Made the mold with tooling gel coat and Fiberglass.
I am vaccum bagging the composites into the mold with a yellow jacket 6cfm vac pump
Material being used are
3 layers of 6oz 2x2 twill
Silmar 249a polyester surf board resin
Breather cloth
Perforated release film
Stretchleon bagging film
Partall paste wax and pva
Pulled around 10 parts from this mold and all are left with tiny annoying pin holes in the finished part
Standard problem wirh vacuum bagging. The Vacuum will force the pinholes.
Parts will have a better VF but not that nice surface.
If you want bith change to infusion.
I hope you find a solution - I’m currently in the same situation.
I’m doing the same thing, vacuum bag 6 oz twill carbon into a mold, and want the best cosmetics I can get - having the same results as you. I use Resin Research epoxy with the slow hardener in case it matters. I also ramp up the vacuum over 15 - 20 minutes until I reach full vacuum.
Predominately I see “pin holes” at the knuckles of the weave, i.e. - where one tow goes over or under the tow perpendicular to it.
Things I have tried:
*Resin rich 1st couple of layers - no change
*1.2 oz. glass on the 1st layer - trapped air between the glass and the carbon
*Clear coat mold - same as glass layer, I see air between the clear and the carbon.
At this point, I’m leaning to no clear coat in the mold, and no glass layer. I get decent results after multiple coats of clear, wet sanding between painting. It’s tedious, but I need to get some parts out.
I have only tried pulling as much vaccum as I can get aiming at 100% vac.
Not gel coating the mold, thickness is an issue with these parts, 3 layers of 6oz carbon is perfect thickness
In my experience, pinholes at the weave intersections are more often due to being on the lean side than anything else. Reducing your vacuum level gives you a higher resin fraction, as does using a perforated film with less holes per inch.
With wet lay vacuum bagging, it’s often a good idea to only pull 80% vacuum. Not only does this give you a more resin rich part, but it means any air bubbles don’t expand as much in the laminate.
Do the pin holes go all the way through the part or are they just in the surface layer? If they are just on the surface, epoxy bar top will make them disappear without a trace if the weave is not damaged.
Are the holes in a pattern that makes it obvious what they are from? I.e. Do they line up with the holes in the release film or a pattern on the mold surface. Or are we talking about holes from air bubbles?
If it isn’t any of those things, I sometimes get tiny holes in the surface from not using enough resin to completely cover it. I have seen some people create holes by pressing too hard with brushes or other devices used to squeeze out trapped air during the lay up too.
Either way, when I have troubles like this that I can’t figure out, I resort to partially curing it before the lay up and fully curing the surface layer before adding more. Essentially, I make my own pre-preg with the carbon fiber sandwiched between 2 layers of window tint film (not perforated). I squeeze out the air bubbles with a spreader and let it cure 2/3 so it is still tacky but there is no more risk of air bubbles etc. it takes about 20 mins with the fast resin I use.
I then pull the cf off the tint film and lay up the surface layer only and let it fully cure. I typically don’t need a vacuum pump for this as the tacky cf just sticks to the mold or pva layer.
If there is complex curves in the mold etc, I make a rigid bladder out of gypsum cement and sandwich the cf between the mold and the bladder with weights on top. The edges of the bladder are sanded a little to make sure they fit.
Once the surface layer if fully cured and I have checked to make sure it is perfect, I flip it over and add the remaining layers. This method minimizes wastage if the cure goes wrong and it is a lot easy for mold with small curves and undercuts. There is also far less chance of damaging the weave during lay up. Not laying up all of the layers of cf at the same time may sound like extra work but you avoid messing around with vacuum bagging which causes me more problems than anything else.
