Saturday, July 17, 2010
Thinking today about rep-rapping, I had the idea of trying to use radiant heat as a way to anneal the build object. this would be instead of a heated build chamber ( which presumably relies on convective heat transfer ), and probably in addition to a heated bed.
The idea is: could heat lamps with infrared output optimized for ABS's spectral properties, combined with the use of black ABS, cause the object to stay hot enough? Some quick reading seems to indicate that the ideal heater would emit 3500nm light to match best with the best aborbtion of plastics [http://en.wikipedia.org/wiki/Infrared_heater]
Maybe like These
I'm also thinking that the sides of containing envelope could be light colored or metal, so that they re-reflect as much light as possible onto the object. A black-colored bed might absorb enough light to cause it to heat without a separate light source.
This of course violates the reprap 12V goal; but it seems possible that a reprap placed in bright sunlight to utilize solar radiation to elevate temperatures somewhat, if the build envelope is designed to optimize solar gain. Solar ovens can easily get to 100C with very basic aluminum foil and a single reflector.
Has anyone tried this kind of approach?
Thursday, July 15, 2010
changing the game, and using kapton tape as a slide
I've been working on redesigning the design for an entirely laser-cuttable x/y stage, and have some neat progress.
This design also uses a rack and pinion system, with a bunch of changes:
1) the linear gear is mounted horizontally, rather than vertically -- the weight of the entire axis is no longer suppored by the gear itself, but rather by a structural outcrop.
2) the axis is driven at four points (two from each side), rather than only a single point. this removes a lot of the shearing/binding issues. this is accomplished using a captive system of gears sandwiched inside the axis itself to transfer power from the stepper to four points along the edges of the axis.
3) a long piece of kapton tape is used as something like a linear slide, significantly reducing the friction between the axis and the linear gears that it rests upon. the axis slides *really* well with the kapton tape.
The result is a working linear axis that can be entirely constructed with a laser cutter, using only a handfull of screws, a $5 stepper, and a few pieces of kapton tape as vitamins. That's fantastic! :)
So far it works pretty okay! There are a couple refinements to make:
4) Right now the gear on the stepper is just press fit -- I really need to key the gears and motor shaft, as the press fit wears quickly with the hardboard.
5) The gearbox is mostly just eyeballed, and there's probably an ideal solution when solving simultaneously for (a) a rack, with (b) two gears of radius R1, being driven by (c) another larger gear of radius R2; all for a given tooth size. Myself and a bunch of other physicist/math nerds at school have each had our hands at the problem, but haven't come up with a fantastic method of solving it yet (start with C, then find all the angles that B can attach to C, then determine if the distance between the centres of the two gears B modulo the gear pitch is an integer for each angle?).
6) This design seems great for the cross-axis. I have a similar design for the supporting axis with a MUCH larger captive gear system in it -- I'm not sure if the friction would be too much in that situation, or if it'd work out okay. (I stick a tiny washer under the gear, to reduce the friction a great deal -- maybe a nylon washer, or some kapton tape might also work out well?).
The alternative might be using a combination of two of these tiny "captive gear" axes, one at each end, for a supporting axis. This adds an extra stepper to the design (which is a negitive, although these ones are only $5!), but it also keeps the whole system fairly low, which would be kind of nice!
If anyone is curious to tinker, I've put the design files up on Thingiverse ( http://www.thingiverse.com/thing:3554 ). Happy tinkering, and thanks for reading! :)
[part 1] [part 2] [part 3] [part 4] [part 5] [part 6] [part 6 video] [part 7] [cogsci.mcmaster.ca/~peter]
Wednesday, July 14, 2010
Sheffield RepRap Users Group (UK)
Venue: The GIST Lab
Address: First Floor, The Workstation, 1 Grinders Hill / Brown Street, Sheffield, United Kingdom, S1 2BX
This month is the inaugural meet-up to help the group find its feet and shape the way it goes forward. It's a loose agenda, and an informal set-up.
No experience necessary. Let's face it, this is the future we're building!
Interested in experimentation and building machinery that can self replicate?
In a nut shell RepRap is an open research project to make Rapid Prototyping Machinery that can Replicate it self ultimately completely but working towards is acceptable, hence RepRap. This event is a meet-up for folks who want to find out more or get involved, and to work on projects that push forward the boundaries of this technology research.
It's not dry research though .... we build stuff too. And that stuff will eventually be able to build itself ... welcome to the self-replicating machine odyssey!
Fore details and a map see :-
The Sheffield RepRap Users Group shares community space with the Sheffield Arduino Users Group (Shacknet)
Amongst others at the GistHub
Wednesday, July 07, 2010
selective laser sintering part 7: x-y axis
Just a quick post -- I've been tinkering with the idea of making an entirely laser-cuttable x-y axis using nothing that isn't laser cut except bolts, nuts, and steppers (essentially things that wouldn't be immediately available at the simplest of hardware stores, plus the steppers).
I thought I'd post my progress so far, even though the latest iteration isn't going so well. Basically driving a long axis from one side introduces a shear force, so you typically would drive it from the center (like with a belt, or lead screw), drive it from both ends (either with two motors, or a long shaft that transfers the drive from both ends), or try and come up with some very precise linear rails and bearings that prevent all the shearing and torquing from happening. I chose to try that last bit, since all the other options involve extra parts (like shafts, belts, or screws), or extra motors. This isn't working out so well, but I still thought I'd post some pictures and my progress for informative purposes (sometimes design iterations that don't work out so well are just as informative as ones that do).
Happy to accept design thoughts from folks who have attempted this before?
thanks for reading!
[part 1] [part 2] [part 3] [part 4] [part 5] [part 6] [part 6 video] [cogsci.mcmaster.ca/~peter]
Thursday, July 01, 2010
RepRap.org DNS change
If you notice a broken RepRap.org related service, please post a comment and Jonathan, Adrian or myself will get on it a.s.a.p.