Thursday, December 1, 2011

Thinned the core and set inserts

I glued the core together but with the 11mm thick it was already very stiff so I shaved it down with an electric plane and 40 grit sandpaper on an orbital sander to get it to around 9-10mm. Cause the flexural rigidity is proportional to thickness cubed, a 10% reduction in the thickness leads to a 33% reduction in stiffness.
Next step was to add the inserts. I'm using just plain M6 stainless flange nuts. Last time I used these and pressed them into ABS plastic washers. The idea of the washer to spread the load around to reduce the stress at anyone point. However, after looking at the Decay boards, they used much small diameter holes to place the inserts into and so this time I going to use just the nut and rely on the smaller radius holes for the inserts to reduce the stress on the epoxy and hope that the 9-10mm core thickness gives enough area for it to stay put.
I had drilled the insert holes (20mm diameter) all the way through the board. I put a small amount of 5 min epoxy in the bottom of each insert hole to form the protective barrier to prevent too long screws pushing through the bottom of the board and delaminating it. The alternative is to cover the end of the nuts with metal ( this is how it is in most production boards I believe) so that the screw can't go through. This is obviously a more robust build but the unevenness of my core thickness was likely to make it necessary to chose a different screw length for each.
Tip: put masking tape over insert holes and then cut the hole out. This will stop the resin flowing onto the wood which takes time to sand back. I've also put some pigment in the resin and getting it on the wood stains it quite deeply.
To fix the inserts I place double sided tape on a piece balsa wood and pressed the head of the bolts ( the the nuts screwed on so that a couple of threads extended out the bottom) into the balsa. This made for a very simple support for the screws that could then be masking taped in place to keep them vertical and centered.
Next step is to actual start glassing. Got all the supplies I need from FGI. I also got a bit of a tour where then keep all the reinforcement they sell to walk-ins! After too'ing and fro'ing about s-glass and e-glass it ultimately came down to the availability of the right weights. So I've ended just going with 200gm woven e-glass, R180 resin and standard hardener ( 25 min working time).
Forecast for the next week is for rain so it looks like I may not get to finish the board in time for my trip to Old bar later this month. Shit!


  1. Hey,

    are this two ply's glued together?

    We are like competing who will finish first:) Some competitive bunch:)


    PS Duno why this comments are not showing by the default? Hm.

  2. yes, 2 layers of 6mm but I thinned the top layer to about 4mm.

    can't wait to try the graphic inlay. should look great!

  3. Hi,
    Where can I find those inserts please?
    Good luck.

    1. Hi. anyplace selling stainless steel nuts and bolts should have them. they are very common ad cheap. if in Sydney, Bomond Trading in brookvale or try a marine supply shop like Witworths.

      googling stainless steel flange nuts should locate your local