[11bravo]

Wasn't sure where to post this.
I build and fly high power amateur rockets and am in the process of building an all/mostly carbon fiber rocket.
I need to make a male plug from which to make a female mould from which to make the nosecone.
Attached is a zipped folder with about all the information I can think of in regards as to what I need.
It would be one half of the nose cone split lengthwise, similar to what is shown in the Alibre file; the shape of the actual nose cone in that file is NOT correct however.
Nor is the shape in the AutoCad file.
They do show the need for a rear shoulder portion.
I do not know how to import a series of points or an equation into Alibre so there are a couple of files from which the information can be found.

Points found in:
Nosecone.lst X y values.xls
Equation found in:
The Von Kármán Nose Cone.pdf

The surface would have to be really quite smooth.
In the long run I would actually need two identical halves.
Not sure what to have them made out of though.
I have some maple glued up but thought of the HDPE(UHMV) today.
Have considered aluminum.
These would be mounted to a flat piece of something and be covered with a surface coat epoxy and some fiberglass cloth to make the mould.
When cured, the mould will be pulled off and these pieces will be set aside.
They will not be exposed to elevated temps other than the heat of the curing epoxy.

Anyone think they could make one out of a 2”x4” to see how well they turn out before committing to the fancier materials?
If so, shoot me a quote for your time and material and we’ll see if we can do business.

Thanks,

Greg

[SORCHEROR]

why not just make the mold out of aluminum?instead of epoxy and glass

[11bravo]

I don't have a way to make an aluminum mold, although someone here might.
Also, I want to learn/practice that method of mould making.

[shibi]

I don't have a way to make an aluminum mold, although someone here might.
Also, I want to learn/practice that method of mould making.

1. What type of carbon fiber/grpahiite are you using?
2. What is the target cure temperature of your epoxy?
3. Are you using an outer mold in addition to the plug? or are you vacuum bagging it.

You have to be really careful with a solid aluminum plug. The thermal expansion of aluminum is a whole lot more than carbon fiber and typically in the cure cycle the aluminum plug may expand more than the carbon fiber, leading to excessive residual stress.

Off and on you'll get a part that looks nice on the outside but the graphite under the surface graphite fabric layers are all broken in bits due to the expansion of the plug during cure.

-S

[11bravo]

mrphyyber, shibi, and anyone else-
Thing is, I want the shape to be pretty close to exact and a wood lathe run by hand just isn't going to be that close.
Second, to turn it I would not only need to use the "split turn" techinque, just by the nature of the nose cone it would need to be turned at the far end without support (cut free of the tailstock).
The guys I know that use a CNC turning center are a little hesitant to try that.

For the method I am using, the plug will need to be exactly the size and shape of the finished nose cone.
And the plug will only be used to make the mould, which cures at room temp, so the plug will not be used during elevated temp curing so it's thermal expansion is not an issue.
See-

http://www.jcrocket.com/nike-asp.shtml

and scroll almost all the way down.
This is essentially the method I will be using but I plan on modifying it a bit and use two halves instead of making a cone, messing around trying to get a plate cut to fit the cone and then making two female moulds off of that.
Instead, mount the two halves to a flat plate and make a double mould in one shot off of that.
Using the Epoxy Surface Coat about 2/3 the way down this page-

http://www.fibreglast.com/showproduc...0Resins-5.html

to make it.
Them lay up the cone halves;
Outer surface and third layer will be some twill that I have; do not remember the weight right off the top of my head.
Middle layer will be unidirectional CF oriented along the length of the cone.

I haven't used this method myself so will probably make a fiberglass version or two before trying the CF; give myself some less expensive practice first.

Thanks guys.

Greg

[elgamiller]

just by the nature of the nose cone it would need to be turned at the far end without support (cut free of the tailstock).
The guys I know that use a CNC turning center are a little hesitant to try that.

why not have a false centre on the end for the roughing out op, then hold on the od to machine the ogive.

Paddy

[mrphyyber]

Wasn't sure where to post this.
I build and fly high power amateur rockets and am in the process of building an all/mostly carbon fiber rocket.
I need to make a male plug from which to make a female mould from which to make the nosecone.
Attached is a zipped folder with about all the information I can think of in regards as to what I need.
It would be one half of the nose cone split lengthwise, similar to what is shown in the Alibre file; the shape of the actual nose cone in that file is NOT correct however.
Nor is the shape in the AutoCad file.
They do show the need for a rear shoulder portion.
I do not know how to import a series of points or an equation into Alibre so there are a couple of files from which the information can be found.

Points found in:
Nosecone.lst X y values.xls
Equation found in:
The Von Kármán Nose Cone.pdf

The surface would have to be really quite smooth.
In the long run I would actually need two identical halves.
Not sure what to have them made out of though.
I have some maple glued up but thought of the HDPE(UHMV) today.
Have considered aluminum.
These would be mounted to a flat piece of something and be covered with a surface coat epoxy and some fiberglass cloth to make the mould.
When cured, the mould will be pulled off and these pieces will be set aside.
They will not be exposed to elevated temps other than the heat of the curing epoxy.

Anyone think they could make one out of a 2”x4” to see how well they turn out before committing to the fancier materials?
If so, shoot me a quote for your time and material and we’ll see if we can do business.

Thanks,

Greg

The easiest/cheapest method would be to find someone local that has a wood or metal lathe. Turning the part would insure it is symmetrical. When you dimension the plug make sure you take into consideration the thickness of the finished product. The plug will have to be under cut to get the finished part the correct size. Once you have a plug, I recommend using casting epoxy to make the mold. It is inexpensive and relatively easy to use. The mold should be 3 piece, 2 outer halves and a plug to insure uniform thickness.