Designing wooden gears

[shoeshine]

Hey All,

I am interested in creating some hand cranked automata for the local kids museum.

Does anyone know of a good reference to design and get to cutting files for wood gears?

software, online reference or even book?

I am finding that I can make drawings that look good but require a huge amout of fiddly hand filing to get them to actually work, even under this kind of low tolerence situation

any info or leads appreciated.

Chris

[myxpykalix]

I think i have some dxf's of gears already drawn do you want them? (have to find).

[shoeshine]

Thanks Jack, yeah, I'd love whatever ya got. especially if you have a set that all work together.

Eventually I'll probably have to figure out how to calculate them myself, but anything to get me going would be great.

[wberminio]

if you don't mind posting them here,I'm sure others wood be interested

[rob_bell]

I found this little app to be very helpful.

http://www.forestmoon.com/software/GearDXF/

[myxpykalix]

I have 28 files that zipped are 3 megs. Can you take a 3 meg file in your email?

[shoeshine]

Yup. up to 10mb
[chris(at)schaie(dot)com]

Thanks Jack.

and I can put em up on my server and post a link if anyone else here wants them.

[scottbot]

This might help.

http://www.woodgears.ca/gear_cutting/template.html

[myxpykalix]

email sent

[dana_swift]

Chris - I have cut wooden gears on my shopbot. Do you know anything about the gear specs you need? I have a program that will give a DXF for any involute gear configuration. It will design inside or outside teeth.

Also when you cut gears use the smallest possible bit, even when you have a large tooth pitch. A 1/16 bit is nice for the gulley detail.

I have cut gears with pitches of 0.25 up to 1.0.

Things I need to know to design two mating gears:

The number of teeth for each gear.
The axle-axle distance.
The diameter of the shaft hole.
The hole diameter and center radius of hub holes.
The percentage height of the involute (65% typ).
The pressure angle (25 deg typ)
The backlash percentage (2% typ)

Once I enter that info, the dxf's are generated automatically. You can toolpath them in PW.

If you are interested, get me the above numbers.

D

[shoeshine]

I appreciate the offer Dana, this is just at the proposal stage at the moment so I dont really have specs yet, but I will definatly take you up on it.

Do you mind me asking what software you are using to generate the DXF?

also Jack, do you mind me posting those gear files? some others have expressed interest.

[dana_swift]

Chris one more thing-

Look into the book:

"Making Mechanical Marvels In Wood"
ISBN 0806973587

It may be of use to you..

D

[ron brown]

I have been playing with something that needs gears. I found this to be very helpful.

http://www.cartertools.com/involute.html

Thanks Rob Bell for the DXF file link. I will try that as soon as possible.

Ron

[gene]

Scott,
Is there a way to draw the gears and save the drawing to be imported into aspire for cutting?

[scottbot]

Gene,
Click on the link that Rob Bell added to this thread. The program the link takes you to will allow you to put in the variables you want for the gear and then saves it as a .dxf

I've used it and it works very well.

Scott

[shoeshine]

Hey Gene,

funny, I was just working with this today.


4676

you can use the http://www.woodgears.ca/gear_cutting/template.html
link to create cutting files. When you hit "print" print to PDF rather than your printer. the vector data is saved. you do need to take one intermediate step through Illustrator or Corel or the like and save the vector data in a way that PartWorks can understand. (I dont have aspire so you might try that directly)

note: you do have to tweak the gears slightly if they are small as the points don't get rounded enough with default toolpathing. ( in the above image I dogboned the bases of the teeth on the planetary gear to make sure it worked. but this was only 3.5" diameter)

Chris

[adrianm]

Partworks V2 (not sure about V1) will open PDF's directly.

I use CutePDF as my printer.

[shoeshine]

Adrian, unfortunately something about the way that site generates the file or the way Acrobat prints the pdf confuses PartWorks. Trying to import it directly using PartWorks v2.015 I get the error that the pdf "contains only bitmap data". Not true. The vector data is there, but I had to run it through Illustrator to get at it.

[adrianm]

Chris, sorry I didn't make myself very clear.

It's the use of CutePDF that creates the PDF in vector format correctly from that site. I had similiar issues as you with the native Adobe PDF writer.

I've found this with other programs/sites. Adobe creates the PDF as an embedded bitmap but CutePDF creates it correctly as vectors.

[john_l]

Scott and Chris, thanks for mentioning that site. Pretty awesome.

Chris.. very neat project. What exactly is that thing?

[shoeshine]

John, it is a Widget.
On star trek set it would be labeled GNDN-01.
(goes nowhere does nothing #1)

actually a friend of mine is a SciFi/Fantasy illustrator and this is a first stab at making a prop of a hand held time machine he had drawn for a series of book illustrations. This iteration is sort of just a proof of concept so I could prove to myself that I could get the gears to work on a small scale. Now i get to go back and add all sorts of gizmos and whizzbangs to make it look all Jules Verne/HG Wells ish. I also plan on cutting a pocket in the back of the case for a AA battery so I can throw in some green LEDs and make it have that creepy SciFi glow.


For the idle curious I posted a video of the workings so he could see it, so I might as well post the link here. Crappy video from my digital camera but it gets the idea across.

http://www.schaie.com/shopbot/videos/MOV01696.mpg

Chris

[gene]

I have something like that ( GNDN-01) on my card . Under my name i have the letters DMA , If i am with snooty customers and they ask i say its Design & Manafacturing Associate. If the customers are down to earth i say dont mean anything.

[john_l]

Smooth. Thats a cool little gadget.

I want to figure out how to make a real life device such as shown below...

In my use, I would need about 3 inches of movement left to right (the rack gear piece) with every revolution of the disc.. but I don't know where to begin. Any ideas?


4677

[john_l]

Honestly, For my use.. I don't need the rack and gear portion at all. I do need to size it for 3" of motion though.


4678

[shoeshine]

Hi John, haven't forgotten about you. I'm just trying to figure out how to calculate 3" of movement and the math is fuddling me.

I think I see a way to do it in pieces and then scribe the motion of the drive disc through a drilled hole. then measure and cut the disc to size. Does your drive disc need to be any particular size?

[gene]

Could you do it like a locomotive wheel and push rod?
A pound pully with a pin that is 1.5" from the center and a rod with a round hole in the end instead of a slot in the rod like above?
I ordered the book and cant wait for it to come. I feel like a kid waiting on Christmas.

[john_l]

Chris, Thanks for thinking on it. If it could be done with the drive disk no larger than about 4"-5" diameter that would work great.

Gene, A simple pushrod is what I thought of first, just as you describe. Although I haven't cut any prototype yet, I think I would prefer how there is less side movement of the driven rod in the second (slotted version) picture above. It seems to me that just a pushrod attached to the disk is going to have a lot more movement there.

Thank you guys for your help.

[Brian Moran]

How about a cam and spring loaded rod? Depends on whether you need the return stroke driven as well.

Brian

[mitch_prest]

i know the drawing is rough..computer crashed..back to pencils.. with a fixed outer gear... diameter equal to the linear distance you want.. inner gear is 1:2 ratio to outer... rotation of the of the input causes the small gear to rotate around the inside of the fixed gear. A pin on the pitch circle of the small gear will travel in a straight line...
4679

[john_l]

I found another that I think I am gonna roll with. I attached pic below. There isn't very much driven weight in my application of this. I think I could get away with wood for the prototype and for longer term use, plastic parts. Maybe the glide could be nylon or something.

Mitch, if the outter ring in your drawing is fixed, does the inner gear orbit as it spins around? Thanks for drawing and posting.

[john_l]

Forgot to attach...


4680

[mitch_prest]

the inner gear pivots on the center of the fixed gear.. that would be your input shaft

[john_l]

Now I get it. Thanks

[mitch_prest]

one more time with the computer... looks way better and even works.. gears were made with a program called geartrax ...in the picture on the right the pin follows a linear path across the diameter of the bigger gear

4681
4682

[shoeshine]

as a quick follow up for those still interested, I cut a set of gears from the drawings generated by the woodgears online generator out of brass and discovered that the tolerances of that soft are not very tight. To wit... they jam. Ok for gears out of wood say 2" in dia. or more, any smaller and the errors in tip rounding creep up to non-functional even correcting for bit radius.


4683

GearDXF seems to be tighter (though I haven't actually cut any of them) but it is a bit harder to figure out how to make sets that work together and it has no function for planetary gears which I need for this project.

I followed up with a search for geartrax and at least from the site it seems to be a plugin for solidworks. Is that what you are using Mitch?

[Ryan Patterson]

Here is a link to a program I wrote for gears. http://www.cabinetpartspro.com/GearMaker/GearMaker_Setup.exe

Rhino also has a plug-in for gears. http://www.rhino3d.com/resources/display.asp?language=&listing=663

[mitch_prest]

yup .. thats the one .. it actually runs outside of solidworks... you figure out what you want and it draws it for you in solidworks... works pretty slick

[shoeshine]

Wow Mitch, geartrax seems pretty slick... until I started looking at the pricing to get a copy of solidworks up and running and then getting the add-on. way out of my price range for these small pojects. ahh well

Ryan, is there any way that your app could generate a planetary gear or a rack for a rack and pinion system?

[Ryan Patterson]

Chris,
If I find some time in the next few days I will see about the planetary gear.

[bill.young]

Stumbled on this video about a wooden car that a Japanese furniture factory made...at least I THINK that's the story because it's all in Japanese...but at around 6:50 in the video there's some footage of a mechanical gizmo that's pretty cool.

http://www.youtube.com/watch?v=Rq6q9cbXM0A

Bill

p.s. Not sure the "Born to be wild" soundtrack fits with the car!