Sunday, August 12, 2012

SUMPOD Heated Build Platform Retrofit

There's not been much progress on my 3D printer during the summer months since I haven't been much home, but this last week I've had a bit of progress.

Where I left off before summer showed I had some challenges to overcome with the build quality.

Failed prints
Mostly I've been playing around with the settings in Skeinforge - which is a hugely complex software for slicing up the 3D model and preparing the g-code for the printer. Using Airtrippers PLA settings as a starting point I got pretty good quality for the bottom and side walls, but the filling still gives me issues. As seen in the picture the print head tears up the fine inner walls in the model and produces big, gaping holes that the printer can't close when doing the top layer at the end.

I suspect this mainly is caused by to low flow of material on the interior walls, but I haven't been able to find the right setting to increase this yet. More testing needed. I might go back to scratch and test with coarser settings, i.e. thicker layers, to see if that helps as well since part of the problem is that the previous layer stick to the printer head.

Another, frustrating, issue is that the printer seems to print when moving from one position at one side of the model, to another at the other side. This leaves a slightly higher stripe of plastic that creates non uniform surface on the next layer. This can be seen particularly good at the center object on the bottom layer on the picture above. I don't think it has to do with residue plastic continuing to ooze from the print head since it seems to consistent for that - but I could always be wrong.

Getting the the print to stick to the build platform has also been challenging. At first I used the provided MDF platform with blue masking tape. Depending on the temperature in the room I had to restart the build 5-10 times before the PLA would stick properly. Increasing the temperature of the print head above 185 degrees C does not help with the brand of PLA I'm using at the moment. I've also played around with increasing/decreasing the distance between the print head and the build platform up until the point of the filament jamming.

Changing the build platform to use glass seem to help a bit - when heating the glass with a hair dryer directly before starting a print. Still takes quite a few tries to have it stick. Seems like the printer doesn't feed enough material at the beginning as well. I'm printing without a raft since I can't be bothered to remove it afterwards ;)

Glass picture frame from Clas Ohlson. Cheap at just over €1.
Still covering the glass with blue painters tape
Seeing heat was the way to go - a heated build platform was the next logical step. I ordered a huge (20 cm wide) roll of Kapton tape from e-bay to avoid having to overlap when covering the platform. Thinking Nicrome wire easy to source I didn't order any, but I couldn't be more wrong. This is one of those things that's really hard to get hold of here in Norway for some reason. After googling and trawling forums I finally found a substitute in a forum thread about styrofoam cutters; Kanthal wire. With nearly the same specs and even surpassing some - like handling very high heat - it seemed ideal.

Glass printer bed
Measuring the area the print head could cover was a bit disappointing. As can be seen from the picture above where I have cut the glass to match. Except for about 5mm extra on the left and right side that's about it (14x15cm). I had to cut one of the corners to make room for the leveling adjustment bolt.

Trying to keep the three wires (in parallel) at the same length of 460mm was a bit of a challenge since not all the traces would be identical in form.

I started by adding a layer of Kapton to the top layer of the glass plate and then proceeded to tape the Kanthal wire to the bottom with strips of Kapton.

Almost done, just need to fasten the wires to the power
source...
Using non-tempered glass, knowing full well that the glass probably would crack during repeated heating and cooling, I still had to try it out. Sourcing, and cutting, this kind of glass is another thing that's not easy to get done apparently. However; having the glass crack during assembly was a disappointment, but again  entirely my own fault being careless with a screwdriver.

I had to try heating it up anyway so I hooked up the (converted) PC power supply and turned on the juice. This taught me two things; first of all - the thermistor (temperature sensor) was the wrong type as it showed 20 degrees higher temperature than it actually was. Fortunately I have another thermistor (also rated at 100K) that I'll try next. Secondly I discovered that the heating was extremely effective - yay! I didn't time it, but it felt like between 10 and 15 seconds between I turned on the power and the platform measured 60 degrees (taken with my heat sensor gun). Not having to heat the whole print bed, but only the actual area needed, probably helped here. The glass also only has a thickness of 2mm. Hearing a loud crack made me turn of the power pretty darn quick though ;)

Side panel of an old G5 Mac Pro... use what you've got :)
So what's next? The Mac Pro cabinet is all aluminum and has an easy removable side panel with 3mm thickness. Adding one or two layers of Kapton tape to avoid a short - before adding the heating wire should make it quite ideal for my purposes. Bring on the hack saw! :)

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