Casting resin ????

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#1

Hi guys

I’ve got a little quandary on my hands and I thought I’d bring it to the brains trust on here :smiley:

I want to cnc machine a female mold from epoxy board. I will be making RC gliders from it , which will be bagged in mold fm glass and carbon etc and post cured at around 50’C.

The problem I have is it is 2m Span , and from nose to TE ( trailing edge of wing) is 540mm. (similar to pic Attached of smaller brother)
The wing part is thin ,but my problem arises with the centre which is at a different angle to the wing.
So if you hold the TE in a flat bench the nose of the aircraft is up in the air by 40mm or so.
Thus I need a tooling board around 80mm to 100mm thick. estimated … I will know exactly what is needed once the CAD is 100% finished.

I’ve played around with other tooling board in the past , and used necuron board on a set of female molds. I have spoken to pleanty of companies but it seem what I need no one makes.

SO… I’m going down the road of casting my own ??? Has anyone done this ?? I’ve spoken to a few companies who said aluminum fill epoxy could be good for what I need.
I need to to be polishable , I use epoxy molds with durance high gloss at the moment.
I know I won’t get that type of Finnish with casting epoxy but if I can get close and then polish the part once out it might be an option.
I would use corian or freestyle bench top solid surface , but doesn’t come thick enough.
I have a set of corian molds which are nice , and I can polish the part well.
I don’t really want to go down the MDF plug and build molds from that… To much time on this bigger project.
I rather machine something , and polish it and have one set of female molds.
I wish I could afford an aluminum set of molds ha ha

So any suggestions , or some positive and negatives would be of great help. I’m sure with the amount of knowledge on here we can come up with a direction to take.

Thank guys look forward to what you come up with :smiley:

Tim

These are gizmo 36 rc glider


Shows you size. These are 900mm wing Span.

Th

#2

I don’t understand why you want such a thick board for this wing?? Surely each side would come out of a board just 40 or 50mm thick?

You can always just glue two boards together too if needed, I think this would be far easier than casting your own.

#3

The fiber orientation on the wing looks wrong. it should be ±45º

#4

I have done experiments with corian glued together. As you can machine a ball from corian and not see the join.
BUT.
When we machined a wing from it , the angle of the airfoil is very low so there is always a point that you have 1mm think material and then the join. This is where we have had issues. It seems to work great when you are cutting on a steeper angle.

And as said , the wing is at a different angle to the main centre body. Also the body is 40mm think and at the angle is it it will end up being around 78mm from bottom of TE to the top of the nose area if your looking at a side profile.
Most of the thickness is waited.

I have though about casting a T shaped block , so the centre is thick and the wings are thin.

Tim

#5

I agree 45 is better for twist , but on a 165g with a solid cnc foam it will never twist being so light
The bottom pic is 2 layers of 100g bias plan weave an it’s impossible to twist , the top pics is 160g 48K and it feels the same. If they where hollow molded 45 is a must.:slight_smile:

Tim

#6

machine the mold oversized and then top coat with a machinable/polishable surface “epoxy surface coat, vinyl ester duratech” then remachine to net shape then polish this is commonly done in industry that is ultra sensitive to bond seems

#7

Thanks KJ.

I’ve often thought machining a foam male plug and building a epoxy/duratec mold over it.
Removing the foam and just polish the duratec. Might be an option and would cut out a lot of finnishing work on MDF plug etc

Tim

#8

Since you are willing to pay for CNC machining why not just have it machined directly from aluminium and polish?

#9

Ask your supplier for close contour paste. This is a DIY paste for making tooling board. (in the shape you like)

#10

Cost… Doing it out of a piece of 7072 aluminium would be $20,000. I agree it would be the perfect way to go.

#11

That’s what I’m going to use Herman. :slight_smile:
After some more deliberation and discussion , I’m probably going to stick with MFD plug’s and do a framed carbon and polymer clay mold with duratec high gloss surface.
all I can get local 5 mins away.

Thanks for you imput guys

Tim