Saturday, July 30, 2005


PLA thermal characteristics

After receiving some sample PLA from Vik, I thought I'd just see how this stuff behaves at our extruder temperatures.

It turns out it melts at a much higher temperature than I expected. I expected it would melt between 130°C and 180°C. Here's what I found:

155°C starts to become noticably glassy, but granules are still quite hard.

170°C starts to deform

180°C granules merge together very slowly (still too viscous to flow in any useful way)

185°C slowly flattens to a single continuous mixture, but still very viscous. Quite meldable at this stage though.

200°C still quite viscous

230°C still quite viscous. I'm not sure it will extrude easily at <1mm thicknesses.

I didn't test further than this because the current extrusion system won't be very happy at any higher temperatures.

This suggests the PLA is an extremely high MW sample. In all likelihood if we can produce our own PLA it will have a lower melting point. In fact we might have the reverse problem where we can't get it high enough.

Monday, July 25, 2005


It is an ex-glue gun. It has ceased to be.

We're picking up subtle hints that our "$2 Shop" glue guns may not be suitable for prolonged use. This, our second victim, is an ex-gluegun. It has ceased to be:

It is not pining for the fjords, and it wouldn't go voom if you put ... hang on, it did go >FOOOOM!< at 220V. No lab personel were injured in the explosion, though nearby an unrelated syringe was shot dead by armed police.

Vik :v)

Friday, July 22, 2005


Quick fixupses 'r' us

The Polymorph saddles no longer leap off the rails of the Meccano prototype - we've cast a 270g lead counterweight and slung it underneath to stop the toppling on sudden stops. Future versions will be balanced more carefully.

Also, our 5V 1A power supply is stable with the larger heatsink and the motors take 0.4A peak (0.15A continuous) each so there is no need to upgrade. This is great, as we're planning to switch to 12V motors eventually and don't want to be burdened with unnecessary work.

I've made a little aluminium block with an 8mm hole through the middle that is handy for joining EVA glue sticks. Melt ends of glue sticks, push and one stick into each end of the hole. Peel off the excess and with great strength haul the block off when cold. Nice, smooth join - should work with 3mm Polymorph rod too.

What else? I've gone off phone lead connectors - too fiddly and too unreliable. So I've chopped the plugs off and used terminal strip. Much better.

This weekend is dedicated to family life, but I expect to work on a version of the turntable that is moved by a cam next week. Real, 3D shapes coming soon...

Vik :v)

Thursday, July 21, 2005


Flat structures from EVA

While these glue gun "blobs" aren't too impressive to look at, they illustrate that we can successfully bond layers of EVA:

Keith and I got the final one going this morning, using the winding pulley mechanism shown below. It's not a puddle - it is actually cohesively constructed in a spiral manner. The counterweight is on the end of the white string exiting to the left:

Bear in mind that we are lowering the table manually, and not compensating for the increase in the relative speed of the turntable as the head moves further from the centre. In all, I think we did well !

We've also produced a glue gun Polymorph nozzle that extruded 0.8mm strands of same. Unfortunately it is not practical to use a standard glue gun mechanism or the systems I currently have here to push Polymorph through at any useful rate. We're experimenting with wider nozzles, and we'll widen it until we get one that works.

We've also put a proper power switch on the RepRap, so I don't leave it powered on at night - the cats might spark it up.

Vik :v)

Friday, July 15, 2005


Closeup of Turntable

Here's a shot of the levelling mechanism and gearing used on the latest Meccano turntable. By adjusting the long bolts under the turntable we can ensure the turntable remains level while it rotates, and adjustment of the long bolts on the large blue pulley allows us to ensure the axis rotates vertically.

Once we've modifed the Polymorph saddles, we'll probably add a cam mechanism to move the carriage as the turntable rotates. This should allow the deposition of shapes other than round bits of tube, without having to develop the electronics and software first. Hopefully we'll have some of the mechanical principles debugged and ready for the other bits.

Vik :v)


Meccano prototype with new turntable

We've got quite far with the Meccano prototype. This is what it looks like now (some samples shown on block in right-hand corner):

Note we've added a 5V power supply, hence the large heatsink. The turntable now has three adjustable legs, and is made of an old sweet tin lid, rather than being a Meccano gear wheel. The toy pistol lower right has turned out to be a good source of strong springs.

We have added the changeover switch from a cars' electric window mechanism. This allowed us to make the carriage and turntable assembly fly wildly back and forth. We have discovered that when the extended turntable comes to a sudden halt, the Polymorph saddles spontaniously detach ("fall off") from the rails, and the whole blooming thing jams!

We will attempt to fix this by mounting the saddles with their supports held vertically. This may also reduce friction further.

We've just realised that our LM7805 power regulator - the one hiding behind the heatsink at the front - is rated at 1A. Our motor takes about 1.5A, so we're rapidly looking into this LM350K variable voltage regulator-inna-can-thingie I found. These beasts apparently happily supply 4.5A to hungry motors, but need a little more setting up.

Vik :v) & 4sh


Polylactic Acid

We recieved a sample of polylactic acid in the mail today. Some preliminary tests with a bowl of boiling water and a hair dryer on max setting were conducted. Results are as follows: It doesn't melt.

Using a k-type thermocouple probe, we checked the temperature put out by the hairdryer at 120C (approx.) At this point a few grains started to turn transparent and welded to one another.

As we have no way of making polylactic acid rod, we can't quite feed it through our extrusion nozzle. Yet. Time to bake polylactic acid cookies...

Vik :v) & 4sh

Wednesday, July 13, 2005


Inverted wire-wrapping

Driven by the scarcity of low melting-point alloys and the wide availability of wire, I wondered if it might not be a good idea to design a wire-wrapping head that deposits fine copper or phosphor-bronze wire.

Wire could be hitched around protuberances on the plastic object under construction, and spiralled against the walls of holes in such a way as to hold components that are pushed into them. The use of wire has been breviously mentioned, but it is not necessary to coat the wire before depositing it. The wires can be insulated and fixed securely in place by overwriting with plastic - or even icing!

It might be necessary to heat the holes slightly to ensure the wire sticks to the walls. It might even be practical to make IC holders for SMT components by strategically laying the wire in lines, and arranging a clamp to hold the IC on top of them.

Wires can be joined by spiralling them into the holes, or around protuberances. In fact, it might be practical to forget holes and develop notched pillars that are wrapped with wire as a kind of socket. These would accept components pushed into the notches after the wire has been wrapped around them:

Where wires cross, the lower wire is first burried in deposited plastic.

No time to test right now, so pipe up if your interests are inclined in that direction - i.e. if you are a secret sewing machine collector or somesuch.

Vik :v)

Monday, July 11, 2005


Afghan Lathe as a web page

Adrian is kindly hosting the "Afghan Lathe" document as a web page so you can pop over for a quick browse. This is the version that shows how to use a power drill as a lathe, and construct a heated RepRap nozzle with interchangable nozzle ends:

Vik :v)

Sunday, July 10, 2005


Going All Curly

We've got the new chassis fully assembled, and we've run off a few unsatisfactory attempts at cylinders. Some fine tuning is required to match the flow rate and rotation rate. We've got a built-in CPU fan to cool the workpiece instead of the ruddy great standing fan used previously.

I think we might be able to build LM7805-based 12V/5V power converters on screw terminal strip, so keeping hot stuff away from potential Polymorph components.

The new frame needs some decent power - for the fan as well as the motors - and signal cabling put in. We've taken to using curly replacement phone handset leads for my signal wires. 4 cores, readily obtainable and easy to stretch around the place. Cheapskates can run up non-curly versions or use the spare ones that come with modems :)

One problem is a decent source of RJ11 sockets. Fortunately a mate discovered a cache of RJ11 female-female adapters, which can be broken in half to provide 2 RJ11 socket. This saved some old phones and blown modems from dissection for the cause.

For power connectors we're just using aforementioned screw terminal strip at the moment. Cheap car lighter extension leads look useful; again they come in curls, have a built-in 5A fuse, ample extra cable for scavenging, and will make plugging the RepRap into a car really easy for use on holiday! I'll grab one next payday.

Vik :v)


The "Afghan Lathe" technique - Updated

I've finally documented the "Afghan Lathe" technique for using an electric drill to lathe and centre-drill. This makes the construction of Adrian's nozzles and various other components possible with common power tools.

This revision is less than half the size of the previous one to download, and contains Adrian's instructions on winding a heater element around the freshly-turned brass bolt.

The second draft is here (446K download) and comments are welcome:

190 People downloaded the first draft. Nice to see they felt no need to comment :)

Seriously though, if anyone does want to improve the document, contact me for the source.

Vik :v)

Saturday, July 02, 2005


Gantry Welded Over Meccano Prototype

Well, the freshly-constructed gantry has appeared. Not finished - and it won't be until we know exactly where to weld the bracing. Paint fumes while welding are not healthy. As it is, my nose feels half full of welding slag.

We'll line it up properly tomorrow with the bolts, then Keith will give the wooden parts a sand down and lick of paint.

This should now let us dangle Polymorph and icing extruders over a moving turntable. It is likely that, following some messy extrusion experiments, attention will then focus on what to make the turntable out of and how to level it.

Vik :v)

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