First mold making - 3d printed buck

[warhawker]

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.
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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.

How is your plank coming? It looks to be a nice design.

 

[thenated0g]

Going to prep the mold to do the second half today.

 

[thenated0g]

Success

 

[Wayne]

That looks a ton better than my first mold!!

Is it mold or mould?

To me making mold is really easy.. I prefer to start with a block of old cheese. LOL

 

[thenated0g]

"Mold and mould are alternative spellings of the same word, but mold is an American form, while mould is popular as a British spelling. Both can mean a furry growth of fungal hyphae; soft, loose earth; a hollow container used to give shape; or a distinctive style, form, or character"

 

[thenated0g]

Being that my first big mold was so easy it got me thinking about what else i could do with it. 3d printing material is not strong enough to withstand vacuum bagging but it can be used to make a nice mold, so made up this shape in fusion360. The idea being that i can fill it with ultracal 30, remove the plastic, and use the produced part as a vacuum bag mold for fiberglass servo covers.



So basically a piece of concrete that has this shape for laying in fiberglass/epoxy:

 

[Hank GB Z]

Looks good. I never worked with vacuum bagging but I did a fair amount of mold making in Art classes. It was always fun to crack the mold open and see the product. Even the failed ones were always interesting.

Hank

 

[thenated0g]

@Hank GB Z Another option instead of vacuum bagging down to this mold would be to line the inside area where you want fiberglass, with masking tape, than build another form on top and pour a top part of the mold. You would have a 2 part mold creating pressure on the fiberglass where the tape was. No vacuum needed.

 

[rcsoar4fun]

Looking good. One quick comment, I *THINK* Ultracal says to mix by hand and not mechanical means. IIRC it seems to introduce heat and speed up curing.

Of course, I have done it.

 

[thenated0g]

@rcsoar4fun Yeah their seems to be multiple pdf instruction sheets. "most" say 100/38 mix by weight but a couple have a different amount. A few of them did say to use mechanical tool for the finest mix. I know you can also adjust the set time by the temp of water you add.

 

[Hawaii Sloper]

That looks a ton better than my first mold!!

Is it mold or mould?

To me making mold is really easy.. I prefer to start with a block of old cheese. LOL

Lol Wayne, I asked him the exact same question last week.
Kelly

 

[Hawaii Sloper]

@Hank GB Z Another option instead of vacuum bagging down to this mold would be to line the inside area where you want fiberglass, with masking tape, than build another form on top and pour a top part of the mold. You would have a 2 part mold creating pressure on the fiberglass where the tape was. No vacuum needed.

Could you simply 3D print both sides of that with a very small void built in. No infill on the print. Then just lay in your material and put the top form on and clamp it.
Kelly

 

[thenated0g]

You definitely could. But going 100% infill would take a ton of time....a couple weeks probably to print and this much solid plastic would probably be $100 worth of plastic at least. PLA has a psi rating of like 7500 i think but i think that is for solid material, i dont know what 3d printed layers of pla would do under full vacuum pressure.

 

[Wayne]

I have seen a few people on youtube do just such experiments. Some with success, some without. Some of these were for composite work, some were for forging/casting or stamping.

Recently saw a video with a guy that was working on making carbon structures for hang gliders. He was using some high tech methods and prepreg carbon. Results were really good compared to some others I have seen. The guy has clearly be working on this for a long time. I'll see if I can locate his video as he has some cool methods he had come up with.

 

[thenated0g]

Got some 1.5oz glass coming for my outer layer. Ill try 2x layers of 4oz-s glass inside that and see how rigid it is. Also got my T-88 epoxy @Doc James Hammond . It was actually not bad on price. $27 for 16oz.

 

[Doc James Hammond]

Mike Francies - ex rocket glider world champion and my good friend, has ALWAYS used pre-preg for his models and they are very very impressive both in design and construction. Right now he is designing a monster sized GPS model using the same techniques. It's "different" to put it mildly but you do get the most predictable and controllable strength to weight ratio that is possible by using pre-preg.

As I mentioned, I have used "epoxy concrete" many times for making small propellor moulds no more than 10" in length, never larger I have to admit, and that method produced a really hard, durable, polished surface. Its harder than tooling gelcoat. I got this wheeze from friends in Russia, who as you can imagine, years ago were the masters of improvisation - they had to be.

Actually we often use "Poraver" mixed with epoxy for backfilling large Moulds. Poraver is a lightweight granular compound similar to Volcanic Pumice that you often find in plant pots. It keeps the mould rigid and stable but you have to provide hard points for clamping as the compound, even when encased in epoxy, is not that hard. But it will turn a hundred pound mould into a fifty pound version.

I have a lot of experience in moulding, since the early '70's in fact but gained exactly as per this thread simply by trying out ideas that came to me, mainly when I am sitting on the big white throne. I now have a few really good ones that I'm going to test in the upcoming months once I finally find a place to put my CNC machine. If my new stuff works - its nothing that scientifc, all in the "heck why didn't I think of that before" category - then I will be happy indeed as it will fractionalize my mould costs and revolutionize the production speeds, and these are things I like.

I'm really interested in this thread actually because its pretty innovative and also because its headed into hitherto uncharted waters.

Love it!

Doc.

 

[Konrad]

Along with learning to make a mold one needs to learn how to lay up the part.

These are more to offer encouragement rather than to embarrass myself. This is the first fuselage out of my 1/4 midget racer (0.15cid) Stinger/Sweet Pea. This was done in the late 70's. I think this shows every possible mistake other than negative drafts and chopped glass. One positive was that I used epoxy.

Later fuselage only weighed half as much.

 

[Doc James Hammond]

Along with learning to make a mold one needs to learn how to lay up the part.

These are more to offer encouragement rather than to embarrass myself. This is the first fuselage out of my 1/4 midget racer (0.15cid) Stinger/Sweet Pea. This was done in the late 70's. I think this shows every possible mistake other than negative drafts and chopped glass. One positive was that I used epoxy.

Later fuselage only weighed half as much.

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Don't you just love the way that resin ages - it "amberfies"

I always did and still do out of habit, lay up the first one heavier than really needed (by now I pretty much know what layup is needed and where) as years ago the incidence of plug destruction when making the moulds was pretty high. The first out of the mould could always be used as a spare plug in case of mouding accidents.

That fuse is PDG for an early effort though.

Doc.

 

[Konrad]

Thanks Doc, but the photo hides a multiple of sins. I'll go into detail when I compare this with the Axle fuselage (a soon to be thread).

 

[Doc James Hammond]

Thanks Doc, but the photo hides a multiple of sins. I'll go into detail when I compare this with the Axle fuselage (a soon to be thread).

Aha...th Axle as I remember did not have a good fuselage at all. Mine was made from polyester and was flimsy to say the least.

Doc.