Archive for March, 2011

Why I <3 OpenSCAD

Friday, March 25th, 2011

So my CNC design is coming along nicely now, and I'm really liking developing it in OpenSCAD.  I'm trying to organize everything well to make the design easy to modify and come up with a good work flow for going from designing individual components, to fitting them together into assemblies, to actually generating the toolpaths to cut out the parts on a CNC router.

One of the cool things you can do if you build full assemblies from your individual parts in OpenSCAD (or any CAD program, really) is do a quick first pass of your design and make sure everything fits together nicely.  Here's an example issue I caught when looking at my X-axis assembly:

One of the pipes that span the X-axis frame intersects the spans of the gantry.  To fix this I can open the include file for the X-axis and change a single line that defines how wide the  spans are or the  spacing of the guide rods, recompile, and end up with this:

Problem fixed!  If I extend this approach and make an assembly for each full functional unit, each axis, each tool head, etc., I can throw them all together and see how my whole final machine will look and identify problems with the design before I start cutting parts.  Moreover, others can also easily see how the hole thing fits together, make changes, and check their mods easily as well.  That's the plan at least.

Laser Vector Grid Construction and Care

Sunday, March 13th, 2011

One thing many people might not know about laser cutters is that they require a lot of regular cleaning to keep them cutting effectively.   You've got to clean the optics on a weekly basis, clean out any little bits that might have fallen through the vector grid and wipe down the depth plunger and guide rods monthly, and oil the linear guides and clean the positioning strip every couple of months.  Who'd have thought selectively vaporizing stuff was so messy?

One other thing that I have to do about every six months is degrease the vector grid (yes, you have to regularly degrease some of your laser parts).  Before I get ahead of myself, I should probably explain what I mean when I say vector grid.  The vector grid is a metal comb that you set the material you're going to be cutting through on top of.  It's designed to support the material you're cutting and allow the laser to pass through it to prevent burning the back side of the material you're cutting.  It gets dirty because you're be blowing vaporized plastic (or resin if you're cutting wood) through it when you're cutting clean through material.

The manufacturer of my laser cutter, Epilog Laser, doesn't include instructions on how to clean the vector grid in their manuals, but they do have a nice guide online here.  I use about a 1:6 ratio of Zep purple degreaser to warm water compared to Epilog's suggested 1:4, and it seems to work fine for me.  I've got a small plastic container that's only a little bigger than my laser bed that I use to soak my vector grid.   It only takes about 12 cups of water to almost fully cover my vector grid in this container, so one gallon of Zep lasts me a very long time.  You'll notice that I've got a pair of rubber gloves in my box of supplies.  You definitely want to be wearing these and probably some goggles while working with the cleaning solution because Zep contains a number of bad things that can be absorbed through the skin (mainly Sodium Hydroxide AKA lye).

After dropping the vector grid in the diluted mixture it will start foaming all on it's own.  I agitate the mixture a bit and keep the grid soaking for a little less than 5 minutes.

After soaking remove the grid and give it a good rinsing.  When done rinsing, shake it out a bit over the sink and let it air dry completely before using it again.  To give you an idea of how much stuff was pulled off the grid, the cleaning solution started off clear with a slightly purple tint and after soaking it's almost black:

And here's the grid after rinsing:

There's still some black residue on there (ABS from the car tag blanks I make) because it was really caked on and I didn't get a plastic pipe out and clean out those cells.  Be careful if you do choose to use pipe cleaners and scrub the vector grid, and just handling it in general, because it's made out of very thin aluminum an is damaged easily.

Building your own vector grid

Because certain materials get the vector grid gets very dirty, I wanted to make some spares.  I threw some 1/2" aluminum honeycomb in on one of my McMaster-Carr orders to see if it would be a usable substitute for the 1/4" cell spacing, 1/2" thick mat that came with the machine.  I was able to cut it easily with a pair of scissors and get one full bed sheet and one that was a little under an inch short from the 24"x24" sheet I ordered.

Unfortunately, it wasn't as rigid as the original vector grid and needed something to back it.  Next McMaster-Carr order, I added some heavy wire mesh to my order.  This stuff cut easily with a pair of side cutters and was easy to fit to the cutter bed.  I set the aluminum hex on top and it improved the rigidity:

It's still not as rigid as the original vector grid but I think it'll work for what I'm cutting and all I'll likely have to do to fix this is switch out the wire mesh for some stiffer perforated metal in the future.  Here's a comparison between the original grid and the new one:

The new, wider spaced grid looks pretty level and, even though it was never a huge problem, I'm hoping the wider spacing will result in fewer burn marks on the back side of the material I'm cutting than the stock grid.

Update:

I've been using the new vector grid for a bit now and I love it!  Also, I talked to the local Epilog sales rep. and he said they ask about $395 for a replacement vector grid. I think I'll stick with my $35 spare for now.

Progress Update – 3/8/11

Tuesday, March 8th, 2011

I haven't been posting any projects, but I've definitely been working on stuff!   If you don't follow my Thingiverse posts, I've leaned a little about character modeling in Blender and made me a ceiling cat for the shop:

I also made some spools for jumper wire that fit in my trusty electronics tackle boxes:

I've also been working on a set of parts that'll attach to a standard Cupcake CNC to add fume hood functionality for a fellow Makerbot operator.  It's not done yet, but the parts I have done make it look like a little oven, which I think is pretty awesome:

I've also been working on the CNC router at CCCKC, which has had a few successful test cuts and should help me finish a few long-running projects I've had on the back burner.  Check out this CCCKC blog post for video and some more info.

Lastly, I've been working on my self replicating CNC project again.  I've decided to make this project even more ambitious and I've acquired most of the hardware that I think I'll need to finish it up, or at least get it off it's feet.  I'm also learning OpenSCAD and doing all my initial design and prototyping in OpenSCAD.  I'm going to try and use OpenSCAD to model all the milled components in 3D and then use OpenSCAD's 2D rendering capabilities to generate the DXF files that will eventually be used to generate tool paths to actually mill the parts.  I'm trying to make the design very parametric and well organized so it'll be easy for me to tweak and easy for others to modify use the parts they have on hand or make new  derivatives.  The CCCKCCNC being up should help prototyping as well.