Making blade from foam using a CNC foam cutter

[chinsettawong]

Dear Friends:

I just finished building a CNC foam cutter yesterday and wanted to try to cut a blade using it.  It turned out quite impressive.  

The blade was cut the way it should be except that the surface was very rough.  I think it had something to do with my temperature control on the cutting wire.  Here is a look of my machine:

The software that I am using now is a freeware and it is able to control the CNC machine to cut a twisted and tapered blade.  However the twisting angle is to be the same across the whole length of the blade.

I plan to make a set of 3 blades soon, but still can not figure what blade profile is the best for windgens.

Also I will have to cover the blade with something for reinforcement.  I am thinking of using resin and fiberglass.  I hope it will work out okay.

Wachara C.

Bangkok, Thailand.

[kitno455]

wow- that is nice. i wonder if it would work better to have a shorter wire, and cut the blades with the primary axis along their length? then you could have twist. you would need a good bit longer screws...

allan

[BigBreaker]

The profile in the picture appears to have undercamber or a concave shape on the bottom of airfoil.  I don't think you can make that with a wire drawn across the length of the blade.

[paradigmdesign]

Very nice work on the CNC machine.  Something that you might want to try, I saw someone using a pink foam, seemed to have a smoother edge than the white stuff, smaller air bubbles inside I think. The graduated-twist tapered problem, is the reason that I decided not to make one of these (that and it looked hard), though you could acheive a fairly accurate graduated-twist tapered design for a blade with one of thoes machines if you cut out many thin sections from the foam and glued them together.  That would only require only a small amount of sanding if you did the sections close enough together.

p.s. If you do figure out how to do the twist tapered design, I am interested in buying some foam airfoils off of you.

[fanman]

hey guys

 imade a prototype blade before out of foam , the blue stuff, it looked great, and then i thought heck i will just put fiberglass matt and resin on this thing, great idea bad results, the resin will melt that pretty foam blade very guickly, but i did find out that wes system epoxy wont melt foam, but it coast alot, thats all i know about that right there. good luck

[willib]

chinsettawong,

i wish someone had said this to me , when i started making my blades .

listen to me.

are you listenning?

go out and buy West systems Epoxy , and some glass mat.

West systems epoxy and glass fibers WORKS beautifully period !!

it hardens in only five mins. it could not be better!

DO NOT even bother trying polyester resin .

My discussion on what to use is just one page back..

http://www.fieldlines.com/comments/2006/2/21/181537/958?pid=3#5

also there is a product that is better than that white foam crud. it is sold as insulation and is blue , it is called extruded polystyrene , it can be had at your local home repair store , Lowes or Home Depot..

it cuts like butter , and sands even better..

[electrondady1]

i think thats a remarkable machine you've created. the surface looks not to bad. when you cover it with    EPOXY RESIN  ,  it should be all right.  you could try the blue extruded styrene as willib suggests it's higher density.

[coldspot]

SWEET_

Nice machine and great blade.

My

$0.02

Look at some 10th scale RC combat Airplane sites

We used to use brown paper bags to cover our foam wings

CHEAP, STRONG and a lot more.

And epxoy not resin.

I even just used automotive clear coat a couple times with OK results

Being that the planes only last about half a meet

That is yes they crash, a LOT.

But thats also how you win

Cutting other planes ribbon close to the tail of the plane

OK maybe a bit over

$0.02

PS: Sa-Wa-Dee

[RP]

I wonder if you could attach something to the ends of your styrene  and give it a few degrees of counter twist before you cut it.  When you release it after the cut would it return to normal with a reverse twist?

[chinsettawong]

I have been thinking about how to make different twisting angles accross the whole length.  One of the possibility is to make baldes into smaller segments and glue them together later on.  I think I will try this method first.

About fiberglassing the blade, I am thinking that I can possibly glue a layer of thin paper on the foam first then use resin and fiberglass after that.  It might work.

Wachara C.

Bangkok, Thailand

[willib]

no

NO NO !!!

It dosnt work!!

you're not listening

if west systems epoxy is hard to find in Thailand , then ANY  clear epoxy is 1000 times better than polyester resin!!

here is why ,

polyester resin has styrene monomers in it , and polystyrene foam is made from styrene ,it sinks in and bubbles up the foam .and a little bit of paper is NOT going to stop it.

if you want to try and reinvent the wheel , be my guest , but dont say i didnt warn you

[willib]

Oh , cool machine BTW,

does each side of the machine move independenly?

you are having a problem keeping the wire taught to make the twist?

here is a suggestion ,use gravity,

a weight on one side to keep the wire taught , with a bearing .

[chinsettawong]

Thanks for your advice.  Of course, I'm listening.

I'll try to find epoxy and keep away from using resin.

Wachara C.

Bangkok, Thailand

[chinsettawong]

The machine has 4 motors and they all move independently.  The wire is tie on a spring which keep it tight and straight at all time.

This machine is very easy to build.  If you are interested, take a look at www.8linx.com/cnc.  I basically copy the design from there.

Wachara C.

Bangkok, Thailand

[paradigmdesign]

While you are correct, that polyester resin eats styrafoam, clear epoxy is not nessissarly 1000 times better.  There are many benefits to using a polyester resin.  For example, most epoxy's are much more prone to damage from the sun's UV rays, and like you said, it is only workable for 5 mins(that is not long enough to glass an entire blade.  Also the epoxy's are much thicker and have a harder time being spread and throughly wetting-out the glass.  Not to mention that polyester is like 6x cheaper than epoxys.

I hope the reason you guys (williB and chinsettawong) are cutting these sections out is  to use for a positive mold, not as foam cores for turbine blades.  The foam that is used in wind turbne blades is a 2 part poar foam, it has a 8lb/cu.ft density and is very, very strong.  But you can't use that foam for molding because you can't cut it with a hot wire (too dense, and super toxic).

* http://www.fiberglasssupply.com/Product_Catalog/Pour_Foam/pour_foam.html

[chinsettawong]

Thanks for your advice.  I don't care if the foam will work on this application or not.  I'm just doing it for an experiment and fun.  

We all always have something in mind and really like to know if our ideas could work the way we think, right?  Right or wrong, let's find out.

Wachara C.

Bangkok, Thailand

[willib]

so hows it comming along?