Dry pipe hood insert

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Jun 12, 2011
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Raleigh, NC
#1
So I am making a molded fiberglass bubble to make a up and over style pipe fit under an a/m hood. Not sure the brand of the hood, the hood isn't mine, helping a friend out. I am following a method I saw on YouTube since I have not attempted mold making before. Made some templates for the center and bottom contour and then transferred those to some thin plywood. Tried to keep about a 1/2"-1" gap from outer hood for air flow.


I happen to have a piece of the hood liner I cut out by request to make the overall size larger. I will try to use this as another template to match the bottom contour of the part since I have flattened out the template for simplicity's sake in the next step.


Glued the wooden templates within some foam blocks.


Then I cut out the bottom contour on a band saw.


That's as far as I have got. Going to get a hot wire cutter to sculpt the rest of it using the center template and contour gages for side to side profile.

I am not sure yet if I am going to go through the full mold making process or just try a quick epoxy layup and then try dissolving the foam with acetone. Looking for recommendations so I can plan on getting more materials if necessary (gelcoat, mold release wax etc)

 
Last edited:

yamanube

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#2
Why not just cut a hole in the liner large enough for the pipe to sit in (with room for motion and SNAFU) then drape some very thin cloth into the cavity you created so it hangs down and creates the "bubble". Let that cure then reinforce it with heavier glass, sand, paint, done?
 
Joined
Jun 12, 2011
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137
Location
Raleigh, NC
#3
Why not just cut a hole in the liner large enough for the pipe to sit in (with room for motion and SNAFU) then drape some very thin cloth into the cavity you created so it hangs down and creates the "bubble". Let that cure then reinforce it with heavier glass, sand, paint, done?
Probably could just going for a cleaner look and more precise fit. And it's easier to bond a pre made shape than try to make a complex shape with one PC of cloth and epoxy. Epoxy takes hours to cure so there's no telling how that cloth would move around during that time.
 
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Jun 12, 2011
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Raleigh, NC
#4
Roughing in with the foam cutter. I made the bottom contour template slightly oversized. It's not a bad idea to have a bit more material than not enough at this stage.
IMG_20180206_191930223.jpg

The overall shape was reduced down to a more reasonable size for both exhaust clearence and air flow.
IMG_20180210_164909544.jpg

Used 80 grit sandpaper to smooth out the surface. This foam sands down nicely unlike regular polystyrene.

IMG_20180210_164859605.jpg

Tried to coat the part with some wax then put 4 layers of 6 oz cloth down
IMG_20180210_185512110.jpg
 
Last edited:

hydrostyler

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#5
Looks like you just glassed your part to that slab of cardboard. :eek: I always brush epoxy resin over the foam to make sort of an egg shell layer. After it cures you can apply filler and primer to get a nice finish before you wax and pull a part or make a mold. Acetone should do a fine job of eating that foam away without disturbing the part, but you may work a bit getting that wooden frame broken loose.
 
Joined
Jun 12, 2011
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137
Location
Raleigh, NC
#6
Looks like you just glassed your part to that slab of cardboard. :eek: I always brush epoxy resin over the foam to make sort of an egg shell layer. After it cures you can apply filler and primer to get a nice finish before you wax and pull a part or make a mold. Acetone should do a fine job of eating that foam away without disturbing the part, but you may work a bit getting that wooden frame broken loose.
Yeah im sure I'll have to cut that base board loose. And the egg shell layer would have been a good idea. Little bit smoother end result for the part. I may just end up doing a little body work on the visible layer.
 
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Jun 12, 2011
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Raleigh, NC
#7
So I did have to cut the wooden baseboard and center template out, not a big deal a cut off wheel made quick work of it. Foam popped out easily, no need for acetone. In hindsight I probably should have made the side to side contour more gradual. But the current shape allows more exhaust clearence and doesn't seem to impede water drainage and air flow through the hood.
IMG_20180211_143629296.jpg

View thru the Hood's air scoop
IMG_20180211_144321654.jpg