RepRap: Builders

Hi all, it has been a long time, but I have something to show.

Hi folks,

I thought I'd post a quick update to my Open 3D-Printable Boot-strappable laser cutter) project. While some of the finishing touches or aesthetic details (such as side panels, or a top) are still incomplete, the machine moves fantastically under EMC2, and I've had much of the design built for some time. The main issue that I'm encountering right now is in aligning the laser beam to be accurate over the course of the 1m x 1m travel area, which I'm finding is not easy (but more on that later). Here's a tour of the printed parts, so far:



The system uses linear rails and pillow block bearings for linear travel on each axis. Upon each of the pillow blocks mounts a carriage -- in the case of the bottom axis, these carriages contain (1) two shaft holders, for the shafts on the top axis, (2) a pinch mechanism to hold onto a timing belt, and (3) either a mirror holder/idler mount (on the left side), or a NEMA 17 motor mount (on the right side). This is the mirror mount version, with the idler for the top axis also visible.



The timing belt goes through a pinch loop to keep it taught and transfer its motion to the pillow block. This pinch loop has an open center, so one can use large loops of timing belt without having to cut the belt and break the loop (I think this is a handy feature, incase you plan on making a larger machine, or using the belts for something else later).



The carriage for the NEMA 17 stepper motor that drives the top axis sits on the right hand side of the lower axis. I'm using the NEMA 17 motors from Adafruit ( [link] ) since they're relatively inexpensive at only $14.





The top carriage slides on the two shafts held by the lower axis, and also contains a mount for the Z-mirror and focusing lens. These optics are relatively inexpensive, and are from Light Object's build-your-own bundle ( [link] ) that a lot of folks on buildlog.net are using to build their own laser cutters.





The NEMA 17 stepper motor brackets for the bottom axis are much as they were in the last post, and have worked out pretty well so far. They mount to the aluminum extrusion with standard M5 bolts, and are reversible -- so they can face either left, or right. These are the same Adafruit steppers as used above, and there are two used on the bottom axis (one to drive each side).





The idler pulley brackets for the bottom axis are much as they were in the first iteration, only I've added a little more support to the design so they can take a bit more stress. They mount to the standard 20mm Misumi aluminum extrusion using the same standard M5 bolts that everything else uses. I've also added in a nylon bushing between the timing pulley and the M3 bolt that it's spinning on, which makes it glide fantastically better. All in all, I estimate that each idler mount with the hardware (minus the pulley) is only a dollar or two -- so very inxpensive. (Thanks to everyone who posted suggestions in the comments of the last post!)




The static mirror mount holds a mirror that deflects the beam at a right angle, from the CO2 laser, down the bottom axis. It then deflects off the mirror held on the bottom axis carriage toward the Z mirror on the top axis carriage, and onto the work piece.



This piece went through a bunch of iterations, largely because it's about 80mm high and needed to be rigid enough to not jiggle while the machine was moving. The hitch to this is that there are a bunch of bolts for mounting the mirror (top) or mounting the whole thing to the aluminum extrusion (bottom), so it can't easily be made solid. In the end this design works out pretty well, and is fairly rigid.



The laser mount was a fun and challenging part to design. The laser is about 2" in diameter, and also needs adjustment screws with another half inch or so of travel on either side. In my design, the laser also sits up 3 or 4 inches off the height of the aluminum extrusion. This is to allow a lot of depth to the cut chamber, and potentially enable some SLS experiments with a broader spectrum of materials than the Open Selective Laser Sintering project was able to use.

In the end, while I had designed some single piece holders, they were too large to print on anything but a RepRap, and so not too useful to the Makerbot folks. They also used a fantastic amount of plastic, so I decided to rethink the design. In the end I settled on using these 3D printable mounts, and mounting the laser tube itself into a piece of ABS pipe. While I was definitely into a "print everything you can" mindset, in this case I decided that a quick trip to the hardware store and $10 was more than worth the 10 hours of printing custom holders. I was also a little more comfortable with tapping the ABS pipe, and believing in its rigidity to hold the CO2 laser at exactly the right level. Even being off by a few millimeters could mean the beam hitting something it shouldn't (like a printed mount), and causing a catastrophic (and undoubtedly spectacular) failure.



This mount I'm actually very happy with, and it fits the CO2 laser wonderfully. Rather than use the CO2 laser for testing, for safety reasons I'm using a laser pointer that I've placed into a long ABS tube for alignment.



The CO2 laser tube tends to arrive in a fantastically large package to keep it safe (here, with a 3D printer and ikea desk for comparison ;) ).



The tube itself is about 70cm long, and about 2 inches in diameter.



The laser mount tube has a bunch of large nylon bolts placed at 120° angles to help adjust the laser path.



Here's the complete optical path, with both axes near their home positions. The total travel is quite large (about 1 meter by 1 meter).









For the controller, I'm using Bart Dring's Laser Interface Driver board. Honestly, I'd considered making my own board, but for just under $150 with the Pololu stepper controllers and connectors for something that's predesigned, it's really not that bad. I figured that the parts and a run of boards would cost me about the same to make, and this has already had the bugs worked out and has run quite well with EMC2 out of the box. I have had nothing but positive experiences using it, and it's even worked out well with the 2 steppers for the bottom axis plugged into a single driver. My only complaint is that it's a bit tricky to calibrate the voltages in on the stepper drivers, but that's more an issue with the spot Pololu's chosen to place the test point, and really you only have to do it once.



With the lights off, it's much easier to see the test beam in this picture. I'm having some issues aligning the optical path, and so I'm at a bit of an impasse. The beam seems to be at the same height at either end of the bottom axis, but in the middle it appears to move up a few millimeters (which corresponds to the entire carriage moving down a few millimeters). This isn't great, appears to get amplified as it moves down the +1meter on the final optical path before being sent to the workpiece. By the time the beam hits the Z mirror when the top carriage is at the far end (all the way to the right), it can wander quite a bit -- say up to 5mm or more. The beam width of the CO2 laser should be about 6-7mm by the time it reaches that distance, and the aperture to the Z mirror is only about 9mm wide -- so any divergence from being true really isn't okay.

As near as I can tell, this dip is coming from a bit of a sag with the rods. Placing a little bit of upward pressure on the bottom of the pillow bearings tends to level the optical path out, and so the rods appear to be sagging -- likely from a combination of their own weight, and the weight of the top axis. The rods are fairly large in diameter -- 12mm, or 1/2 inch -- so I didn't expect any sag, but I've also never constructed a machine that has a meter of travel before. It's not clear to me whether there's a quick hack I could do to help support the axis (perhaps sticking another piece of aluminum extrusion under the pillow bearings, along with some tiny wheels for it to travel on and keep the distance constant) -- or whether there's a better and inexpensive solution, like moving towards something like Bart's Makerslide v-rail based aluminum extrusion. I've noticed that the lasersaur folks seem to be using aluminum extrusion too, and are also dealing with similar distances to my design (I think their travel is about 2x4 feet, which is about the same as this design at 3x3 feet). That being said, I've noticed they've been in beta for quite some time, and haven't seen a video of their system cutting at full travel, so I'm not sure if they're also having issues with sag in their aluminum extrusion system at those large distances. Doing a couple of quick sag tests with some spare extrusion, it looks like it definitely sags less than the rods -- so it definitely has the potential to be a replacement if it comes to that. I'd just feel safer if there was an existance proof out there first for such large travels.

That's my quick update! Because this is an open project, I've posted the Google Sketchup and STL files to Thingiverse (available here: [link]), though there are still a few bugs left with alignment and such. Still, there are a bunch of interesting design elements that might be useful for other projects.

Thanks for reading, and please feel free to send along your comments or suggestions!
~peter
[Laser Cutter part 1] [OpenSLS Part 8] [cogsci.mcmaster.ca/~peter/]

Hot plastic. My extruder was running on the hot side, Nophead suggested this was due to the difference between the internal and external temperatures and he was spot on. Whilst I had originally constructed my Thermistor lookup table using a temperature probe clipped to the outside of the nozzle the inside was running a good 40 to 50 Deg C hotter. The problem is fixed now and a new thermistor table is in place all with the help of an Arduino based tool to help the process along.

Hi folks,

I thought I'd take a second to make a quick post about a bootstrappable open laser cutter design that I've been working on. I know I haven't posted relating to the Open Selective Laser Sintering (SLS) Project much after the Reciprocating Laser Cutter. Much of my lack of work on the project was due to our local hackerspace moving over the course of several months (when I had to help construct the new space), before quickly having to finish my PhD and begin a postdoc.

I love having access to a laser cutter. One can construct rather large items fairly quickly, and the materials available (like acrylic) mean that not only will one's creations be structurally sound, but they'll often look wonderful too. While my dad and I have been tinkering with our own 3d printers for a couple of years now, I still feel very much a beginner in constructing 3d models, unless using a tool more geared towards programmers (such as OpenSCAD). That being said, when I was introduced to laser cutting, the relative ease of designing and working in 2.5D as well as the (even more rapid) time to go from design to physical prototype simply made my creative self very happy. I remember several times waiting impatiently at the laser cutter for it to cut out the next sheet of some design I'd made that afternoon -- and upon assembling it, realizing how silly it was to be impatient that I could design, fabricate, and assemble some fantastic machine in only a few short hours. Not only for the OpenSLS project, but also for other creative projects, art, and tinkering, I greatly miss having access to a laser cutter, and decided to investigate how expensive it would be to construct one.

Several other folks have already been in this exact place, including the lasersaur folks ( labs.nortd.com/lasersaur/ ), who aim to create a fairly large format open laser cutter, as well as Bart Dring's excellent work on the open buildlog 2X laser ( www.buildlog.net ), a smaller format cutter that uses mostly off-the-shelf components combined with a few custom CNC-made parts. When I started thinking about this a month or two ago, Bart had just released his new design and had begin shipping the first kits to folks, and had quite a waiting list built up. I decided to get on his waiting list, but that I'd also get ahold of some of the parts that I could (such as the laser and power supply) to get a head start.

When the laser arrived, I ended up realizing just how big the tube is. With a tube approximately 70cm long (not including the mirrors to steer the beam), I learned that most of the length of most laser cutter designs is taken up by the tube. For example, with the Buildlog 2X design, the tube sits along the entire back of the machine, while the front includes both the x/y axis in the cut chamber (about 2/3 of the volume), as well as a separate area on the right that holds the electronics (about the remaining 1/3 of the volume). This is similar to a bunch of other designs, including the Chinese laser cutter we were using at my old hackerspace. I decided that while the ~20x12" cut area of the Buildlog 2X laser was great and much larger than what I had used before, that if the tube plus optics was nearly a meter long, I might as well make the cut area as much of that space as I could, and just stuff the electronics (which are relatively small) somewhere else -- say, under the tube. Making one axis a meter long meant the other might as well be a meter long too, so that the cut area would be square. (Put another way, I realized that from a cost standpoint, increasing the size of the machine doesn't really add a great deal of expense -- but it increases the utility by expanding the size of what you can build. I remember hearing Bre Pettis say that one of his thoughts, after having used a laser cutter for so long now, was that he had wished they had found a larger one).

Using these rough guidelines and inspired by Bart's design, I worked on designing and constructing my own laser cutter. Bart's design is really great, and he's put some wonderful work into it. Not only that, his v-rail design looks to make creating even large machines relatively easy. Unfortunately, with such a large demand for his parts, I decided that I might have to try an alternate design, and went with a more traditional bearings-on-linear-shafts design. The buildlog folks have amazing solidworks skills, but being new to building laser cutters, I decided to just sketch something out on a piece of paper, order a bunch of t-slot parts, and figure it out as I went.



The general design keeps very much with what other folks have been up to -- a t-slot frame, where the laser sits at the back, and a 2-axis CNC system sits in the front. Most of the difference is that I've added some room at the back under the laser to hide the electronics. Keeping SLS in mind, I'm also trying to keep a bit of height in the build chamber itself for future tinkering.



The "top" axis consists of two shaft mounts at either end (that mount atop the pillow blocks), one containing a NEMA17 motor mount, and the other an idler pulley mount.






The carriage for the Z mirror and focusing lens mounts on several smaller pillow blocks as well. Like the buildlog design, I'm using the inexpensive mirrors, lens, and the respective holders from lightobject. The idler and carriage have mounts for these parts, but still need some work. I also still have to add the tension mounts for the "bottom" axis belts to the shaft holders.



The "bottom" axis is driven at each end by a NEMA17 stepper. I thought this might be easier than using a single dual-shaft stepper in the middle, and designing my own drive system. It does require a bit more electronics (namely a second stepper controller on that axis), but otherwise should simplify things mechanically quite a bit.



The steppers are the standard, torquey steppers that Adafruit sells. I think the dual-shafted steppers used on the Buildlog 2X laser have nearly twice the torque, but there is very little friction in this design -- so these should be more than okay.



I'm on iteration 2 or 3 on most of the parts so far (since this is a learning experience for me, too). The second iteration of the NEMA17 holder is pictured above -- it has mounts to fit in standard 20mm t-slot, and is reversible, so you can flip it around (for the other side).



The idler design is very simple and low-cost, but I'm not sure it will end up working in the end. Here, instead of a bearing, the idler cog simply slides upon an M5 machine screw, while two jam nuts ensure that the screw holds in place and doesn't move. This seemed to work great before I started tensioning the belts, but now there appears to be quite a bit of friction, so I'll likely have another look at this design, and try to find some small (inexpensive) bearings.

---

That's my quick update! While the design is still a work-in-progress and I'm refining and printing out the custom bits, the rest of the parts are all sitting on the workbench waiting to be added in as soon as the axis design works pretty well. It's kind of been my hope that using these 3D prints I could get the system to work well enough to then design and cut out a more precision set of axis parts using the cutter. That being said, as I learn how to design for strength and resolution limits the quality of parts is getting better, and the latest set of parts is remarkably rigid -- so much so, that I'm hopeful they might not need to be replaced, and could serve as a long-term set of functioning axis parts for the machine.

I'm very much planning to make the source files available on thingiverse when I have a working design, in the hopes that folks with a reprap, cupcake, or thingomatic who are also interested in using their 3D printer to bootstrap their own laser cutter might find them helpful.

thanks for reading!
~peter

HacDC, Washington DC's hackerspace, is building a Prusa Mendel. You can track our progress at the HacDC website (linked above) or if you're really interested, see what's going on behind the scenes on our wiki page.