After building the box for MegaMax I decided to try a big print. The blue 3 face cup is 130mm tall and took a little over 15 hours to print. No delamination! It’s a miracle the extruder kept working!
Well, OK, not the whole enclosure, just the parts that hold it together.
MegaMax can print big stuff but he’s had problems with large prints delaminating. The answer seems to be enclosing the printer to keep the prints warm while printing. I designed this box and 3D printable parts to hold it together so that I can take the box apart easily to work on MegaMax or move him to other locations and put it back together when I’m done. The box is 38″ D x 28″ H x 32″ W.
The box is made of 1″ PIR foam with corners suitably notched to accommodate the printed parts. MegaMax has a 450 Watt heater in the printbed so the box gets super-toasty inside. I suspect it gets a little too toasty but haven’t made any measurements yet. I’ll soon be moving the electronics out of the box. I didn’t do anything to seal the seams in the box because it doesn’t seem to be necessary. I did tape the edges of some of the foam boards with clear packing tape to prevent damage.
Design and stl files are available at http://www.thingiverse.com/thing:269586
One of the biggest problems with FDM 3D printing is hot-end jamming. There seem to be a lot of causes, most of which are not readily identifiable when a jam occurs. One thing I have found is that after a hot-end jam I can usually grab the filament and manually push it and get it flowing through the hot-end again, though it is too late to save the failed print. The most common means of driving the filament into the hot-end is to pinch the filament between a gear and a bearing and have a motor drive the gear, either directly (with 1.75mm filament) or via a gear reduction/torque multiplier arrangement (3mm filament). When the hot end jams, the large force applied by the gear over the small area of the filament that is pinched between the gear and bearing usually chews a divot in the filament thus destroying the grip.
A couple weeks ago I started designing a 3mm filament extruder for 3D printing. My hope is that this extruder will provide sufficient force on the filament to prevent hot-end jamming from ruining prints. My design uses two counter-rotating 6-32 nuts twisting on the filament (like the way your hands twist in opposite directions when you give a “snakebite” to your friend) to drive it into the hot-end. One is a normal, right-hand threaded nut, the other is left-hand threaded. When the nuts turn in opposite directions, the torque that would try to twist the filament is cancelled while moving the filament forward and reverse without twisting.
The motor has to turn about 1.26 times to move 1mm of filament so there is a huge torque to axial force conversion. The gear diameter is about 30mm. That 1.26 rev moves the gear about 119mm at its perimeter. That means there is about a 119:1 increase (ignoring losses in the gears, bearings, and nuts) in the force at the filament compared to the force at the gear. That force is applied over a larger area of the filament than the usual pinch arrangement, so it is less likely (I hope!) to carve the filament and lose grip. I tried stopping the filament by grabbing it with my fingers and holding as tightly as I could but it didn’t even slow down.
The firmware in the printer has to be tweaked so that it knows exactly how many steps of the motor are required to drive 1mm of filament. The formula is:
32 rev/ 1 inch X 1 inch /25.4 mm X 200 steps/1 rev X 16 microsteps/1 step = 4031.496 microsteps/mm
For initial tests I just input 4031.5 using the rotary encoder on the LCD interface to the RAMPS board in MegaMax.
Here are the parts that I used:
Left hand threaded tap: http://www.amazon.com/gp/product/B006YITGY8
5mm brass tubing: http://www.ebay.com/itm/360828686174
5x16x5mm (625Z) bearings: http://www.ebay.com/itm/321062568303
I also used a NEMA-17 motor from a QU-BD extruder.
You can DL the STL files for the printed parts here: http://www.thingiverse.com/thing:261037
Test printing will start in the next day or so and I will post another video showing success or failure.
After a long series of manipulations, the CT scan derived face was successfully used to make a pencil holder (of all things!). It is about 100mm high and took about 9 hours to print. You can find files that you can use to make your own mash-ups of my face on thingiverse: http://www.thingiverse.com/thing:203856
Today was spent researching all the manipulations involved in getting a CT scan into printable form and I managed to get a print out of it. The process starts with DeVide where the dicom data from the CT scan is processed using a dual threshold, decimation filter, and stl writer. The stl file contains a lot of unwanted stuff, in this case, soft tissues inside my head that add triangles but won’t be seen in the print, so those are removed by applying ambient occlusion followed by selecting and deleting vertices by “quality” (which will be very low values for vertices on the interior of the object). This process invariably blows small holes in the desired surface, so you apply a “close holes” filter to fix that (which closed up the nostrils very nicely). Next you open the stl file in netfabb and rotate and clip unwanted external stuff and apply repairs as necessary. Finally, drag it into slicer and scale it. slice and print.
While investigating software to extract bone data from CT scans and turn it into 3D printable STL files, I played with a CT scan of my own head that was used to treatment plan orthodontics. I have been using DeVide to process the data and finding it is not only easy to use, but a lot of fun!
The animated gif was made by sweeping the lower threshold of a dual threshold module from -800 to 900 in steps of 100 with the upper threshold fixed at 1400. The effect is to strip away the lower density tissues leaving only dense bone at the end of the sweep. I saved the result of each run as a png file then converted to an animated gif using an on-line service.
I recently acquired a B&L Balplan biological microscope (about $200 on ebay) to look at really small critters and decided it would be nice to be able to record some of their antics. After a few measurements with a caliper and about 30 minutes with Sketchup, the design was ready to print on MegaMax. Initial test results, seen below, look pretty good! The camera is a Logitech Quickcam Pro for Notebooks (seriously, when are they just going to start using model numbers?) that can capture video at 960×720 and 15 fps. The camera is not a current product at Logitech but can be picked up for $10-20 on ebay. The still and video were captured using quvcview running on my laptop (ubuntu 13.04). Logitech’s software works great on Windows. The image below shows “horns” on the head of a pinhead sized bug that was crawling around in my work room. Magnification is 640X!
The adapter design and .stl files will appear on Thingiverse soon.
See the vase being described at the end of the Hack-a-day video posted below.
After a year’s work designing, building, scrapping, redesigning, building, and working through software and firmware issues, the MegaMax 3D printer is now functional. It has some common 3D printing issues like printed objects peeling up off the glass printbed. Tweaked settings in Slic3r, ABS “juice”, and Aquanet hairspray have all been tested with moderate success in attempts to improve adhesion to the printbed. Finally, have_blue gave me a block of foam out of the Stratasys printer to try out and it seems to work better than the other methods and doesn’t require heating the bed! Further experiments to be conducted post-haste.
More info on this project can be found here: http://wiki.milwaukeemakerspace.org/projects/megamax_3d_printer
The video shows the last few layers of the calibration cube “printing” at 414% speed (according to my LCD display).
The Bucketworks 3D printing meet-up on 8/12 paid off big-time! Gary Kramlich helped me debug a problem that was preventing me from flashing the firmware on the controller board for the MegaMax 3D printer. After a few tweaks I was able to get it moving.