STL sheet for printable sonic screwdriverSketch of Screwdriver
Off to the left is a picture of what the finished sonic screwdriver should look like. Here’s a picture of the parts I’ve designed so far. Assembled properly, these parts should be able to be assembled into the lower half of the sonic screwdriver.
After my recent design-print fail, I’m going back to the drawing board (slightly)1 wiser. If nothing else, I like to think what I have so far is pretty neat. 2
After my design-print failure I thought it was about time I recalibrated my ‘bot:
Starting from scratch, I’m using the 0.5mm test pieces from Spacexula’s calibration set. Before starting I set Skeinforge->Carve->Layer Thickness (mm) to 0.4. Thus, I came to test piece 815.1. The piece came out well, but I noticed that where the Z axis raises there is some slight blobbing and just before the blobbing, some sparse areas I can see through. Otherwise, great interlayer adhesion. The height of the piece is 10.25, 10.31, 10.30, 10.55. Throwing out the high and low, there’s an average of 10.305mm. It is 22.29mm x 22.29mm.
Skeinforge->Carve->Layer Thickness (mm) to 0.38. Test piece 815.2. Again, slight blobbing, very small sparse areas and great interlayer adhesion. Piece height is 10.39, 10.40, 10.18, 10.19, we’ll call this 10.29mm. It is 22.41mm x 22.13mm.
Skeinforge->Carve->Layer Thickness (mm) to 0.36. Test piece 815.3. Slight blobbing, very small sparse areas and great interlayer adhesion. Piece height is 10.25, 10.31, 10.14, 10.30, we’ll call this 10.275mm. This one was 22.33mm x 22.29mm.
I’ve been slowly working on the design of a printable (and fully MakerBottable) sonic screwdriver. This model of the sonic screwdriver is built up of a number of concentric cylinders, has several significant overhangs well in excess of 45 degrees, and is larger than the MakerBot’s built capacity. In order to deal with these design problems, I modeled it in sections.
In order to make the overall result something I could just pop/snap/slide together I designed it making some sections which were split vertically and other sections which slide around those sections to keep them together. In order to make the parts quickly printable I designed all the parts at around 0.5mm thickness.
About 40% of the way through the print one of the vertical sections wasn’t coming out properly – probably because it was too thin. The parts were too thin and flexible and ended up tearing between layers and just being too flimsy.
I also noticed something odd – the extrusion was too thin on that side of the model. I can’t be sure why this is happening – but I suspect it’s due to the extruder not getting a good enough grip. Perhaps I need to floss the extruder pulley or install a new extruder idler wheel. However, it doesn’t explain why the extrusion was too thin on just that one side and no other spots.
I tend to see the world through WordPress eyes.1 When I find (or write) a clever bit of script that would be useful to a WordPress website, I tend to convert it into a WordPress plugin. I did this with my PieChart Plugin and a few other knick-knacky plugins.
It occurs to me that it would be relatively easy to build a WordPress plugin that searches through a post/page, finds Amazon links, and then turns them into affiliate links… I think this could be useful in several of my sites, actually.
The interesting thing about this model is that it combines some of the best parts of Darwin and MakerBot and what appears to be a Bowden extruder.
The very nature of FDM1 means that the robot will only move the Z axis a little bit every once in a while. One of the design drawbacks to the Darwin was that the heavy extruder head (motors, gears, heating elements) were so heavy that the entire robot would rock or vibrate with the lateral XY movements. MakerBot got around the heavy extruder head problem by moving the platform in the XY and moving the extruder head only up and down. This design decision isn’t without it’s tradeoffs, however. One downside is that their build area is much smaller than a Darwin. Another downside of the MakeBot design is that once the object being built reaches a sufficiently large volume or height, moving the object around quickly on the XY platform causes it to vibrate, shake, and become somewhat unstable.
One of the main improvements inherent in the Bowden extruder is that it allows you to take the heaviest parts of the extruder head, separate them from the rest of the extruder head, and move those heavy pieces to a different location. Using a Bowden extruder makes a Darwin style robot much more feasible – the small moveable print head won’t have the mass to cause the robot to become unstable.
It seems that combining either of the X or Y movements with the Z probably won’t matter all that much, since the Z axis will only move about 0.33mm or so per layer and the Z axis typically doesn’t operate at the same time as either the X or Y axis. Combining the as the new RepRap version II, Mendel, design shows us that combining the Z axis along with either the X or Y axis, but not both, can lead to a very stable configuration.
What I like about the Ultimaker design is that it would appear to incorporate some of the best parts of the MakerBot and Darwin designs. It appears to have a bolt/nut/T-slot MakerBot style assembly structure using thin lasercut wood pieces for the body. I found these parts to bolt together very quickly. Contrast this to the Darwin/Mendel structure using lots of nuts and threaded rod and printed plastic parts to hold it together. At the same time, by making use of a Bowden extruder and the Darwin body shape, it appears to be able to use most of the interior volume for printing.
I suspect it probably uses fewer parts than a typical Darwin, but I can’t be sure. I also have to wonder about the cost of lasercut wood versus the cost of nuts and threaded rod.
I placed my order for a MakerGear Enhanced Operator’s Pack on 8/11/2010, it shipped the same day, and arrived today 8/13/2010. My extruder has been working really well and without problems with ABS since my last rebuild. I’m really hoping I won’t need these bits any time soon…
I recently bought the Perhaps with a joule thief?)1 Since I know very VERY little about electronics, I’d appreciate some diagrams, descriptions of parts, etc.
If you’re interested in this project or just want to help, I’ll gladly accept any assistance. Let me know if I can help with any printing projects in return.
Thanks!
Why do I get the feeling I’ve seen the guy on the right before??? [↩]
