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DICKEYBIRD
02-06-2008, 06:48 PM
Guy Francis over on the Home Model Engine Machinist forum posted this link that allows one to design gears interactively, print them out and even animate them. http://woodgears.ca/gear_cutting/template.html Very cool app!

I printed one to a .pdf file (PDF995) and it looks like they're generated as vector files. Now where did I put that .pdf to .dxf utility I had?

rockrat
02-06-2008, 07:47 PM
I always thought that a pdf was a final operation type of thing. I wonder if Guy is generating a dxf (or raster) first and then converting it. If so, a quick email to him might get what you want.

Let us know if you find (or remember) the converter name.

rock-

torker
02-06-2008, 07:54 PM
That thing is cool! Would be neat if you could add another gear or so. Ya.. I know, you can't please evryone!

d1ulookin4
02-07-2008, 12:10 AM
It looks like he's implemented it as a Flash Movie, so it's probably all vectors internally. He's probably not got a dxf as an internal step, but it's worth inquiring.

I did an animated planetary assembly "toy" page a couple years ago, when I had time for games like this.

http://www.d1ulookin4.com/PlanetaryAssembly/

-Eric

John Stevenson
02-07-2008, 03:42 AM
Don't overlook this site.

http://www.hobbing.com/

.

Dawai
02-07-2008, 04:59 AM
Only thing annoying me at the moment, I save the full html page.. The java applet won't run on my saved page.. Any clue as to the difference?

It shows the gears and all.. but.. too early, or too late to figure it out..

DICKEYBIRD
02-07-2008, 10:10 AM
Well now, if you print the gears using the print button in the program, print to a .pdf print app (I used PDF995), import that into a .pdf to .dxf file converter (I used CAD-KAS PDF 2 DXF at http://www.shareup.com/downloading-24214.html) you get a nice .dxf file that loads up in a CAD program just fine! The curves unfortunately aren't true arcs (they're short little line segments)

Probably not good enough for milling a "real" steel gear but certainly good enough for drawing plans or CNC routing wooden gears for projects...how 'bout a nice wooden clock?:)

http://i57.photobucket.com/albums/g227/DBAviation/GearTest.jpg

d1ulookin4
02-07-2008, 02:02 PM
I put a fair amount of work into trying to draw a true involute curve in flash. I eventually gave up and just used line approximations. I was just trying to get a close image, not actually machine one. I'd guess that the approximated one is close enough for anyone doing wood projects. My dad has cut a few of these out of wood using the scroll saw. There's far more error in his (or probably anyone's) ability to make the cuts than the pattern itself.

From what I recall on dad's venture into wooden clocks is that most clocks don't use an involute cut. I think it's called a cycloid gear or something like that.

Google will turn up a few lisp programs for AutoCad (or intellicad) that can draw true involutes. They are not trivial, but they are accurate. I'm sure there are options for other cad programs as well.

-Eric

rockrat
02-07-2008, 09:34 PM
Eric, that is a fantastic webpage. I taught engineering students for a bit and in our kinematics class this was always something fun to learn about. Show them a planetary gear setup and ask them what turns. Then show them a tangible example and everyone is suprised.

How long did it take you to program?

rock-

d1ulookin4
02-08-2008, 09:33 AM
I can't remember exactly how much time I spent on it. I think I probably spent more time trying to draw a true involute than on anything else. After giving up on the involute, my next attempt was to try to use spline curves, but I gave up on that too. I finally settled for straight lines for the segments.

Like many of my shop projects, what I ended up with isn't what I started out to make. ;) I started out trying to draw an animated gear. Then I thought one animated gear was boring, so I had to figure out what to do with them. I probably spent a week or so on the gears (including the futile attempt at the involute), and another week or so on the planetary train. If I were to do it over, I think I could pull off the involute, using a couple of tricks.

At that time I was very comfortable with Flash programming. One of the nice things about Flash is that all of these objects ("movie clips" in the flash vernacular) can be rotated simply by setting a property. Now, I haven't touched flash (or programming in general) in about two years, so it would take a while to get back into it.

I think the frame rate is 12/second. An interesting "artifact" of the movie is that you can get the gears to "appear" to move backwards with the speed control. This is because of where the updated (angular) position is at the current speed, with respect to where the previous one was. This is pretty much the same phenomenon that occurs when looking at the lug-nuts on a semi-tractor in a movie. Depending on the speed of the tractor and the refresh rate of the camera, sometimes they appear to go in reverse.

-Eric

DR
02-08-2008, 11:27 AM
Question...what is it with gears and hobbyists? I've been in the business for 30 years and never had the need to cut a gear. I have purchased gears from Boston Gear which were very affordable. Even broached splines in stock gears, but never had the need to cut one.

d1ulookin4
02-09-2008, 10:51 AM
I don't know DR... That is a great question. I don't think it's really out of "need". I would guess it's more the challenge of it. It's easy to think of analogies and parallels (climbing Everest etc), but it certainly draws more than it's fair share of hobbyists.

It doesn't take long on Google to find lots of hobbyists spending months, if not years designing and building stuff that you can buy for a few dollars. It's never the economics of it.

I'd have to say for me, it's the learning that I value, not the one or two gears that I will ever actually "crank out", so to speak. I've spent many years of my life learning stuff that is interesting, but in all likelihood, I will never use. I guess it's probably a healthier addiction than many of the alternatives.

-Eric

rockrat
02-09-2008, 07:57 PM
Hobbyist or not, if I buy a gear cutter, I can cut a gear. If I can buy a gear for the price of the cutter, why not just make the gear I need. Pay for the cutter, and if I ever need to make a similar gear again, I'm in the clear.

I need a gear for the lathe to get into different threads than are available on it currently. The cost of a gear cutter is about the same as the gear. So if I buy the cutter, I can make all sorts of gears in the dp range for the lathe.

But sometimes, you cant buy the gear (or rack) you need. This happened to me a year or so ago. It was just easier to make one.

http://bbs.homeshopmachinist.net/showthread.php?t=19816

Now at work I would never setup a design that would call for a one off gear. I would just order one there.

rock-

boslab
02-09-2008, 08:03 PM
nice to be able to drive a stick shift all the same if you know what i mean
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