Closed cell foam blanks and rocker

[RichR2]

Up to now I’ve always used EPS cores that I’ve hotwired to make my blanks. This approach allowed me good control of the rocker shape on my boards.
I’m now making a pocket board and have decided to try closed cell foam which can't be hotwired. The plan is to make a rocker table and have the board on that while its bagged and curing. I’m aware there is some ‘spring back’ after doing this, so how much extra rocker should my table have if I’m aiming for a finished rocker of 10cm (on a 100cm board)?
Or… is there a better way of controlling rocker shape when using closed cell foams (not keen on the skerfing approach though)

[jespin4845]

I put in rocker with a carbon patch on top with weights and vacuum

Put it 6.5 inches, springs back to 4 inches

This is 1 inch thick divinycell , no need to kerf

[RalfsB]

If you have one side of the board covered with carbon and rails wrapped, and epoxy hardens while your board is on a rocker table, there is literally no springback. I think that the rails are the main factor that makes the whole construction very solid.

[BWD]

Thermoform the rocker so you don’t get stressed/broken foam cells. Best way to avoid foam breakdown over longer term.

[merl]

Thermoform the rocker so you don’t get stressed/broken foam cells. Best way to avoid foam breakdown over longer term.

Can you give some details? There was some discussion earlier that it might be possible to form the rocker in high density foam just with a heat gun. Is that what you have in mind, and have you actually tried it on a full scale bit of foam?

[BWD]

Rocker jig, a well supported sheet of plywood bent to desired rocker. Make rocker jig with solid rails cut from plywood with jigsaw.
Heat lamps heat gun or hot water to heat foam till soft.
For Corecell this is 170 F, not sure about d-cell.

For water method, put blank on jig, cover with towels or blankets.
Boil some pots of water. Make sure it is enough! Probably about 4-6 Liters.
Pour them over the assembly. Carefully. Outdoors.
Make sure to do some dry runs to verify alignment and fit on jig etc.
Place conformable weights on top - bags of dirt or sand work well.
Let cool a few minutes. Done.
Alternatively save the offcuts from your rails and make a top to your jig so foam and hot blanket sandwich can be mashed in a closed mold.
Or you could try to use a half bag to vac the blank onto mold while heating but that is likely more of a pain in the neck.
Hot water method is messy and may sound silly but it works well and has the minimum tooling requirement.
Works great on foam 20mm or less, haven’t tried thicker.

[RichR2]

I've heard of heating the foam in an oven but not using hot water...interesting approach. Does it cause shrinkage in the foam like oven heating does?

[downunder]

I'm a bit jealous of you guys getting relatively cheap d-cell or c-cell

A 5mm c-cell sheet is $150 here...

[longwhitecloud]

do u know what would work well. the cheapest thinest ply, vacuumed onto polystyrene with gorilla glue (foams slightly) and covering in lanolin or similar. soo strong..

[thewindego]

In Canada corecell is about same. 6mm 4ftx8ft sheet is $160 plus tax