Just to re-enforce Matvd’s comments, resin control on the second layer is critical, pre-wetting the carbon on a bench with a calculated volume is a good way to get this right. See – http://www.compositescentral.net/showthread.php?t=4618
But in your case transferring the carbon to the mold/layup could be tricky, due to size.
It might be a good idea to consider another core method like using Soric or something. A bit heavier but far less learning curve; as you’ve already said its not an F1 car… What ever you do is going to be FAR better then steel hood.
I think the rear hinge points will be getting a little close to the edge to have HC go back that far. I didn’t think of bringing the HC right to the edge of whatever material I use for the hard point though. That would probably be stronger and look better on the bottom side as well.
When you do the wet layup do you layup the few first layers and bag that like the video or do you do it all at once?
I can’t seem to find anything on Tufnel. Do you have a link that can get me started?
Do Tufnel and G10 thread well?
If machine up some aluminum pieces I was going to coat it with epoxy first to avoid contact with the carbon fiber. Would that be enough or should I wrap it with fiber glass too?
Tufnol makes a wide range of laminates, but I believe the one commonly used for hardpoints is a phenolic laminate. The equivalent in the US is Garolite, but be careful, there are many different flavors of it. You can search McMaster.com for Garolite and read about the different versions…
yes,the g10 in your link is the stuff.its also listed as fr4.i buy it from mcmaster carr.its listed as a phenolic.
im doing similar layups in one shot.i do the bottom plies first.then i pre preg the top 2 plies.then lay in my hc and hard points.by this time the bottom plies have setup a bit.then i lay on my top plies.bag down.then i pull a light vacuum for about 30 to 45 minutes.this further lets the bottom plies firm up.then i go full vacuum.wait another hour.then in the oven.the waiting period is critical to getting a nice pit free part.if you dont let the bottom plies firm up.you will get craters next to the hc.your wait times will vary with what ever resin and hardener your using.its best to do a test piece on a piece on aluminum or something similar.just do a small square throw a piece of hc in the middle with the same amount of plies you plan on using on your hood.
you will want a second set of hands if you plan on doing this in one shot.you wont have fun trying to lay large plies by yourself.
Yes tufnol is a phenolic (plastic) laminate that is like wood, although it is actually a plastic. It can be threaded (although I wouldnt use it for structural mounting threads), its very tough, hardwaring. Gives off a horid dust when you are cutting it or sanding however so make sure that PPE is worn.
When doing a wet lay using honeycomb I will usually try to do it in a one hit process rather than post bonding it and laying the inner skins after the first has cured, although you can secondary bond/lay-up. I have found that if secondary layup is required it is best to place the HC onto a wetted out layer of cloth as it will bond far far better than if you just brush resin onto the back of the laminate and place the HC on. This is because the HC will push into the wetted out cloth and give it more bonding surface area.
I agree wit the comment from kmt63 about pulling the vacuum slowly although I find that this has more to do with making sure that the laminate/bag are pushed into corners fully and that the HC has not moved as it can slide about a little bit if your not careful whilst pulling the vac. I do know what he means about the first plies firming up which gives a nicer surface finish however you do have to be careful that they do not go too far before you finish the lay up or bagging.
G10 and G11 are simply fiberglass/epoxy laminate. FR4 is a fire retardant version of the same.
Has anyone ever put a thermocouple under their hood? I’d imagine it gets pretty hot right above the exhaust manifold, especially once the engine is turned off and air flow stops. If the resin doesn’t have a high enough heat deflection temperature then the composite could distort.
Good point… Typical West System epoxy has relatively low distortion temperature 140F. There are other epoxies out there with much higher distortion temperature but most require some amount of post-heat treatment. A good vinyl ester would probably be good in this application; I believe most of these are +200F.
not too hard. Roll it onto a 2" plastic pipe then roll it off in place like the top of a pie. Make sure the pipe is longer than the widest part of the laminate.
If your hood is a racing only hood it probably won’t have the underside support structure that an oem hood has, that would be a weight penalty. If you are going to use hinges with the hood you will want to make steel or stainless steel threaded brackets that will be laminated to the underside of the hood. Otherwise the cf will just crack out with just a threaded insert in it or just an autobody type push on thread tab.
I would just do 4 layers of 3K or 6K… vacuum infuse it or autoclave dry carbon to keep the resin content ratio in check. If 4 layers of 3K ends up being too thin ( .040" or 1mm) then secondary bond some core mat to the underside.
Gel coat does add weight on such a large part. Think of it this way… every gallon of gel coat weighs 9 lbs. You will need about 1 quart of clear gel coat… about 2 lbs of added weight. Your going to spray on about 1 quart of clear coat… another 2lbs. But like you stated it’s not an F1 car… and even they have to use a xxxx load of clear coat that adds weight… makes their sponsors happy to have their name sparkling on the car.
I just sprayed some resin on top of a carbon fiber fender to burry the weave and give it a deep look. I sprayed about 25 mils of resin over the cf. That fender weighed a crap load more after.
That sounds like a good procedure. I don’t have an oven but I imagine that is more dependant on the resin used. By light vacuum do you mean approx. 20" and then shoot for a full 30" at full? I am a little worried about the HC print through which makes me want to do it in 2 stages but a couple test pieces with your technique won’t hurt.
I don’t know why I missed this before but I got a bit worried after a responce about som NADI core in another thread I made. I always planned on using US composites 635 which has a Tg of 150-190 according to their FAQ. It didn’t state C or F but I am suspecting F since that would be similar to other epoxies. With a bit of googling it seems underhood temps can get up to the 210F range. What happens to the expoxy when the Tg is exceeded? I don’t have an autoclave or access to one to use high temp epoxy so I may be SOL. What are the disadvantages to using VE? Has anyone used a standard epoxy on a hood with sucess?
Once again I can’t express how much the information you guys are giving me is helping. It fills in all the holes I can’t find answers too. You’re the best guys. And if anyone happened to check out my build log you can see I love posting pics to help others down the same path and this will be no exception succeed or fail.
And if anyone happened to check out my build log you can see I love posting pics to help others down the same path and this will be no exception succeed or fail.