Re: Slightly warped PVC foam


Mike Bergen
 

Sam provides an excellent response.

I recommend the peel ply approach opposed to the saran wrap as the plastic
wrap will give you a resin rich surface in the finished part which is not so
desirable. As Paul Buckley states it provides a better surface for secondary
bonding.

The other thing that I recommend is heat scoured polyester peel ply as I
mentioned in the talks that I gave at AirVenture. This kind releases from
epoxy resins better than the rest. Aircraft Spruce has it but you will see
that it is a bit more expensive than the rest: Part # 01-14825

I would recommend that you apply the peel ply to both sides and when you do
the second side apply the peel ply and then flip it over onto a piece of
plastic such as Saran Wrap and place you weight on the already cured side.
As it was said make sure your work surface is very flat for this.

Mike B

On 8/22/13 9:26 AM, "Sam Hoskins" <sam.hoskins@...> wrote:

Chris, welcome.

This is one of the kind of questions that new builders have that turns out
to be no problem. Warped foam is no big deal. Here is why.

When you are building a composite sandwich, the part doesn't become rigid
until the whole sandwich is complete. Take, for instance, your piece of
warped bulkhead foam. You lay it on the flat table and it's all
cattywhumpuss. You fret, worry and consider ordering new foam, but it's
not a big deal.

Now, you decide to glass one side with a single layer of BID. After it
cures, you may still have a warp and it will seem very loose and floppy.
Again, no big deal.

The key to a straight piece comes in when you glass the opposite side of
the sandwich. This is when you should make the big effort to make sure it
is laying flat while it cures. Naturally, your table must be flat. Before
the time the second layer cures, you may see that the piece isn't perfectly
flat, because of previous warpage in the first steps. Again, no big deal.
Simple weigh down the part with enough weight to hold it flat while
curing. You could also use pins/small nails to hold the edges down, but
using small weights is the easiest. You can apply saran wrap on the wet
epoxy to keep the weights from sticking, or you could use peel ply dacron.

Let it fully cure before removing the weights. As long as the second side
of the sandwich is nice and flat during cure, you will have a good part.

Clear as mud? Let us know how it turns out.

Sorry, can't answer the FS110 bulkhead question, as I built the two place
model and don't have the single place plans.

Sam


On Wed, Aug 21, 2013 at 1:28 PM, n7188u <n7188u@...> wrote:

**


Hi,

I am starting construction of my Q1 bulkheads and have a couple of
questions:

1.- On examination of the materials I have, I discovered that my 3/8" PVC
is slightly warped (not flat). I know that once I laminate it it will be
stiff so I will hold it down flat in my workbench with a couple dabs of 5
min epoxy but wondered if there is a trick for flatten it a bit. Maybe
slight application of heat and placing a flat weight on top of it?.

2.- I noticed that the plans call to not glass FS110. As much as I looked
I cant find where in the plans this eventually gets glassed. Well, I have
to admit just perusing the plans after the bulkhead construction section
but I can't seem to find that info and I am curious.

Thanks,
Chris







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