Monday, September 06, 2010

Wondering what the fuss is about



In which your narrator wonders what all the fuss is all about?

I guess I just don't get it. When you work with a plastic, after a while you get a feel for what it can do and what it can't. I started getting along along quite happily with no heated bed and ABS.

I print with a 0.3 orifice at an axis speed of 16 mm/sec. I suspect that I could kick it up to 22 mm/sec without a lot of drama, but I don't want to take the time out to play "who can print fastest" games at this point.

Once I started doing thin walled pieces and no infill my warping problems virtually disappeared. Most of the pieces I design have a largest dimension <= 90 mm though I've printed a herringbone rack that was 250 mm long. My acrylic print table temperature stays at about 25-30 degrees. You also don't find my prints warping after a few days from the internal stresses that Bogdan has talked about. I've seen that with HDPE. I was also printing with cross-hatched infill in those days, too.

I got into thin walled, no infill after I realised that if I went that way I got pretty fast prints that way at lower print head velocities.

Watching you guys reminds me of the first and second year architectural studio students that I used to lecture to back in my university professor days. They'd make models of buildings out of either "shipboard" {2 mm solid cardboard} or carve them out of expanded polystyrene foam treating it like it was so much cool butter or cheese. We used to say "form follows chipboard". If you followed the careers of those students they usually spent the first five years of their careers designing actual building that got built that looked as if they'd been carved out of cool butter. That's an extremely expensive way to design and build buildings. Those guys either got out of the habit fast or wound up doing architectural detail drawings for other designers who'd developed a feel and respect of the potential and limitations of the materials that went into their buildings.

Around here I see parts designed like you were more used to using an expensive CNC milling machine to carve parts out of a block of steel or aluminum.

That looks really cool but begs the fact that you're not taking advantage of the strengths and avoiding the weaknesses of the material you're working with, viz, plastic and extruded plastic at that. Somewhere along the line with Reprap we got the idea that we ought to be able to design parts in any shape we wished and whatever the material wanted to be be damned. You can see the trouble it's caused us in the chase after things like heated beds and support materials. We're spending a lot of time on that chase when we could be designing killer apps that make having a much simpler reprap machine very desirable.

That's just an old architectural technologist talking, I suppose.


I've included a link of the telepresence hand that I'm currently designing. That is human sized, btw. The largest part dimension is a touch over 80 mm. No warping whatsoever on any part.




Thin walled, no infill, snapped or glued together. There'll be a few screws in it to secure some elastic bands that return fingers to their rest positions. I haven't figured out how to secure elastics bands with snap on parts or glue yet. I'm thinking about how that might be possible all the time, though. :-)

21 comments:

Renoir said...

I've also been wondering that - many of the reprap parts are fairly 'blocky' and look like they've been CNC'd from a solid block. I assumed that it was to make them easier to bootstrap by other means, like by using CNC or other subtractive methods. That doesn't mean we can't have a set of reprap only parts, though.

As far as most parts go, all you need is a collar or tube around the bolt shanks and webs in between to connect. The centre of the parts can be hollow. It would be an interesting excercise to see how little material you need?

Forrest Higgs said...

My point, exactly! We spend far too much time redesigning our 3D printer and far too little time designing our parts. :-)

Glowing Face Man said...

That hand looks very impressive.

Giles said...

Fair point, but for me the first time I decided that I needed a heated bed was not because I experienced warp, but because I had trouble getting the ABS to adhere during the print. The initial layers stuck, but then the print would break off half way through. The obvious solution for that is to use a raft, but then the finish on the bottom of the print is not so good.

jbayless said...

For a machine tool, stiffness is a critically important factor. So if I were printing RepRap parts, I would certainly aim for a high percentage of infill.

For printed parts that aren't meant to be used in a RepRap though, low infill/thin wall is certainly a good option.

Forrest Higgs said...

Make no mistake. No infill, thin wall parts are very strong if thoughtfully designed.

dracolytch said...

Different people build for different reasons. There will always, ALWAYS, be a section of people who want to keep it clean and simple (I am one of these). However, there will always be those who push things a bit. They'll add complexity to extend boundaries and features... But they'll need folks like you to re-simplify things to make them practical again. It's a cycle. Do not fight it or try to change it... Acknowledge your role in the cycle and continue on your path.

Forrest Higgs said...

What do you think I'm doing? :-)

CryptoQuick said...

Very valid points. Infill is probably unnecessary and can even cause problems in the integrity of the final part. If it's easier to make thin-walled parts from just about any RepRap setup, rather than fine-tuning and tweaking a system for optimal every-part production, it's only natural that this new design paradigm be fully considered and perhaps even adopted as standard practice.

The next step is for you to lead that revolution, Mr. Higgs. Although I'm no expert and I have no RepRap, I feel this is an important avenue to be explored, and if new RepRap Mendel or Huxley parts can be produced as thin-walled variants, then it's only natural you should be the leader of this revolution!

Although my opinion means little, I push you to develop thin-walled RepRap parts!

Forrest Higgs said...

"it's only natural you should be the leader of this revolution!"

No I shouldn't. I've got an ongoing project in which I am using the thin walled, no infill philosophy.

As always, people can do what they will in Reprap. I'm merely suggesting the thin walled approach as an alternative to the several ways things are being done now.

Buzz said...

Hey Forrest:

TO answer your question/statement regarding how to attach elastic to plastic without screws.... use a wedge or a knot. eg: print a plastic wedge that fits loosely into a similarly shaped hollow/slot/cavity, then put the elastic through the cavity so it exits at the thin end of the wedge, and inset the wedge in-set. stretch the elastic well beyond it's normal operating limits, and push the wedge in hard. it'll never move again. ( the elastic holds the wedge in compression, and the wedge holds the tension from the elastic).

similar results can be achieved with knots - either through-hole and knotted onto itself, or knotted around a solid object like a rod or cleat.

Buzz.

Forrest Higgs said...

I'd been thinking about the wedge option. I'd have to use more of a diamond than a wedge to get it to print right, though. That's pretty hard to do with parts that small. :-(

Frank Davies said...

I use Art Of Illusion, and one reason that my things look blocky is that it is difficult to subtract out the centers leaving the walls. Of course this is letting the tool influence the design, just what Forrest was talking about. Maybe I need to learn enough about AOI scripts to make one that will turn a solid shape into a shell. I suspect that to really take advantage of the thin wall method, you would need some insight into what stresses the part would take so that you could add reinforcing struts (kind of like bone).

fdavies

Forrest Higgs said...

Frank: With AoI I never try to make hollow objects. I just leave them solid and then don't put infill in in Slice and Dice. Nothing to it. :-)

kliment said...

Forrest, for attaching elastic bands, start with a loop (rubber band), and have a plastic part with a circular protrusion and another plastic part with a matching citcular hole. Put the band on the protrusion, glue/weld the plastic bits together, thread it through whatever you need it to go through and repeat on the other end.

Forrest Higgs said...

kliment: Nice idea! I think I may try that. :-)

Supertwang said...

A quick question...

what are the pros of the Reprap over the Makerbot?

I'm new to the whole 3D printing thing, and want to dive in with the right machine...

thanks for your insights!

Dave

Forrest Higgs said...

I'm not the guy to ask that question. I think it's good to do 3D printing. Exactly which machine you use is largely a matter of taste to me.

Makerbot and Rapman {which I use} you can buy as complete kits. With Reprap Mendel you can either buy it as a kit from several sources or build it from scratch yourself. It's a few hundred dollars cheaper to build it from scratch.

I'm convinced that my Rapman with the special 0.3 mm extruder orifice that I use gives higher quality prints than other systems. I haven't had my system side-by-side with either a Makerbot or a Mendel, so that assessment is very subjective, however, and is based only on comparing pictures published on the web.

Guy said...

just out of curiosity, has anyone tried printing a thin walled shell and then using a syringe to fill it with a hardening resin and catalyst? Or concrete for that matter...

Forrest Higgs said...

Guy: I believe nophead did some work with that several years ago.

Sublime said...

For attaching the elastic, you could tie a knot in the end of it and then slip it though a key hole shaped opening left in the plastic and your done. Or alternatively you could leave a U shaped hole and hook the end of the elastic over the tang in the middle of the U.