RepRap: Blog

Labels: darwin, NextGen Science Fair, Průša Mendel, RapMan, reprap, Sampo

This is a Double Wade extruder http://www.thingiverse.com/thing:6989 being wired up for testing. This assembly saddles across the X axis with one extruder overhanging. With the use of the Prusa-style X carriage http://www.thingiverse.com/thing:6805 with PLA bushings running at 6000mm/min I can now span more of the X axis than I could with the standard Sells-style carriage, and Mendels tend to have more room on the Y axis for me to take up with extra extruder.

Note the twin terminal strip blocks for a head disconnect mechanism. They're clamped around some small nails, and loosening the screws on one side will allow you to remove the whole row of spikes at once like a plug. But this one won't shake loose :)

This is using FiveD/Teacup firmware on a single Arduino Diecemila to control "Custard Slice" (yes I name my RepRaps too).

Vik :v)

Labels: reprap

Lifted from a Eureka Magazine Article. "The 'Airbike' is made of nylon but, according to EADS, is strong enough to replace steel or aluminium and requires no conventional maintenance or assembly. It is 'grown' from powder, allowing complete sections to be built as one piece; the wheels, bearings and axle being incorporated within the 'growing' process and built at the same time. Because it can be built to rider specification, it requires no adjustment."

Vik :v)

Labels: 3d, airbike, bicycle, printed, reprap

I've been printing little green targets from PLA and white(ish) ones from IMPLA. The IMPLA needs an extra 10C heating, layers thinner than 0.4 and inter-layer cooling. In other words it is no fun to print with.

So, frustrated I took the whole lot outside, lined them up against the wall:




and shot them:



You can see in the aftermath, both green PLA targets have chunks missing from them. One white IMPLA target is split but holding together. The 3 BBs embedded in the wood on the left show the level of impact.




Useful stuff, but I'm not sure if it's worth offering for sale as it is so tricky to print with.

Vik :v)

Labels: filament, impact, modified, pla, plastic, reprap

I've recently been experimenting with the loading of various fibres into CAPA and PLA. This started out as simple strengthening for the 3mm PLA that I sell, but the addition of 20 micron x 1mm nickel fibres makes it conductive. Dunno how useful this will be yet but it certainly allows RFI shields to be printed.

Then I hit on a brainwave: short polyacrylonitrile fibres. There are normally used to reinforce synthetic rubber. But they have another use: The feedstock for carbon fibre.

My trick is to mix polyacrylonitrile and similar materials in with PLA or CAPA. This is then turned into filament, which in turn is printed into an object on a RepRap - this tends to align the fibres.

The object is then encased in a ceramic and heated to the vapourisation point of the PLA or CAPA. You then have a ceramic mould stuffed with oriented polyacrylonitrile. Introduce an inert atmosphere and raise the temperature and you have a mould full of carbon fibre. This can be surface-activated in the usual ways, or coated with vapour deposition before being vacuum-encased in epoxy to form a complex, 3D carbon fibre composite object.

Yes, I am looking for sponsorship :)

Vik :v)

Labels: capa, carbon, composite, epoxy, fiber, fibre, pla, reprap

Labels: hot-end, RapMan, reprap

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Labels: Maker Faire, New York City, NYC, reprap

Hi All,
I just wanted to let you all know that the Reprap "Blog of Blogs" has just been upgraded to use the new Yahoo "V2" pipes technology! (today)

For those that live under a rock ( or are new) this is the URL for the meta-blog of around 100 reprap blogs:
http://pipes.yahoo.com/davidbuzz/reprap_aggregation_pipe

..and this is a brief from Yahoo on the new technology, which went into BETA about a week ago.
http://blog.pipes.yahoo.net/2010/06/09/yahoo-pipes-v2-engine/

Happy Blogging!

Buzz.

Labels: blogs, reprap

I got irritated by the thought of a large chunk of wood that could be replaced by printing. So I'm tinkering with these modular panels about 100mm a side, scaled to fit the frame 3 abreast using the same fittings as their wooden counterpart.

Here you can see an Arduino with a simple prototype board on it. This holds 2 of TIP122 drivers for the heater and an experimental DC extruder. Alternatively it can hold 2 EasyDriver stepper controllers. Basic, but hopefully reliable.


They interconnect with 2xM4 16mm screws and trapped nuts. Objects can be anchored on pillars with 40mm M3 or M4 screws, or against the module's surface with 30mm ones. Here are some preliminary prototypes. I've attached them to the current "Simplified Kiwi Mendel" known more affectionately as Lemon Slice.

Speaking of slices, I caught my hand on a falling mandoline and have to rest my left hand. fortunately thumb works so I can sneakily enter blogs from bed on my phone...

Vik :v)

Labels: kiwi, mandoline, Mendel, module, panel, printed, reprap

I have finally managed to print tiny little ball-chain gears that work with 3.3mm and 3.5mm diameter ball-chain and still fit on the NEMA17's 5mm output shaft. The trick is to print the gears in two pieces.

As you can see in the photograph, I print two 4mm thick sections of gear and put them on the shaft with an M5 washer sandwiched in between. Make sure the teeth are lined up on both gears. This gives a channel to guide the ball-chain down the centre of the gear, and grips the sides of the balls adequately. As the gears age, it will also stop the balls grinding their way too far through the PLA, though I must admit that my experience with ball-chain Z axis gears suggests this will not be a major issue.


The gears themselves are designed to be "spiky", but the vaguearities of the printing and rendering process lop the spikes off and leave enough by accident to produce a functioning gear! SCAD and STL files are here: http://www.thingiverse.com/thing:2009

As the gears are stuck on the shaft of the NEMA17, and the original Mendel Y Motor Bracket is thicker than the length of the NEMA17 drive shaft, a new motor bracket is needed. Also, the ball chain cannot take tight corners well, so a 608 bearing is mounted on the frame cross-member to act as a pulley. The same arrangement is fitted to the other side of the frame making the Y Idler Bracket obsolete. There are knock-on effects on the bed design and X Carriage which I'm still working around.

Vik :v)

Labels: ball chain, gear, Mendel, reprap, small

Having had a lot of fun with the Afghan Lathe - which is still fantastic for machining extruder nozzles out of dome nuts - I've found that using a drill press the wrong way round is a lot easier for central 3mm bores in the extruder. Apologies for the cross-post, but people seem to have found it very useful elsewhere:

http://vik-olliver.blogspot.com/2010/02/drilling-down-middle.html

I'll still be working on the brass tube extruder, but I'm going to get a few Mendels working first, with technology I know is reliable.

Vik :v)

Labels: barrel, bore, extruder, lathe, reprap

Well, guess what? Supplies of suitable belt in New Zealand have completely failed to materialise. This comes as no great surprise to me, but must typify the situation in developing parts of the world. So, I am going to do a beaded belt (aka ball-chain or bath-chain) version of Mendel, using no fancy belts at all. The only problem is that the X & Y gears need to be very small to have enough resolution.

Well, the improved stepper drivers we're using have a slightly higher resolution than the old ones - not as high as the 16 micro-steps or more claimed by the chip specs, but useful. Also my printing skills have improved. This means that it may be possible to match a slightly larger chain with a slightly larger printed drive gear and better 0.1mm accuracy.

If that fails, it's time to break out the frickin' big "laser" ...

To the workshop!

Vik :v)

Labels: beaded belt, frickin' big laser, Mendel, reprap

Managed to blow the 4.7 Ohm filament at around 200C. By this time the wires were red hot, and a weak spot blew under the Kapton dammit. No matter, I have a New and Improved 6 Ohm version, all-ceramic insulation with double-twisted nichrome on the inputs to ensure a lower temperature on the input lines. I think it is those local hotspots that cause the Kapton to decompose. But hopefully I've just eliminated the Kapton - for the barrel insulation anyway; I might still use it to attach the thermocouple to the barrel for the moment.

Vik :v)

Labels: brass tube, ceramic, extruder, heater, reprap

Finally got over the flu that I brought back from LinuxConf 2010. Mendelssohn is now printing properly with a stepper-driven extruder and a new heating element/barrel design. This is essentially the old hack using a radio aerial and a heatsink. The M4 nozzle (not shown) fits inside the feed tube, so increased pressure forces the nozzle into a shoulder at the end of the tube. So the more pressure, the better the nozzle seal. The shoulder is created by slowly cutting the tube with a pipe cutter.




I'm dip-coating the 3/16" brass tube in fire cement slurry, drying this, and then wrapping the dry ceramic in Kapton to protect it while I wind on about 6 ohms of nichrome. If the Kapton gets vapourised, the heater element will not then short out on the brass tube. The heatsink traps the extruder as well as cooling the end of it, and also acts as an anchor point for connecting the extruder assembly to the X carriage.

Works so far. No lathe needed, no PTFE, no creep, no leaks.

Vik :v)

Labels: aerial, brass tube, extruder, heater, heatsink, nozzle, reprap

I'm very happy to announce the opening of an exhibition of RepRapped artworks collated by Bronwyn Holloway-Smith, Rhys Dippie and myself. The exhibition is at Massey University in Wellington, New Zealand. Most of the 10 exhibits are resurrections of lost items from the Te Papa collection. It was great fun setting this one up and my particular thanks go to Bronwyn for setting everything in place.

The sperm whale's tooth in particular has a curious aesthetic charm, and the tapa beater is the largest thing I've ever seen RepRap'd.

Vik :v)

Labels: art, exhibit, exhibition, museum, reprap, te papa

OK, so as always I cheat a bit. I used the ancient art of lost-wax casting, substituting PLA for wax. It burns/vapourises away cleanly at low temperature and is relatively benign stuff. So, how do you go about turning your PLA RepRap output into metal?

I took one standard-issue Mighty Reprap Power Ring in PLA as a test subject, and stuck on a few bits of 3mm PLA where I thought it looked useful. At the highest point, I stuck a simple printed cone of PLA to act as a filling hole. Then I painted it with thinnish plaster of Paris mix. While that dried off a bit, I mixed up more plaster and snipped into it about 30cc of uncompressed household fibreglass insulation. They only need to be about 5mm long, and are mixed in to disperse as well as you can. This will help stop the mould cracking (or, more to the point, hold it together if it does). This stiff mix is packed smoothly around the object, taking great care to not trap air bubbles like I did.

I wrapped masking tape around the bottom of a jar (initially sticky-side out) to make a disposable paper casing for our test subject. It looks black in the photo 'cos it's well-baked. Then, a couple more spoonfuls of plaster bedded said plastered bundle into place in this little paper pot. The pot was dried overnight in a desiccator, then baked at 150C for 15mins to drive off moisture. Next, the pot was inverted over a wire stand and foil drip-tray - out of deference for me not being in trouble for mucking up the oven. The temperature was raised to a scientific "11", and stayed that way until the conical filler hole looked absolutely clean, though slightly browned.

During that time, I fired up the ol' furnace (renewable fuels, etc.) and melted a load of pewter. With the mould still really hot (and thus safely dry) I poured in the pewter and left it for a 1/2 hr or so to cool off gently. I definitely did not impatiently have-to with a can of "Freeze Spray."

With the aid of tongs, the flat side of a 160g pein hammer was strategically deployed multiple times (Adrian will remember my skill with this tool from an earlier occasion) to reveal an amazingly faithful reproduction of the ring. The pegs sticking up are where pewter got into the vent holes. You want this to happen - just trim the excess off and file down. Same goes for the filler hole, just pop the scraps back into the clearly-labelled "Scrap Pewter" box.

After a stiff brushing under hot water, I was allowed in the house - no, I mean the ring was cleaned up and presentable. An air bubble was trapped inside the ring, resulting in a blister of pewter. But pewter is soft stuff, and you can easily correct problems like that with woodworking tools and a file.

If you do all this, do take basic safety precautions. Also be wary of using metals that melt at a higher temperature like aluminium. They cause plaster of Paris to decompose in undesirable ways and you need to research it properly.

Vik :v)

Labels: casting, lost, pewter, plaster, reprap, ring, wax

The boys & girls of Mrs Cornwell's class at Oratia School in Waitakere were kind enough to invite me along today to help with their topic of inventors and inventions. Hello room 16! I took the RepRap Child along for its first day at school, and we made a Mighty RepRap Power Ring. I left them with lots of small samples, some Polymorph to create their own inventions with, and a Christmas Angel to put on their Christmas tree. I'm sure I spotted one or two budding inventors and inventrixes there!

Vik :v)

Labels: oratia, reprap, school

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)

Labels: cicada, Käfer, reprap

I've got the Z axis going on the Mendelssohn design. In the picture here (RepRap is tilted so the bottom faces the camera) you can see the ball-chain drive connected up to the two Z threaded drive bars. The shiny pulley is a 608 bearing with some great big washers either side of it. Side note: If you put M4 nuts on an M4 bolt, the exterior diameter of the nut is 8mm and it fits perfectly as the axle for a 608 bearing.

The 4.5mm beaded chain gears are the same as used on the RepRap Child/Phoenix machine that built Mendelssohn. Printing a gear with a grub screw and captive nut was too hard, so I devised a clamp-on gear that fastens onto the NEMA17 shaft using an ordinary hose clamp. The tensioning pulley makes installation of the Z drive chain much easier on this prototype than the Darwin.


If you want to see it in operation, here's a video of it. I've stuck a mole grip on the X axis to add a bit of weight, and in case you can't see the ammeter it's running at 250mA. It ran like this for 20 mins, cycling up and down without overheating the motor or the EasyDriveV3 stepper driver. The OLPC is just powering the Arduino board - though some magic is needed to stop the OLPC powering down its USB ports at inconvenient moments. Once that's sorted I'll be able to power a RepRap using Ralith's minimalist RepRap command line utilities.

Vik :v)

PS I've since made the Y axis move back & forth using helicopter belt but need to print new bits to do it properly. People are asleep now, so I'll leave that for tomorrow.

Labels: Mendel, Mendelssohn, reprap, z axis

Well, you've seen the nice diagram from Ed so here's what the framework looks like when you put it all together. One change becomes immediately apparent - there is no longer room for a cat to hide inside or under it. Things seem to basically fit, though it might be an idea to wrap tape or plastic shim around the Y bars to ensure they're gripped firmly.

There is a little flexion at the top of the assembly. It is possible that with the right speed of head movement at the right height we could get some vibrations building up, however I have not fitted the board holder or the Z axis guides, which may well add more rigidity.

The extruder holder is a simplistic design, basically because there are not enough 625 bearings in my part of NZ to build a Mendel (Gary just cleaned out the local supplier!). I found PLA on silver steel slides just beautifully, so I'll be using that approach for the prototyping. For the vertical guides I'll probably just push some CAPA in for the moment.

So, now comes the tricky bits - saddles, gears, pulleys etc. This prototype will probably experiment with 3 types of belt drive - 4.5mm ball-chain as successfully used on Darwins for the Z, E-Sky EK1-0503 model helicopter belt (sadly not quite long enough for the proposed X axis) on the Y, and if I can print gears for the 3.5mm ball-chain that'll go on the X axis. If not I'll install the standard Darwin X belt.

Vik :v)

Labels: Mendel, Mendelssohn, reprap