Sunday, August 26, 2012

Successful Print

A small followup to Fridays post. I've been doing more printing and the print head clogs up roughly at the same time every time with the result of a ruined print and needing to yank out the PLA. The increased value of the extrusion-multiplier had nothing (or very little at least) to do with it either. After a failed attempt I measuring the temperature on the push fitting to 60 degrees C! Too hot to touch.

Aluminum foil heat sinks.
I had a couple of small heat sinks, but no thermal compound and way of fastening them so I brought out a sheet of aluminum foil which I folded, cut and attached to the print head.

I also added a fan blowing air over the improvised cooling solution. Not pretty, but as a proof of concept more than good enough. Press "Print" and wait...

Roghly three hours later I had my result:

A little bit of cleanup needed, but apart from that very nice.
Pretty much perfect! The print head oozes a bit so there's small bits/balls of plastic here and there that needs to be cleaned up, but over all I'm very pleased with the result.

Friday, August 24, 2012

SUMPOD Heated Build Platform Part 2

I've been using the last week to put together "Heated Build Platform Mark II" consisting of aluminum sheet instead of glass. As I mentioned in my previous post I had an old Apple Pro cabinet where the side cover can be taken off easily. Being 3mm thick makes it perfect for this project.

Only negative thing was no access to a workshop or proper power tools...

I ended up using the non-metal wood hand saw.
Having read somewhere that it is possible to cut aluminum with blades meant for wood I though why not give it a try with my existing equipment.

Marked, taped and ready...
The saw was a cheapo so no big loss if it didn't work out - which it did :) I can't see any damage on the blade afterwards at least. Sawing aluminum this way is hard work so I won't recommend it if you have an alternative though.

New vs. old print bed.
Using the old platform as a template made it easier to drill holes in the right places etc. I made sure to tape the surface with masking tape first and to clamp the aluminum between two pieces of wood to avoid splinters. Sanded over all the edges with fine grit sanding paper afterwards.

Test fit.
Not shown here I made sure to test the heating functionality thoroughly before threading the wires and installing the platform.

Aluminum is a great heat-spreader, insuring pretty even temperature over the whole surface so that's great! Using a metal platform is not without it's drawbacks though. There's ample opportunity to electrocute yourself if you're not careful. Therefore I added two layers of Kapton to the underside before laying down the heat-wire. I might ground the plate at some point, but I'm not too worried since the platform will be warm when the power is on so I really don't want to touch it when it's active anyway.

The shielding on the wires I used are good up to 90C, which is more than enough for PLA, but If at some point I'm going to print ABS I probably have to rework that part.

Wired, levelled and ready for first print.
My second thermistor (RH16-4A104GB from MMC) worked out much better as well, being off by only one degree C. More than good enough for my purposes. I installed it roughly in the middle of the underside of the platform directly in contact with the aluminum and sealing the whole thing with Kapton.

Made sure there was enough wire to avoid it getting stuck or ripping anything loose.
Having made a few test prints there's no doubt the heated surface makes a huge difference in making the PLA stick to the surface. I haven't had one false start. That is, the plastic sticks on first try every time. I've had a couple of prints where very thin details becoming unstuck during the print, but for the most part it's been extremely good.

This time around I've been testing Slic3r which I like a lot for it's simplicity compared to Skeinforge - it's a lot faster as well being coded in C++. It seem to be a bit courser though. When it comes to fine detail and thin walls it sometimes leaves gaps, even when I have selected solid fill. That's something that I have to figure out.

The next issue to solve now is the feeder/printhead mechanism. I had the print head clog up three times the last couple of days and I'm still trying to figure out why. It seems to only happen on longer printruns and my initial guess is that there's a combination of several parts getting too hot. I've been playing around with increasing the filament extrusion-multiplier as well so there's a chance that's the reason. More testing needed :)

Just in case I ordered a new, and more compact, print head last night from QU-BD. Hopefully I will be able to use my existing Nema 17 stepper on this one. The bonus is that I eliminate the bowden tube and any slack in that type of setup. There is a disadvantage in moving more weight onto the y-axis so I'll have to test before saying anything for sure, but I might have to move the y-axis motor to the back of the printer frame and re-rig the belt.

So far I've been using the Sprinter firmware, but I think my next project will be to upgrade to Marlin since I've heard it's a bit better quality wise.

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
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! :)