Vacuum bagging

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xantipo

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May 12, 2009, 9:41:01 AM5/12/09
to F22 Builders
Yesterday I did a simple vacuum bagging test to get the feeling of the
process . I didn't think too much about it before I started and
actually allowed all possible mistakes to take place. This way I hoped
I could identify most of the basic problems one can expect later
on.Here are some of the facts and questions that surfaced from the
test run.
1. The vacuum pump unit worked fine although there is a small leak
( power off pressure falls to atmospheric in about 10-15 minutes). I
suspect the leak is in the pressure gauge threaded coupling.
2.I only waxed ( twice) an area of about 10cm wider than the
laminating surface. Wrong! Besides other problems it makes a lot
harder to remove the sealing tape. Question: How many layers of wax
should be applied? I'm using Honey wax and no PVA. Does PVA really
improve the process?
3.I cut the glass layers too short. I had some difficulty aligning the
cloth with the foam. Question: Cut glass in rectangular pieces or try
to aproximate to the foam shape?
4.Peel ply, release film and breather layers worked quite well.
5.Vacuum bag. Working with the sealing tape was a bit caotic. The
thecnic recommends putting the sealing tape in the bag and not on the
table. That makes things a lot more complicated especially if you're
working one -handed on a 1.2m wide table! Question: Has anyone used
the tape in a different way with positive results?
6. Resin. That's where things got really bad. First I used a fast
epoxy ( gel time 54'@20ºC).Room temperature was around 16ºC ( looking
for trouble here!). So the resin had high viscosity which made weting
very dificult. Second, I didn't mix enough quantity and had to double
the amount for the top layers of glass peel ply and release film.
Still it turned out to be insuficient and the laminate was resin
starved along the outer edges.On the production runs a slower resin
mix will be used and preheated for desired viscosity.

Other questions:

Perforating the foam takes a long time. Any tips to shorten this
operation?
What´s the best way to shape the final bulkhead? While cutting the
foam is easy it seems one loses the shape references after the
lamination. It looks like double work. Why not laminate rectangle
sheets a cut them to shape later?

Any feedback on this?

Bill Scott

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May 12, 2009, 10:06:57 AM5/12/09
to xantipo, F22 Builders
My experience with vacuum bagging.
- about 4 layers of paste wax on the table
- apply sealing tape to table with its protective cover on top
- attach the vacuum bag material to one end where you bring the tubing in.
- use a slow epoxy
- I use a dremel tool with a 1/16" bit to drill the holes in the foam. It
goes quite fast.
- I've never used a release film as shown in the plans, however I had to
cut down on the vacuum pressure so as not to suck too much resin out. I
found that 14 to 18 in Hg worked well. 25 in Hg is too much.
- I cut the glass to foam shape oversize and foam about 1/2 in oversize.
- If you put the foam face down on the table then you can see your lines
after it comes out. After curing cut just outside of your line with a
bandsaw. The blade dulls very quickly, but keep that one bandsaw blade for
that purpose. A dull blade will continue to cut the glass. If you don't cut
off the rough stuff on the edge then it is more difficult to remove the
breather cloth and peel ply.
- If you have it set up right, you should get resin coming up into the
breather cloth, but not so much that it feeds into the tubel
- When you have the bulkhead epoxied and breather cloth on, with extra
strips leading away from the tube, then remove the covering from the sealing
tape and lay down the vacuum bag, making sure you put a tuck in several
places so it will pull tight around the part.
Good luck
Bill Scott

Menno

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May 12, 2009, 10:19:59 AM5/12/09
to F22 Builders
Perforating the foam can be done with a 'nail board'. Take a piece of
wood, drive in nails in the right pattern, cut off the head of the
nails.
Put the foam on some cheapo tempex foam or the like, and drive the
board in by standing/jumping on it. Make sure to make the nailboard
much wider than the 'nailed' area of the board, so you've got some
lever to get the nail board off the foam again.
Still it is a lot of work.....

Fiberglass will ruin normal (jig)sawblades very quickly. You can use a
jigsawblade meant for cutting tiles and the like. It's actually not a
sawblade, but a blade with sanding particles on the cutting side.
After I found out about this blade I used it for building 2/3 of my
boat, and the blade is still cutting like it's new. Works great.

Ian Farrier

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May 13, 2009, 6:03:25 AM5/13/09
to F22 Builders
In reply to

On May 12, 2009, at 2:06 PM, Bill Scott wrote:

> - I've never used a release film as shown in the plans, however I
> had to
> cut down on the vacuum pressure so as not to suck too much resin out.

Rather you than me Bill! This is definitely not recommended and I
would never do it that way.

> 5.Vacuum bag. Working with the sealing tape was a bit caotic. The
> thecnic recommends putting the sealing tape in the bag and not on the
> table. That makes things a lot more complicated especially if you're
> working one -handed on a 1.2m wide table!

It is not that hard and you will find it easy with a little practice
- we do it that way all the time, and always single-handed. Putting
the tape on the table is not recommended as you will get many more
leaks, and some could be very hard to stop.

> Perforating the foam takes a long time. Any tips to shorten this
> operation?

Buy perforated foam only - very common now, and does not cost much
extra. Otherwise use a nail block as Menno suggests.

> What´s the best way to shape the final bulkhead? While cutting the
> foam is easy it seems one loses the shape references after the
> lamination. It looks like double work. Why not laminate rectangle
> sheets a cut them to shape later?

That is the only way I do it, and is how it is always done in
production. Cutting out bulkheads and glass twice is not fast.

With regards,

Ian Farrier

Farrier Marine (NZ) Ltd
Farrier Marine, Inc


bu...@terrigal.net.au

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May 15, 2009, 8:35:08 PM5/15/09
to F22 Builders
Hi , when you are vacuuming flat panels it is far cheaper to seal the
bag down with packaging tape . Tacky tape gets really expensive for
the whole bag . I just use it around the hose entry . Regards , Jim
Buckland .
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