Wednesday, February 1, 2012

The board that should have never been Pt. 1

It all started out fine. The goal, to be able to assemble and glass the board in one pass. I pre-made the inserts, rails cut to size and flame treated, stitched 450gm glass so only one pass was necessary, moulds to hold it all together.

And was I focused, oh yeah. The steps were almost choreographed. So focused and impatient that I ended up forgetting to insert the carbon tape and the footpad reinforcements and the white pigment!!!!!! So I ended up with an efficient, good looking wobble board

....But lots of good things came out of this . One of them was not the board (it's a real pig) but I tried a lot of new things with this one. Some worked brilliantly, some limped over the line but have potential and some ... na.

So the score is:

Do's - 50%
Dont's - 30%
Do know's - 20%

First things first

I started the clock ticking and poured the resin. R180 from FGI with slow hardener because I wasn't sure how long it would take. Pot life is about 40 mins but this extends to a couple of hours workable time once its spread out and the heat generated by curing can easily dissipate.

First I applied just a single layer of mould release onto all the mould pieces.

Then the glass and mould over the top.

Note the Velco (top and bottom) used to hold the mould pieces together. Reusable and strong and can be easily adjusted.

Then it was time to put all the pieces together. This took about 40 mins. I used a paint brush and fingers to get resin into all the joins including the inserts and rails etc. One of the snags was that because I was thinking that the wood grain would just show through, I could not mark the planks in order to make sure they went into the right place. The board is not completely symmetrical so it mattered where every piece, including each insert, was placed. I spent a lot of time working out where bits when. I think next time I need to stick something on each piece to remind me were it all goes. How to do this without contaminating the surface?? Don't know yet. Possibly using Super 77 spray adhesive which Dave tells me works a treat and doesn't interfere with the epoxy bond to the core. Brokites also use this stuff to stick the carbon cloth in place. I could stick tags on and pull them off once its laid down. Doing this would have saved about 15 mins and some angst.

I spent some time preparing the rails. Abraded them and flamed them with a propane torch. 2- 3 close quick passes with some time for them to cool a little in between passes as the plastic will distort. The surface of the plastic at the end felt cindered almost a little chalky. I was careful not to scorch it as I had seen in previous experiments that as soon as you see brown scorch marks on the outside then bubbles will have already formed inside and the plastic will be brittle.

No photos for this stage cause I was focusing (too) hard.

After all assembled on a flat surface I put the next layer of glass, peel ply, paper towels (bleeder material stand in) shade cloth ( a tip from Dave that this stuff makes for great breather material and it did.

Into to full vinyl bag, sealed with packing tape and evacuated it to 80% of vac . At this stage , still on the flat table.

Then I moved the whole lot onto the rocker table jigs which I had covered with felt carpet underlay to reduce the chance of puncturing the bag. Then clamped it down using ratchet straps.

From the first resin mixing to now was 1 hour 33 mins.

With the core not being pre-glued flat, the concave profile across the board was exactly as designed and virtually no spring back given there was not stresses locked into the board width-wise.

24 hours later...

Because the mould pieces around the heal and toe side where the same thickness as the rails it was very little resin caked on the outside of the rail and this also meant that the excess fibreglass could just be trimmed with scissors. The pictures about are of the board straight off the table after trimming off the excess.

The trick I picked up was to put the excess glass away from the mould pieces first so that there is only a little bit of glass overlapping from the rails to the mould. Do this all the way around because when you do this you can then very easily just snap the mould pieces away from the board with the risk of delaminating the rails which is always a risk given that even under the best preparation the glass plastic bond is still not great.

With a core thickness of only 6mm and 450gm/m2 cloth top and bottom the board was very flimsy; very little stiffness lengthwise and in torsion. The unidirectional carbon straps in an X layout were the key to locking it all into place but without these nada.

So decision time. My wife suggested turning it in to a sign. I suggested that was inappropriate and asked her to please leave the room:)

With just a single layer of wood and the more economical glass it is the cheapest effort so far but I decided to go ahead and try to fix it. Nothing ventured nothing gained. In hindsight a nice sign might have been the way to go...

Wrap up of the good 50%

Full bag - yep. Reusable, no wasted tacky tape or vac film which saves about $15-$20 given the small quantities I buy, reliable. If the board has more curves on the top it might have been necessary to add some pleats to the bag to have some excess to conform to the curves as it doesn't stretch very well. With the table surface fully enclosed in the bag the chance of the table being distorted is greatly reduced as the forces top and bottom are balanced. In my previous attempt the force was just down on the board which meant that the table could bend up to meet it and concave disappeared

Mould pieces - yep. Allowed the held everything together very tightly, reduced drastically the amount of effort needed to clean the board up after coming of the table. This is especially true compared to puring the rails and then having to cut the excess wood and glass off. Also allowed the whole 'kit' of core pieces to be really squeezed in together tightly ( and even more so when you bend it into the rocker table as there is some compression even with the slight curves baked into the board) which helped get a good bond but also helped make up for the inevitable gaps due to the slight mismatches between rail and core.

Laying it up flat first - a very solid base to work from and so was just easier to work. Certainly made it easier to work the resin in with the resin roller. Gave much easier access to the work space. Generally just more convenient. Clamping it into the jigs after laying it up flat was easy and again very convenient.

Shade cloth for breather material - yep. Worked great.

Using a fibreglass roller to work out the air bubbles   - yep, again worked well. I have since found out that it might also help greatly to put resin down on the rocker table surface first and wet out the glass on a separate table before laying it over the resin'd surface. This was there are no air bubbles to start with so no change of ending up with the voids on the underside. The top side is a different story and in the absence of plastic topsheet material, pre-curing seems to hold the greatest hope for a shinny finish with graphics and an opaque background.

Assemble in one pass - hmmm. It added more work and time pressure to the layup but it was very efficient to do it all in one pass. For larger volume production runs I think that pre making a kit is probably critical as it will allow processes to be run in parallel rather than in series which is the time killer. However, for 'micro' quantities of production I think there is a middle ground needed if the board shapes are more complex ( surface profiles etc). While it did eliminate the waiting periods for letting inserts cure and then rails stick an then the core planks to glue, I think it would be a bit more difficult to shape all the pieces if the board had several layers. I need to think this through some more because each example against I come up with makes me think of a solution to. Here are some of the issues and resolutions that come to mind

i) Difficulty managing multi-deck shaping because of the large number of unsecured planks of wood - solution use wood the thickness of the board and cut it into narrower strips ( 25 mm). Make them longer than the board and tack glue them or clamp them at the very ends only. Then you could shape the surface, then route out using the template and clamp the pieces in place with the mould to continue working it around the rail areas.
ii) Fine tuning of inserts needed when they are not poured into the core. Just get the sizes more accurate when making the inserts outside the board. Either make the holes in the template a little oversized as the bearing on the router necessarily makes the cutting surface stand off from the template a small amount , enough to required hand working of the inserts to get them to fit. Could use round ABS plastic rod for the inserts as per The mighty might brokites.
iii) Mismatch of the core with the mould - don't screw the mould up in the first place. Make sure the rail widths are exactly the size of the router bit. I feel another home made tool coming on here.

The pro's for this process is that its possible to stockpile many of the pieces needed and then produce a board quickly as needed. Where there is a desire to make a number of the same or similar boards, this hands down necessary. For one and two off's, its a great deal more convenient and fits better with the pieces of time I have available to work on it and a desire not to have the long series of wait times. Both both cases the lack of lateral stresses baked into the board means your concave with survive the test of time.

Con's are that you need to be much more accurate in making the various components otherwise the efficiency gains are lost through having to tweak every bit to make it fit properly. It also potentially makes the shaping process a bit more difficult unless you can find a was to hold all the bits together when shaping it.

I think I am talking myself into persevering with the approach another couple of times.

Next post will be the on the Don'ts....


  1. great post, and um sign :-P
    you could tack the boards with some hot glue at each end. Kind of like they use on some strip kayak making then just knock them off when ready.

  2. Is it "fixed" already? :) Looks quite good, shiny...

    I was just about to do the same layout, but with some bamboo. Now will rather wait to see the next post:)


  3. Hey D. Yes I have fixed it with the carbon and another layer of 4 oz top and bottom . structurally it turned out very well but the finish was hideous. used felt underlay as breather and turned put to be quite lumpy so resin pooled in big lumps of diif colors:(

  4. Do you think that it is a bit fiddly right now only because it's the first time you have tried it that way? It works for brokite so i guess patience is the way to go.

  5. Hey Peter,

    Yes. I think you're right. Brokite do it smoothly and I can see that once the bugs are ironed out it could be very quick. I am going to have another crack at the same board only wiht the process improved.