A snap-together RepRap? Faster, easier, and RP friendly?
July 27, 2008 06:21PM
I would like to start a discussion about and a movement toward a single fastener design that could inch us closer to a fully repRapable design. The vision, as I see it, is a single, versatile, and modular coupling mechanism that could be copied and pasted throughout the design.

Much of the time it takes to build a RepRap is spent twisting bolts with an allen wrench. As we progress to a design that contains more RepRapable parts and less steel bar, we will have the opportunity to embed in them the ability to mate and attach to other parts. Furthermore, a snap-fit design could drastically streamline the whole process of assembling and disassembling a RepRap.

Using a top-down approach, here's how I look at it:

The coupler could:

- Use a traditional beam design, but with some sort of easy-release capability (press here, and the junction releases). An example: [www.coe.uncc.edu]

- Use a twisting motion to lock the pieces together. There could be a male and female end, the male end having a bump on the side that locks-in to the female end when twisted. (Think about how a BNC connector works, but in plastic, and without the pesky conductors. [en.wikipedia.org]) One downside of this approach is it seems less scalable to heavy-duty applications. While designs like the cantilever can be used multiple times around the same interface (think two "hooks" per side of a rectangular piece, all removable by squeezing around the circumference), a design that requires a rotating motion could probably only be used once.

- Use a ratcheting type motion, like removable cable ties. Perhaps our interfacing components could have male and female cable tie-like ends at the interface, and assembly would be as easy as inserting and pulling.

- Use a bag-buckle type interface. This is an extension of the cantilever idea, but with a flatter cantilever. Check out [www.hohm.com] to see what I mean. I personally like this idea, because it seems expandable and push-release-friendly.

I am sure there are oodles of other techniques out there. The question is which of them is best suited for the RepRap design?

Here's another page for inspiration. The twist-lock seems intriguing.
[www.umei.com]

P.S.
A sister post, [forums.reprap.org], talks about a repRappable design for the diagonal posts. This would be a perfect first-application of our coupler.
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 27, 2008 09:11PM
Sounds like a great idea to me. At some point the nuts, bolts and screws will be the hardest parts to get and aside from anything else, this would eliminate most of them as they're used to connect bits together.

For me, that has already happened as I was collecting most of my parts over Christmas and the specialty nuts and bolts store was closed. I discovered that some of the different sizes are hard to come by at the mega hardware stores.
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 27, 2008 09:46PM
Interesting idea.

It should be noted that most (if not all) mechanisms that use rotary motion along the axis of the joint for locking/unlocking won't be portable to rotor shafts, etc. That is, anything that needs to rotate shouldn't be made up of pieces that are locked together in this way, as they could (possibly) come apart.

However, different methods of locking can be combined into one joint to give a more secure part. For example, if you put a pin through a pinhole in that twist-lock [www.umei.com] in such a way as to stop the piece from rotating after locked, then perhaps it would be less likely to unlock itself.

Similarly, other locking methods can be combined together to form a more secure joint. Just a thought.
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 28, 2008 02:24AM
I think that you probably could print plastic blind rivets.

Like these...
[www.plasticsfasteners.com]

This would have the benefit of being able to buy them,
and still be one less non-printable part.

They do come apart, though they're a bit harder to
get apart than they are to put in.
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 28, 2008 03:48AM
My second home computer that I got in 1983 was assembled this way :-)
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 28, 2008 04:11AM
There's always the option of interlocking slots, and a little glue to hold it. Not quite as elegant but simple and easy
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 28, 2008 02:52PM
greenarrow Wrote:
-------------------------------------------------------
> There's always the option of interlocking slots,
> and a little glue to hold it. Not quite as elegant
> but simple and easy

Or, similar to this idea, you could design a standard connection with an opening for a heating element (like a soldering iron or something) such that when you insert the heating element, the pieces melt and weld together, forming a solid joint. This could work for joints that don't need to be disassembled, seeing as the main build materials are thermoplastics.
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 28, 2008 05:12PM
I've used these things before:



They're called box rivets, I think. Sort of a ratcheting push rivet.
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 28, 2008 08:14PM
@Steve

I like it, but some kind of casing may need to be devised to keep them from twisting apart - looks like they're good at resisting tensile forces, but not torsional ones.
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 28, 2008 10:54PM
Keep the ideas coming! smiling smiley smiling smiley We should also make sure that the joint is easy to disassemble. It's nice to think that we'll put the machine together once, but unfortunately people make mistakes and sometimes parts need to be taken apart to get at other parts. smiling smiley
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 28, 2008 10:55PM
Hey Steve. I like the ratcheting push rivot thing! How are these removed? Could we attach a lever somewhere that would release it?
Ru
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 29, 2008 04:19AM
Quote

Hey Steve. I like the ratcheting push rivot thing! How are these removed?

If I recall, you can grab and pull hard. The teeth slip before they break. Course, that might not be the case in whatever material we use.

Also, these may be tricky to fabricate well, as they have lots of little overhangs. I guess you could make flat T shaped ones without any difficulty.
Re: A snap-together RepRap? Faster, easier, and RP friendly?
July 29, 2008 11:32PM
Hey guys,

If you come up with some good ideas in .stl, post them up in this thread and I'll build them using an SLS Machine to give you an idea of how well it would work. SLS is the king of RP'ing Snap fits.

The only condition is you allow me to use the design as samples for our customers. Snap fits are always quite impressive for our sales guys to show off.
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