newbie needs help

General Composites Discussions Composites Talk
#1

Im sure that with this being my first project, I am biting off more than I can chew. I have an old dash instrument gauge cluster that is comprised of 6 round gauges, and i wanted to replace the cheap 1970’s plastic with carbon fiber.
I attempted to create a mold of the dash using fiberglass mat and polyester tooling resin from USComposites.com. I soon realised that just doing an overlay would be easier to do. I took fiberglass cloth and attempted a “practice run” using the 3:1 epoxy resin. All went well, so I figured I would proceed with the CF. Well this is where the problems begin. I saturated the CF and started to overlay it. Working from the center out, the cloth would shift and i wouldnt have enough material in some areas (even though it was grossly cut over sized) So i pulled it all up and started over. Did this twice and was to frustrated to try it again the same way, So i started from the left and worked to the right. It worked excellent until i came to the last gauge hole. The cloth has become so wrinkly that it cannot lay down with out it being overlapped.
I just gave up on it and used it as a learning experience.
So my questions are:
Should i have tried to vacuum bag it?
Why after a day or two is the epoxy cured CF and fiberglass cloth still flexible? does it need a second layer of cloth added?

If anyone in the San Fernando Valley (Burbank area) is willing to help via hands on, I will pay you for your time.
Sorry for the long post, just frustrated…

JohnnyZ

#2

I usually recommend against overlays. If it’s possible to replace the part, then I suggest making a mold and then a finished piece.
If you’d be interested in taking a composites training course, I have a program in Monrovia. We cover everything from mold making to working with pre-preg, and everything in between.

#3

TET i tried PM’ing you but your box is full.
I am interested in this course. Can you give me a little more info about it.
1 day course, or multiple weekend courses?
Cost involved?
Thanks
JohnnyZ

#4

I’ve cleaned up my box. You can resend the message.
The program consists of 2 classes. Part 1 covers model making, mold making (tooling), and basic composite fabrication. Part 2 is more for actual production of parts, using wet layup, infusion, and prepreg laminating.
Classes are Tuesday and Thursdays from 6-9pm, and are 5 weeks long.

#5

TET sent you another PM

after poly resin cures, is it still flrxible with only one layer of CF, should I have used a second layer to make a flat piece more ridged?

#6

are you sure your mixing ratio was 99% correct, and have you stirred the mixture up thorougly?

and, just in case, are you sure your resin is for laminating and not pouring? (i had a clear polyester resin that was not curing properly when laminating fabrics, but in the pot it was curing fine. then i found out it was meant for pouring into models and such)

#7

The only thing i am sure about is, i used those “fancy” 3:1 pumps and the epoxy resin is the stuff from uscomposites.com
I mix for about 5 minutes scraping the sides and bottom of the mixing cup. After its cured, its not sticky or soft, its just i can still bend and manuver a single layer flat panel of CF

#8

pumps are not a very good method of mixing epoxy. you should always use a good digital scale accurate to a tenth gram. And mixing for 5 minutes is a bit overkill but I guess its better than not mixing enough. as for your panel, if you only have 1 layer of carbon it will be extremely flexible since its at max 1/4 mm thick. either you need to use core with carbon on both sides or addition layers of carbon or glass.

#9

Yeah, a single CF layer will wrap around a pencil…
however, it should spring back straight, if the epoxy is cured properly. Does it stay bent, or does it go back flat?
Remember, they use CF for springs :slight_smile:

#10

The USComposites ratio pumps are actually pretty good. Accurate to 1% or better even at small quantities of 100 grams of resin. I have them out in the shop at the mixing stations so my guys can get the amount very close to final. But I make sure that the perfect ratio is finally achieved with an precision digital scale.

As for the carbon fiber sheet, of course it will be flimsy like a wet noodle with only 1 ply! Even 2 plies of 8oz twill is pretty flimsy. 4 plies of 5.7 twill (with proper fiber orientation) starts to make stiffer panels. Carbon is stiff and strong, but it’s not magic.
Epoxy from USComposites it’s not very good though IMO. Not sure what it’s made for, but it has pretty low tensile strength and hardness. The fast and medium curing 635’s are just ok, but the slow is pathetically soft and flimsy even after post curing. Stay away!

#11

the problem with the pumps are when they loss there prime and fart, which tends to happen when the container gets low. It really depends on personal preference though.