RepRap: Blog

A very retrograde I2C controlled stepper controller which is, at the same time, very powerful and easy to build.




It seems to be able to push a 2.4 amp NEMA 17 at 4 KHz and a 0.5 amp tin can stepper at 800 Hz.

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Labels: I2C Reprap SN754410 PCF8574 stepper controller

Segmented aprons work just as well in ABS as they does in HDPE. I didn't even bother changing the Skeinforge settings. Just make sure that the first layer tracks for your raft measure 2 mm wide {so that it sticks to your acrylic print surface} and you're good to go.


Mendel part x-carriage-lower_1off in HDPE {left, white} and ABS {right, amber}

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I treated Mendel part z-leadscrew-base-bar-clamp_2off in the same way, viz, a segmented apron. You can see what this looks like in Netfabb.



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I'd heard that people printing Mendel were having trouble printing the largest pieces of Mendel in anything but PLA. Since PLA filament is hard to acquire in the US at this point I thought it would be nice if those hard-to-print parts could be printed in some other plastic. Since I am working with HDPE right now, I decided to have a go with HDPE.

The trial part I've begun with is x-carriage-lower_1off. I've discovered that a segmented apron positioned 0.5 mm away from the perimeter of the part does the job of successfully suppressing warping. Here you can see the spacing between apron and part.



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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

In which your narrator fits the last piece in the puzzle of how to use HDPE in 3D printing and accidentally discovers several other wonderful things for the holidays.


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These research notes are also in the wiki, for people who want to hack on the idea:
http://objects.reprap.org/wiki/Powder/Plastic

It's a wiki, so go crazy. (It takes 90 seconds to create an account and start editting.)

Yes, if we step back and look at what a belt does instead of simply trying to replicate existing ones.



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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

There are two machines coming together in the Bath University RepRap Lab, and I am building a third at home. Here they all are together with the Mendel prototype that made many of their parts (the rest were made in our Darwins). It's almost as if they are reproducing or something...