First mold making - 3d printed buck

[thenated0g]

***forgot to post this here, i had posted it over in the "show us what you are working on thread"

So as i stated in the video i made 2 mistakes right at the end which messed up my resin to cloth mix. I forgot to add more resin for the final layer of my layup (peel ply) and the roller sponge needs to soak up some resin before it starts working so i had about 1/3 less resin than i expected and it dried out, plus it only has vacuum for about half the setting time. But i did get to try out the whole process and it went really well. Really happy with the ultracal30 as a mold. Its very easy to use. My mold prep consisted of 2 layers of waxing and it released very easily without any problems.
The outer layer does look ok but it is very spotty, you can see dry spots throughout, but the biggest issue is that its just not very rigid. Even the carbon doesn't feel rigid at all. I know it will add a bunch of rigidity when you have the top and bottom with all those curves glued together. But it did give me confidence that this is going to work. I can very easily see the parting line all the way around. Ill go heavier on the resin this next time and maybe add one more layer of 6oz. This was also my first time using peel ply (which you rip off afterward) and i am very pleased with the rough surface it leaves behind for gluing to later.

At first i was worried about how difficult it would be sliding such a long mold into the bags would be but i had sanding/rounded the edges off of the mold and it slid in very easily for how long it is.

Oh yeah this layup from outside inward:
1.5oz eglass
2x layers of 6oz sglass


---------------------
After looking at the materials i have on hand i am going to add some more layers of fiberglass and some wood strips in between layers to create spars. Also adding some reinforcing layers in areas where i will be creating holes, elevons, and hatches as well. So it will have about 1.5x more fiberglass overall and about 2 times more in areas where i will be cutting into the shape later.

Then after testing that to see how rigid it is i will do another piece with some colored chiffon cloth, which i have used in the past and looks amazing.
Basically it will be 1.5oz E glass on the mold and than the colored chiffon followed by the rest of the layers of cloth.

top:

Robot coordinates - circuit board - yellow Fabric | Spoonflower

Shop Robot coordinates - circuit board - yellow custom Fabric by coggon_roz_robinson for sale on Spoonflower

www.spoonflower.com

bottom:

jungle charcoal grey Fabric | Spoonflower

jungle charcoal grey custom fabric by elmira_arts for sale on Spoonflower

www.spoonflower.com

 

[thenated0g]

 

[Konrad]

Can you show us a detailed shot of your chiffon finish?

Also what is that black piece that looks like a partial spar? I didn't see any load spreaders at the ends. If it is a spar is there a reason it doesn't go full span?

 

[thenated0g]

I don't have the chiffon yet. It should be here for the next time I pull a piece from this. As far as the spar not going all the way out, it gets too tight at the ends for it to go very far it's pretty tight in there. The spar is probably way overkill. I just wanted something in the middle to stiffen that area up.

 

[Konrad]

When ending a stiffener I try to add load spreaders (extra glass or carbon cloth) to try to keep the stiffener ends from pushing through the skin as the wing flexes (inflight or on a cartwheel landing).

 

[Konrad]

I was thinking that maybe Wing helper might help. I’m thinking a spar might not be needed. But rather a shear web between the top and bottom skins. If the molds/plugs were generated in CAD I was thinking it might be easy to generate a cross sectional spline to make a shear web out balsa. Just offset the spline to take into account the skins This shear web could run full span. I think this would be better and cheaper than a partial span carbon stiffener.

 

[lonzobrown]

I've been researching two-part mold making for several years now, but at some point I realized I just got to stop reading RC group threads and just get to it and I'll make whatever mistakes I make.

I also wanted to incorporate 3D printing into this to get a better shape than something I would do by hand. So there was two options now. Do you 3D print the negative molds like rammyrc or do you 3D print the positive buck and then make molds off of that. After reading some of the troubles people have had with printing out full molds and the fact they would take a ton of plastic. I decided to go the positive buck, 3D printing and sand and finish that and then make two-part molds the old fashioned way off of that piece.

Now because I knew I could make any number of mistakes and have to start over from scratch either in the 3D printing phase or on the mold making phase, I decided to take one of my designs that I knew already flew well and then size it down much smaller, 900mm wingspan, to use less plastic and materials if it's a total waste and I have to just start over from scratch.

One thing that became immediately apparent is that my ideas for plane design drastically outpace my current fusion 360 skills. In particular, I couldn't figure out how to get my wingtips how I wanted them and so once again I just said well. This is the way it's going to be. I don't want anyone thing to start hanging me up. I want to keep going so I just made the wing tips blend over into a point. I was actually pretty happy with how they turned out once I 3D printed them.
View attachment 11110

View attachment 11105View attachment 11106View attachment 11107View attachment 11108View attachment 11109
Using my hotwire cutter, I designed up a foam version as well and cut it out of some nice rigid foam, basically just to get access to the bottom beds to have a nice perfectly shaped working area when I'm gluing and sanding and that type of stuff.

This morning I glued all the pieces together and sanded any large overhangs and then took some thick epoxy and gave a nice coating across all the top surface. This epoxy has a set time of several hours so it'll have time to ooze out and self-level and fill in some of those grooves and low spots from the 3D printing.

To be continued.

Nice information