Saturday, April 21, 2012

Prusa Tips & Tricks: Why Layer Height Matters

After getting my printer fully calibrated and so forth, I began to experiment with the different settings available inside of slic3r to determine how different parameters affect the quality output of my printer. I found that what affected quality the most was layer height, not only would lowering the layer height make the ribbing on a print less prominent, it also created more precise angles within the model.

I decided to create a comparison of a model using layer height as the variable for determining quality. As you can see, I achieved pretty good results using a 0.5mm nozzle. When printing at 0.1mm layer height or lower, any slight errors in calibration are greatly exaggerated, any slight miscalculations in the amount of plastic being extruded can wreak havoc on quality.

Another issue with layer height is the time it takes to print an object. Printing something at 0.1mm takes 4 times longer than at 0.4mm. When printing large objects this has to be taken into consideration when selecting an appropriate layer height.

In conclusion of my makeshift experiment, I found that my Prusa prints optimal quality at 0.2mm layer height, good to know. 

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!

Tuesday, April 17, 2012

The Prusa Build: COMPLETE!

It has been a solid six months since I first embarked on building a Prusa RepRap printer, and last week I finally printed my first print! (yes I have been printing non-stop for a week, hence the week delay for this post) The final build stages before my first print were to assemble the hot end from MakerGear, mount the PCB heated bed, and attempt to wire everything up in some sort of cohesive form. The hotend ended up being a very finicky and almost ended in complete disaster; the connection inside the cured heatcore broke, so I ended up making my own MakeDue hot end from salvaged MakerGear parts which has been working very well so far. After I got the hotend working, I mounted the PCB heated bed and went through a series of slightly dodgy upgrades which I will cover in more detail in a following post. The wiring is still a work in progress, I plan on cleaning the wiring up some time in the future.

My first print was the symbolic RepRap shot glass. The print turned out much better than I expected, I was dreading the big blob of goo that most reprap bloggers write about, but was pleasantly surprised when the print actually resembled the desired object. I used Sprinter firmware with Slic3r for gcode and controlled the printer using Pronterface.

I  put kapton tape directly on the PCB heated bed as a quick fix for a piece of glass. There were some uneven areas on the PCB surface, but overall it did not severely effect print quality.

After my surprising success with the shot glass I went about fine tuning slic3r settings. I followed an excellent blog post tutorial for slic3r calibration that can be found on RichRap's blog,
I would highly recommend reading through the post as it clearly outlines how to properly calibrate Slic3r settings. After my calibration was complete, I set about testing the capabilities of my new Prusa. I started with some gears and pulley parts, and then went on to experiment with lower layer height with a Yoda head. I also began to experiment with the effects of extruder retraction while printing a bracelet from thingiverse. I found that changing the amount of retraction even 0.5mm and adding a little bit of Z lift between moves significantly changed the amount of stringing on a print.

I'm really blown away with how straightforward printing has been and the significant leaps and bounds in quality that I have experienced over the last week. Over the next few days I am hoping to post some of the simple improvements I have made as well as a few observational posts regarding the effects of layer height and other slic3r settings on print quality.