A way to improve the laser-cut gear tooth profile accuracy (2)

In my previous post, I talked about generating gear profile with illustrator script. Now it is time to laser-cut it out of the script. The laser-cut I have access to is VLS6.60 from Universal Laser Systems. Installed with a 60W laser source, this machine is mostly used to cut plastics, wood and paper. A big problem of laser-cutting is the profile tolerance issue as the highly concentrated laser beam basically evaporates the shape profile that it moves through, although it might be only a little. Here is one example how a laser-cutter is causing some tolerance issue:

This piece of 1″ x 1″ square acrylic turned out to be 0.9895″ in width after laser-cutting. Apparently 0.005″ of the profile width on both sides was burned out by the laser beam.

This explains why my first cut of gears (shown as below) didn’t mate so well. You can see clearly the the margin between the cut gear and the design profile.

While, this is not the end of the world. The good news is that the cutting tolerance is quite consistent for the same setup ( material type, thickness, cutting power, speed, etc.). If we know the profile loss will be a certain number, and expand the profile in advance for exactly this amount. Will we be able to compensate the profile loss? The answer is YES! Ok, now let’s apply this to the gear cutting. Since I already have the profile generator code which I described in my previous post, all I need to do is to find my high school math text book, and figure out how to calculate a vector that is “d” distance parallel to another vector. Here is a diagram of the expanding algorithm. Pay special attention to joints where two different normals are rooted at the same points. For quick and easy coding, I am using angle bisector (green dash) to generate expanding profile:

Spend some efforts on the coding and make sure all the math is correct. It really pays off when you see the original gear profile and expanded profile appear in the same illustrator windows!

Time to check it out on the lase-cutter, the profile is now getting really close to its design:

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A way to improve the laser-cut gear tooth profile accuracy (1)

 

Laser cutter is a piece of amazing equipment that makes it possible to quickly turn your design into physical parts. When it comes to cutting gears, you will need to take the following 2 points into consideration:

  • Reliable gear tooth profile.
  • Acceptable cutting tolerance.

1. Reliable gear tooth profile.

I won’t address the whole mathematics behind the gear theory here since I am not majored in Mechanics. If you have interest in the theory, you can simply search it online and mostly likely you will be buried with tons of information out there. However, if you just want to get the job done, there are a couple of options to automatically generate the gear tooth profile, mostly of which are for spur gears:

Available tools:

  • Google SketchUp has an involute spur gear plug-in that allows you to create spur gear profile and then export to dxf using the stl/dxf export tool.
  • GearDXF is a specialized program that designated to generate spur gear profile and export to dxf format.
  • An quick and easy to use online Gear Template Generator that allow to interactively create gear on its webpages and export through print function.

CAD data from manufacture:

  • Rushgear.com has a whole database of different gear types. They are specialized in gear customization and manufacture. So you can download their pre-made gear CAD file and do whatever you want with them.
  • York Industry, same as above, offers CAD model for their gear production. But most of their CAD models are for timing pulley.

What if none of the above resource solves your problem? Then here comes the ultimate solution: Generate your own profile on demand! I am basically taking reference to the wonderful work that is published by msruggles on Thingiverse.com. What you need to do is to download the “gear profile.xlsx” in which msruggles has put all the spur gear equations in. You only need to change the teeth number of the gear that you want to generate and the spreedsheet will take care of the rest work. Based on this, I rewrote all these equations into Adobe Illustrator Javascript. So by clicking the “Run” button, I can generate any spur gear!  Here are some snap shots of the scripts and result:


90 teeth, 48 pitch, 1.875″ pitch diameter


25 teeth, 48 pitch, 0.571″ pitch diameter


10 teeth, 48 pitch, 0.208″ pitch diameter

In my next post, I will take about laser cutting these generated gear and how to overcome the tolerance issue.