RepRap: Blog

One of the problems with PLA is that it shatters when stressed, rather than bending gracefully. This problem is solved in ABS by adding impact modifiers - basically synthetic rubber blends - to give some flexibility under stress. Luckily, I found an impact modifier that is compatible with PLA and does not significantly alter the melting point. At about 1/3 it makes PLA this flexible without fracturing:

I've got to run a few more printing tests on it, but it's looking promising as a material that offers the durability of ABS with the reduced environmental footprint and ease of extrusion of PLA. Oh, I suppose I'd better figure out what it'll cost me too :)

Update: I flexed some back & forth 100+ times and got bored trying to break it.

Printing with it is much trickier than plain PLA. It wants to coalesce into one lump, and you really need cooling between layers.

Vik :v)

Labels: ABS, filament, impact, modifier, pla, plastic

... a successful days collaboration, see hydraraptor.blogspot.com/2009/11/hacking-with-erik

Before:


After:


PLA on ABS on PLA:

Labels: ABS, ooze, pla, support

ABS is a superb building polymer, but it does tend to curl up and delaminate as it's laid down because of thermal contraction. Inspired by Nophead's work and the heated base done by Metalab, I decided to try a very simple solution. I ran a build with a cheap hair-dryer (right) clamped above my RepRap machine blowing on the build.

The result was perfect: there was no curl at all; the part built as flat as a pancake.

I had to insulate the extrude head by wrapping it in fibreglass wool and putting a piece of cardboard on to exclude the draft: the hot air cooled it too much...

The head was running at 240 ^oC. I put a thermocouple thermometer on the base at various locations around the build as it progressed. The result was a pretty constant 60 ^oC. Measuring the temperature of the part during the build with an IR thermometer gave 70 ^oC. Measuring the components of the extruder (including the motor) gave temperatures just below 40 ^oC; I directed the hair-dryer carefully to minimise the flow of hot air over them and the electronics.



And here is the part fitted (right). This is the prototype granule extruder coming together. The part is the guide that stops the screw-drive rotating as it's driven against the polymer granules. I made the hopper (green) in the Strat as my RepRap was in bits the day after I'd finished the design for that.

Watch this space...

Labels: ABS, curl, warp

I've managed to put together one extruder from the bits of lasercut prototypes Ponko have been cutting for me. It slotted straight in to the Darwin head exchange mechanism, but was a bit loose. I've got a better extruder base already being cut by Ponoko so I was expecting that and simply wrapped it with tape. The extruder motor is a little far away, so a temporary heave-to has been executed with a cable tie. Sorry, ugly. Is also fixed already.

I've loaded it with ABS and am now printing components with it, as you can see in the photo, as well as a classic Mighty RepRap Power Ring. I've fitted the ABS extruder to a Darwin to try my hand at testing out ABS, Imagin Plastics were kind enough to give me a 50m sample of 3mm ABS natural. Looks good, and I should be able to get it for under NZ$20 per 100 metre coil.

I've found ABS to be generally the hardest plastic to work with. It needs high temperatures, high pressures, and isn't that keen to laminate. You have to work in thin layers to keep lamination, which slows me down. It does score on accuracy and tidiness, however, as the paste-like exudate stops fairly rapidly even without a valved nozzle.

You need to have your nozzle mounted very rigidly, because ABS is not that easy for the hot nozzle to plough through if there are any rough bits sticking up from the surface. This is another reason I found to use thin layers and go slowly.

Getting ABS to stay down on the bed is hard too, but by accident I made one of those handy discoveries: With an eye-dropper, put a few drops of acetone (methyethylketone for the new-fangled) on a wooden extruder bed where the printing will take place. This hugely improves the adhesion to the bed, BUT IS VERY FLAMMABLE! Just bear it in mind, and keep the big can of acetone well away with the lid on just in case, eh? (PS What pen do you label little acetone bottles with? It all gets dissolved off when I spill it!)

Things bode well for an alpha release of the Ponoko lasercut components kit. I'm getting excited about that, and it should tie in nicely with the imminent arrival of Zach's new shipment of extruder motors on the RRRF site.

Oh, the curly-white wave flowing over the top of the big washer holding the extruder barrel is an ABS leak between the PTFE insulator rod and the top of the brass M6 extruder barrel. I hadn't anticipated the need to seal it, but the ABS starts pressurizing some way up the PTFE rod and squooshes out the gaps in an organic way. I'll seal the gap with PTFE tape when I install the latest extruder clamp assembly off the pending prototype lasercut run.

Vik :v)

Labels: ABS, lasercut, ponoko, reprap

It is surprising what can be built without support material. Kyle Corbitt has designed a RepRapable solar collector described here.


The structure is made up from a triangular lattice like this : -



The risers only overhang 30°C, so they are no problem but the horizontal beam looks like it should need support material. Kyle asked me to try building it without, so I gave it a go. Here is what it looked like after it was made: -



Very hairy but basically sound. This is it after being cleaned up with a scalpel: -



It took about 45 minutes to make and used only 7g of ABS, not including the raft. Head travel while not extruding was about 42% of the filament length but as I move twice as fast as I extrude that was only 21% of the time.

Despite the risers only being about 3.7mm thick it is very strong and rigid. I loaded the centre of the beam to 1.5Kg and it showed no sign of breaking. I also loaded one end to 6Kg with no sign of movement, so the beam could easily support 10Kg and possibly a lot more.

At the top of the base beams the triangular section goes down to zero width. The top four layers are only one filament wide so are very fragile. I don't think they add much to the strength so it would be better to truncate the top of the triangle. Interesting though because it is the first time I tried to make something this thin (0.6mm) in ABS.

Enrique added an option to make the infill go along the length of bridges but it is not actually needed for this shape. The top beam has an inverted triangular section so the first layer of it is just two parallel outlines which span the gap. The rest of the beam builds out from this at 30° so it does not matter which way the infill goes. The first few layers did sag a bit but the top of the beam is flat. An inter layer pause may have reduced the sagging.

So this looks like a good way to make large structures that are light and quick to build, but still strong.

Another example of getting away without support here.

Labels: ABS, support

I made Adrian's coat hook in ABS for an exhibit at Cheltenham. The only problem is that my machine broke and it took me a week to get it working again. See hydraraptor.blogspot.com/2008/06/catalogue-of-disasters



This was designed by Adrian, sliced by Enrique's software, extruded though a nozzle made by Adrian. It took about 40 minutes and used about 8g of ABS costing $0.16.

Labels: ABS

Adrian asked me to try his door handle design in ABS. Here is how it turned out: -





It took 2 hours to make (not including the raft) with a 25% fill. It seems like it would be plenty strong enough.

I added a 4.2mm hole for tapping for an M5 grub screw. I didn't teardrop it because below a certain size that is not necessary. It came out slightly under 4mm so I ran a 4.2mm drill through it and then tapped it M5.



Here it is with the screw fitted: -



ABS is a bit soft for tapping, so I think a captive nut would be a better design. We don't have any compatible doors so I did not try it out.

I think it came out very well, but being a perfectionist, here are a list of the defects: -

• The faceting on the cylinder is noticeable because it seems to be made of only 32 segments. I think this is just a setting in ArtOfIllusion rather than being due to simplifying the mesh to 0.1mm resolution. AOI is intended for rendering, where surface shading normally interpolates the normals to get a smooth effect. In real life you need a few more line segments.
• There is scarring where I removed the strings with a knife. The anti-ooze mod should solve that.
• There is some brown discoloration, which is also indirectly due to ooze. When the extruder ends a filament run it turns off, lifts slightly and moves quickly to the start of the next run. Sometimes that leaves a string, sometimes it snaps and leaves a peak of filament sticking up. That rubs against the nozzle and picks up burnt plastic from it. Hopefully the anti-ooze valve will fix that as well.
• The start of the first filament came unstuck. That is because I do the first layer at a low temperature to allow it to peel from the raft. I raise the temperature for subsequent layers but I don't wait for it to heat up before I start the second layer because of the ooze problem. I stuck it down with a bit of super glue.
• It is slightly warped along the length, but it does not matter in this design. I am hoping post heating in an oven before removing from the bed will reduce that significantly. Using PLA would also reduce it.

So I am pinning my hopes on anti ooze being the cure of all ills!

Labels: ABS

I have developed peelable rafts and a reusable bed for ABS: -



That has enabled me to make these Darwin parts before my extruder broke again: -



Details here: hydraraptor.blogspot.com/2008/05/stepping-up-production.

Labels: ABS

Acrylonitrile butadiene styrene (ABS) works really well in the RepRap extruder. Its melting point is 105°C which is less than HDPE so it does not stress the extruder as much thermally. It is harder than HDPE and PCL so it is quite tricky to get enough motor torque without the clutch slipping. Loosening the top springs on the pump and tightening only the bottom springs helps as well as lubricating the filament with oil.

Its warping is a lot less than HDPE and a bit more than PCL, but the main advantages are that the die swell is low and the filament is very compliant. It follows the head movement accurately even when extruding 0.5mm filament at 16mm/s. That gives objects good definition and sharp corners.



It is also much harder than the other two plastics and makes very rigid objects.

Read all the details here: hydraraptor.blogspot.com/2008/04/absolution and for comparison my evaluation of PCL is here: hydraraptor.blogspot.com/2008/03/chalk-and-cheese.

Labels: ABS