Any idea's for my project?

General Composites Discussions Composites Talk
#1

I have this big screen tv that I really want a stand for and unfortunately since no larger tv’s are made any more there is no stand I can find for the life of me that is 30" deep to support it’s size. There is a stock stand but after 2 years of searching no luck, it is a discontinued model after dlp was fazed out. Can anyone help me out on how to get started? From my research it looks like a foam or wood core would be the best(easiest) option. Was thinking of a simple design, a base board then 5 large poles like the picture below.
My questions

[ol]
[li]How would it look with just carbon fiber wrapped around the cores without using the vacuum method?[/li][li]If I sand and then paint it will it be perfectly flat?[/li][li]The tv is 250 lbs, would a foam core approach be strong enough?[/li][/ol]

#2

I think it would look cool. Design is part preference part function. You could probably do without the center post if you wanted a more usable space in the middle. You could add a shelf or two if you wanted space for devices. As for strength, you can make it as strong as you need it to bee. Weight wont’ be much of an issue for a piece of furniture. I’ve done some experimenting with cardboard tube wrapped in carbon and made some incredibly strong pieces, especially in the direction of the length. Plus the cardboard tube i used was fairly rigid and allowed for the use of shrink wrap tape. I did those wet layup with polyester and they seemed to be pretty nice. If you wrap them nice you can minimize sanding and finishing. The top could be a piece of wood, which is probably easier to work with than foam for a beginning project. MDF is easy to work with and stable. As for flatness… I’m sure it’d be fine for a tv. If you do the table separate and just laminate it first for strength and see how it looks, then if your not satisfied with the fibers, sand it and laminate a nice piece of twill (or whatever your preference is) on top and keep it super straight and clean. After that cures light sand it to even it out but not sanding into the fibers, then coat with resin, sand, coat… maybe two or three times until you’re satisfied. Then sand it down to like 600-800grit or so, keep going if you want, then polish and it’d look great. make the legs, attach by using some carbon tape or cloth, the tape is easier to work with for bonding and looks cleaner.

Sounds like a good project. I’ve been wanting to do something like this myself.

#3

You have a lot of options as far as construction goes. A lot depends on what you are willing to go through to put this thing together.

If the weight of the TV is bearing on or near the ends of the panel (over the columns), then you most likely wouldn’t need the center support. The columns could be store bought carbon tubes or something wrapped with carbon (or any other material for that matter). Wood dowels, cardboard tubes, etc could be used to create the shape.

The panels could be made of wood or, as suggested by Sammymatik, MDF. Foam can create a light part but there is extra work involved. If the carbon is just for cosmetics, the way I would go about is somewhat like building a surfboard. Cover the bottom of an MDF panel and let that cure. Once cured, flip it over and route the top edge with a roundover bit. Cover the top and down the sides. Squeegee off the resin which will also remove the air under the material (if you do it right). Let that cure and then trim the overhang. Hot coat the surface to fill the weave. A second hotcoat, this time with wax or other surfacing agent (if you use polyester resin). Then sand and polish.

#4

Ok starting to sound more doable. I am really liking a foam core however due to it being a whole lot lighter. I can get large sheets of foam easily and maybe use some plastic tubes for the poles. The tv is 250lbs, I would hate to have the base break and damage the tv, would it be strong enough? It seems even with the strength of carbon fiber with an area of around 60"x30" would it bend/bow in the middle? Maybe if I cut out a middle section(s) of the foam and connect/wrap the top and bottom carbon fiber?

#5

I would not bother connecting the skins, definately not in the middle. (shear loads are highest at the sides, and even then, 250 lbs is hard to lift, but in basics it is nothing.)

Get your core thick enough, that is about the only factor influencing bending properties.

If you want the shelf to look thin, chamfer the edges.

#6

Ok sounds good. The base on the tv is smaller then the actual width of the screen so there will be 10" on each side not supported by the tv base. Using the foam core how many layers of carbon fiber would you recommend? I currently have a yard of the link below. I wasn’t thinking about the cost, about $40 per layer based on the entire area I will need for each shelf! Is there a cheaper option, like maybe using kevlar then carbon on top? Or can you recommend anywhere with cheaper carbon fiber cloth?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=121264794096

#7

Kevlar won’t be cheaper… U can do glass. Or just use some wood that already is strong and laminate it with carbon just for the looks.

If u want a fully composite structure you could also do a two ply surface with a rib structue underneath for rigidity… I could draw a picture of what mean. But it would be a bit more work and probably star moving into dry layup and vacuum infusion. It would be ridiculously light and strong.

#8

Not to insult you but you don’t sound like you know a lot about composites. Just to give you some idea of the strength and stiffness that can be achieve, I’ll use one of my companies products as an example. It’s an underground utility vault. Basically, it is a composite box. The dimensions of the base are 54" long x 37" wide x 36" tall with two lids set into the top.

Part of the criteria for the vault is that it has to pass several rigorous tests. One of the tests is called a horizontal cover test. The unit is placed in a test fixture in such a way that a hydraulic press can act upon it. The unit is loaded to 15,000 lbs ten times (design load). We measure for deflection under load and it can’t deflect more than 0.500" or it fails the test. The force is applied through a ten inch square steel plate centered between the two lids. After passing the design test, the unit must withstand a load test of 22,500 lbs without breaking. This unit passed both portions of the test.

The wall thickness of the base is 0.250". The lids are hollow. The top and bottom plates of the lids are 0.250" thick and they are tied together with four 0.250" thick hat section ribs. This entire product is made with E-glass and iso polyester resin. Nothing exotic. I hope that gives you some idea of the structural value of composites. Even a minimal amount of material, if designed and used correctly would not be phased by 250 lbs.

#9

Yes I know almost nothing other then some small projects I have done with epoxy resin. Just really want a place to put my dvd player, cable box, games… LOL. Maybe it is best to start with cheaper materials and just create one of the shelves. Is there any material I can use and keep it under $75 for one shelf, start with that as a beginners project. I can just ditch the carbon fiber approach and get it painted at a nearby shop if it works out.

#10

Roger this sounds very interesting but hard to imagine. my background in architecture and cars has me thinking of this box as some mixture of waffle slabs and or floor pans in a car is this in the ballpark?

#11

Pauls325,

There is some special geometry built into the unit. The lid skins are separated by 2.5" with the aforementioned ribs acting as ties between the top and bottom plates. I’ve included a picture that shows a portion of the unit in the test fixture. As can be seen in the photo, there are undulations in the walls of the box that create stiffness through shape. The side walls are just a single laminate, 0.250 thick. No cores, no additional stiffeners (other than the molded shape).

The force from the ram acts through the load cell and steel plates. It is a tremendous load, and quite frankly, I wasn’t certain we’d acheive the desired result but after several iterations of the product we were able to pass all the required tests.

As I said in my previous post, I just threw that example out as a testament to what can be done with composites. I’ve noticed, on this and several other forums I visit, that we sometimes go overboard with the things we are trying to produce. Sometimes simpler is better.

#12

So what in the world is that box used for?

#13

They are basically used as very large junction boxes for the fiber optic, telcom, electric industries, etc. Cables are brought in underground and joined or rerouted from the vault. You’ve probably walked over them a thousand times in the sidewalk and never noticed them. Most are made of polymer concrete but we went a different route with all composite.

The only thing you see is the lid and the uppermost surface of the box when it is installed.

#14

Oh yea, I think I have seen something like that before.