Strutural Carbon Fiber Bracket

General Composites Discussions Composites Talk
#1

I need to make a bracket for my racing kart so that I can setup an additional brake caliper. The bracket would be two identical flat pieces that are “L” shaped and about 6" square. The brake caliper that would be mounted on the bracket would be a backup system so it will not be setup to the primary braking unit. I have some 11oz 5HS, 5.7 2x2, and some 5.5 plain weave carbon. I was looking at making it out of 3-4 layers of the 11oz 5HS carbon as the center portion with 3-4 layers of the 5.5 plain weave on each side of the 11oz. See below:

_________5.5@0 degrees
_________5.5@+45
_________5.5@-45
_________5.5@90
_________11@0
_________11@+45
_________11@-45
_________11@90
_________5.5@0 degrees
_________5.5@+45
_________5.5@-45
_________5.5@90

Is this overkill or am I on the right track? would I be better off using all 5.5oz or more 5.5oz with less 11 oz? Thoughts?

As an example if I had it made out of steel it would be probably 1/16-3/32" thick and out of Aluminum it would be probably 1/8" thick. I would guess that the carbon piece using the above layout would be pretty close to the 3/32" to 1/8" thick.

This will also be my first attemp at vacuum bagging. I’m normally used MAS epoxy resin with Medium hardener for wet layups. For vacuum bagging I guess I would need to use the slow hardener so I could lay it up and get it in the bag before it gels. Are my thoughts correct on this?

Thanks,
Chris

#2

If your peice is flat, as I would think. You can maybe use a FB mat or something for some space if you need some thickness buildup.

But, my main point is…you can always do a compression mold, against 2 sheets of metal, etc if you have it around. Might be easier than vac bagging something that is flat?

#3

I had thought about the compression mold. My idea was to layup a large flat sheet about 9"x7" on a piece of plexiglass. Then once this flat piece had cured I would trace out the patterns of the two brackets and cut them out. I have made a couple of other pieces like this and it seams to work out well.

I had a thought about laying it up on the plexi and putting another piece of plexi and compressing it. The problem is getting enough force to compress it. Even if I placed approx 200lbs on it, the area is approx 63 square inches which is only about 3 PSI and if my cals are correct this would only equate to about 6.5inhg. Am I looking at this right??? If I am then it is not alot of pressure and that is why I was considering vac bagging. If I could get 20inhg that would be somewhere in the 10 PSI range.

other thoughts???

#4

I’d use waxed glass and not arcylic as whenever I have try laying up on arcylic (or Plexiglass) it would fully crosslink even with wax and PVA…

Test small amounts before doing a large one…

#5

I’ve laid up carbon directly on plexiglass with epoxy resin without using any mold release and had it pop right off…

#6

I’m not sure about that, but what about using c-clamps as your pressure? I was also thinking sheets of aluminum, or even laminated wood (like many cheap shelf and desk systems.
if you clamp them down hard, the piece should be more than putting 200lbs on top?
also, maybe add a layer of peelply and breather on each tool first, so you can suck up some resin, without having to make it push out the sides of the 2 tools.
I hope that made sense :slight_smile:

#7

If you are worry about the molds sticking, use Delrin aka Acetal. There’s not many things that stick to Delrin.

#8

Here are the results.

I did end up laying it up between two pieces of plexiglas and putting approximately 250 lb on it. The sheet size was about 12"x12". I then cut out each bracket from a CAD pattern. Over my original layup schedule I also added 2 layers of 5oz kevlar each between the 11oz and 5oz carbon. These kevlar layers can be seen in the pictures. These brackets are super strong and stiff.

#9

nice work,well done 8)

#10

nice work there. what if you wanted to create a bracket that had bends?

#11

How did you cut that piece? I tried using a dremel and thin cutting wheel on thick pieces, and it took FOREVER!

#12

the reinforced cut off wheels cut carbon very easily up to about 1mm thickness,not tried any thicker than that.

#13

Try checking out Fein tools, not cheap but works great!

#14

I used a carbide jig saw blade. It lasted just long enough to cut out the pieces. Then used a belt sander to smooth and straighten the edges. Worked out really well.

Rotozip makes a carbide cutting tool that I have used in the past that works and dremal has a roto bit that works well also. With the dremal bit you have to take it slow because it heated up real quick if I put alot of pressure on it.

Cutting out the bracket was the easy part. The hard part was drilling the holes. I still don’t know an easy way to do that!!

#15

I used a carbide jig saw blade. It lasted just long enough to cut out the pieces. Then used a belt sander to smooth and straighten the edges. Worked out really well.

Rotozip makes a carbide cutting tool that I have used in the past that works and dremal has a roto bit that works well also. With the dremal bit you have to take it slow because it heated up real quick if I put alot of pressure on it.

#16

i would use an air saw. i had problems inthe past with air saws that i had bought from harbor frieght, but the problem started there. a 20$ air saw just doesn’t compare to a 70$ or 120$ air saw. i cut as think as 1/4 inch laminates, and so far that i’ve had my new husky from home depot for 70$, i haven’t had ANY of the problems that i had with the other. such as, too much pressure or too thick part and it wouldn’t cut. it would just throw air.

#17

I use the habour ones but I get the warrenty so if it fails, pay the 5 bucks and get a new one. I go through about 4 a year. I use a husky too and never a problem with it

#18

i use harbor ones too i bought the 2 year waranty for 10.00 i get a new saw every 2-3 weeks no charge you cant beat that deal but the problem i had with them they started telling me saws were on back order so i bought 3 more with waranty