Often laser cut parts get attached at 90 degree angles, using finger joints, or screws and t-slots, but there may be times when you want to stack pieces of wood and have them aligned…
Pegs might be the answer!
Here’s a few photos of the pegs I’ve been experimenting with. For these pieces I don’t have a lot of room to have multiple pegs at opposing angles, but I can see where that might be useful. For these pieces the peg is really just for assembly alignment when gluing it all together.
My recent acquisition of a Meade ETX-90 telescope with computer go-to system for locating objects in the sky got me thinking that it would be nice to have a system to locate objects in the sky when you’re looking through binoculars or a telescope that doesn’t have a computer and motors to drive it. To that end I came up with the idea of mounting a green laser pointer, commonly used by astronomy nutz to point out objects in the sky to noobs, on a cell phone or tablet running a program such as Google SkyMap or Skeye.
CAD rendering of the parts
After much thought and a few prototypes I came up with a system that allows a laser to mount on a phone and that assembly to mount on a tripod, a handle, or a telescope. The tube that holds the laser has adjustment screws to allow the laser to be aligned with the SkyMap on the phone. It also has to slots that fit over standard gun sight rails. On one side I have a phone/tablet bracket that has a gunsight rail and slides into the laser tube, and the other side can be used for a rail that mounts on a tripod or a handle. Extra rails can be mounted on telescope tubes. I haven’t yet designed a binocular mount, but will soon.
Parts printing on MegaMax
I printed the parts on MegaMax with Octave fluorescent red filament (that’s why the colors vary in the photos- the flash apparently excites the fluorescence in the picture with the handle). All the parts fit VERY tightly together but I included screw holes for extra security. The phone/tablet mounts on the bracket using velcro tape. I think it may be better to print or buy a cheap case to fit the phone than screw it to the phone/tablet bracket. I’ll be posting the design files to Thingiverse shortly.
Years back, I used to throw a lot of cocktail parties. Between myself and two good friends, we owned five cocktail shakers and 35+ martini glasses. During the parties, we’d typically be the only three people shaking martinis for all the guests. Though that’s awesome, it also means we missed out on much of the socializing and mingling during each party. In preparation for a recent birthday party, the solution came to me: Use Lasers! So, I laser cut ten coaster-sized pieces of basswood and then laser engraved my twelve favorite Martini and Champagne cocktail recipes on them. I also cut stands for them that had a laser engraved “best practices” guide for shaking Martinis – you know, the things that bartenders are typically too busy to do for you: Chill your glass before pouring your drink into it, shaking your drink until it is sufficiently cold, etc. The drinks have recipes that taste better than what most bartenders will make for you, because they include things like an amount of lemon or lime that they’re too busy to squeeze into your drink. The party was an even more awesome experience for me, because I wasn’t only shaking drinks all night. It was also even more awesome for the guests, as they found that great cocktails are super easy to make! And who doesn’t like to make things? Also, the carbonated Gin & No tonic is real crowd pleaser! See my previous post about home carbonation for more info, and note that all types of inappropriate things can be carbonated: Gin, Ardbeg Corryvreckan, grapes, etc!
Wanting to up the ante a bit after having the Makerspace laser cutter chop out hundreds of city blocks to form a big map of MKE, I decided to laser cut a 24” by 18” halftone image! As it required the laser cutter to carve 10368 circles out of an off-yellow piece of 98 Lb paper, the cutting took 1.3 hours and produced quite a bit of confetti. I’ll display this with a purple (rather than black) paper behind the off-yellow laser cut paper. In person there is an interesting transition from an abstract purple/yellow shape into a black and white image as one moves further away from the image. You may even want to sit back from your monitor to improve the “image quality.”
Check out this video of the laser cutter in the middle of cutting 10000 circles! Note the mysterious logic employed by the laser cutter to determine the order of its cuts.
I imported a photo into GIMP, and desaturated it to produce a black and white image. After bumping up the contrast and darkening it slightly to nearly saturate the darkest areas (and avoid any totally white areas), I brought it into Inkscape. Inkscape can create halftones in a two step, manual process. The first step is to draw an 8 pixel by 8 pixel circle in the upper left corner of the 1133×720 pixel image, and select Edit->Clone-> Create Tiled Clones. To create a rectangular grid of halftone dots whose sizes are set by the color of the image below, use these settings:
From a quick test cut of a particularly dark area, I found that I needed to add an offset between each row and each column to account for the kerf of the laser. I.e. the laser beam has a cutting width that is wider than that of the line, and so in the darkest areas of the photo the halftone dots overlapped, causing a large section of the paper to fully detach. That led me to make this test strip with 11 shades of grayscale, evenly spaced between pure black and white. I laser cut this test strip with various offset distances between the rows and columns in order to arrive at the optimal 10% extra offset between adjacent rows and columns shown in the above settings. Note also that the smallest size circles may not even be exported from Inkscape due to their infinitesimal dimensions (i.e. if you export as a .pdf). The minimum gap between circles with 42% speed and 100% power on an 1133 pixel wide image blown up to 24″ is 0.79 pixels, which is 0.017″.
Applying these same settings to the image created a 128 by 81 array of circles, for a grand total of 10368 vector objects. In my first trial run last weekend, I found that sending this much data to our 60 Watt Universal Laser takes 5 minutes and results in a print error I noticed only after hitting start! After 1.3 hours of vector cutting, I found that a few of the rows and columns were shifted a bit from their intended location. It’s not clear whether this had to do with the print error, or if the paper moved slightly during the cutting process.
In order to improve the second version (shown at top), I chose to move away from the rectangular grid of halftone dots – recall that Kays and London teach that hexagonal close packing is for champions. The reason to abandon the rectangular spacing is to improve the dynamic range (i.e. to make the blacks blacker). For example, rectangular grids of circles pack at an “efficiency” of Pi/4, which is 79%, whereas hexagonal close packing results in a pi/6*sqrt(3) packing, or 91%. That means that the darkest sections of the image will be darker, as more of the light colored “front” piece of paper can be cut away. See the image below, and note that the hexagonal pattern does indeed appear darker.
It turns out that Inkscape doesn’t easily permit this. I ended up spending an hour or two fiddling with the column and row offset settings using my 11 black/white tone test strip to find settings that gave the hexagonal offset with the closest, even hexagonal spacing between adjacent circles. The following settings worked great for an 8 by 8 dot on the darkest square of the test strip:
I test cut this yesterday, sending ¼ of the data at a time to the laser to avoid printing errors. However, part way through the cutting, cut-out paper circles stuck to the long air assist nozzle of the laser head (ironically) hit a washer I was using to weigh down the paper to prevent movement while cutting. The paper shifted by about 1mm, which was enough to make some adjacent halftone dots overlap and cause others to have a visibly wider spacing.
In the process of cutting that photo, Shane happened by and mentioned that vector cutting 10368 objects may be just as fast as the typically-very-slow raster cutting time. With three clicks, I turned off the vector outline of the halftone dots, and selected a fill color. After test cutting a row, I found that he was right. Check out the difference between raster (100% speed, 100% power) and vector (42% speed, 100% power) in the darkest section of the image – the area with the closest spaced circles:
The vector halftone dots are perfectly circular, though the edges are a bit rough. Some of them have a very small border and so are a bit fragile. The raster halftone dots are not very circular, but the edges are very smooth and the boarders are slightly wider. I chose to raster cut the 24″ x 18″ image, and found that the raster cutting time of 1.4 hours was nearly equal to the 1.3 hour vector cutting time.
Note that many programs can create halftones, though often the results will not be suitable for laser cutter use:
The next step is to laser cut this image into wood. Also, Inkscape will let you draw any shape to create tiled clones from – so please do share photos of any halftone images you create with star shapes!
Join us for The Greatest Show (& Tell) on Earth at Wisconsin State Fair Park September 23rd & 24th, 2017. Admission is free. A joint presentation by Milwaukee Makerspace and the Betty Brinn Children's Museum.
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