Friday, June 3, 2011

laser table mark iii

So, I've mostly completed the frame for the "Mark III" version of the laser table. I decided not to use the previous version because of a change in options to mount the lasers. The drafting table just didn't have enough space for the flush mounts.

The features of the new table are:

* built from 2x4s so it's sturdier (but also heavier)
* the table top is hinged and has legs built in so it can be used flat or lifted to be an angled surface
* used pocket screws to hold stuff together... looks less "engineery" while joins are stronger

What remains to be done:

* figure out some way to mount stops for the tabletop legs to hold it at an angle
* cut some mounting rabbets out of moulding to hold the plexiglass surface just below the center of the laser beam
* cut the plexiglass down to fit in the rabbets :)
* mount the flush mounts at the correct angle to cover the entire surface
* rejigger electrical stuff to run off floppy disk power lead
* see if running lasers in series will work better than in parallel (currently using the parallel setup)
* wax paper on acrylic and see if the projector works

Then I can start on the software phase.

I should probably also think about attaching a trap for the laser light at the edge of the tabletop, but for right now I just want this sucker to work.

Way more info after the jump.

Why The New Design

With the previous "drafting table" style setup, I was going to need to find a way to mount the lasers so that they could be calibrated to keep the beam sweeping just across the top of the plexiglass. I found some cheap speaker mounts at Altex that were almost perfect for hanging the laser's tube off of and could be swiveled around to any angle, but it was starting to look (and feel) super hackish at that point. While pondering what to do about it, I found out Aixiz has now started selling laser table kits for $65 or so and they sell mounting brackets for their lasers for $4 each.

One of the biggest problems with the first test version of the table was getting the laser to line up in the right planes. A flush mounted laser would basically remove the hassle of trying to get the x and z factors right and leave only the rotation of the laser itself to worry about (assuming you mount it at the correct angle) in the y plane.

In short, it'd make it so easy a caveman could do it.

But the drafting table's edges were too narrow to handle the width of the mount. So I decided to just put the plywood top back in and use it as a drafting table. :)

Features and ToDo

As mentioned above:

* it's built out of 2x4's (sturdier, but heavier). Using 2x4's for the top enclosure gave me enough space for the mounts, plus it allowed me to rip 1" legs from the side supports and put a hinge on them.

* hinge at the front of the table top so you can swing it up to whatever angle you want, but the lasers will hold their calibration. I imagine that adjusting the web cam and the projector is going to be a pain in the ass, however.

* made use of pocket screws with a jig from Kreg. This made joining pieces a freaking snap, and I believe they are stronger joins than what I got from using carriage bolts and wood screws previously. Although the table frame would benefit from braces, it's sturdy enough that I'd trust it with about 75lbs on the tabletop and there's no wobble.

* actually sanded this one, so less splintery ouchy action!

As for the ToDo, there's only a little bit of carpentry-pretend left to play:

* cut some supports for the plexiglass out of molding to hold it up just below the plane of the lasers

* cut the plexiglass down a little in width to fit the table I goofed up the calculation for the width of the tabletop, so the whole thing ended up being exactly 2' wide (rather than 2' 2").

The rest is getting is the hard part:

* rewire lasers to run in series, and figure out how to power it all off a floppy disk power lead (5V.. only need 3.2V)

* figure out where to put projector+camera and if there's anything I can make to help in calibration of those suckers.

* building a PC from scrap parts and getting the software up and running

So, basically, got a lot done, but we're far from finished. :(

Woodworking Lessons

I think the big takeaway is that pocket screws are pretty damned awesome, and that you should avoid using larger lumber than you need to use. I could have probably gotten away with using some 1x4's instead and just turning them on their sides for the tabletop frame in order to get the space I needed for the laser mounts. However, the 2x4 came in handy when making the fold down legs for the tabletop.

The other big thing I learned was to stop sweating the measurements so much. Although I did start off with a rough sketch of what I wanted in order to calculate how much lumber I'd need, I didn't worry about figuring out every single cut to the 1/32nd of an inch like I did for the drafting table. I also would use a piece I cut (such as the first leg) to measure the cut for the next leg, rather than pre-marking everything out on a board and losing accuracy to the kerf.

And this bears repeating: the pocket screws are damned awesome. I was able to accomplish all the joins single-handedly. The only thing I needed an extra set of hands for was to hold the tabletop frame upright while I was screwing in the hinges. They also let me get away with using less hardware (2 pocket screws are lighter than 2 carriage bolts), and use less lumber (no need for weird supports).

There were some disadvantages, though. Once the screw is in, you aren't getting it back out without destroying either the screw or the wood (and it'll most likely be the wood). The Kreg screws also use a funky square head... not a problem since the jig kit I bought came with an attachment, but still. Finally, if you're going to use this setup, be sure to rip the boards to 90 degrees. Having the rounded ends of the 2x4's didn't create too many problems, but things didn't sink together as snugly as they could have while I was lining up the boards to be clamped.

Finally, I'd like to say: Sanding. It's not just a good idea. It's the law. I used 120 grit (also had some 320 but that turned out to be wishful thinking) and hand sanded the table. I've learned my lesson and will hunt for a belt sander or something... but the wrenched shoulder was worth it. The el-cheapo stud wood I was using is pretty much splinter and snag free, and I was able to get most of the "hello I'm a n00b and bought stud 2x4s for a furniture project" tell-tale stampings rubbed off. Probably would have been much better if I'd cut the 2x4's square before using them, but oh well. Lesson learned.

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