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Notes
No release was used on the foil. 2 layers of foil used, burnished with paper cloth to reduce texture. In places where the foil tore, the gel coat penetrated the layers and stuck. The chassis came out, but foil stuck to the mold and was picked off.

Small void near the motor mount corner, however on the outside of the piece. Use JB weld to patch Used green world modeling epoxy- The epoxy is significantly harder than the surrounding gelcoat making sanding challenging. 2 layers of 1.5 oz chopped fiberglass mat. 3.5 oz of total gel coat used. About 1 drop to .1oz oxidizer to gelcoat. Insufficient gel coat to fully wet out the whole sheet, edges completely dry. Center of mold seems over saturated with edges unsaturated. Gelcoat unlike epoxy doesn't wick though the fiber glass. spread more evently, it will look under saturated before vacuum pulled.


Roller used to work out air bubbles between layers. Foodsaver bag did have release sprayed inside before placing mold.
Standard bag used, triple seal, light vacuum pressure, stopped when cardboard started to deform.

The resulting mold is very textured, needs a wet sand and polish. Start with 2000 grit.
Mold may need more layers of reinforcement for molding CF chassis. More layers are needed. The mold is still a bit floppy. sand the back with low grit paper, 80, then use regular fiberglass resin to add a few more coats.

I should have practiced sanding on the other chassis I had.

The patching went well. The epoxy mixed up, filled holes and hardened as expected.

The sanding was another story. There were small voids in the gel coat that became exposed when sanding. I may get some kind of advantage to degassing the resin before layup.

I also can faintly see the pattern of some fibers making me think I have taken this as thin as I could. I was using 500 grit for wet sanding.

It seems that I really should have been tying to sand the aluminum.

I am going to polish what I have done so far. I will use some clay to fill the hole in the epoxy. The clay will leave some dull spots when I make a chassis, but it will help me get to the next step.

After that I can try to fill holes with resin and a toothpick.

Your showing tremendous patience while dealing with a steep learning curve , wish I could offer any advice other than keep going as every step is getting better .

Thanks. I see so many projects on here by truly talented and experienced folks. I hope that seeing a process in progress makes people feel more confident in trying something new and not to feel discouraged if results don't come out great at first.

I'm getting better, but I am also lowering the difficulty level. The RTR gt tub is about the easiest next to a tq10 style.

I have used clay to fill in the micro holes in the mold I made. That was worked for me in the past, but it would have to be redone every mold use. If I can make this work I can try and use epoxy putty to fill the holes enough that the mold would release. The holes in the photos left as would fill with epoxy and cause a failure on making a chassis. The putty should prevent that and let me see if it would be worth trying with epoxy. I would think think any finished part would need lots of finishing. The white dots are where they clay is, the dark grey is epoxy.
Zoomed out you can see the holes are actually small.

I did a quick sanding to the back with 220 grit sandpaper and added another layer of fiberglass mat reinforcement. I switched with polyester resin to epoxy. I wetted out the dry portions of the previous work and with the new layer 4oz of resign was used with medium 3:1 hardener. I wasn't able to remove all the air bubbles from between the layers.

I tried to degass the epoxy and even with 'thin' epoxy I wasn't able to remove bubbles in my canning vacuum. The resin was just to thick.

The epoxy took longer than expected to cure up but it did once it was indoors. The mold is still too flexible to make a part on maybe 5-6 more layers would fix this .

A few days on the epoxy continued to cure and was even stiffer. 3 layers is not sufficient for a permanent mold, but the flex is good for testing.

Going to make a test chassis today.

I added release to the mold and cut down the carbon fiber to fit. For this test I will only build up 2 layers.
I am using a really thick patterned fabric for this part. It’s very thick so only 3-4 layers will be enough for a chassis. It’s going to have a distinct look. The thick fabric won’t work well for curves but the flat gt is a perfect place to try this.

Specifically this is 12.3 oz plain weave 12k carbon fiber tape. It is .022" thick. Part# FG-CARB12310
'Normal' carbon fiber would be 5.7 oz plain weave 3k .01" thick.

This time around I have a few different fabrics and weaves to try out.

I mixed up 2.6 oz of 4:1 fast hardening resin. Lated up 3 layers of the carbon fiber due to an excess of resin. I applied release to the inside of the vacuum bag and put a layer of perfed release film before sealing. The initial bag wouldn’t seal so I made this a 2 bag operation. That held vacuum.

Success!

It was challenging to remold because the flanges were not smooth. The item was not fully cured so it still had some flex.

The mold looks like it will be able to cast another The chassis needs to be trimmed but looks quite good. It is much stiffer than I expected. When it full cures over the week it will be extremely rigid.

8.7 oz original weight vs 4.2 for the untrimmed and undrilled carbon blank.

I used too much resin and would up with a lot that I will need to clean up.

I am building this up to see where improvements need to be made.

There was a lot of curl in the front of the chassis at the edges.

I had to grind down an awful lot of material to get a flat area for the bulkhead and nose mounts to be flush. A few things may have caused issues. There was too much resin, causing ripples in the finished surface.
The curves in the mold flanges made wrinkles in the on the inside of the nose.
The the notch on between the bulk head and main chassis was messed up.
The outside edges of the front chassis curled up.
Holes were too close to the edge.


Improvements to try:
Use more fabic to resin it should look 'dry' before molding.
cut relief cuts in the fabric for the front bulkhead. Maybe remove the flanges on the mold in that area
fill in the notch on molding/ sand out the notch on the mold.
The flanges on the chassis in flat spots need to be flat. Trim excess material so it doesn't rest on the flange. Cut the flanges off the mold and build new ones.

I need to make the flat area flanges wider and drill the holes before trimming. Everything fit on the front end, but If i countersink the holes they will extend beyond the edge of the chassis.

The goal with this try isn't just to make a functional chassis, but make a mold that will successfully make one without dozens of hours of finishing required.

I always thought this would be a cool thing to try. Keep working at it and soon you’ll have some really nice one off chassis and other parts.

romulus22 wrote: ↑Sun Mar 26, 2023 10:01 pm I always thought this would be a cool thing to try. Keep working at it and soon you’ll have some really nice one off chassis and other parts.

Go for it. A few tools make it easy, but to just try it out you can simply mold a big lump of clay into shape and use bondo fiberglass repair kits to make something quick.

I watched the you tube videos from easy composites for a while before I jumped in
https://www.easycomposites.co.uk/learning
It's a great way to turn a quick in-expensive build into a months long more expensive build.

Working on a ‘real’ chassis.

I think that trimming the fabric before the layup would help. So I used some spray glue to stiffen up the carbon fiber and attach some paper to the chassis to make a pattern I ran out the previous fabric so I started this one with another kind of different one this one is also a heavy duty 9oz cloth. It has an irregular pattern that creates directional stiffness.
So for this one I am alternating layering.

I used 5 layers of this 9oz fabric.
Weight: 9osy
Weave: Plain
Tow Size: 12K WARP
3K FILL
Thickness: 0.020"
Thread Count 8 x 8 per inch

This seems to be a very forgiving process.
Mistakes were made and the product still looks good. I still used too much epoxy at around 1 to 1.5 oz though due to a vacuum failure I lost pressure and didn’t get resin though all the edges.

The pre cut pieces seem to have improved the quality of the cast.

I think the mold is done after only these 2 casts. About a quarter sized piece of epoxy stuck to the mold and ripped off the chassis. I’ll let things cure it more and try cutting it down after .

Progress is sometimes figuring out what doesn't work.

The polyester tooling resin is absolutely not compatible with the vivid+ autowrap. The tooling gel causes the wrap to pull away from the object creating voids in the mold. What confuses me is that the first time I tried this it didn't happen nearly as much so it seemed viable.

I know that aluminum foil worked as a wrap so that I going to be my next attempt, after I clean up from my current mess.

Once more try on the rpm style 8090 style chassis. Armed with a bit of experience.
Wrapped in aluminum over clay. All the flat areas were built out with clay. I applied the foil with spray adhesive leading to a slight bumpy surface. I burnished down the foil with towel the wet sanded with 2000 grit sandpaper.
It’s far from the perfect finish I had with the auto wrap. I think it will be fine.
I made 1.5 oz of gel coat and used MUCH more catalyst than previously, about 45 drops. Apparently for colored gel coats 2x the catalyst is required. I added some extra because of the lower temperature. It went on thick and smooth.

I am hoping that I get an even cure without much crazing. It looks better than any of my past attempts.
it cured much more quickly than my previous attempts, a soft set in about an hour and a full hard cure overnight. I am hoping to get an hour or two to be able to add the reinforcement tonight.

There has been a recent jump on the price of resin. I went to get a quart of bondo fiberglass resin and it was nearly $30! Looks like I’ll be finishing this out with epoxy.