Gear tooth as a height map?

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Mand
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Gear tooth as a height map?

Post by Mand »

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 increasing shade of grey as you approach the flank, and the root fillet would be quite dark, approaching black as you get to the root circle. For a normal spur gear, the height map would be basically rectangular (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 idiosyncratic (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 abnormally 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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Re: Gear tooth as a height map?

Post by ArtF »

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
steve323
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Re: Gear tooth as a height map?

Post by steve323 »

Art, would blender create an image using a light source?  Or can it add a gradient where the amount of grey is exactly proportional 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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Re: Gear tooth as a height map?

Post by ArtF »

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. :)

Art
Mand
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Re: Gear tooth as a height map?

Post by Mand »

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

...MeshLab is great, but also hideously complex and confusing. While I can get it to render lovely depth maps, I unfortunately 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 reconsidering drawing the depth map by hand using 256 shades of gray. Since I'm futzing around with epicycloidal teeth, this will be easier than it sounds, but also nightmarishly tedious.
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ArtF
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Re: Gear tooth as a height map?

Post by ArtF »

Hi:

Its fuzzy , was a long time ago, but I remember also trying
to get orientation 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
Ya-Nvr-No
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Re: Gear tooth as a height map?

Post by Ya-Nvr-No »

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
Attachments

[The extension has been deactivated and can no longer be displayed.]

3dgear3.JPG
3dgear2.JPG
3dgear1.JPG
Last edited by Ya-Nvr-No on Sun Mar 25, 2018 12:37 pm, edited 1 time in total.
Mand
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Re: Gear tooth as a height map?

Post by Mand »

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

...incidentally, what software are you using? I?ve had difficulty with the various options I?ve been trying thus far.
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Re: Gear tooth as a height map?

Post by Mooselake »

Mand wrote:I'm trying to see if I can cut crown gears using equipment that's both idiosyncratic (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 progresses.

I'm on a less adventurous 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".  Unfortunately it's being delayed for the snowbank blocking the shop door that's impeding the shop expansion needed to add to the tool collection.  Not sure I can get the 7K pound Fellows on eBay past Mrs. Moose or the 1000 mi shipping distance.

Kirk
Mand
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Re: Gear tooth as a height map?

Post by Mand »

It's occurred to me I've been accidentally 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 combination 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 questionably 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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Re: Gear tooth as a height map?

Post by ArtF »

Hi:

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

Art
Mand
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Re: Gear tooth as a height map?

Post by Mand »

Had (yet more!) guests recently, so I was delayed in responding -- 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 fingernail, hence the roughness. The height map also got a bit squashed, since the penetration of the laser is not perfectly linear with power. If I were being paid to do this I think I could establish an adjustment 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 fortunately all I care about! Yay!
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crown-gearpic.jpg
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ArtF
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Re: Gear tooth as a height map?

Post by ArtF »

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 orientation, for laser engraving.

Art
Dan Mauch
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Re: Gear tooth as a height map?

Post by Dan Mauch »

Hmmm I'm wondering if a modification of what I did with herringbone gears would work for you. The modification 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.Then 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
Mand
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Re: Gear tooth as a height map?

Post by Mand »

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

...although, 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 reassembled 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 ;)
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