Wednesday, April 18, 2012

Prusa Tips & Tricks: Y-Axis Bed Mod

While building my Prusa, I found certain areas of the build process to be seriously lacking on the documentation front, specifically the Y-axis and the hot end. From my humble experimentation, I came up with a simple Y-axis carriage that allows unimpeded movement, is light weight and simple to make.

The first step was to cut a 9.5in x 9.5in square of plywood and then cut it into three pieces to form a middle section and two extensions as shown in the picture. I screwed it together with some screws I found laying around and voila:

The first time I tried to mount the square piece I found to my dismay that I only had about 70% mobility on the Y axis form the plywood hitting the frame, significantly lowering my maximum print area. Hence, the reason for the "H" shape of the Y axis bed, giving the extension pieces just enough height  so that it clears the front of the frame. You can see how the wooden extensions clear the frame in the picture.

After some initial printing directly onto the PCB heated bed with Kapton tape, I quickly found that the PCB was not perfectly flat, so I began looking for some flat material that I could print onto. I asked around on the RepRap forum about whether people using glass were using heat treated glass or just normal glass. I found that the majority had found that any type of glass would serve the purpose. I quickly found a glass pane from an old picture frame that fit perfectly across the X axis of the bed. I was initially worried about the extra two inches that stuck off the Y axis (the clear part in the picture), but I soon realized that it was a great way to remove the pane right after printing as it wouldn't heat up as much as the rest of the glass surface. As an added bonus, I could move the glass around without getting oil from my fingers on the actual printing surface. I covered the glass with Kapton tape, clipped it on to the PCB heated bed with butterfly clips and it printed beautifully.

My one problem after getting the pane of glass all rigged up, was that I could barely get the heated bed above 90C with the element constantly on. The underside of the PCB was heating the air and losing precious heat meant for the printing surface.  I had read on a blog about someone using a piece of cardboard as insulation. I decided to try it out as an alternative to the spray on insulation that seems to be the most popular solution. It ended up working extremely well, it took half the time for the bed to get up to 100C than it had before, now it heated up in approximately 5 minutes. In the last picture you can see my most current setup. It has been working great, I can print at 95C for relatively large pieces and have absolutely no warping. I pull the pane of glass off after printing, let it cool on the table for a couple minutes, and the piece breaks off with a little bit of force no problem.

Overall, I am really happy with my Y axis bed design. I hope that for newcomers to RepRap, this post will help to demystify one of the build processes that I found had the least documentation. Good luck!