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Shytalk

Cardboard Cutout Dome - Basis For A Plug?

58 posts in this topic

i know there are lots and lots of whiz kids out there that are up to this task!

one of the main drawbacks of making a dome is making the plug first, so i thought if someone could make a template that can be printed onto a4 and then that in turn can be stuck to some thick card then cut out and folded into a slightly smaller dome former that will need minimal filling to get to the dome plug shape...

does that sound sensible :unsure:



i kinda mean something like this.

post-796-1173467504_thumb.jpg


but about 10mm smaller than the finished dome plug.


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The problem I see with folding a shape into a dome plug base is that it has no support underneath and will probably collapse when you make the dome on top of it. If you are making a full size dome and do not wish to do the traditional plaster method (built up with boards and plaster slopped on), there is an alternative. First trace the outline of half of the dome onto some wood and cut it out. Repeat several times. Attach the cross-sections into a "flower" design - this will be the rib cage of plug. See illustration below:

post-130-1173471518_thumb.jpg

From here you have two options: One - attach large slabs of foam (not spongy - very solid foam [cannot remember technical name at present]) into the rib cage with car body filler. The foam must rise above the ribs. Once solid use a plane to trim the foam down the ribs using a plane so that it follows the contours of the dome. The plug will last a long time (more so if it is sealed with something).

post-130-1173473266_thumb.jpg

Two - alternatively affix foam slabs well below the edge of the ribs and build up with plaster. The rib system with car body filler and solid foam (must not squish or bend at all) produces a very strong plug. If you are doing a scale build, do the same thing except use cardboard for the ribs and plasticine for the other materials. The rib method I find gives a suitably reusable plug and is very strong (I have used it before) - I am not sure whether or not the time taken is more or less, but you do not have the problem of the plug drying out (plaster) or collapsing (foldable template).

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thanks red

Alan used a similar method to the one you have described here http://www.projectdalek.com/i...ost&p=27998

but i was thinking of making a classic dome by having a card dome inside then skimming that (with a former) with lightweight filler then when that has set doing the last 3 or 4 mil with a resin based filler... it should be strong enough to use as a dome by itself or to be used as a plug if required ...

its worth a try!! and it should be pretty cheap to produce.

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I seem to recall that domes, even made of card, are very strong shapes. Good idea Gary. Who's going to take this further?

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Strength is indeed the key here. Maybe a card dome made from separate hexagons and pentagons is in order (with tabs glued or stapled on the inside). We'd have to ignore the chamfer and the bottom row would need trimming.

For an idea of what I mean, think one of two things...

1, a classic leather football or 2, a Carbon 60 molecule.

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yes thats what i was thinking of!

ah! but what size hexagons would be needed to assemble a dome that is 10mm smaller than the dimensions of the classic dome?

here are a few examples of hex domes http://hexdome.com/links/index.html

and you can even make domes from simple geometric shapes like triangles too.

post-796-1173512859_thumb.jpg

and i will be more than happy to give it a try..

i am going to start on the dome for my next build (i have far too many bits left over from this build not to build another) :P

but dont tell the missus :unsure:

i think i will have to wine and dine her a bit before i break that to her :lol:

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tut! after reading my own post (something i try not to do) it only makes me realise what s**t i talk sometimes.

i have noticed that on the site i linked to in my last post ... about half way down the page there are links to "dome software"... i think that could be of assistance to someone.

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After a lot of maths I have managed to make you a template:

post-130-1173523513_thumb.jpg

You will need 16 of these printed (1:1 scale so slightly bigger than A4 - might have to use A3).

The dome will be slightly blocky due to limitations, you will use have to use more filler. The quad at the bottom of the of the main triangle is the champfer surface. All above this should curve. If you wish for a higher number of slices for your dome plug, please ask and I will re-calculate the numbers and draw a new one. I chose 16 as it easier to put together, however you may wish for a 64 slice version for greater strength. I did the template as a triangular strip as the maths for producing a template in the form of a geosphere is trickier. If you wish for a geosphere than ask and I will re-calculate.

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post-796-1173532465.gif

wow.. thanks

now all i need is access to an a3 printer.. im sure i have seen one at work somewhere

thankyou

Edited by shytalk
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Hi Shytalk,Redgeneral :)

Firstly thanks 4 the template you put up Redgeneral ,of course i had to print out 16 copies & try them out :D...

I just printed them out on A4 (looks like a dalek dome :D:o ) i was just wondering guys have either of you tried this yet ?, if you have 16 pieces for a slightly undersize plug/mould,would 17 or 18 pieces put together give you a full scale dalek dome? ....

After patiently cutting & putting together 16 panels you have realy given me food 4 thought Redgeneral & Shytalk,i am thinking about using stiff cardboard or even tin/Aluminium next,maybe even plastic panels could work,i am always looking 4 a easier quicker way than plaster & then fibre glass method,thanx guys 4 idea :)

Jeff

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hi

i am in the process of trying this (thanks again Ian for printing and delivering the segments) so far in between everything else i have stuck the paper templates to thick card and cut out about half of the segments... also i have made both the 4mm undersize former and the final size former out of perspex .... hopefully this weekend i will have got a bit further ... i will post here with pics if i do... in the meanwhile if anyone else is at a loose end and fancies trying it feel welcome :D

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Jeff, using 17 or 18 will result in a classic dome that is far too wide at the base and still no taller (also it won't fit together). The template was designed so that that it would be just under size for the dome in all directions so that a surface could be made on it. It was also desined to use only 16.

The templates are just over the size of an A4 - it is important that you do not shrink them down to fit on an A4. It makes the dome even smaller and there can be issues with shrinkage (distortion).

If you wanted to build a dome out of only templates on a material like aluminium, I would have to recalculate and rebuild the template so that it was full sized and have many more divisions than just sixteen (probably > 64). Even then you would have to add curvature to it with a hammer to get it perfect.

Garry (Shytalk), I hope everything goes well this weekend with the dome making. If you encounter problems or if you want the dome to be more defined (more segments), then contact me and I will make any adjustment you desire. Be aware the maths is tricky and the drawing takes time, so I might not get back to you right away (hopefuly next day at the latest).

If you could post pics of the construction, then it should help others who might be contemplating the using same method.

Good luck!

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Hi folks

Garry...

Only too glad to glad to help. Have Tardis will travel.

I was very tempted to run a second batch and try them myself, may still do that later.

RedGeneral

Yes, 3D geometry is tricky stuff - I never really mastered it so thanks for creating the template B)

You can actually get 2 onto a sheet of A3 paper if you arrange / print them "top and tail" next to each other :)

16 Panel should be OK to support a lightweight coating and you could temporarily fit make a hexadecagonal :blink: base plate and stuff it with something like styrene beads / packaging thingies if you were worried about it distorting.

I suspect that using too many more than sixteen segments, whilst giving a smoother initial curvature, could lead to a risk of assembly errors

I had wondered about the geodesic approach but you're back with 3D geometry and some fiddly joints

Segments... mmm... now where did I put that Chocolate Orange :lol:

Ian

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I dont know if you've seen it or not but the new DWA comic has a build your own dalek "hat" using a hanging basket liner.

I did some research and discovered they come in multiple sizes. No even if it was a a start of to renforce something you've already done, might be worth looking at.

In addition with regards the frame method suggested for support, how about usig a hanging basket? I know it sounds weird but have a look on ebay there are loads, and you'll get the drift of where I'm coming from

Good luck

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Hi Redgeneral :)

Thanks 4 that ,as i said Food 4 thought very much so :D .....

My thinking was along these lines of getting the cut out card/tin/plastic panels very close to a full scale dome

then coat it with something 2 build it up 4 size/strength/smoothness,it is a road i shall go down just 2 see eh

either that or it's back to the Wok with flared bottom tin colar idea hehe :D

Jeff

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