RepRap: Blog

Mac Goes RepRap (one day...)

2009-11-21T14:37:00.005Z

Mac|Life magazine recently approached Mark Frauenfelder and others to envision a future product from Apple. Mark's entry was based on RepRap (left). More details here.

Of course, if Apple do that, they'll have to GPL all its designs.

And I'm guessing it'll be a RepStrap, not a RepRap...

Pathetic Fallacy

2009-11-16T22:42:00.004Z

My old Darwin in my home workshop has just finished printing me my personal set of Mendel parts:

Like any proud parent, it was uncomplaining about the chore, even though - for all it knows - it is printing its own replacement.

(I fact I shall keep the old machine so I can double my production rate; and besides it has tremendous sentimental value.)

It's taken me a relaxed couple of weeks, just queuing up prints between experiments, and not leaving the machine running while I was at work. I'm sure it would be OK, but I'm not 100% certain what the insurance company would say in the unlikely event of being confronted by a smoking ruin:

IC: What are all those chemicals in that charred cupboard?

AB: Oh, fertilizer, weedkiller - I do a lot of experiments on plants; various volatile organic solvents. But they weren't the cause.

IC: Uh huh?

AB: No - I have a self-reproducing machine, and I left it running while...

IC: You left a self-reproducing machine running?

AB: Yes, but it's quite safe. It can't reproduce without human assistance, and...

IC: But you left a self-reproducing machine running on its own?

etc. etc.

Anyway, now off to hack the documentation as I build...

Printing the Rapman

2009-11-16T21:07:00.002Z

Yesterday, klaszlo, a member of the Rapman users' group wondered how he could get spares for the gear pair on the Rapman 3.0. For many of us, the whole point of Reprap machines is to print our own spares rather than tormenting Ian at BitsFromBytes every time we break something.

Do you want to read more?

Bogdan's acid test

2009-11-16T03:20:00.003Z

After having proved that we could print long beams in both HDPE and polypropylene, Bogdan suggested that we give the method an acid test.

Do you want to read more?

More printing large objects with HDPE

2009-11-15T16:11:00.004Z

I pushed the length of the 5x20 mm beam out to ~180 mm this time. I got a little bowing because the tension plates began to uproot the raft during the last few layers of the print. For more...

Revisiting HDPE

2009-11-14T14:05:00.007Z

Once I established that using pads and guy flanges suppressed warping in large dimension objects printed in ABS I decided to see if the same method with HDPE. Basically, I printed a 5x20x145 mm bar guyed to pads on the raft.

Some years ago, when I was working with HDPE on my Tommelise 1.0 Repstrap printer the big problem with HDPE, aside from a tendency to warp profoundly, was finding a surface that it could be printed on. I found that I could print on art store foamboard. This material is about a quarter of an inch thick, typically and consists of plastic foam sandwiched between two sheets of plastic coated paper. HDPE would stick to that quite nicely. Unfortunately, however, this material tended to perish when exposed to the hot extruder head of Tommelise 1.0. It also lacked the structural strength to resist the tendency of HDPE prints to curl at the corners.

Recently, Bogdan Kecman, a Rapman user in Belgrade, has been making a serious effort at working through the problems presented by HDPE and polypropylene as printing materials. Yesterday, he was kind enough to offer me advice about what sorts of materials that he found HDPE would stick to. In the list he gave me it appeared that polypropylene sheet offered the best option for printing HDPE. I happened to have a few sheets of 9.5 mm polypropylene left over from my milling work with Tommelise 2.0 earlier this year, so I quickly converted one of these into a print surface for my Rapman 2.0 printer and got to work.

Guying HDPE prints from Forrest Higgs on Vimeo.

After a few false starts and a careful go at leveling my print surface, I managed to print my guyed beam successfully with no peeling of the raft and NO subsequent curling or warping of the beam.

The beam was printed using Skeinforge with a 40% hexagonal fill. the raft was printed at 220 C and the beam at 225 C. The extruder head speed was set at 16.8 mm/sec and the feed rate at 46 rpm. I am not completely satisfied with the surface quality of the beam. I suspect that I am extruding a bit too cool. I will be exploring these kinds of settings in coming days.

One of the most important discoveries of this exercise is Bogdan's discovery of polypropylene as a printing surface for HDPE. It is sticky enough to keep HDPE rafts solidly on its surface and strong enough, in thick pieces to successfully resist HDPE's tendency to curl and warp during the printing process. Without Bogdan's discovery, guying would have been impossible with HDPE. Polypropylene sheet is also readily available and cheap as well. I shaped it into a print surface for Rapman with ordinary hand tools. It behaves a lot like acrylic plastic except that it isn't brittle at all, a characteristic which makes it much less risky to work with.

HDPE has several advantages over more conventional plastics like ABS and PLA. It is a single polymer and not a witches brew like ABS. When you print with it you can, if you get close to the print head, detect a mild, pleasant odor from the hot HDPE. Try the same thing with ABS and you get a very different experience. HDPE also can be had for about $5.50/lb {~$12/kg) compared to $9.75/lb for ABS {$21.50/kg} and $10/lb for PLA {~$22/kg}.

HDPE also constitutes a very large fraction of plastic waste worldwide if we ever get around to developing small scale plastics grinding and filament extruding equipment that will get us into recycling.

Please understand that I am not suggesting that everyone run out and buy lots of HDPE right now. We have a lot of practical experience using PLA and ABS and we shouldn't dump that. Different plastics have different uses. What is nice, however, is that it looks like we have another one to add to our list, which, like PLA, has not heretofore been used in commercial equipment.

I am very excited because Bogdan Kecman is going to be testing the pads and guying technique with polypropylene in the next few weeks. If he succeeds, we will have a printable plastic that costs about $4/lb {$8.80/kg}. THAT will be a brilliant development for the Reprap endeavour.

Continued guying

2009-11-12T13:20:00.007Z

I went down to my hardware stockists and acquired a piece of 5.56 mm acrylic sheet to replace the 3 mm sheet that came with my Rapman. That done, I printed my guyed, 5x20x150 beam again using ABS and printing at 16.8 mm/sec. I processed the STL using Skeinforge and used a 40% hexagonal fill.

I removed the beam immediately after printing it...

... and stripped off the raft.

I am not able to detect any bowing in the resulting beam. The raft on which the beam was printed was rather coarse as you can see in the pictures in the previous guying blog item. It may be that there is some very small amount of bowing that is lost in the roughness of the bottom of the print caused by the raft. If there is, I suspect that it is much less than 1 mm over the 150 mm length of the beam.

The STL for the beam with the guyed flanges looks like this...

I would appreciate it greatly if others would try to print this beam in ABS on other Reprap printers so that I can confirm my results. If you are interested in trying this you can get the STL from here.

Thanks.

One thing in passing. If you are going to print ABS onto an acrylic print base, something I can recommend highly, I'd strongly suggest you get one of these.

It is a scraper used by professional house painters to clean enamel off of windows. It separates ABS rafts from your print base very quickly and cleanly with a minimum of drama.

Guying long prints

2009-11-11T08:18:00.009Z

I'm an architect by training with a keen interest in the history of building technology. In the Middle Ages, architects compensated for the lateral thrust generated by domes and vaults with butresses. In the 20th century architects dealt with inflatable buildings by using guy wires to anchor them to the ground.

When you print long, tall objects in most polymers the ends of the object tend to try to lift off of the print surface. Ordinarily, one uses a raft to more tightly secure a printed object to the print surface. For objects up to about 40 mm that method works nicely. When one goes beyond that, however, the printed object tends to peel the raft off of the print surface.

I spent a lot of time working with HDPE several years ago. HDPE has terrible tendency to curl at the edges. At that time, I thought it would be a good idea to print pads next to the ends of a long printed object and guy the ends down. This spreads the force generated by the upwardly curling printed object. You can see a first effort at this here.

I was trying to print a beam 150 mm long by 5 mm wide by 10 mm high. You can see the details of the pads that spread the tension force and the plates that carry that force down and spread it onto the raft in this closeup.

The idea worked, so I increased the height of the beam to 20 mm and tried it again.

That appeared to have worked, too. What was interesting was that I could easily peel the raft off of the acrylic printing plate and was able to easily peel the raft off of the printed part. The guy flanges and pads can easily be removed with a mat knife.

After I removed the beam I noticed that the curling force during printing had actually bent the rather flimsy 3 mm acrylic printing plate provided with the Rapman printer. The downward bowing amounted to 2 mm over the 150 mm length of the beam.

It seems likely that if I use a thicker acrylic printing plate that I can reduce the 2 mm bowing on the bottom surface of the beam. I will see if I can purchase a heavier print plate tomorrow at the hardware stockist's.

I will also measure the bowing of the beam over the next several days to see how much it ultimately distorts.

Wednesday morning: I measured the bowing again a few minutes ago. It is still 2 mm.

I found a bug!

2009-11-11T05:03:00.004Z

A New Zealand cicada by Rhys, Bronwyn and myself. CC-BY-SA licence. Hope to put the files up soon.

No, it didn't print in one piece. It's kinda like an Airfix kit, requiring some superglue and a blowtorch. But it comes out pretty darned well.

Vik :v)

Reprapable Solar Power

2009-11-10T12:50:00.006Z

We've discussed reprapping solar panels for a long time, and - of course - our semi-conductor printing capability isn't quite up to that yet.

But it should be possible to reprap a small-scale solar array like a miniature version of the industrial one at Daggett above.

It would use reprapable solar-powered steerable mirrors. Those would be an autonomous motorized gimbal mirror support with a tracker that keeps the sun's reflection pointing the same way at all times (onto a solar boiler, say). The idea is you'd reprap out a load of these, then walk round a field putting them down. They'd all align themselves and start delivering solar power...

I think the trick is to black out a corner of the mirror except for a small circular spot in the middle of the black. Each steerable mirror has a detector on a flexible arm that you place where you want the reflection of that spot to be. Feedback keeps the spot-reflection on station, and hence the main mirror also on station. A really clever design would combine the spot detector with the local solar cell that provides the motor and controller power.

I look forward to the first version on Thingiverse...

Rack and pinion

2009-11-09T22:06:00.005Z

I've wanted to build a Reprap machine that didn't include a lot of ironmongery for a long, long time. Indeed, I developed a tool script for designing involute profile gears way back in 2006. Last year I milled gears and racks. This year I'm printing them.

You can see the completed rack with the pinion here.

Oddly, though the rack was 190 mm long, it didn't warp significantly.

An end to ooze II

2009-11-05T14:36:00.002Z

Ages ago, I put code to reverse the extruder at the end of plotting a sequence of line segments into the Java host software, thinking, "That might be useful someday." I set the default so that it reversed the motor for 0ms to turn the feature off, and forgot about it. Seeing Erik and Nop's post below, I thought I'd better finally try it out...

Above is the result - perfect! (Ignore the dark splodge in the middle of the square; that was crud on the extruder falling into the build; I should have cleaned it first.) Normally there'd be loads of string between the L-shaped nozzle-wipe bit and the block being made. Now there's none.

I'm running at an XY feedrate of 3000 mm/minute. At that rate setting ExtruderN_Reverse(ms) to 200 and ExtruderN_ExtrusionDelayForPolygon(ms) to 400 seems to work nicely.

The delay figure is how long the extruder runs before starting an XY move; this allows the polymer to move back down the barrel to take up the slack.

An end to ooze and support material found ...

2009-11-03T22:30:00.004Z

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

Before:

After:

PLA on ABS on PLA:

RepRap Extruder Design with OpenSCAD

2009-10-27T15:19:00.010Z

→ www.flickr.com

RepRap Extruder Design with OpenSCAD
After falling in love with the new Mendel design I want to try out the PLA Adrian sent us (thanks!) so we need a new extruder which I want to build with parts available here at Metalab. We use different DC Motors for the extruder with a different mount than the steppers in the ingenious Mendel extruder design which I used as an inspiration. I only changed the way the insulator part is mounted since I like our T-slot mount very much. It is very stable and I don't want to glue the insulator like in the Mendel design since I'd like to be able to take it apart. The motor mount will be parametrized so that you can adapt it to different motors by just changing one value.

As you can see in the screenshot I model the extruder in OpenSCAD openscad.org. OpenSCAD is a very cool open source parametric solid 3D CAD modeller available under linux, mac and windows. If you like programming and 3D printing you should have a look at OpenSCAD since it is more like writing code than juggling triangles and vertices like in Blender or AoI. It's Solidworks for programmers :)

the designs of the extruder so far can be found here: http://reprap.svn.sourceforge.net/viewvc/reprap/trunk/users/metalab/models/scad/printed_lasercut_extruder/

wizard23
http://reprap.soup.io

The RepRap Factory

2009-10-25T16:53:00.002Z

For some time we have intended to set up a RepRap Factory at Bath consisting of four machines that will be dedicated to printing RepRap parts for others. We shall then sell these on at cost.

This video shows this beginning to come together. We could drive the factory machines off their SD cards, but it is more versatile to drive them off host computers. But we don't want to dedicate one computer per machine.

It turns out to be pretty simple to drive multiple machines off one host computer, especially under Linux. I just set up one account per machine. All the accounts had their own copy of the reprap.properties file. These were identical except for the communications ports, which were set to /dev/ttyUSB0, /dev/ttyUSB1 and so on.

I then just opened a terminal window for each machine in a separate desktop, executed xhost +, did an su to the appropriate users in each window, and ran the RepRap host software. I ended up with one desktop per machine (hint: put the desktops in the same relative places on the screen as the RepRap machines are around the computer to avoid confusion). I could easily control them all.

The bandwidth needed to send the G-Codes to the machines is nothing special, so even my weedy old laptop could keep up.

I'm pretty sure one could do the same trick under Windows using the Run As... utility.

Faster production means more RepRaps...

Printing in space?

2009-10-19T12:45:00.008+01:00

Will RepRap work in space? We did an airmile whipround but didn't have quite enough for one of those fancy parabolic flights. So we took the Russian approach and just flipped Mendel instead...

Here's a photo of prints of the same object file in positive and negative g. I would say which one is which but we muddled the order and honestly can't tell the difference.

So it can print in positive and negative g, I guess zero will just be middle ground?

MakerBot Love

2009-10-14T20:23:00.004+01:00

Just in case you missed it over on the MakerBot Blog, Fynflood proposed with a MakerBot-made engagement ring. His girlfriend said yes :-) I shall presume to speak for the entire community and say we all wish the happy couple a long and prosperous life together.

Copper Plating Wire Glue

2009-10-14T19:22:00.009+01:00

I suggested previously that it might be possible to create PCB's by copper plating wire glue to create a low resistance section of track. Also, parts of the glue may be buried beneath plastic to maintain a high resistance, by preventing the plating process in order to make resistors. Anyway, I made a small PCB on our commercial machine, which consisted of a 3mm diameter channel that was later filled manually with the glue. Anyhow, after connecting the PCB to the positive terminal of a power supply and a small copper pipe to the negative, I left it overnight in some copper sulphate solution, with the power supply left at 0.1A (higher currents do speed things up, but the results aren't as tidy):

Anyway, it seemed to work, and after a few attempts there were some important findings:

The resistor shown was roughly 10mm long and its resistance came to 2kΩ, so it looks like wire glue has a sufficiently high resistance to make useful resistors. Unsurprisingly the copper plated sections had a resistance of 0Ω, and could be soldered to very easily (unlike the circuit produced using the solder extruder).
The track needs to be connected to the power supply both before and after each "resistor". Otherwise, the track is only plated up to the buried section of wire glue.
The entire copper plating process is much more even if a small amount of sulphuric acid (car battery acid) is added to the copper plating solution.
We need to be able to make several sections of track per PCB, and it is going to be a bit of pain to connect each section to the power supply. As an alternative, I included a small "bridge" whereby the track is only supported by a small section of ABS, such that it is easy to snap out afterwards to create two independent tracks. It seemed to work (see pic below), although its not as clean as I would like, but a support material extruder would help with this enormously.
It is very important to leave the wire glue to dry sufficiently (at least a few hours). I did make a few attempts where the glue was not completely cured, and virtually no plating was achieved, even when left overnight.
I did try producing the PCB using PLA on Darwin - it seems our infill settings result in the structure being porous. Of course, this could be easily remedied by altering the settings. However, if we change the infill such that some parts of the structure are porous and some aren't, we can allow the copper sulphate solution to seep into the structure; allowing track to be plated that is contained within plastic. This may prove very useful later on if we ever get around to doing things in 3D.

Now where is that paste extruder.....

Costing Mendel

2009-10-14T16:07:00.004+01:00

Mendel comes in at £395 for the lot (in the UK).

Assumptions are:

- Using RS (UK) for bought in standard stock (fasteners, bearings, bars, studding and belts)
- 4 off NEMA 17s, @ £20 each
- RP parts @ material cost of £20 (assumes no commission)
- Thick sheet cost (inc cutting cost) @ £20
- Electronics are Zach’s Gen3 @ £110

Raw data can be found in the Mendel assembly data sheet on the wiki. A tabular summary is also available on the wiki.

Here’s a graphical breakdown:

Mendel Uploaded!

2009-10-13T15:21:00.003+01:00

Done. Woohoo! The mechanical solid-model files are now complete which means all Mendel designs (mechanics, electronics, firmware and software) are now totally available on SVN:

https://reprap.svn.sourceforge.net/svnroot/reprap/trunk/mendel

For mechanical aspects:

Mendel cartesian bot files (STLs, and even AOIs*) for printing are in /mechanics/solid-models/cartesian-robot-m4/printed-parts

Mendel extruder file for printing is in /mechanics/solid-models/extruders/pinch-wheel/wedge-604

SolidEdge users check the readme in /mechanics/solid-models/cartesian-robot-m4/

Documentation for the mechanical construction to build your own Mendel (!) is now on the wiki. Documentation for electronics, firmware and commissioning is being written now. It’s all editable by anyone registered. If you’re building any aspects of Mendel please feel free to improve the documentation in true open-source fashion.

Here’s another short video ;-) of some of Mendel's mechanical improvements.

Mendel's improvements over Darwin from Rep Rap on Vimeo.

* massive thanks to Paddy and Adrian for their hard work on tying this up. (And also especially to Ed – AB.)

Getting ready for Mendel

2009-10-07T15:59:00.004+01:00

I have done some file reorganizations in the RepRap subversion repository to tidy things for the Mendel release.

Under the location https://reprap.svn.sourceforge.net/svnroot/reprap the (partial) directory structure of the trunk is now (the links are for browsing):

trunk/mendel/electronics - the designs for Mendel
trunk/mendel/firmware
trunk/mendel/mechanics

trunk/darwin/electronics - the designs for Darwin
trunk/darwin/firmware
trunk/darwin/mechanics

trunk/reprap/host - the Java host software (common to both)

The Darwin designs used to be under trunk/reprap, and they still are for the time being to avoid breaking links. But eventually I will remove those.

Some of the Mendel data is already there, and we'll be adding the rest shortly.

Hello World

2009-10-04T15:57:00.013+01:00

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

Rhys

Mendel's first print!

2009-10-02T16:50:00.005+01:00

Thanks to hard work from Patrick on assembly, and Adrian on getting the new extruder board working, the mechanics of the Mendel printer have just been brought to life:

Sweet.

Oh, and I've just finished re-working the design to make the whole kaboodle printable on a 10 cm x 10 cm bed. Good news for MakerBotters ;-)

My Extruder Doesn't Work. What Can I Do?

2009-09-25T01:35:00.004+01:00

this is probably one of the most common cries of anguish heard from new RepRap owners. The picture on the right shows two common modes of extruder failure. In each case, the symptom is that the filament cannot be pushed through the extruder, or requires enough force to damage the filament even when the nozzle has been removed and the barrel is hot enough for molten plastic to dribble out of it.

To find out what is going on, take the cooled extruder apart and look at the filament inside. If you can't get the filament out of the PTFE or PEEK spacer, the chances are that your spacer has got hot and the filament has bulged inside it. Use hose clamps or a metal sheath to stop the spacer from deforming. You will probably need a new one.

If you see a blob of plastic sitting directly on top of the heater barrel, you have a gap. Any space between the top of the barrel and the end of the hole that it fits into will accumulate plastic. This plastic will not all be molten, and will cause a lot of friction on the filament as it enters the barrel. Typically the extruder will run for a while, but mysteriously clog up if you let it cool and restart it. Or it may just jam solid.

The cure is to taper the top of the barrel to ensure it is driven into the PTFE or PEEK spacer, and to remove the thread from the top 1mm or so of the heater barrel. If the hole has not been tapped all the way to the end, this will let the heater barrel reach the bottom of it. It is important to clear any remaining melted filament before fitting the barrel back!

Vik :v)

Mendel Apollo

2009-09-17T21:35:00.009+01:00

While preparing the Mendel files, we’re all building prototype machines in the Bath Uni RepRap lab to get a mini factory up and running. Whilst the other guys are building three standard issue Mendels, I’m going to scratch an itch I’ve had for a long time: it’s that "how big can this thing go", itch ;-) My single motivation is to have a large enough build volume to manufacture all of the printed parts in one single shot. This, in my mind, makes for a much more independent self-manufacturing machine.

I laid up what a single shot build might look like and found the area for printing all the parts, with enough spare room for evolutions, to be 440mm square (marked with a blue line in pic below). That’s 5 times bigger than the standard Mendel build area.

I’m going for a build area of 350 mm x 550 mm. Whilst this achieves the same area as 440mm square, it yields a more manageable footprint out of the Mendel architecture and caters for the fact that most print jobs are rectangular, not square. I modelled the variant design (I’ve dubbed it Mendel Apollo after the 440 coincidence) and here’s a pic comparing the two volumes. Note: the Apollo model is fairly naked: electronics/brace plates need to be added.

So the Apollo’s a big machine, and with its size will come all sorts of wonderful problems. Structural for sure… how will the M8 components fair? No doubt reinforcements will ensue. Will NEMA 17’s pull the bed around OK? There will also be a huge test of reliability for the one-shot build, specifically for the software and extruder mechanics.

I think this will be interesting. I believe it will be a bit of a milestone if we ever get that single shot replication and in doing so it may establish some mechanical limits. But before I can scratch the itch, I need to keep going on getting the standard Mendel files finished… grrr