In the past I have installed high density foam inserts into compsand boards after the skins have been installed (corecell) and they were easy to sand flush because the density of the surrounding foam was similar. I am now in the process of building a timberflex style board and want to install the inserts into the 1.5 lb foam below the veneer. I am concerned that I will gouge the eps foam when I am trying to get everything flush and that the foams will compress at different rates while bagging the veneer that a bump will be produced. Hoping somebody has done this before.
Thanks
Bill
Bill, I am not an authority on this, but just for the data point, when I have underlain the timber (bamboo) with carbon fiber for reinforcement, after bagging I found the area stood proud of the veneer (just a little) so your concern may be valid. However, after glassing it seemed not to be much of an issue.
I’m not big on the insert thing though. My thoughts are that in the end, your box is still bearing against foam (although HD foam) and that foam is bearing against weaker foam. Seems to me that the real strength of the install is in the flange attaching to the bottom lam. That is where I would concentrate my energy.
all the best.
Thanks Greg,
Although I do have a different theory, I too am not an authourity. I think that plastic boxes (in my case it's for a mast track which has considerably more loads than a finbox) induce high pressures at the top and bottom. The top can be relieved by a good bond with the outer skin (as you have suggested) but the loads on the bottom of the box are being relieved by eps foam. Now if I can spread out the load the actual pressure will reduce to something more manageable by 1.5lb eps. Just my thoughts. I have done it this way for a compsand and it's held up to some good dumps (mast breaks, etc). I'm glad to hear that bump formed in the veneer reduce after glassed. I guess I could double up the hotcoat in that area to even everything out.
Thanks again
Bill
Hey Bill.
I assume you’re using core-cell inserts that are slightly deeper than your boxes… I cut the inserts on a 10" mitre saw so that they’re approx 1/4" larger than the finbox all around.
Rout a hole into the eps to the exact size and depth of your inserts and glue them into the core… Your insert will be flush with the eps and require no sanding… If bu chance they are a bit proud, tape around the perimeter with masking tape and sand flush… The masking tape will prevent the gouging of the foam you mention above…
Don’t worry about the vac.bag squeezing the different foams un-equally , this won’t happen … The skin , whatever it is, acts like a flat load spreading plate so any point load crushing should never happen… As long as your inserts are set in accurately routered holes you should have no dips …
Greg: The HD inserts act in 2 ways … By spreading the torque forces of the fin over a larger HD footprint they actually increase the flange-like effective area at the sides and bottom of the box… They are also less likely to let any water into the eps core if the box was to loosen or had any leaks due to voids or bubbles in the resin pour…
Hey Bill.
I was responding to your post as you were replying to Greg and I guess I just assumed you were talking about surfboard finboxes…
Depending on the thickness of your windsurfer the other option is to “post” the box down to the bottom skin…
We used to do this with Tuttle boxes and mast tracks that were going to see a lot of beating… You basically extend the sides and the bottom of the box by wrapping it in Core-cell which is deep enough to glue up to the bottom skin as well as the sides and deck…
This was a needed when we started using fins that were up to 20" long in our boxes… The Tuttle race boxes were designed to bond to both deck and bottom…They wouldn’t last if not…