Need help designing concrete form

[brian]

I've been asked to make a form for a table base.
The base will be about 1-1.5" thick.
I've made a scaled down version today with two layers.The pictures below show the concept.Below the red lines would be removed on the real version.
I was thinking the best way to approach this was to make the form upside down with a male & female mold out of blue SM styrofoam.
Does anyone have any tips on how to approach this.

Thanks Brian

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[jhicks]

Brian, I am just knowlegeable enough to be dangerous on hot wire foam cutting but believe if i were looking to do this, i would consider EPS foam and a manual hot wire foam cutter. Depending on how many and what tolerances are I think you could create a jig or template to follow and simply guide the hot wire cutting wire and slice through/off or carve out where you want.
Lots of low cost handles, kits, and systems to accomplsh in a simple manner all the way up to fully computer controlled systems like mark at foamcarver has up in Minneapolis area.
he would be a god advisor on this one as well.

[brian]

Jerry
I considered hot wire but due to the compound curves on the under side I ruled that method out.
I forgot to mention this will measure 24 by 36"

Thanks Brian

[Brady Watson]

Brian,
What are the dimensions of the model in XYZ?

If you can, send me the model in some 3D format & I'll see what I can do to help set it up.

-B

[brian]

Brady
The diamensions are X 42,Y 24 Z 15"
The design has changed a little from the pictures but any help to create the male and female molds would be much appreciated.
I'm hopeing to get my hands on some "Ducite" from Lafarge so I can make this about 1-1.5" thick.

Thanks Brian

[Brady Watson]

Do you have a model for me to monkey with? If so, send it on over. Even if it isn't the latest version, you'll at least get a visual on how to do it.

-B

[brian]

Thanks Brady here's the file.
The curved surface will be 1" thick from the surface down.The rest of the material below that would not be there in the actual finished model.
I was planning on making the mold so the table base was upside down(legs pointing up)it will be easier to pour that way
The file is too big for this forum so I will email it to you

Thanks Brian

[Brady Watson]

Brian,
You are going to have to do some fancy footwork in ArtCAM to get it to machine the way you want it to. By this I mean, you are going to have to slice the model from the top, and then again from the bottom, with Top slice1 being Side A, and Bottom Slice15 (if it takes 15 slices for entire model) as Side B. As with anything else, there is always more than one way to skin a cat.

This is essentially what Cut3D (and PartWorks3D) will do for you when you slice a full 3D model. In order to get all the details from the back side, specify a distance below the cut plane just shy of the base of the model. For example, the model is 15" in Z & the cut plane is centered in that 15" at the 7.5" mark. Specify an 'overcut' distance of just under the centerline height, like 7.495". This will make sure that when it slices both sides that it gets all of the undercuts.

As with any complicated model with compound undercuts, CNC isn't always the most efficient way to go about creating a mold - especially one that you plan on pouring media into. If I were planning on creating a mold for poured media, I would create 2 plugs out of foam. One that was inverted (with legs up) and one that was my relief offset 1" to the inside and made positive. I would then lay fiberglass into and over each plug and trim as necessary. Review 'Surface Casting' - http://207.234.149.99/surface/SurfaceCasting3e-500.wmv Then you will have both the inside and outside of your model. From there, assemble the inside and outside, fair and smooth and now create your multi-sided mold with flanges that meet each undercut section. Then you are ready to pour in whatever media you want.

You can also take a cross-section of the model in several places, like a boat hull, and create plywood stations. Then pull fabric over it and glass up your mold that way. For this project a fiberglass final product would probably be a whole lot easier than pouring media.

Anyway you slice it, this is a challenging project...but it isn't impossible. Hopefully I've given you some useful ideas and haven't confused you...

-B

[brian]

Thanks Brady
It will take me a while to digest this.

Brian

[btk]

Brian,

If this is going to be made of concrete and will only be 1.5" thick, then I am assuming that they are NOT going to wet-cast this, but rather hand lay-up a very very very dry concrete concrete mix. If this is the case, then you only would really need to make the outside of the mould as the inside would be hand placed and hand smoothed/troweled.

Without using large amounts of polymer add-mixtures, wetcasting something that thin is a recipe for disaster and next to impossible (unless you are using GFRC, in which case you would not need a two part mould either as the concrete and glass fibers would be sprayed into the back of the mould box).

If you are doing as a dry/hand layup situation,
you would essentially would be machining a bowl. The concrete craftsman would then hand lay the dry mixed concrete into the mould and when complete, demould the piece and wet polish the face to get rid of the orange peel effect left by the styrfoam.

Brian

[bcammack]

Personally, I'd cull out the excess waste with a hot-wire and then finish up the job with a convex Stanley Sureform tool. With regard to the ShopBot, I'm reminded of the old saying, "When all you have is a hammer, everything pretty much looks like a nail."

[brian]

I'm hopeing to get my hands on a product called Ductile.I've seen furniture made by this product less than an inch thick.They boast that it has ten times the strenght of traditional concrete.
It is self leveling and used in complex forms.I just need to find someone who will supply it in small quantities.
I don't like the idea of hot wire cutting because of the fumes it produces.

Thanks Brian

[eric_schumacher]

http://www.metropolismag.com/webimages/1337/OmerArbelChair2_514.jpg

I've seen that stuff it's called ductal. Check out this chair made of ductal. It was done for Lafarge as an example of the strength. If you can find this stuff in non bridge sized quantities let me know. I have some concrete sculpture designs I'd love to remake.

[evan]

I would love to find a source for it also... so if you find one please let us know.

Thanks & a Happy New Year to all you Botters out there.