In Part I, I introduced the derivative of RichRap’s 3DR printer that I’ve been working on. I’ve had some people at our work’s maker space ask me about various decisions I made in this design. Almost all my decisions are based on the idea of making this a grown-up Printrbot Simple. Here are some of the characteristics/parts is will share with the Printrbot Simple:
- Use 8mm rods. Since the Simple has 12 LM8UU bearings, I can reuse the bearings from the Simple (the 3DR uses 6mm rods)
- Use fishing line, just like the Simple, for motion control (except I’ll be using a different line)
- No heated bed, just like the Simple
- Use micro switches for end stops, just like the Simple (the 3DR uses Hall effect end stops)
- Keep it small, like the Simple (and the 3DR). Although it will have a 170mm diameter bed, compared with the 100mm x 100mm bed on the Printrbot Simple
- Allow printing all parts on a Printrbot Simple (more on this later)
After my last post, I discovered a few changes I needed to make. Here is the preliminary list, before I decided to allow printing the parts on a Printrbot Simple:
- The parts were a little too large to be self-replicating. These parts would need to be printed on a 180mm bed, but the 3DR bed is 170mm. So I changed the design to be a little smaller, with a maximum dimension of 164mm
- I discovered I didn’t have easy access two of the stepper motor screws. RichRap left an large opening for this purpose. I added small round holes (which you can below on the outside wall, near the extrusions)
- Relocated the ribs stiffening the smooth rod sockets since they blocked hex key access to some of the stepper-motor screws
- Removed the triangular “foot” in the center
- Moved the stepper motor mount farther from the extrusions. I’d read reports of a very tight fit, and experienced it myself, so I moved the mount to provide a little more clearance
- Added a chamfer to the holes in the motor mount on the side with the motor. I was having some extra material here from overhangs, and the chamfer eliminates the need to clean up the holes
- Added side slots so I can feed wires into the sides of the extrusions in case I can’t fit all the wires through the middle of the extrusions
- Added nut traps for the M4 nuts used to hold the base and top parts together
Here is the new design for the base:
And here is a view from the bottom:
The “curve” where the parts meet is now less pronounced in order to keep the parts small enough to be self-replicating. This was all looking really nice, and I even printed out a test part.
Printing on a Printrbot Simple
While I really like the design above for it’s clean lines, the parts are too large to print on the Printrbot Simple’s 4” x 4” bed. The top and bottom parts have a maximum dimension of 6.5”. I thought about doing something like the “pay it forward” program available for the Kossel Mini. But then ProfessorBean on the RepRap forums gave me the idea of breaking up the larger parts into smaller parts. Hence was born a new iteration that can be printed on a 4” x 4” print bed, and thus a Printrbot Simple can entirely spawn this printer. How cool is that!
You can see I divided each of the previous base pieces further, so there are now a total of nine base piece, all held together with screws and nuts:
With all these parts, I wanted to make assembly and alignment easier. In the next photo you can see I’ve made several changes:
- Added nut traps
- Added bumps and dimples for self alignment
I really like the way the parts assemble without requiring fiddling to get them lined up well. After three evenings printing, I had a completed base:
A few days later I got the glass base plate and used RichRap’s bed clips to hold it in place:
It turns out I’d positions the holes for a 175mm diameter print bed, but he glass Borosilicate glass that I ordered was 170mm in diameter. I was going to either move the holes closer to the center, or make larger clips. And then I had another idea, which was to make spiral clips that would allow different sizes, and help center the build plate:
On the left you can see the bottom of the clip, which has a spiral that will push against the glass. Here is a photo showing the clips installed:
These clips are still not large enough, so I modified the clips after taking this photo. I’m currently printing out a new set of clips.
I also need to reprint the green part under the clip. My original version didn’t have a nut trap, whereas my current design does. Having a nut trap will make it much easier to tighten or loosen the screw from above, without needing to reach underneath to hold the nut.