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Author Topic: Gear tooth as a height map?  (Read 276 times)
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Mand
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« on: March 20, 2018, 10:02:04 AM »

OK, this is weird, and probably foolish but: does anyone know where/how I might create/acquire a height map for a gear tooth?

This would be an image looking "into" a gear tooth, such that the highest point (addendum circle) would be shaded white, while the lowest point (root circle) would be black. The face would be an increasin g shade of grey as you approach the flank, and the root fillet would be quite dark, approachi ng black as you get to the root circle. For a normal spur gear, the height map would be basically rectangul ar (since you're looking at the gear tooth edge-on).

Why I'm trying to do this: I'm trying to see if I can cut crown gears using equipment that's both idiosyncr atic (uses height maps not GCode) and also utterly unsuited to the task in general.

...as for why I seem to be doing things entirely the wrong/hard way, well, I dunno, it seemed like an amusing challenge? Plus this way I could create abnormall y huge crown gears (20x20"). I'm thinking I can build the height map by hand using an image editor (just coloring in many many boxes with differing shades of grey), but I thought I'd see if there was a more accurate method first...
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ArtF
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« Reply #1 on: March 20, 2018, 04:08:24 PM »

I can picture what your doing, but I havent any idea what wil do that other than
perhaps an STL viewer, I think blender can for example, load the STL , rotate it so the tooth
is being looked down on and ask it to grey scale it.

Art
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steve323
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« Reply #2 on: March 21, 2018, 01:30:53 PM »

Art, would blender create an image using a light source?  Or can it add a gradient where the amount of grey is exactly proportio nal to the depth?

Adding grey scale colors to set the depth seems like it will introduce lots of errors.  The teeth may have lots of tiny ridges on surfaces that are supposed to roll smoothly.  I am curious to hear how it turns out.
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ArtF
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« Reply #3 on: March 21, 2018, 02:01:59 PM »

Ive only done it once, long ago now, and I cant recall what software I took
the grey scale from. It gave be a fairly good gradient, but I suppose end finish
liek ridges would depend on the modality ued to make it, some are more
tolerant of such things. Smiley

Art
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Mand
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« Reply #4 on: March 22, 2018, 09:46:07 PM »

For the benefit of other lunatics, a brief update: I've been fiddling around with an STL (as suggested above, thanks!!) using MeshLab.

...MeshLa b is great, but also hideously complex and confusing . While I can get it to render lovely depth maps, I unfortuna tely have not been able to figure out how to make it change the origin of the depth mapping -- so it is lovingly rendering depth data for the flat of my source gear. Which is a nice white disk, because it's a perfectly flat surface.

In other words, I've yet to find a way to cause MeshLab to render the depth map starting from the face of the gear teeth rather than the top or bottom surface of the gear disk.

Foo. Close, but no cigar. I'm reconside ring drawing the depth map by hand using 256 shades of gray. Since I'm futzing around with epicycloi dal teeth, this will be easier than it sounds, but also nightmari shly tedious.
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ArtF
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« Reply #5 on: March 23, 2018, 06:41:49 AM »

Hi:

 Its fuzzy , was a long time ago, but I remember also trying
to get orientati on right. It is possible as I recall. You need to tell it to rotate
the gear so the tooth is Upwards on the Z, though I havent a clue how anymore.
 I tend to use 2d software more than 3d, and when I face a 3d problem like that
I code up something to do it. ( The only real benefit of being a coder.)

 Art
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Ya-Nvr-No
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« Reply #6 on: March 25, 2018, 06:25:38 PM »

you talking about something like this?
artcam can create 3d bitmaps of 3d objects (in this case an stl import)
the bmpfile is of the single tooth


* 3dgear1.JPG (71.54 KB, 907x429 - viewed 23 times.)

* 3dgear2.JPG (38.33 KB, 696x549 - viewed 18 times.)

* 3dgear3.JPG (37.23 KB, 539x419 - viewed 17 times.)

* geartooth3dBitmap.bmp (6806.3 KB, 1320x1320 - viewed 25 times.)
« Last Edit: March 25, 2018, 06:37:03 PM by Ya-Nvr-No » Logged

Mand
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« Reply #7 on: March 29, 2018, 11:27:18 PM »

Wow, thanks! Apologies for my delay in respondin g, I was out of town. Iíll do a test run on the machine tomorrow and see how it turns out.

...incide ntally, what software are you using? Iíve had difficult y with the various options Iíve been trying thus far.
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Mooselake
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« Reply #8 on: March 30, 2018, 11:52:43 AM »

I'm trying to see if I can cut crown gears using equipment that's both idiosyncr atic (uses height maps not GCode) and also utterly unsuited to the task in general.

I'd like to hear more about your project as it progresse s.

I'm on a less adventuro us project to make a few gears using a 1950 metal shaper (which, while not predating paper tape controls, predates me), also for fun and to answer the ever present wifely question "What did you buy that for".  Unfortuna tely it's being delayed for the snowbank blocking the shop door that's impeding the shop expansion needed to add to the tool collectio n.  Not sure I can get the 7K pound Fellows on eBay past Mrs. Moose or the 1000 mi shipping distance.

Kirk
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Mand
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« Reply #9 on: March 30, 2018, 02:58:10 PM »

It's occurred to me I've been accidenta lly cryptic in all of this -- what I'm trying (again, foolishly) to do is develop a way to create a crown gear or rack gear using an engraving laser.

The laser can modulate power based on a grayscale heightmap, so if I can figure out the right combinati on of gradient and engraving passes, I think I can make a "rack" that's usable for certain purposes. The teeth will of course be limited to a fraction of the depth of the engraved material, so this whole idea is only questiona bly useful (even for wood clock type things), but there are certain cases where it might be useful to me.

The laser can't, naturally, generate a real tooth form but it might work well enough. For example, I might be able to cut a spur gear which has a crown gear embedded into the upper face. This lets me get pretty funky with designs while using only one tool.

In theory.
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ArtF
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« Reply #10 on: March 30, 2018, 07:12:38 PM »

Hi:

   You should soon be able to generate depth maps from within Vexx, which in developme nt now loads
STL's of any type.

Art
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Mand
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« Reply #11 on: April 16, 2018, 11:58:46 PM »

Had (yet more!) guests recently, so I was delayed in respondin g -- I've managed to semi-successfully cut a crown gear with a laser using the info posted above by Ya-Nvr-No, shown (attached) with a quarter for scale.

You'll notice some roughness on the outside perimeter of the crown -- this is because the laser turned out to be more accurate than I'd expected (and my software, meanwhile, LESS accurate than expected), and so my final circular cutting pass left a wee smidge of full-height material at the edge. Which was broken off with a fingernai l, hence the roughness . The height map also got a bit squashed, since the penetrati on of the laser is not perfectly linear with power. If I were being paid to do this I think I could establish an adjustmen t curve, but I'll leave that as an exercise for the reader...

...anyway, point being, it seems to work well enough for extremely low-force low-revolution purposes, which is fortunate ly all I care about! Yay!


* crown-gearpic.jpg (517.37 KB, 3024x4032 - viewed 18 times.)
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ArtF
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« Reply #12 on: April 17, 2018, 07:43:58 AM »

Mand:

 Way to go. Excellent job.

  The next release of Vexx will have a module to load an STL and get
a grey scale image of any portion of it, in any orientati on, for laser engraving .

Art
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Dan Mauch
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« Reply #13 on: April 17, 2018, 11:43:13 AM »

 Hmmm I'm wondering if a modificat ion of what I did with herringbo ne gears would work for you. The modificat ion would be that you laser cut two rings. One that was a full blank base and then the second would be a ring the inside and outside diameters set to the width of the tooth. Glue the the ring to the blank.The n using a stepper set parallel to the X axis this would be an A axis setup. Now you would use the A axis as an indexer to cut each tooth at 90 degrees. That way you would need only the tooth profile and a single pass for each tooth. See
https://www.youtube.com/watch?v=N4BpWN26Iy0&t=214s  but again instead of the 15 degree angle you would cut at 90 degrees.

Dan Mauch
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Mand
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« Reply #14 on: April 18, 2018, 10:58:07 AM »

Amusingly enough, I'd *just* seen that video!  The technique would definitel y work I think (and I've even got an indexer), but alas my laser doesn't have the headroom to fit everythin g.

...althou gh, now that you mention it, I do wonder if perhaps I couldn't cut the crown teeth as a rack, using the variable-power engraving to add a bevel cut to each tooth (so that they come out separate, and can be reassembl ed into a circle). With some kind of centering-ring jig, and enough glue, it might actually work. Although, at that point, I should probably just knuckle down and clear out the garage so that I can access my mill and lathe, and start working again with the proper tools Wink
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