Ultimate Rep Strap

Just for fun....



Ultimate repstrap...

A set of pdf drawings that can be cut out of acetate sheet and folded/stuck to make outline reprap parts (ie empty 3d models, a bit like card board but better) complete with holes etc for puting pins through just as if you were molding them.

Then either Mold them with molding compound (acetate stays on as permanent in situ formwork) or fill with polymorph ultra fine grains and dip in boiling water.

The advantage to molding with polymorph is if it is too distorted it can be recycled with another attempt at the drawings.

I guess the alternative is building a hand held extruder and making like the machine.

Grin

aka47

Hi aka47,

... i knew some german metall-etching companies, which make similar 3D-objects from flat metal-sheets.

Look here: [www.tamasoft.co.jp] - with the papercraft-designer you can convert a 3D-STL-object in a paper-modell for cutting and folding.

When you mill the outlines with a CNC, then you can make the same from thin aluminium-sheets, so you can fold them to 3D and infill with polyfilla, plaster or similar.

So you have a stiff and rigid ready surface and can have the stability of the infiller ...

Viktor

Hmm

Thin Aluminium now that's an idea, if thin enough you could cut it out with ordinary steel scissors or tin ships. Then bend up the bits by hand or with the aid of some simple small vice technology.

There is some soldering alloy stuff about somewhere for soldering bits of aluminum together. I remember seeing it demo'd at a couple of land rover shows I went to.

So a soldering iron plus tin snips plus (maybe a craft knife) and some casting resin plus the relevant pins & bits to put through the holes gets you a set of Darwin Parts so that the RepRap can actually be a RepStrap.

Wow that's what I call Bootstrapped, Open Source, Appropriate Technology.

When I am messing about with Robotics etc I tend to draw up sheet components in Qcad print, scissor, stick and then try out. If it works I print stick it to a sheet of thicker aluminum and then cut/bend in the manner already trialled. Drilling if necessary any holes I marked up in the cad drawing (It's easier when flat).

It's almost a shame (but not really as it's fun to see whats going off) the Darwin is all poles. The base section could have more rigidity as a thick MDF box with one side mostly cut away sqr porthole style. This could give some degree of environmental control and double as something very robust to screw all the bit's back to.

Hmm mdf base/box, origami formwork + minimum of poles etc

We'll be using an old car scissor jack next to raise/lower the platform (Z axis)

Chortle. Or is it........

aka47

Scissor Jack

Scissor Jack

Hmmm

There's an idea.....

Aren't we getting pretty close to printing some of these parts within say 30 days?

... i have to wait until January with the next massive orders, as my actual private limit is reached ...

But some infilled sheet-work is possible, so why not experiment with this idea?

As printing a complete 3D-object with high accuracy is heavy time-consumpting, so why not print only 3-layered surfaces (1 layer for the hinges, 2 additive layers for stiffness of the side-parts) or mill from thin plastic-sheets (with half-carving the hinges).

The sheet should be very fast completed, then fold to the 3D-object, glue or melt the edges together, insert tubes for throughputs and feedings and then fill with polyfilla or beton ...

The surface-finish is so good, as the bottom of first layer (or absolute perfect with milled plastic-sheets) and the edges could be finished with paste or filed after filling.

Viktor

OK

Scissor Jack

Ta da

See attached PDF for idea its simple in a picture form but complex to explain, So I drew it.

Inkscape is pretty good for quick pictures.

Another way to lift the table up and down without a stepper at each corner.

Umm unless you can get steppers with planetary gearboxes this one may benefit from being a servo.

A little movement in the x plane on the lead screw makes for a lot in the Z direction ie table top.

I think is is a multiplier, but don't know what without sitting down and working it out.

cheers

aka47

PS I like the ideal of extruding foldable parts in three layers tacticaly hinged. kewl.

Hi aka47,

... you need two synchrone scissors for good accuracy, they aren't linear and the load-stability is different in height, so the screw-drive-elevator is actually the better alternative.

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By the way: look at the appended image - i constructed a simple L-shaped test-object with holes, exported it as STL and imported and unfolded in pepakura-designer.

Actually the designer can only print the flat, maybe i can extract the lines to generate a vector-drawing for my Repstrap-mill or convert to DXF or so ...

Viktor

Paper version is kewl.

Doesn't pepakura require you to pay license before you can actually print a design ?? That was the impression I got from skimming their web site.

Anyways the results are extremely promising. If this was done in thin aluminum you wouldn't need the glue tabs as the corners could all be soldered and would be water tight then.

Ummmm You would have to choose a side to leave off as the opening to pour the filler/resin into too.

But other then the observations most excellent dude.

If we could produce a set of foldables I would'nt mind having a go at them as I have a little time at the moment but no cash. (If I could get time and cash together all at the same time I think I could be dangerous).

What is interesting is that pepakura even sorts out the tubes. (Although we would be putting real pins in here).

aka47

The welding aluminium stuff using a blowtorch is

[durafix.com]

There is someone in the UK sells it as well, the site above is in the states.

It was very popular at the land rover shows as land rovers have aluminium bodys

aka47

And available in the UK (and therefore Germany I guess)

[www.welduk.com]

I got my Tig welder from these folk (but have'nt had chance to use it yet though)

Cheers

aka47

Print - Fold - tape - Insert pins - Fill

I love it!

You could even make a fill material out of waste plastic bottles.

If someone could give me a scaled drawing that I could print out the simplest part, I'll try it.

I also thought about using a dremmel with the McWire and carving out molds using wood. However I like the print and fold idea better as it can get to more people faster.

... printing unfolds from imported STL-objects with pepakura is possible without registration, but you need it for exporting in other formats and saving your changes in the PDO-file ...

When i'm working with milling, then i didn't want the glueing supports, so i'm searching an alternative, which should outputs vector-paths (HPGL would do for example) too.

AFAIK some CAD-programs (for sure Amapi3D) are capable of unfolding 3D-objects too, some make this as bitmaps vor the UV-maps, others can output vector data or do it as normal internal geometry for working with.

Has someone more infos about such tools? Especially a CAD-system for cutting and bending housings and 3D-objects from metal-sheets?

Viktor

Print - Fold - tape - Insert pins - Fill

If waxed paper were used it could release better if you wanted to remove it afterwards. It might be necessary in this case though to scale the blocks up a touch before conversion so they are right size after the form is removed.

Or would a fraction of a mm difference on the outer edges of some items make any difference ??

I guess if the fill side was a/the side that mated with another part then it's dimension would be correct if filled to the top.

There again providing that all are out by the same tiny fraction it shouldn't matter for any of the parts that I have seen so far.

If unwaxed paper were used I guess you would have to make sure that what ever you were filling it with didn't soak into the paper too much before an initial set had taken place. You wouldn't want. I guess this is why my original suggestion was acetate sheet rather than paper.

Paper on the other hand is so much more available and above all cheap...

I guess the most critical component for anyone wanting to boot strap would be the Extruder. Paradoxically looking at the design it is arguably the part that least lends itself to this method.

I am not for one minute suggesting that we don't try, only that I expect that one to be most difficult/challenging.

On recycling bottles etc It is usual with casting resins to add into the resin some form of filler. I wonder if it is feasible to add in fine chopped bits of plastic (Old but cleaned bottles) as well/instead this should make the resin go further providing to much is'nt added. If too much is added it would de-rate the pieces mechanical characteristics. Something to experiment with I guess.

Plastic bottles are most usually (but not always) PET PolyEtheleneTerapthalate (Completely wrong spelling). AKA Polyester. As is Kevlar, Mylar, Melinex & Melinar just differing brand names and formulations. (I spent too long doing IT with ICI). The usual culprits are fizzy drinks bottles.

Print - Fold - tape - Insert pins - Fill

Hmm sounds like a strap line to me.

aka47

PS

I don't think/feel that progressing work along this front should get in the way of the folk who are wonderfully/thankfully doing precast parts for mail order.

The two are pretty much complementary, folk with more cash but less time (Those currently with a job, in a prosperous country) are unlikely to have enough time/necessity for the kitchen table approach to boot strapping.

Necessity hopefully becoming the absentee parent of successfully invented children.

aka47

On the subject of milling and folding.

Diabond looks pretty useful, this could be milled (Top layer and middle) leaving th lower aluminum layer as a hinge.

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.

... good idea and faster to engrave then solid aluminium.

I have some bigger sized 3mm thick sheets in my stock, so i'll try when the stronger millhead is there (in January or February) ...

Viktor

Hurro Viktor

If milled with a pointed mill having a 45 degree angle/cone or even a square ended bit set at 45 degrees glue placed along the inside of the fold just before folding should be enough to hold it whilst molding.

I can actually see a market here for diy repstrap items in kit form. Sheet pre milled plus resin + filler. With Templates and drawings available in Open commons or GPL for those who want to cut and score by hand or some other means.

We just need a machine that can drive a dremmel or some such.....

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.

Hmmmm

I seem to remember someone turning out potting resin in mix in the bag packs.

Sort of a plastic bag with two compartments and a clip on divider.

Two part epoxy was in the bag one part in each compartment.

Remove divider, massage bag till mixed, cut corner of bag and pour.

The surplus set in the bag and could be thrown away relatively safe.

(If you did'nt use it for something else )

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.

Looks like someone beat us to it in some ways and they are suggesting using pepakura too.

[www.instructables.com]

They look to be folding up a chassis/case using ABS and home made ABS/Acetone Weld/Glue.

Clever....

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Necessity hopefully becomes the absentee parent of successfully invented children.