Wednesday, February 03, 2010
Mini Me
Just before he left to Starve in the New Zealand Wilderness Ed did a new RepRap design because he "had to get it out of his head". It was a mini version of Mendel. You can see it on the left in the picture above - a still from
Josef Davies-Coates' short documentary on the Bath RepRap Lab. The machine uses M6 threaded rods and M3 nuts and bolts (as opposed to the M8/M4 used on Mendel) and NEMA 14 steppers. The reprapped parts are about 30% of the volume of those for Mendel, which is to say it could reproduce three times faster.
This is a completely unsupported design for the moment (we haven't got the time...) but we have put the STEP file for it in the RepRap repository at
https://reprap.svn.sourceforge.net/svnroot/reprap/trunk/mendel/mechanics/mini-mendel
because it's so neat, and some of you might like to play with it...
Here's a close up rendered by M.BrittCrane:
Thanks!
On reflection, I think that putting the material spool underneath is not a good idea: it tends to jam. Better to have it on a separate reel above (which would make the machine even smaller).
Labels: mendel mini desktop 3D printer
Tuesday, February 02, 2010
Multiple object saving and loading
I have done an implementation of .rfo files (see http://reprap.org/bin/view/Main/MultipleMaterialsFiles) in the Java host code. These allow you to load up a set of STLs, then save the whole lot as an .rfo file for re-loading later.
It's a bit experimental, and I need to fix it so that you can load-rfo, edit, then re-save. But if you want to play it's in the repository at https://reprap.svn.sourceforge.net/svnroot/reprap/trunk/reprap/host
It's a bit experimental, and I need to fix it so that you can load-rfo, edit, then re-save. But if you want to play it's in the repository at https://reprap.svn.sourceforge.net/svnroot/reprap/trunk/reprap/host
Monday, February 01, 2010
Brass Tube Extruder Update
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)
Vik :v)
Labels: brass tube, ceramic, extruder, heater, reprap
Sunday, January 31, 2010
Many useful little things...
In which your narrator continues his relentless campaign to get the steel out of Reprap machines and improve the percentage printed.
Do you want to read more?
Saturday, January 30, 2010
Mendelssohn & LCA2010
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
Friday, January 29, 2010
Paste Extruder - The first test
Paste extruders seem to be all the rage these days. They would allow RepRap to utilise a load of new materials to increase the replication count, and also enable us to use a soluble support material. Zach came up with the Frostruder MK2 , and it seems to be the best way of tackling the problem. Zach's idea was to use high air pressure directly to force the paste out of a syringe rather than to use a piston driven by a motor. The real beauty of Zach's design is a relief valve that is able to exhaust the high pressure air from the syringe. This prevents any paste oozing from the nozzle when extrusion needs to stop, a difficulty thats plagues a lot of motor driven systems.
The main difference between this design and others is in the valve. Patrick came up with an idea for a pressure valve based around some reprapped springs and a cam, to clamp a piece of silicon tubing and cut the air pressure. We control the position of this cam by using a simple reprapped tacho, an optoswitch, with the entire mechanism connected to a DC motor.
Secondly, the frostruder design has the high pressure acting directly on the paste. I initially replicated this, but found that for relatively "thin" pastes, the high pressure air was able to bury directly through the paste and come directly out of the nozzle. I employed the use of an intermediate bung between the paste and the pressure. However, the ooze from the nozzle is substantial due to the increased friction unless the bung and the syringe were coated in silicone grease. Adding the grease results in virtually zero ooze.
In addition to the valve, we hacked together a compressor based on a 2L drinks bottle, and a car tyre inflator. What is particularly nice about this is that the tyre inflator is 12V DC i.e. we can control it directly from the MOSFETS on the Extruder controller. As yet we haven't hooked a pressure sensor into the system, but its something we intend to work on(or rather its something we want to replicate)
The above was my first test with the extruder on the machine, attempting to find an appropriate axis speed for a given pressure. The extruder started and stopped with pretty much no lag or ooze. I was manually starting and stopping the extruder by hand with a second optoswitch (We haven't got the firmware sorted yet), which is the reason for any large blobs at the start or finish. I was using the soluble support paste I described in a previous post, I guess each line shown in the picture above dried in under a minute.
All in all, the entire setup cost about £20, I'll be posting some more results next week after we get the entire thing to be controlled by the host software, which should also bring better quality results.
Wednesday, January 27, 2010
Build a better RepRap: $80,000 Prize
The Foresight Institute has announced its Kartik M. Gada Humanitarian Innovation Prize to design and build a better RepRap. There is an interim prize of $20,000, and a grand prize of $80,000. They consulted with the core RepRap team before the announcement and we were initially concerned that the prizes might drive developers to secrecy in order to give themselves a competitive edge. As you will see they have addressed those concerns by making it a condition of winning the prize that solutions should be pre-published and made available under a free licence. For ourselves and on your behalf, we would like to thank the Institute for the enthusiasm that these prizes demonstrate for the RepRap project and for their magnificent generosity.
Reprappers: to your designs! To your experiments!
Upcoming server outage
We are pleased to announce that RepRap.org will have a brief server outage at 8:00 PM on Wed, 27 Jan 2010 Pacific Standard Time. This will last no more than an hour, and ideally will only take 15 minutes.
This will be at 04:00 Thu, 28 Jan 2010 UTC.
(We're moving servers.)
Regards,
Sebastien Bailard
RepRap.org
This will be at 04:00 Thu, 28 Jan 2010 UTC.
(We're moving servers.)
Regards,
Sebastien Bailard
RepRap.org
Labels: server
