RepRap: Blog

With a lot of work going on on putting pen-plotters in RepRaps for PCBs (and other things), it seemed to me that we might re-visit an old idea.

That idea was using oil to assist separation of support material. Now that the Java host software does full overhang support calculations, it seemed that we might combine the two: a pen plotter with an oil-filled felt pen would run over the top layer of the support after it had been laid down to make it easier to break away when the part was finished.

Above is a brief experiment I did by hand. The L shape was built 'the wrong way up' forcing it to need support. Both the part and it's support were PLA. I paused the build at the last layer of the support deposition, and wiped corn oil over the support with a Q-tip. Then I resumed the build. The support material did indeed separate much more easily than it does without the oil.

If a support layer was simply plotted twice when it was the last support layer under the part, once with the polymer, and then once with an oil-filled felt tip, this would give the same ease of separation. The same pen plotter could be used with an etch-resist pen to make PCBs, such as these designed to make reprappable electronics simple. Two birds; one stone.

Labels: pcb, support

... 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

The latest Java host program in the repository now contains code to compute the support needed for overhangs automatically. Above is a screenshot of it working - the L block bottom left is being deliberately built the wrong way up so that it needs support. The layer currently being computed is shown in the diagnostic window. You can see the cross-section of the object itself (blue) and the support for the overhang (brown).




Here it is part-way through the build. You can see the support pattern at the front, and the pillar of the L-shaped object being built at the back.



Here is the build finished. The supported bit is at the front.



Here is the part after taking it off the machine viewed from underneath with the support still in place.


And here it is in its final form with the support separated.

The program allows you to specify a support material for each material in the RepRap machine by name. As the RepRap code allows you to have several logical extruders all talking to the same physical extruder you can use a material to support itself by copying its entries in the preferences file (sort the file first to bunch them together) then renaming them from Extruder_0 to Extruder_1 (or whatever). You then change the infill pattern of the support to whatever you want. Here I set it not to outline, only to infill, and not to change the direction of the ply between layers.

The support cleaved pretty easily from the part with a penknife blade, but I suspect that this would have been harder had the underside of the part been undulating rather than flat. Of course two extruders would allow - for example - a friable paste to be used as a support (my current favourite: cornflour mixed with a gel of PVA glue and methanol - to be blogged when I have some results...).

The supports are only computed by the host software when it is saving G-Codes to a file. The reason for this is that the software has to do the calculation in reverse - from the top down - so that it can know what's immediately above the layer it is currently creating. It can only do that by writing each layer as a temporary file, then concatenating them all in reverse order to actually build from the ground up when it has finished.

If you are interested in how the use of a CSG representation makes the support calculation easy to code, take a look at the

     private void supportCalculations()

function in the class LayerProducer.

As you can see, I have not exactly tested the code on the world's most complex shape, so all this should probably be regarded as experimental...

I'm off for a week to give RepRap talks in Wales and then Spain. When I get back I'll try it on something a bit more challenging, and when it's working properly we'll do a release.

Labels: host, java, overhang, support

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