the point of contact will move along the surface of the gear tooth involute surface. The inner area of the driving gear tooth will engage the tip area of the driven gear and as it rotates through, this contact point will be eventually be at the tip of the driving gear. As all of this is happening the gear teeth that are about to mesh have a certain amount of clearance that grows smaller as they too begin to completely mesh.

It is the geometry of the gear teeth that allows the smooth transmission of power without binding and conflict in the case of a too tight condition, or backlash and high impact damage in the case of a sloppy fit between the teeth.

I would be happy with line segments as small as .001" by the way, thanks for checking that out. I have been using Anvil 1000 (CAD Program) for the stuff that goes to the waterjet and as I zoomed on the tooth detail, I could tell it was far in excess of the precision we needed for our applications. Maybe seat of the pants, but there you go.

Re: Lasercutting Spur Gears?
 

Now that you mention it: for anyone intending to use this shape, I think I should make exactly clear how I got the 0.001" segments--I said something about it earlier, but I'm not sure if I was explicit enough. So, to replicate my 84 tooth, 0.7 module gear (with 6 mm bore), do this (these instructions assume you want an "accurate" model for CAD work--if you're setting a toolpath, you'll need to eliminate some excess geometry later, and make adjustments for your CNC machine):

1. Go to the DXF/SVG Gear Generation Utility v0.98, and set the following options:
   • Gear Type to Spur Gear
   • Diametral Pitch to 0.03628571 (i.e. 0.7^-1*25.4/1000, which converts 0.1 module to the diametral pitch--its inverse, then converts to inches, then divides by 1000 for the fun of it--this is where the precision comes from; we're tricking the applet into giving us lots of line segments, then scaling them to meet our needs!)
   • Number of Teeth to 84 (or whatever you like, really!)
   • Pressure Angle to 20 (that's what these PIC gears were, but Boston, Martin and others make both 14.5° and 20° pressure angle gears--they aren't compatible, so be sure what you've got)
   • Addendum to 1.00 (a guess, because I don't have the exact spec on hand--but this is a logical value)
   • Dedendum to 1.20 (again a guess, for the same reason--this uses the fine-pitch AGMA Imperial spec)
   • Shaft Diameter to <cleared> (don't bother--it's made of segments too--unless you're feeding this straight into a CNC machine, and have no CAD capability, in which case, this approximation will have to do)
   • Mark Center [sic :p ] of Gear with Crosshair to <checked> (because it's useful for drawing--when you set the toolpath, don't include it, though!)
   • Format for Result to DXF (if you can use SVG, go ahead...)
   • Offset Amount to 0.000 for drawing purposes, or some appropriate value for your machine--this varies, and you'll have to find out for yourself.
   And press Go!
2. Save the file that comes up for download somewhere.
3. Open it in your favourite 2-D CAD program (AutoCAD 2004 in my case) and go to View | Extents, which shows everything.
4. Select everything, and type in the command window the following
   Code:

   ---

   scale
0,0
0.001

   ---

   This shrinks the drawing (scaled about the centre point) by a factor of 1000, which is what you're looking for--remember we made the whole thing 1000 times too big by dividing the pitch by 1000 (small pitch number=big teeth).
5. Now type this:
   Code:

   ---

   c
0,0
0.11811

   ---

   This puts in a 6 mm bore circle.
6. Now draw a circle centred at the centre, and with radius snapped to the endpoint of the crosshairs (which were drawn in automatically by checking the checkbox!). The circle's diameter is your pitch diameter--and if it isn't, you messed up! Don't cut that!

Otherwise, you now have a gear like mine! If you measure the individual segments that make up the gear teeth, you'll find them to be around 0.001" long, as opposed to between 0.028" and 0.036" long if you hadn't done the factor-of-1000 thing. Of course, you need to know whether your CNC machine will cough and die if force-fed about 13411 different line segments at once! (That's really how many there are.)

Of course, you may be able to model a gear with a simple pitch circle (or cylinder in 3-D); maybe this is wasted effort? (It depends on why you want a gear-shaped thing--if it's cutting, of course you need the shape; if it's drawing, usually, the pitch circle is enough.)

And for the Pro/E users out there--use that formula thing (that I mentioned earlier) instead, if you can get your head around it! Don't mess with an approximate .dxf, if you can help it, especially because most of those 13411 segments will spawn an attached surface on the model (which makes everything ludicrously slow), if it doesn't annihilate your sketcher, resulting in one of Pro/E's endearing (and sudden) crashes. (And if you use Pro/MECHANICA for anything, use a plain old cylinder--or load a simplified rep!!! :eek: )

Re: Lasercutting Spur Gears?
 

I dont know about much about making gears but I can tell you a good place to purchase spur gears!
http://www.martinsprocket.com/
We used 20 degree pitch spur gears from this company in our 3 speed shift on the fly transmission

This year we made a sprocket for 35 pitch chain using our high schools CNC mill. We used a drill bit and put holes all the way around the aluminum disk. Once all the holes were made we toik a mill bit all the way around the outside leaving half circles for the chain to catch

They can be seen here: http://www.tahsroboticsteam.org/Pict...n/100_0716.JPG

Re: Lasercutting Spur Gears?
 

If you want to learn alot about gears, then check out this link:
http://www.sdp-si.com/D190/D190cat.htm

You can get a free hardcopy too.

Re: Lasercutting Spur Gears?
 

Sandrag,

We use a laser here at my facility. For the robot, we have made structural channels (arms/masts), pulley discs chassis side plates and drill motor mounts to good effect in the past couple of years.

I'm told the cutting tolerance on our Trumpf laser cutting machine is about +/- .002 inch in thin material (say under .25 inch thick). Given that, and making a quick judment call, I would avoid cuttting any gear teeth with a tooth thickness less than say 50x to 100x that (so minimum .10 or .20 inch chordal thickness at pitchline)

#25 chain/#35 chain sprockets are a natural for lasers, especially handy are large diameters for arms etc, . Cut 25 chain sprockets from .100 inch thick aluminum sheet, just be sure to use a strong hard alu. alloy.
Large diameter sprockets can be sandwiched against a stiffener disk if needed for stability. (stifferner disc could be 1/4 inch plywood, alu, lexan)


Drop me a line if you are still gathering info on this gears/sprockets/laser cutting etc. A short phone conversation would probably be worth an hour of working through postings.
Jesse