Making a carbon fiber rc10t chassis the Competent way

[JosephS]

It’s been about long enough since my last chassis. Since I ordered my sons rc10t re-releases I thought I should make some chassis for them.

I seem to be getting better year over year. Hopefully I can make something meaningful to them. As well if the tooling comes out well I’ll have my oldest make a chassis.

I’ll re-read my previous threads but I already know I need to build new tooling to make a quality chassis.

I am fully sacrificing a nose plate as well as well as chassis that was in good condition to begin with.

This is of course to put off the current build even further. I should be building an edinger I collected parts for years and can finally start on. So here is what I did instead

Sanded to get things flatter

Sits flat on the tile

Using bondo and release

Previous attempt notes here
https://www.rc10talk.com/viewtopic.php?p=540329#p540329

Relevant Notes here
https://www.rc10talk.com/viewtopic.php?f=113&t=48258

The T3 chassis at the end of this thread
https://www.rc10talk.com/viewtopic.php?t=47048&start=60

turned out well and fixed a few issues I was having with the April build. It was a good runner without being overbuild. Did well considering the steel pole I ran it into a full throttle.
though this was a direct pull and not cast from tooling.

Looks like the resin ratio should be less than 1:1
I never solved the issues with wrinkles in cast parts, though on the 2 part made from direct pulls the inside was smooth. I think the wrinkles are partly caused by excess resin.
The wrinkles make the part NG since the finishing is excessive.

I don't have any gelcoat. Given the summer temps. I am not sure that I can use it without waiting for fall.

8 layers of plain weave 3k 5.7 oz fabric should be about 2.1mm thick
Switching to west system from US composite resin. I am also switching to a ultra slow cure resin. It is supposed to be more rigid on full cure than the faster set ones.

[JosephS]

Nothing shows off what you missed in finish better than clear coat.

Takeaway
Spotting compound is only for the smallest holes

I think I made good progress. The chassis is flat, the area between the nose plate and the chassis are filled.

I also evened out the sides so the metal lip is smooth.


The clear coat should provide a mirror smooth surface for the tooling.

[JosephS]

Mounting up the tool to an acrylic blank
And waxing

Release

• 2 coats of clear Eastwood 2k clear
• 6 paste wax
• 3 coats of man’s 2300

Build Up
Clay was used to fill the nose and tail as well as to form a bead around the chassis

The width of the nose and tail were widened to that the tooling would not curl or round in those areas

The height of the wall was increased with clay to reduce rounding near the top of the chassis.

The rear bulkhead stay has been a challenge to mold and will continue to be. May just build a wide bulkhead and use shim/washers to build the gap.

[JosephS]

I am out of gel coat and will try using the remaining epoxy I have from my previous batch as a surface coat that will be backed by satin weave fiber glass

Coats will be .4 oz resin .1 oz hardener

Will be applied by brush


This was not successful. I was out of vacuum bagging materiel. Then I decided to use some clay to hold the sides down, completely forgetting that other times I had a release film between the clay and the resin.

I'll have to see if anything comes out of this.

Results
The Clay pulled away but release film would be better
Epoxy is a fine surface material for a few pulls

[JosephS]

Have not been documenting,

Technique
This technique seems ok for my skill level. I cast what I am calling a fiberglass slipper. It conforms to the surface well, but is still thin and flexible so it can demold without cracking like a stiffer mold would. I then make sure I can demold it, then reinforce it.

Resin
resin west 105 the west resin is slower setting and helpful
mixing 5ml epoxy 1ml hardener

Getting the fiberglass to adhere to the side is challenging


Clean Up
cleaning brushes with alcohol hand sanitizer works and allows reuse.


Vacuum Bagging
I can not vacuum bag this material. it consistently punctures the bag, even 2 layers
The square edges from the backing likely caused this

Reinforcement
I went and reinforced the sides of the chassis with additional layers of fiber glass.
The side reinforcement worked but filled in some of the mold gaps with resin.

I used a scrap of carbon fiber that I used on one of the sides. It is exceptionally more rigid than fiberglass. This was wet layed and roughly conforms to the sides of the chassis.



After the sides set I have added a nose to tail wide carbon fiber reinforcement on the outside. Single layer of 3k carbon fiber that are edge scraps. Slightly to wide on the nose section. Since I can't vacuum I placed the chassis flat on a ceramic tile. I added a round support in the tail with foil faced clay. I did the same for the nose. I noticed the chassis was not resting fully flat. I added a 10# weight to the center to keep enough pressure to make the mold flat to the chassis.

I am hoping to keep voids to a minimum so that the mold remains still when I cast in it. I want to retain the straightness I worked to create.
I am going to use carbon fiber for mold reinforcement, It is more expensive but seems to what I should be using at my skill level.

I have concerns the cast I made will deform if I try and cast from it.



Mold
I am going to attempt to make a new buck from this mold using bondo. The idea is that it is hard enough to machine and smooth enough to surface. I should be able to shape and sand the piece enough that it can be vacuum bagged without breaking the bag. As well it should be strong enough that it doesn't deform under the vacuum pressure.

This is a whole lot of effort to avoid using MDF . By the time I'm done with the bondo, reinforcement and making a new tool from the bondo piece I could have paid for the tools needed to work mdf.

[JosephS]

Used Bondo to make new chassis tool

Release
Didn't document

Resin
Bondo Kicks too fast
First batch of bondo and it kicked before got it off the board.
It’s over 100 degrees.

I mixed the bondo in the mold.
This didn't work well creating spots of raw resin

I was able to demold the bondo and there were several spots of completely unmixed bondo.

Results
The overall surface is good quality. It seems I could cast out of this.

For what it’s worth the mold didn’t sustain any damage

Once this cures over night I’ll fill in the surface spots and see how to reinforce it.

I am thinking plaster…

[JosephS]

The bondo has cures as much as it will.

I needed to fill the hollowed out portion of the blank.

I used 50/50 5 minute quickset and. Quick Crete. This should make any truck double fast.




Hopefully this combo cures as opposed to a soft set. I wanted the quickset to make a finer face on the piece.

[JosephS]

Clayed up to the board and starting to apply release wax.

Hopeful this will make a good mold.

[JosephS]

For mold making tomorrow
3 payers of paste wax applied
1 layer of mans 200 wax

Need to apply
1 more layer of mans 200
2 layers of mans 2300

do NOT forget to put release on BOTTOM of mold

Spray release on bag.

Coat mold with 1 layer of epoxy and let set till tacky
use alcohol to clean brushes

follow with next coat of epoxy then reinforcement


Using chopped fiberglass as primary mold material.
Back nose and tail sections with carbon fabric scraps stiffness is required and chopped mat can't make enough.


Follow up chopped mat with woven fibers .prevents fiberglass splinters from forming.
Cut fabric in strips to conform to edges. Chopped mat will bridge and gaps.




Parts will need vacuum, glass fiber does not conform to shapes



Will need breather under backing board to make sure edges don't poke hole in bag
Will need release film and breather over top of mold.

[JosephS]

Release
Added mans 200
2300 and parafilm

Layup
Did 2 coats of epoxy on chassis then added reinforcement

The thin layer of fiberglass satin weave was not comfortable enough for what I was doing,

First coat 15 ml

First coat 15 minutes

Second 20

2nd 20

The resin was pooling on top of the wax an release, this was expected and when it starts to thicken is a good point to spread it more


After that 2 oz resin mixed
I split the resin into 2 separate 1oz pots. This was an excellent idea. The larger batch would have kicked even sooner. Use some from each pot to reduce the total volume . This will make each pot last longer



exotherm-pot-life-and-gel-time
When mixing larger batches of resin and hardener the amount of time that elapses before the epoxy starts to thicken/harden in the container, is very important. As the exothermic reaction starts to build, the “Pot Life” of the epoxy quickly shortens. Pot Life is the time you have after mixing epoxy to the relative time you have to pour the epoxy; to the time the epoxy becomes incapable of performing/providing a desired outcome. An increase of 10°F above the average 77°F will usually shorten the pot-life by 5 minutes.



Added satin fabric backed with chipped mat then tail to nose with mono direction cf for stillness

After applying 1oz of epoxy the second oz kicked and smoked.

It may make more sense to discard resin that begins to smoke. I thought I was getting show through from the carbon fiber but it looks like the resin burned and actually boiled while on the mold.
All of the layers closest to the tooling were set before this was applied, so it should not cause bubbles in the surface.





From West Systems 105 resin + 206 Hardener Data Sheet

Mix viscosity (at 72°F) ASTM D-2393 ............................................................ 725 cps
Pot life (100g at 72°F) ........................................................................ 20 to 25 minutes
Working time, thin film* ................................................................. 90 to 110 minutes
Cure to a solid, thin film* ...................................................................... 10 to 15 hours
Cure to working strength ............................................................................ 1 to 4 days
Minimum recommended temperature ....................................................... 60°F (16°C



This caused me to rush…

I started adding the cf as I was on the chopped mat.

I then tried bagging

The release film was no. Conforming creating many wrinkles. I called breather under the mold in a bag as well as on top


The is Still a vacuum failure.
The bag evacuated but the pump never registered a seal. I am running the compressor non-stop to keep pressure on.

I am not sure if this is poor technique or poor quality bag material.

[Dangeruss]

Well... there's a use for a kitchen vacuum sealer I'd a never thought of...

Sorry to hear about the problems. Those aren't quite so funny.

[JosephS]

I think I actually picked that up from this forum. There was someone from aerospace who made their own cf chassis .

The problems are no big deal. I think my poor compressor can overcome the leak. It’s an oil-less compressor made for intermittent work I am pressing into continuous duty. Seems to be holding up and keeping pressure on the mold.

[JosephS]

In my rush I did not clean the brush I used and that is a lucky break for me.


The vacuum leak is slow in the bag so I have been running the compressor mostly on to compensate for it,

Since the brush is soaked with the same resin that is on the chassis once the brush soft sets I’ll give the compressor a break

[JosephS]

I removed the parts from the bag.

It looks like the bag I put under the mold, wrapped around and got wedged under the flanges. Not at all intended.

The breather released with little issue. This may indicate not enough resin since some of the breather wound up in contact with raw carbonfiber

The part of the nose that is supposed to hold the bumper is tweaked. since the resin is soft I re-positioned the part and I am using clamps to hold it down for the rest of the cure.

There are burnt spots on the breather.

Right now the resin is still soft so I am not at all tweaking or touching parts.

Everything is releasing so either my release amounts are great or my resin is not right.
At least things are looking good for now.

[JosephS]

Originally pasted in the wrong thread

Takeaways

• 3 piece construction not right
• Release just fine
• Chilling resin slows cure
• need 3 layers of breather ( results had some wrinkles)
• trim all fabric neat helps

Mold
The mold needs some work still.The mold seemed ok enough to do test in. I made the beads far too wide and that didn’t leave enough space for the height of the tub. I used clay to extend the sides, will use jb weld in the future

Release

• 3 coats paste wax
• 2 coats mans 200
• 2 coats mans 2300

Construction

Made a 3 piece outside.

Made a chassis bottom and 2 sides a separate pieces I see that this is how the fusion speed tubs were made.

The bottom has a bunch of small defects I can sand out.

Used the 5.7oz 2k weave.
Used 3m 77 as a stabilizer



Resin
To keep the resin from kicking fast I popped the cans in the freezer for 5 minutes. As well made a small ice try to hold the mixing cups and mixed resin batches.

Layup
This worked well as the resin is taking a long time to cure. I need it.

Took my time, wore gloves and tried to work everything into the corners.applied a bunch of perforated release film and breather over.


Also…

I made sure to trim and snip as much of the fabric as I could, nothing over the edge of the mold at all and relief cuts under the bulkhead support.

I should have used more breather, I think that will help with the wrinkles.


I could pull vacuum, but the bag would fail. Went for a double bag and don’t really have confidence that will hold.