Part and Design Choices
Using threaded inserts was new to me. I was introduced to the idea in one of CNC Kitchen’s videos where he tested various styles of threaded inserts. Check out his video to learn how useful threaded inserts can be. https://youtu.be/G-UF4tv3Hvc.
I had various ideas in mind as to how I could assemble the printer. Screws in inserts, screws in plastic, screws and nuts, and cable ties. My previous printer used cable ties quite extensively. Cable ties are alright but are not the strongest, neatest, or most maintainable. Screws in plastic are neat but aren’t very strong. They also tend to be easy to strip so maintenance on the printer is limited. Once you install and remove a screw once or twice it generally strips. Screws and nuts work well but nuts aren’t as convenient as inserts. Inserts are clean, convenient, strong and allow for multiple assemblies and disassemblies.
Laser Cut Steel
The main frame plates on the printer were made from 6mm steel plate. I chose laser cut steel because I hoped it would be strong, accurate, cheap and quiet.
I want to be clear the strength of the frame is excessive. The steel frame has far more strength than a printer should ever need. The Prusa Mk3 printers use aluminium frames (I presume this may be to keep weight low for shipping?). Aluminium is great but doesn’t work for my design. I don’t have the skills or tools to weld aluminium and my design has a spot-welded frame.
Laser cutting was used to ensure that the finished frame was square and accurate. I had all the sheet metal parts laser cut and etched. Small 3mm holes cannot be cut by a laser cutter. In these situations, centre marks were etched to ensure they were accurately positioned. I decided laser cutting was an affordable way to outsource accuracy. I could cut a frame myself however it was easier to use an already accurate machine to do all the precision work for me.
I also hoped steel would make a quieter frame than my previous printers wooden frame. I thought that dense, small sections of frame may produce less noise than large wooden sheets. I have no real data or evidence to support this theory, it was merely based on personal observations and guesses. The finished printer was much quieter than my previous wooden design, whether this was due to the frame or not, I cannot really say.
Price, steel seemed to be cheaper than aluminium. The pricing on the laser cutting seemed to suggest that the steel was going to be cheaper overall. The aluminium bed carriage cost around 40 - 50 dollars to cut one piece. The rest of the steel frame cost the remaining 20 dollars or so.
As previously mentioned, aluminium was used for the bed carriage. This was simply to reduce the mass of the moving bed carriage. Less mass on an axis is a good thing, it reduces ghosting, skipped steps, and allows for faster printing.
The 3030 aluminium was chosen because it is common and cheap. In reality, I just used it because Prusa printers use it.
Printed parts were used as part of the frame. This was because 3D printed parts are easy, cheap and popular. Other printers use printed parts with great success. The printed parts don’t seem to be the limitation when it comes to 3D printing accuracy. ABS was used for all printed parts. This was to ensure that parts remained strong even when near the hotend or heated bed. All the plastics together used less than one kilogram of ABS, this fit with the goal of being affordable.