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Gaps for Glassing

Old 01-11-2017, 12:42 PM
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acdii
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Default Gaps for Glassing

My B-25 has the removable bomb bay hatch under the wing, and I want to build up the gaps so that when fully glassed, they are very thin and hardly noticed when assembled. Since the piece under the wing is longer than the doors themselves, I will have a large gap then the part then the seam for the doors, then about 2" of fuse and the other gap. I want to reduce this gap down to about 1/64th if possible. Going to use 1.4 ounce cloth, so how big a gap should I leave for the glass to obtain this finished gap? I don't have the cloth yet, and it will be a while before I glass, and the filler will need to be on the removable part, not the fuse side, or the wing may be hard to install, it is tight as it is now.

Going to use plywood to fill in the gaps, want it snug, but not so tight that the glass gets rubbed.
Old 01-11-2017, 01:59 PM
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One way is to glass over it when going the wing. just before it fully cures, use a sharp thin blade and a straight edge and cut it loose. The use a filler to build up the area behind the glass edge!!
Old 01-11-2017, 06:53 PM
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acdii
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That would not last long though, the part is removed every time the plane is assembled and filler most likely would start chipping off. The plane travels in 5 pieces, two outer wing panels, center panel, fuse and bomb bay section. The section that I wont a thin gap on will screw to the wing after the wing is attached to the fuse so there are no holes visible. This is why I want to use ply to close the gap. I don't know what the thickness of the glass wrapped over the edge will be.
Old 01-11-2017, 09:54 PM
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Get enough glass to build your parts with the glass return on the edges. That way you can fit it with glass when building. When you finish glass, do it with it all assembled and then cut your parts away. New glass should lock in to the old, assuming you use finishing epoxy. WB Poly dont know.
Old 01-12-2017, 05:32 AM
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acdii
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Going to be using WB Poly on this one. I guess I could do the fuse first, then determine the gap difference before glassing the bomb bay section, and add on plywood to build it up. Still waiting for confirmation of the order, says it takes two days to process, so I don;t know when it will arrive, but my McMaster Carr stuff should be here today or tomorrow so I can at least get back to building the stab.
Old 01-12-2017, 06:57 AM
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scale only 4 me
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Originally Posted by acdii
That would not last long though, the part is removed every time the plane is assembled and filler most likely would start chipping off. The plane travels in 5 pieces, two outer wing panels, center panel, fuse and bomb bay section. The section that I wont a thin gap on will screw to the wing after the wing is attached to the fuse so there are no holes visible. This is why I want to use ply to close the gap. I don't know what the thickness of the glass wrapped over the edge will be.

I was hesitant to post because I wasn't sure of the question

You're not going to get the glass to wrap around a tight bend or 90 degree edge,, it just wont happen, if you try the cloth will just lift at the sharp edge, That why ByLoudDesign suggests cutting it that way.


Build the gap as tight as you like, then just paint those edges to seal,, if we're talking 5/8oz cloth and epoxy,, done right, the finish thickness once you fill the weave is only about the same as a couple coats of latex house paint.

good luck

Last edited by scale only 4 me; 01-12-2017 at 07:08 AM. Reason: crazy ***** formating
Old 01-12-2017, 07:09 AM
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acdii
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OK thats what I was looking for. thanks. I have an idea how to finish it now. I have some .5 oz cloth that I can use to seal the interior of that bay with, which can be pulled tight with some snipping around the curves. so I will apply that layer first and wrap it on the outside, then lay the heavier cloth flush with the edge. That will work.
Old 01-12-2017, 07:21 AM
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I second ByLoudDsign's recommendation. Use the ply to build the structure up completely with the 1/64 gap you want. I have done this several times and using the Dan Parsons thinned epoxy method of glassing I glass the fuse with the hatch in place. Once fully cured I then use a razor blade to cut the hatch loose. As soon as the hatch is loose I run thin CA around the edges of the fuse cut out and the hatch to enhances the adhesion of the glass/epoxy. A light sanding of the edges and you should be good to go.

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