RepRap: Blog

Now Adrain's got the polymer extruder valve tuned, we've got loads more control over the extrudate. Which begs the question, why nozzle wipe? From experience this procedure ups the risk of what we affectionally call "nozzle crap" - unwanted bits of filament getting attached to the nozzle. So now there's the option to skip that and move straight to the next layer. The only side effect is cooling is eliminated, which might be a problem for small parts, we shall see...

I recently acquired and built a Freeduino kit from nkcelectronics. The freeduino board is a clone of the Arduino and is 100% compatible, right down to the pin placements. It was a painless build, and the board worked right away. If you want to have a machine where you've built all the boards yourself, or you want to save $10 and buy a kit, this board is for you. Or, if you just want a board that is as free as free can get.

From the Freeduino website:

Freeduino is a collaborative open-source project to replicate and publish Arduino-compatible hardware files. The Freeduino Eagle SCH, BRD and Gerber production files allow users to create boards that are 100% functionally, electrically and physically compatible with Arduino hardware.

Inspired by some of Nophead's experiments, this is a water filter insert made in RepRap. Actually, it's a bit of a cheat: the model for it is a simple disc. But I've enhanced the host code so that you can plot multiple outlines of an object one inside another. Add that to the fact that you can set the infill width to whatever you like and the part becomes trivial to make. It took about 20 minutes in my home Darwin to build.

In general these enhancements mean that you can make the boundary of an object thicker (therefore stronger) and do a sparse infill, thus both saving material and reducing build time overall.

If you set

Extruder0_NumberOfShells(0..N)=1

in the properties file you get a single outline as normal. Setting it to bigger integers gives that number, one inside another. Setting it to 0 suppresses outline plotting altogether.

Also, if you set

Extruder0_ExtrusionInfillWidth(mm)

negative that suppresses infill hatching.

Anyway. Here it is filtering some non-potable water as input. (Mark you, I wouldn't drink the output, either...)


RepRap water filter from Adrian Bowyer on Vimeo.

Despite all evidence to the contrary, the noise on the soundtrack is not a Sopwith Camel that has just received the coup de grâce from the Red Barron. It is my neighbour's lawnmower. I'm glad to say that he has removed the Lewis gun...

...using a reprapped door handle.

This was printed on top of the latest mod to my Darwin, which I recommend as it

1. Is simple to add, and
2. Saves lots of messing about with the Z-axis screw drives and zeroing.

It is a Z Bed. It consists of a piece of MDF held down by three (not four) screws and nuts. Between it and the bottom bed round each screw are some stiffish springs. With this, it becomes trivial to set up the Z=0 position so that it's exactly the same distance under the extrude head just by eye. You move the head about, adjusting the Z Bed's pitch and roll until it comes out right.

The trick, of course, is not to raise the Z Bed too high; then the head doesn't collide with it when you're moving the head about. Being cleverer than I, you should be able to manage that...

This is just a little test one. I shall replace it with a piece almost as big as the base below it. It'll have two screws in the front corners, and one in the middle at the back.

Oh. And now we can go out to the scullery:


Reprapped door handle from Adrian Bowyer on Vimeo.

(Well. We could before. But not using a cool reprapped door handle...)

To get the door handle design, see the RepRap objects library here.

Here's a reprapped coat-hook:



It took me 12 minutes to design in Art of Illusion, then I set it running in my home RepRap machine. The quality is a bit splodgy because, since I upgraded to the Arduino, I've been trying to maximize my build speed, and I have overcooked the outline printing rate a bit; I'll back it off for the next one.

Anyway. I went out for the afternoon, then I came back. Now I have a coat-hook that I didn't have before. Utterly trivial, except:

1. I have somewhere in my lab to hang my lab-coat, as opposed to draping it over my camera tripod:


and

2. An economist once told me that the world market for coat-hooks is bigger than the world market for gas turbines...

The design for the hook is in the RepRap repository here.

Labels: coat hook, products, utility items

Looks like we have a failure mode for PLA corner brackets. This picture shows a relatively recent bracket torn apart by the forces of fitting an 8mm rod into it and over-tightening one of the grub screws.

As you can see, the break is hardly a neat delamination, and the line of separation is at the apex of a teardrop-shaped hole. The corners also have little plastic in them, even after being squared off so they parted easily too.

As a temporary solution I am putting bolts through empty holes to hold things together. We'll see how it goes, but I think we may need to remove some of the unwanted honeycombing from the design and beef it up a little. I'm also installing the next one upside-down, so the apex of the teardrop is at the bottom of the bracket.

Vik :v)

Labels: corner bracket, failure, pla, reprap

I've got a 30kg test batch of PLA filament ordered up in New Zealand, which I'll distribute at cost. So if you'd like a 100m roll or two, shout up. I'll dispatch overseas, but do check the swingeing NZ Post overseas rates first. A roll is 420mm diameter and about 30mm thick, weighing approx 800g. If you want larger quantities, I'll put another order in for you no problemo.

Also, PMB Electronics of New Zealand now have the L298N and L297 stepper driver chips in stock at reasonable prices and low volumes. Tell 'em Vik sent ya. No, I'm not on commission. I've asked them to consider stocking Arduinos too, but mentioning it again wouldn't hurt :)

Vik :v)

Labels: pla, pmb

Untitled from Adrian Bowyer on Vimeo.

Here is the new polymer valve in operation.

A solenoid pushes a short length of piano wire across the flow. This stops it instantly, giving a much better finish to constructed objects, and also stopping the polymer oozing from the nozzle when it is idle.

The AoI files for the design are in the subversion repository here. The solenoid I used is from RS: 250-0827.

I have also checked into the repository the changes to the host Java code and the firmware for the Arduino needed to drive the device. Note that, in the latter case, the new firmware disables the maximum (but not the minimum/zero) optoswitches on the RepRap machine's axes. Few people use these anyway, and - as pins on the Arduino are tight - it is better, I think, to use them to add new functionality.

Exactly the same code will drive the metal deposition head that I blogged here.

Labels: polymer extruder, valve