Sunday, October 04, 2009


Hello World

Hi! My name is Rhys Jones, you may have seen my name mentioned on the blog before, as I previously worked on the first reprapped circuit as part of my undergraduate degree. After that, Adrian kindly offered me the opportunity to do a PhD on RepRap, specifically I'll be investigating the use of multiple materials, so you'll be seeing my face around here for a few years.
Anyway, I've had a couple of ideas of ways that we could improve the current process, which I'll be investigating over the next few weeks:
  • Circuitry - When we tried depositing solder the results were far from perfect, whilst I'm sure it could be improved, I'd like to give an alternative a try. Wire glue (A.K.A graphite mixed with adhesive) has been bounded around as a potential material for producing RepRapped resistors, but the resistivity is too high for producing circuit tracks. Instead, it may be possible to produce the entire circuit board out of wire glue, and then electroplate the resulting tracks with copper afterwards. Whilst this does require another process, if we are clever about designing the boards, we should be able to bury parts of the track under plastic. This should prevent these parts of the track from being plated with copper, and thus keep a high resistance i.e. we could make both track and resistors with the same extruder. Another nice benefit is that adhesives have a much lower surface tension when compared to molten metals, so we should be control the material much more easily and produce more detailed circuits.
  • Speed - The vast majority of the time taken to build a component is spent extruding the infill. Instead, I think it should be possible just to extrude the walls and only have infill surrounding the major features (holes etc.), leaving several large voids within the part. At appropriate layers during the build, we could then replicate a casting process in order to fill the voids. A potential material for this could be Sodium Acetate, commonly known as hot ice. It's really cool (though not literally), dead cheap, can be made (at least theoretically) using nothing more than vinegar, bicarbonate of soda and a few other items from your kitchen, plus it can "freeze" almost instantly when required.
  • One shot build - I really like the idea of a machine that can build all of its own parts in a single build. However, as it stands such a machine is going to be too big to be practical for a lot of people. A way around this is to make more use of the vertical space by building one component directly on top of another. Previously, Adrian blogged about the use of oil to separate support material from the build. However, the same process could be applied for building on previously built components. It would probably take a major release to make the most of this, but I spy six corner brackets and several other components on the current Mendel design that this technique should work well with.
Of course, all of this is conjecture and could be complete rubbish:D

Hello Rhys,
Some great ideas. I look forward to seeing your results.
Using sodium acetate may not be such a good idea, I tried using(homemade, so you might get different results) sodium acetate, but I was never able to super cool it enough before it started to precipitate in the syringe I was going to extrude it with. Though you could try extruding it from a heated barrel onto a cooled surface. Though why use sodium acetate? Sodium acetate is brittle and dissolves in water, these are not good properties of structural parts. Why not use polyurethane plastic casting compound?
I tried filling HDPE objects with PU manually about 18 months ago.

It makes strong objects and reduces warping but is a bit messy. I not sure how easy it would be to automate the PU mixing and keeping the nozzle from blocking.
>I was never able to super cool it enough before it started to precipitate in the syringe I was going to extrude it with.

I did try making some homemade sodium acetate last week. I did manage to get it to supercool and indeed freeze on demand. However, it seemed that I didn't reduce the mixture down sufficiently as it still remained relatively "slushy", and defiantly not suitable for structural parts. I'm going to give it another go shortly.

>Though why use sodium acetate? Sodium acetate is brittle and dissolves in water

Once the casting process was complete, I was planning on then covering the cast material with plastic using Mendels head exchanger, so the solubility in water shouldn't be an issue. Also, I thought with it being water soluble, if it ever were to freeze within the extruder, this would be easily fixable.
Point taken about the brittle nature of the material, but if its completely encased in plastic should have at least some protection but to be entirely truthful I'm unsure as well. Of course, there is only one way to find out which is actually do it.

The main reason I've suggested the material is I liked how its possible to control when the material starts to precipitate. Although if you've had issues with it freezing prematurely maybe its not ideal/ the procedure of making it needs to be refined.

>Why not use polyurethane plastic casting compound?
I'll look into this too :D but I'm a little concerned that if we are to speed up the process we need a casting compound that solidifies very quickly, and in doing so I think its possible that we block the nozzle.
Sodium acetate may not be useful for structural components, but if you can extrude onto it, it might make a good support material. After all it is water soluble.
>After all it is water soluble.
And if you reduce this mix after, it's completely reusable. It's probably a little too fluid to control in standard form though, and may need to be incorporated into a gel.
i have always wondered about using a polyurethane foam has a filler, it is solid, and light, i would think there has to be a way to make something like it that could be poured in during the build that will take up space inside and add strength i know they make a soy based foam now that is of the open cell variety.

i like the sodium acetate idea has a reusable support material i would like to see if any one could make progress on that idea.

though in my opinion i do not think we are along far enough for printed circuits to be done redly its a great idea and i want to see work done on it, but i just dont see how it can be done with out allot of trade offs just yet.
I'm hoping too that this may be an alternate support material option, somehow. We may have to print a "containment box" for some support. Somewhat annoyed at Stratasys having a patent on Aquazol as a support material.
Its one thing to print out structurally strong parts out of metal, its quite another to have it easy to solder with with typical 60/40 or Sn/Ag solder.
I've looked at a number of conductive adhesives at work and none of them can be soldered to.
I still believe that the best option is to have a ink print head or a permanent pen directly onto copper clad board and etched with ferric chloride which is fairly easy to get a hold of everywhere and can last forever (through electrolysis), the only downside is that they need to be drilled afterwards.

So there you are the best solution,
Print directly onto copper bard with an ink head or permanent marker (ink head would be nice)
Etch normally with available etchant.
Let the RepRap drill the holes out.

Because in all honesty I don't believe you'll be able to get better money to performance to use a metal with low enough melt or as a slush to be able to be economically viable to the current method.
I have doubts also of how fine of control you'll get for super fine parts, cause you'd need to cater to SMT, for things like DQFN, TSSOP and BGA packages that would need to be heated underneath for good solder flow.

My apologies for the long post
> Its one thing to print out structurally strong parts out of metal, its quite another to have it easy to solder
> I have doubts also of how fine of control you'll get for super fine parts,

Thats precisely why I am going give the metal deposition route a break for a while. Instead I am going to try electroplating wire glue/conductive plastic with copper in a separate process afterwards. Once clad in copper, the solder should adhere to it nicely.

>Because in all honesty I don't believe you'll be able to get better money to performance to use a metal with low enough melt or as a slush to be able to be economically viable to the current method.

I agree, but there are some *potentially* very nice benefits of metal deposition.
>I have doubts also of how fine of control you'll get for super fine parts

Me too, but who knows until you actually try it.
Silver paste may give you better conductivity although costly.
I havent yet tried it out, but one idea I had on the printed circuits thing was to use carbon nanotubes mixed with something. I bought a little tester pot from MUTR to try out in my copious spare time. I was going to mix some up with capa and see how I got on. Obviously wouldnt be able to solder to it, but maybe a nanotube infused capa would make for a conductive hot glue?
Two problems with using nano tubes.
The first is that they are difficult to make in large quantities, and thus even a small amount is quite expensive.
The second relies on the first, you just can't get the stuff easily, which fails on the whole concept of everyone, everywhere can make it.

Sometimes current tech is actually the most abundant and easy to get a hold of, such as my suggestion of just using the RepRap as a plotter to draw a circuit onto copper cladded board, then etch and drill.

Good thinking though, nano tubes are naturally more conductive than silver, where silver is the most conductive natural metal at room temperature.

Quickie question Rhys, whats your PhD going to be in?
The pot of nanotubes that I bought cost me less that £5, and I reckon it would go a long way. Presupposing it worked, it is certainly a lot cheaper than buying copper clad board for etching.

I admit that the I hadn't considered the ubiquity of nanotubes in the third world, as this was just a theory I had only planned to test for myself, but I went back to MUTR to check the price and size of the pot I bought and, typically, I can't find it listed. So I guess your point about them being difficult to get stands.

Still, I feel that as the technology advances, and the use of carbon nanotubes becomes more and more widespread, the price will drop and the availability will rise.

I would have thought that if one can source the sorts of electronic components for a reprap, then it wont be long before nanotubes will be readily available too. In my case, I had planned to get them at the same time, from the same place as my CAPA.

I understand that the ultimate goal is for a more ghetto approach. Scavanged parts, grow yer own PLA, print everything you need, and pass on to your neighbour, etc. But at some point, -somebody- is going to have to buy a new microcontroller or voltage regulator or something and that is going to have to be an order from the sort of place that holds, copper boards, ferric chloride, solderpaste and, possibly, nanotubes.
Be careful with nanotubes. I read they are as dangerous as Asbestos fibres:
Out of curiosity, how does ferric chloride (or any of the other pcb etchants) react with the plastics we extrude?

The toner transfer method for etching relys on melting the plastic in the toner onto the copper board, so would it be possible to print our circuit in CAPA, say, onto a copper clad board and then etch it in the normal way?
nophead: Yes, the safety datasheet that came with mine warned the breathing and handling precautions should be observed. Thats one of the reasons I havent started idly experimenting with them yet. Time, of course, is the main one, tho :)
Certainly ferric chloride doesn't react with PET as I have stored some for 15 years in a water bottle and it hasn't leaked out yet. It doubt it would react with any of then plastics we use.

To get plastic to stick to copper I think you would need to heat the copper to something approaching the plastic's melting point.

But why not just use the toner transfer method? It would seem easier and much higher resolution.
nophead: I have never etched a pcb, so I am not 100% familiar with the ins and outs, and the problems involved. I merely asked because I only just thought of it and Grogyan was talking about printing to a copper board (presumably form a Reprap).
Maybe I've completely missed the point, but why do we need a material with a greater conductivity than copper, pretty much every pcb has copper track?

I understand that it would be nice to have a very high conductivity, and I'm sure there would be some very novel applications for it. But it seems a case of running before we can walk. Also, isn't it more about resistivity than resistance which is an entirely different matter. We are in the very nice situation where we can control the thickness of whichever material we wish to use (within reason), increasing the thickness will the reduce the resistance to whatever we feel necessary.

>whats your PhD going to be in?

I'm going to be investigating the use of multiple materials to attempt to make more functional parts and reduce the part count of the machine. The official blurb we used when applying for funding for those interested is below, though its purposely nonspecific.

The next version of the RepRap RP machine will be released around May 2009.(errr maybe not :D)
This will considerably increase the range of materials with which RepRap can
work. This means that it should shortly be possible to use it to manufacture
components with graded, or anisotropic, or functional properties (or all three)
simply by depositing different materials at different locations and in varying
patterns to build single or multiple solids. This PhD project will research the
exploitation of such properties in novel applications, with particular emphasis
on reducing component-count in engineering assemblies currently requiring
several components made from different materials. This will, of course, include
reducing the component count of the RepRap machine itself using the same
methods. The project will also look at placing such exploitation in both an
industrial production environment as well as its primary use in the home. This
will be facilitated by the extremely low price of the RepRap machine, the whole
of which can be acquired for less cost than a single cartridge of build material
for a well-known commercial RP system.
I like your creativity! I look forward to seeing more of this stuff. I'm particularly interested in the electroplating of conductive glue, that's a fantastic idea if it works as intended.

Just a notion I've been throwing around in my head you might like to consider, too; It might be possible to use the Reprap to produce moulds or castable shapes for moulding. This could lead onto something like a cast-able Plastruder, so the whole assembly could be "printed", moulded and cast out of some heat-resistant material like ceramic. A single-piece, printable, solid plastruder would be nice, I think!
I tried dissolving PLA, which works in lye, which Stratasys' Waterworks seems to contain. I dissolved some Stratasys support material as well, which took about equally long.

You can buy lye in normal stores. It is used to remove a congestion in your sink... or to dissolve PLA more quickly.

Be very careful with lye, it can cause permanent blindness when you get it in your eyes! Seek advice from experts when unsure how to use it!
Very interesting Erik. Does that mean we can use PLA to support ABS and then dissolve it away with caustic soda (I had to look up lye as I never heard of it).
Or potentially vice versa with acetone to remove the ABS; assuming it doesn't dissolve PLA as readily.
With regards to electroplating, I have done some research because I'm interested in dynamically procedurally generated electrical connections.

You might consider copper suspended in a gel paste that can be extruded onto the resistive wires. Ideally the electroplating will pull the copper out of the gel and the water will evaporate leaving a minimum of fuss.

Also look into how electrolytic capacitors are made. It involves creating a suspended aluminum oxide resistive barrier between plates in an electrolyte.

For all of those who are interested in third world reproducibility, lye and similar electrolytes can be made from wood fire ash which has calcium carbonate, and other useful water soluble goodies.
Why not use Chrome or Silver acrelic conductive ink for making circuits? Or maybe a conductive paint like:
Or possibly using lengths of conductive thread or just use copper wire, automatically cut to length and placed at the appropriate locations?

I guess it depends on the conductivity required and the current expected to be run through the component. However, building circuits by layering plastic, conductive trace, plastic with holes at appropriate connection points and then more conductive trace could work. Build it up in 3d with resistors and capacitors build vertically into "holes" between layers and filled with an appropriate material. Seems like a spool of conductive thread or appropriately sized copper wire could be economical as well as easy to obtain.

Rather than an extruder the part would pull and cut a length, either vertical or horizontal and place it on the previously extruded plastic layer. Then cover it with an appropriately designed plastic layer once all traces have been placed.

Does that sound too complicated?
Also, electronically conductive HDPE is available:
I was wondering if you hadn't already come across the research done at Brunel University regarding printing circuit boards on paper

"Circuits are, literally, printed onto paper using ordinary printing presses. The key to the process lies in the ink, a special patented formulation, which conducts electricity."
As far as I'm aware (I could be wrong) the problem with the conductive ink approach is that solder does not adhere particularly well with the ink. Whilst it's possible to create the pcb, securing chips and other components becomes tricky....
A solution to that problem is actually to use an adhesive like super glue to glue all the parts in place. Then use a conductive ink to bridge the connections. The only problem with this is that with the circuits I made, the conductive ink had shrinkage issues and so once it dried, would crack and create bad traces.

What I tried was to take a sheet of acrylic and use super glue to paste down surface mount components, then use an epoxy based silver conductive ink pen to draw the traces. It worked, although to interface motors and wires was a hassle and the real deal breaker was that I would have to go over traces several times to fix voids.

In theory you can cure most conductive inks by cooking them at a specific temperature for a short time. I tried this and it worked but was still prone to having the traces lift off the board I was using.
This site: has some lower melting point but conductive metals that seem to be within the range of the current extruder temperature. These are for use in BGA and other ROHS compliant soldering, according to the website. Maybe they hold some promise as a conductive deposition metal.
"Solder does not adhere particularly well with the ink."

I used to study at Brunel University which is why I had heard about this approach, I was fairly sure that they had been able to create fully working circuits with components attached to the paper. You would have to follow up with David Harrison, or Blue Ramsey. (Both really friendly and helpful people BTW) as to how the components were attached, as I cannot remember the details.
I'd sort of like to see one particular subtractive method: Hot-wire polystyrene foam sculpting.

It is particularly suited to a casting method related to lost wax, because the mass of the positive form is so low. A link to a simple procedure can be clicked through, above.
The latest installment of Cory Doctorow's 3D-printer novel, Makers, talks about printed omelettes.

It would be possible to have a peristaltic pump with a tube for egg mix, and another tube for air, and set the heater barrel to a temperature that cooks eggs slowly enough that they're semi-firm as they leave the print head. Not that I think this necessarily should be done, it's just fun to see science fiction talk about things that are already possible, but haven't been tried.
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