Monday, November 28, 2011

Cut core and poured rails

Today was my first attempt at using a router to cut the cores and I was very very happy with the way it turned out. A small victory but a victory none the less.

Routed around the top and bottom templates using with the templates on top. I used Deans tip of putting double sided tape down (under the template and under the board) and no clamping was needed. I used a inverted flush trim bit which has the bearing at the top and cut all the way through.

Instead of routing a channel for the rails I cut all the way through the core. My top deck extends out on to the rails and so it need the poured rails to be flush with the top surface. To create the channel for pouring the rails I put packing tape on the underside of the board to create the channel.

I poured the rails as well and fell into a trap for young players - forgot to level the table properly and because I didn't mix and q-cell in the resin ( going for clear rails) it very quickly flowed to one corner at the expense of the others.  This was quick to remedy and so its curing away as we speak.

The rail channel is 9.5mm x 6mm x 3.16m and used about 240gm of resin (c. 120 mls)


  1. Congrats!

    It's getting there! I like all drilled holes on the template, easy to work with (yeah, when I've started didn't look at Brok. site:(

    Interesting, the Excel says 3.16m my board perimeter X 6(3 on tips)mm X 12.5mm = 186g of resin (see 27 June blog). Very tick epoxy tho.

    Hey, but did varnish it! BEAUTIFUL! One single tea spoon of varnish. Sanded first with 400 grit and used credit card to spread. Minimum 250g package of Gold spar original gloss marine will do a lot of boards:)

    Also, spring back is minimal 1 week after assembly, 2-3mm. But this is not finished since 1 fiberglass layer still needs to go on top.


  2. Thanks Dean.

    Thats great to know about the varnish. Gold Spar original gloss - I'll check out our local Withworth marine. Is it specialist stuff?

    Good news about the spring back. So is that around 10% of the rocker?

    Re the resin, was that the weight you measured? Board perimeter is actually 3.16m (guessed at it last night when I was posting) and BoardOff says 250gm. thats the weight without any q-cell or talc. I think you mentioned that you used some thicker in it. I most commonly see people talking about 15-20% q-cell by volume so this might account for the lower weight.

    My table wasn't flat so I had a bit of over flow on one side so might have used a little bit more than necessary.

    Brokite are very cool, hey. They've got a very slick set up. I'd like to try their design by use wood core and replace some of the carbon with s-glass. (mostly cauae of $$$)

  3. Cabosil (HDK N20) I'm using as a thickener, 186g measured all together. Didn't use it for top layer glass but I did use it for gluing 2 ply wood with glass between.
    Your rail is ticker since is all the way trough, now I see.

    I'm puzzled now with my board perimeter? :) Will double check!

    Looks like spring back is 10% of the rocker!

    Will you epoxy seal wood before varnish? West S. says to use 120grit to get a good teeth on epoxy first and than varnish it, but 400 worked for me:) Looks like mirror!


  4. Hey Dean. Definitely going to try the vanish idea.

    I have been thinking that I would seal the wood with epoxy and let it go tacky then put it all together. I've realised that for the graphics I need to have a white background so I've got some white epoxy pigment that I'll paint on. I also read on a forum somewhere that sealing the wood helps prevent air bubbles due to the wooods porosity.Paulonia seems very dense so not sure how much the epoxy will actually get into woods.

    Its good to have some real data on spring back. I'll update the note in BoardOff.

    Working on oven tonight. Have a simple temperature sensory from Jaycar that opens at 60 degrees. If I put it close to the light bulb I should be able to get it 50 degrees at the surface of the board. Bit dodgy but I am jsut keen to get this board done for a trip in 2 weeks.


  5. I've only just stumbled across this blog, great stuff. It would be great to see how you poured the rails actualy. I'm wondering how flexi or britle they will be, at times a straight resin pour can be very delicate in the strength and flex areas.

    1. Hi and welcome.

      Afraid I don't have any photos of the actual pour but it was straight forward. I used a plastic squeeze bottle ( like the kind you use to dispense tomato sauce or soy sauce) and used it to very slowly pour the resin into the channel made by routing all the way through the core and the carefully placing masking tape on the underside to form the channel. Other folks route most of the way through the core but leave 0.5 mm wood underneath and then sand the excess wood off after pouring.

      In terms of flex (in particular I mean how stiff it is, noot how far it can bend before breakign) my feeling is that is no different to using ABS plastic as the elastic modulus of the materials is about the same (both about 2.4 GPa) and elastic modulus and cross-section shape are the only determinants of stiffness.

      Brittle is another story and I don't have a solid answer.

      I have a much older board my brother made and it has poured rails (no thickener or milled fibres, just resin) and it was resiliant under general use but i hit a couple of rocks in c. 15-20 knots of wind and it cracked through. I had a similar experience with my first board which use ABS plastic. Full speed into a rock and the rail dented and the fibreglass cracked across the tip but the rails were intack other than the dent.

      Both cases where pretty extreme so in the normal range of use I think they are 6 of one half a dozen of the other.

      The downside of ABS, most plastics for that matter, is that getting a good bond with the epoxy is hard. You need to rough it up, clean it with alcohol and flame treat it ( in that order) and even then the bond strength pales in comparison to the epoxy, epoxy bond. Delamination due to poor bond on the ABS rails was the death of my second board (though I didn't not flame treat them properly).

      So, the two schools of thought I haven't signed up for are:
      i) poured rails with some reinforcement such as milled fibres of cotton flox to improver strength. Great bond with laminate, generally cheaper to do than ABS which is $$$ but not so good with large point impacts.
      ii) ABS - not brittle, great with point impact and can be cut to size and glued in at time of laying up board, bends a long way before snapping ( v. large elngation to breaking but then your fibreglass will crack a long time before you get to that point). Downside is a lot more work to get a good bond and even at its best is inferior to epoxy epoxy bonds.

      Have you got a project underway?


    2. Thanks for that reply.
      I figured out how you'd pour it after reading a couple of times "properly"
      Reason i asked that is because I've had a bit of experience with making stitch and glue kayaks. I would mix the same sort of filler to fill the joins and a different type of mix to laminate (glue). While it was very very hard when set it would not take a huge amount of flex when dry unless backed by glass tape and would crack. I found that it really had no strength on it's own laterally but would cop a fair hit with a hammer.
      I was wondering if you put a rocker in the board would the rail take the bend well or crack.
      Im just getting into the sport and soaking up everything i can. trainer kite in a week , lessons in a month or two. :-)
      I don't have a project "yet" although i did try your spreadsheet but the extra programs need to print to file etc just didn't like my pc.
      I ended up using Google sketchup pro to draw the board to scale, export as a pdf and print, worked a treat. I have a board pattern glued to some ply at work and will cut it out tomorrow i hope.

      Sketchup is fairly easy, was the use of the box tool, line tool, arc tool, then draw export as 2D drawing, save as pdf and you have the file ready to print.