Saturday, July 29, 2006


Sign For a RepRap

We've had a wee bit of discussion on an idea which we can't really take any further due to lack of all sorts of important stuff like time and resources. But it deserves to be blogged nonetheless. Perhaps someone will even take it to The Reprappers Blogspot, where people who are actually doing some building live :)

The general concept is to use a CNC router to cut sheet acrylic or polyethylene to form the basic essentials of a RepRap prototype for keen hobbyist developers. This is a little controversial, because it isn't a pure-bred RepRap and it isn't a made-from-scratch masterpiece. It sits somewhere in the middle, shuffing its feet uncomfortably. There are two main areas in which this idea has some merit:

1. There is a thriving CNC router community who know a thing or two about desigining axes and stuff. They often have the technology and curiosity necessary to want to play with RepRaps.

2. It turns out these things are readily accessable at reasonable prices to all and sundry, including those to whom CNC is one of the Dark Arts. The local signmakers are a secret clan of machine shops.

Signmakers, you see, take vector drawings and use computerised routers to cut shapes out of sheets of acrylic. These sheets can be up to 10mm (3/8") or so thick, though a reasonable thickness for one-pass cutting is more like 6mm. Holes of 3mm and greater can be cut with the general routing bit. Acrylic and polyethylene are reasonably inexpensive, so materials for the thing could be <$50 for all parts. But...

One of the reasons RepRapping is so appealing is you only pay for what you use. With CNC routing you pay for all the material, and then you pay extra for the "cutting lines" needed to hew your part out. So someone would need to convert the basic "Da Witch" parts, or ther functional equivalents thereof (we've a few sensible changes in mind already), to a 2D vector image (AI, DXF, SVG etc.) using a minimal amount of cutting. Instead of being full of lightening holes to save plastic, for example, the gears would be solid. Other designs are undoubtedly better, but we do know Da Witch actually works.

Given this plan, anyone in a conveniently civilized spot with sufficient cash can then stroll into a signmakers, say "print me one of these on so-many millimetre/inch acrylic, my good fellow, and be snappy about it," and come out with a funny look and snap-off sheet of flat-pack RepRap bits.

It's a thought.

Vik :v)

When I first read about the 'Rap, I envisaged the appearance of shops like the copy-and-print ones common in most cities, but for hardware. This could also be a solution for the supply of more expensive parts of a RepRap tool chain - you might send out for the use of an LCD printer, for example.
Initially, yes, but as people discover what useful and powerful things RepRaps are that will change. Users will be able to implement completely new ways of doing things, which is kind of exciting.

Copy shops will still be useful for extremely energy-intensive productions, or possibly ones that work faster than is practical to maintain in a home environment.

Vik :v)
Great piece of thinking, Vik!
I've actually been tempted to make a repstrap out of legos... the holes on the Technic blocks are the perfect size for a us 10 threaded rod...

I've already got the X axis of my smaller prototyper built (mostly) out of legos... essentialy a platform on wheels that moves back and forth accross the Y axis...

Currently, the rest of my design is based off 1x6 wood (though so far all the pieces have been cut down to about 1x1x6 so a 1x1 could suffice... and I may pick one up for my next set of trials...)

(unless I've got my repraps confused) I'm basing my y axis off that of "Da Witch", and then turning it verticle for my z axis... I'm staying away from gears in my design (and I have to wonder how accurate these signmakers are... can the average one really make a gear of that size?)

This sounds like a nice idea... but I've set the bar lower for myself... I'm trying to create a repstrap with just a saw and a drill... (and a soldering iron to make the cuircuits... and I haven't figured out the extruder head yet but I have decided that that is the first piece to get prototyped and replaced in the repstrap!) I am using a chop saw, but if I maintain 1x1x6 throughout the entire project (and the design I'm currently tossing around in my head would have a 1x1x8 or so piece in it so my 1x6 stock wouldn't work) it may move to 1x1 stock which is a lot easier to cut by hand...

My only issue is straight holes without a drill press! and I'm going to find a feesable, repeatable, method for drilling them in 1x1 stock before I'm done!
I LIKE the sign idea! Thinking well outside the box! I also like the "reprap shop" idea - perhaps one day, places like public libraries and cybercafes will have reprap booths in them...
Lord Cat, have you spotted those inexpensive drill guides they sell for hand drills? They help a lot.

One trick to use in a pinch is to get several small pieces of wood, like 3/8 inch plywood. Carefully measure and mark each block, drill them one by one and then stack them one on top of the other with glue. If you then drill through all the holes a once, the errors average out, and if forms a decent drill guide which is more accurate than wobbly free hand drilling.
Links to simple drill guides, for ideas:


About the CNC sign cutting idea... I think that could be effective approach to jump over several basic steps.

At the same time, I think if there was (or is?) a good set of plans on the RepRap Wiki, one could build a copy of Da Witch or Godzilla very quickly. Sitting down and cooking up my own set of parts and dimensions would take me a good chunk of time, instead I could jump strait to building things with the mix of tools I've got sitting around right now.
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