Mold Layup Schedule

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#1

[FONT=Tahoma]Hey Guys,

I’m working on laying up a new mold and after 3 layers I’m debating about my schedule.

The mold in question is quiet large at 14’x6’. Originally, it was going to be 12x 1.5 oz (450 gsm) layers total with coremat layer on the outer laminate to help the stiffness. I’m definitely going to bring the thickness down to 8 layers and I’d still like to use the coremat for additional thickness/stiffness. I’m going to be careful about saturation. Typically I always try to have symmetric layups so I’m questioning if it makes sense to move the core layer between the 4th and 5th layer instead of further out like I originally planned. This way I’ll have 4x 1.5 oz skins on either side of the core. Any ideas?

The mold will produce bagged CF/core parts.[/FONT]

#2

I’d add the core after the 6th layer of fiberglass. Maybe half and half is better I’m not sure, but I’d add the core towards the back. Have you thought about just bracing the mold with 2x4? I brace my big molds with 2x4 and never notice any change. Some use metal, but I was told that the expanding / shrinking rate of polyester / vinyl ester resins are closer to the expanding / shrinking rate of wood. Metal I hear expands / shrinks much faster and further which would put spider cracks in the mold.

#3

Yeah, I think further out is the way to go. I’m coming to the conclusion that thick molds typically are not built with symmetry in mind, where thin laminates benefit from this because there is WAY less material in play and the core is a greater percentage of the overall part. In a mold you want really stable layers closest to the gelcoat and this is achieved with thickness; I’ll end up with just over 3/8” of mold thickness before the core.

As far as support I’m going to use metal with floating attachment (to the flanges) so distortion due to expansion will not be a problem.

#4

To help stop print through from your supporting frame, place a thin layer (1/2 inch) of PU foam between the back side of the laminate and the supporting frame. This will work with a wood or a metal frame although it is easier with wood as you can use a series of tack nails to hold the foam to the frame. Then fibreglass the frame into your mould.

This helps stop print through due to differing expansion rates of materials, I have been doing this for a number of years and it has never caused me any problems with the mould warping, the fibreglass takes care of that.
Its an old trick that I was shown by an old and very experienced boat builder years ago…

#5

Thanks Matvd. The geometry of this mold is actually quiet good for interface to supporting frame, only light attachment will be required and gravity will do the rest. The frame will only be applied to the flanges so the actual mold surface will have no chance of being affected by the frame.

The final mold thickness should be sufficient enough to reduce the odds of print through too; even if just on the flanges.