Tuesday, February 26, 2013

Filament feeder

My printer uses 3 mm filament. 1.75 mm filament is also available. A hot end can support only one diameter, so when you buy a hot end, you have to decide if you want to use 3 or 1.75 mm filament. Switching to another diameter means buying a new hot end. The filament I use is quite stiff and springy and has a strong tendency to tangle. This get worse to the end of the spool, where the diameter gets smaller and smaller. I can imagine this less of a problem if you have 1.75 mm filament. This makes feeding the filament to the printer a non trivial task. In my first setup, I had a spool with filament laying besides the printer. That was far from ideal, because I could not leave it alone. I constantly had to monitor the unwinding and every few minutes, I had to untangle the filament. It would be great, if I could start the system and leave it alone until the print is ready. In my current setup, I use a printed spool holder.

Printer and spool holder
The spool holder has bearings for optimal unwinding. To avoid tangling of the filament between the spool and the printer I use a PTFE-tube. To prevent the tube from getting pulled into the extruder, I have printed a washer which is placed at the end of the tube at the extruder. It lets the filament go through and blocks the tube from getting pulled into the extruder. Up till now I am very happy the results of this setup: now I can start a print that takes for example five hours and leave it alone until the print is ready. Mission accomplished!

Thursday, February 14, 2013

Optimize (PLA) print

Update Slic3r
The first improvement in print quality was achieved by upgrading Slic3r from 0.7.1 to 0.9.8. As described in my post of last January 17.

My first print was a glass from thingiverse. The foot printed fine. The stem was troublesome. I had to blow air (with my mouth) to get a reasonable quality.

Left blown by mouth, middle with small 40 mm fan, on the right with big fan mounted in the printer frame
When printing the stem, the nozzle keeps adding hot PLA to the same small spot without waiting for it to cool down and harden. I added a small 40 mm fan to automate my mouth blowing. When I tried the glass again with this fan in place, it turned out that the airflow of the small fan wasn't enough. See the glass in the middle on the image above. In this interview with Alessandro Ranellucci, the developer of Slic3r, I noticed that he had a fan mounted in the back of his printer frame. I took a fan scavenged from an old computer power supply and mounted it on the frame using some tie-wraps.

A fan is mounted on the printer frame using tie-wraps
I noticed that when  printing big objects (objects touch a lot of the printer bed surface), the corners will bend more when the fan is on. So for some objects you want the fan on and for others you want it off. I installed a switch to easily switch the fan on and off, depending on the object to be printed. I assume a heated bed will take care of the bending in case of printing objects that touch a lot of the printer bed surface, but for now switching off the fan works okay for me.

Finer steps
My printer has a 0.35 mm nozzle and I originally had the layer height set to 0.25 mm. You can set this value in Slic3r. I tried a value of 0.1 mm. Slic3r will do all calculations necessary to deliver the right amount of filament for the height and speed setting. The result was very smooth. Downside is the much longer print time.