One ring to rule them all?

[Clive S]

Had another idea and amazingly I found a CAD program I actually like, it's a miracle! It's not for everyone in fact it's probably some people' worst nightmare but it's right up my ally. Instead of using your mouse to click where you want something you type it out in a sort of programming language.
http://www.openscad.org/

I used to use openscad a few years ago for 3D printing I think then it only produced stl files also it wouldn't import much into it or output dxf etc.

[Rufe0]

Hello everyone
Wonder if I can get your opinions on this?

I think making this out of 100x100x5 tube would be too weak. It would weigh 100kg so making it thicker isn't really an option. I think 150x100x3 would flop around and generally not be very rigid. So that pretty much leaves me with the option of making it in two halfs and bolting it together. Something like this



This drawing is of 100x100x10 with 20mm connecting bits, or 25mm. Each half would weigh 77kg without connecting bits, near 100kg with them.

I'm thinking bolting it together like this, red circles are bolts.



Each connector would be welded at one end to C shapes and bolted at the other. Then they would be bolted to each other.

I don't think it would be solidly connected enough though. I think the 0.1mm better deflection gained from using the 10mm wall tube instead of 5mm would be lost in the less than solid connection between the two.

I think it would probably be fine if the cutting force is straight front to back or side to side but if it's at all diagonal then there would be all sorts of twisting and skewing forces that would ruin accuracy and rigidity.

I'm just struggling to find a way to make the thing really rigid enough and still light enough for two people to carry when disassembled.

Any ideas or thoughts? Thanks

[Rufe0]

Just realized how todo it much better than this using solid flat plate bolted together to make a custom box section, kinda like a cardboard box, don't know why I didn't think of it earlier, I've not been sleeping right....will do some drawings soon.

[Robin Hewitt]

I have always thought that the best way to make one of these beasties would be to start with a sheet of 3 mm steel and rent some time on a 2kW laser. I'd go for 3 mm because it has a bit more flex in it so you can key in a few good bends to make it super rigid

[Rufe0]

I'm going down the rabbit hole a little bit, Alumina Porcelain has a specific modulus, stiffness to weight ratio of between 4.8 and 16(imperial units). Steel is about 4.1 and aluminium isn't much better. So Alumina Porcelain is potentially 4 times as stiff per kilogram....

[Rufe0]

I have always thought that the best way to make one of these beasties would be to start with a sheet of 3 mm steel and rent some time on a 2kW laser. I'd go for 3 mm because it has a bit more flex in it so you can key in a few good bends to make it super rigid

Mmm 3mm is going to be real floppy on the straight bits though. Curves give strength yes but you can't make the whole thing a curved surface.

I'm wondering if aluminium would be better as I could use 30mm thick plates to make it up which should be fine to be tapped for 10mm bolts, so tapping into the 30mm width. Would make it a bit simpler and I think just through sheer width would resist bending at the joint.

[Rufe0]

Hello again, refining my ideas. Trying to get the thing in around 300kg total. It means using 50mm thin wall tube in some places. Trying to get the base about 100kg, the uprights about 100kg and the gantry about 100kg. I had some exact weights calculated but drawing it out again I realized I could make it 100mm narrower overall so that will be a decent weight reduction in the base atleast.

I'm thinking the base might look something like this. 50mmx3 square tube apart from where the rails connect would be 50x5. Anything thats all one colour is a welded 'frame', anything thats a different colour would be bolted together.



And the rest would look something like this.


or more like this


The footprint would be 1m x 1m and the working area would be 500mm x 500mm, which is fine.

What do you think?