Monday, January 30, 2012

Peel Ply FYI

Not that this all that relevant for kiteboards but I thought that this was interesting none the less.,%20SAMPE%20(Anaheim)%20MDC%20950072.pdf

In a nutshell it says if you are going to laminate over a cured surface that has had peel ply used over it then you have to clean and sand it v. vigorously as the release agents used on nylon release films will contaminate the surface and cause a weak bond.

This came up in the context of looking at precuring topsheets and playing with the idea of making the skins with peel ply incorporated as part of the 'stack'. That is

- fibreglass scrim or surface tissue ( <2 oz)
- graphics
- nylon release film

The release film being used in place of layer of glass so that a colored background can be applied to the decals instead of having to apply a second, coloured layer of resin after the resin in the surface tissue has cured.

Apparently non-coated nylon will chemically react with epoxy though would have thought that it might need to be done at elevated temperatures to get this to happen or at least insulate the curing stack so that the heat generated during curing can be held in to assist the process.

Maybe using densely woven but thin cotton material might be a better option.

Pre-curing topsheets

I got some great help from XSWind on kiteforum re pre-cure topsheets. Here's the link

... and here's the guts of it.

The purpose is to obtain a thin skin which is resin as that is the only way to obtain a full and deep gloss/sheen.

The topsheet is wetted out on just a sheet of normal glazing glass and then vac bagged flat, there is a or two trick here but I will leave you to discover them to make it perfect.

yes I vac bag mine.

The objective is to make a cured and finished thin laminate.

Thickness is up to you but I normally do a 2oz or thinner scrim layer with decals next followed by a layer of 4oz. Leave to sure then bond

If done right you end up with a completely finished fully glossy outter surface to your board.

Once the topsheet is cured leave thay Maylar if you like sheet attached, dont remove it.
skuff the top sheets bonding side with 40 grit and clean the dust off. Now simply go to your rocker table lay up the normal structural layers and put the pre-cured top sheet on and after the normal vag bagging process has been done, you can remove that film layer to reveal the goodness.
Another tip is "a simple addition to the pile before bagging"

Friday, January 27, 2012

Full Vac Bag

Here's a couple of shots from yesterdays activities. Below is a shot of the dry fitting with the board and mould fully enclosed in the thick vinyl vac bag.Velcro is used to pull the two parts fo mould together tighly. I tried bending the board across the width to length wise to see if the gaps between the planks would open up. They stayed together well enough and I'm guessing if small gaps to open up they will be filled quicly with excess resin from top and bottom.

Here is a visual of the problem I mentioned yesterday about the lack of tight tolerances on the core mould due to me getting the rail width mismatched with the diameter of the router bit and so having to 'hack' it.

I decided to try to have a bit of fun with graphics rather than get to artistic at this stage. I've printed the images on tissue paper and am just working out the best way to add them. The options are to pre-cure a top sheet and put the graphics on the back. Only drama there again arises from mismatched rails.They were 4.5 mm this and the core material is 6mm. So, I've have to do a bit fo profiling on the core and there are a couple of compound curves there I'm worried will cause too much bridging. Alternative is just to use peel ply in the vacuuming and then lay the graphics on top and follow it with an coat of epoxy. The down side there is that it will require elbow grease to get a good finish.

I'd love to try the pre-cured but we'll have to wait and see if I'm up to the challenge.

Thursday, January 26, 2012

Graphics and topsheet finish


After chatting with Peter on the blog and looking around on kiteforum, I think I've finally got a way to make the finish in the top of the board glassy right off the table.

If you search 'Porker' on the kiteforum board builders forum you'll find a really great looking board with a gloss finish right off the table. The maker doesn't give any details of the actual steps except to refer to it as 'pre-cured'. Eureka!!!

I'm guessing this just means a light ply of glass layed up on a sheet of plastic to get a mirror smooth finish on one-side, the side that will face up. Once this is cured it can be used just like the topsheet material Durasurf or PBT which has proven very difficult to source in small quantities in Australia.

So my thinking is just wet out a think layer of 3 or 4 oz glass on a perspex sheet, place a layer of peel ply over the top to blot away the excess resin and leave the surface rough so that you get a good mechanical bond when you use it as a top sheet. But wait, here's the rub. If you use clear resin first, lay the encapsulated graphics down ( I've printed them on tissue paper) then peel ply it. Give it a few hours and then apply a coat of white resin , peel ply it again. By letting the clear layer cure first, the white resin over the top of it won't infuse into the graphics like happened to me last time when I only left it a half hour or so. Any the opaque background means that you won't see any of the voids etc in the layers of laminate when it placed on the top in the lay-up.

Bit fiddly but it means that the topsheets can be made in advance and stock piled.


Core setup

Today I cut the core out and did the first dry fitting of all the bits I put together so far.

The overarching goal for this evolved to be more about getting the process of making the board run smoother and try to eliminate the multiple curing cycles needed for inserts, rails etc by being able to do them all in one go. While in principal the approach of putting a kit of pieces together and then gluing everything together at the same time as doing the glassing is right approach, I've come to realise that efficiency is lost if the pieces you create are not within very tight tolerances. For example, i used the same size speed bore for the moulds to make the inserts as I did for drilling the insert holes in the template for the board. However, it turns out the the moulds for the inserts where not drilled vertically, just a little bit off but enough that each of the inserts needed to be sanded to fit and I lost about 1 hours and did lots of fiddly dusty work. So, next time round I'm going to focus on getting the tolerances on everything very tight.

Anyhow, had a chance to tinker today. Cut the core and did a dry lay up of the core 'kit' and tried a new reusable vac bag made from thick vinyl.

First thing was to put double sided tape down to hold the loose planks while i routed around the template

Then without any sanding I did a dry fitting to see how tighly the whole thing would hold together and if enough pressure was being applied to hold the rails on.

The pieces of the mould are pulled together using gaffer tape. Soon after this shot, the tape tore under the pressure. Then I had the ah moment and stuck some Velcro ( hook and loop) at both end. Worked like a charm. Was adjustable, strong and when is clamped down inside the bag, it hold tight.

The core needed a bit of trimming here and there. This was because I made a mistake when I got the rails material cut. I got 10mm strips but my router bit is 9.5mm. This was enough to require re-routing the moulds to accommodate the larger rails and of course the freehand work was a mess so the rails were not a tight fit straight away. After about 1/2 of work it was all good.

I put the mould and core inside a full bag mag of thick vinyl. The long sides I sealed with tacky tape but just used masking tape at the opening where I put the board into. Sealed very well and was easy to under. I went with the thick vinyl because the plan is to lay it up flat, put it in the bag and evacuate it and then form it in the jig. Having the full bag means that I won't have the problem of the table surface bending because this time the clamping pressure is on both sides. There will be a lot of pressure on the bag at the points where it lays on the jigs so I thought that think vinyl was the way to go.

I made the bag very oversized. The vinyl seals to itself very well and so the oversized bag, I suspect, help get a really good seal.

Monday, January 23, 2012

Graphics and substitute reinforcement

Philip the kite surfboard maker gave me a tip on doing encapsulated graphics. Print them on tissue paper using an inkjet printer. To make sure the tissue paper feeds through the printer without getting crumpled you can spray an A4 sheet of standard paper with a very light coat of spray on adhesive such as kwik grip in an aerosol can( that you can buy from Bunnings hardware) and press the tissue paper onto it. Worked like a charm.

I guess you need to make it very light so that you can peel it off again and so that you don't make it water proof. You can encapsulate the tissue paper between layers of glass or just press it into the top before you bag it. Apparent both work well and for the top surface, at least, the extra scratch resistance of encapsulating it is probably not an issue.

I was going you 2x200gm layers of eglass on this board but in persuit of the goal of reducing the number of steps I 'lashed' out and bought some 450gm 0/90 stiched e-glass. This should be stronger than the 2 layers of woven e-glass because stiched material is basically 2 layers of unidirecetion glass with a small about of bonding agent and then layers stitched together. This removers the crimp that reduced the strength and effective elastic modulus of the reinforcement.

453 gm stitched e-glass
It comes in 1270mm widths at FGI and this turns out to make it more economical than buying the 200gm woven fabric because its wide enough to use for at least 2 boards if not 3 whereas the widths the 200gm came in meant that it was enough for one board width and a lot of wastage.

However, this is likely to make the board stiffer than BoardOff would estimate because the 50% reduction in the theoretical elastic modulus of e-glass used to model the woven fabric will probably underestimate it for this fabric. This means a stiffer board.

I was eyeing off the triaxial glass but the lightest weight is 750gm/sqm which would translate into about 1.4 kg compared to around 800gms. Given its a light wind board the extra strength and weight might be overkill.

Sunday, January 22, 2012


I started working on getting the rails formed for the LiteBoard kit. I'm using 10mm ABS plastic strips to try to avoid waiting for the pour rails to cure.

I had the local plastics shop cut the ABS off cut sheet I had into 10mm strips so they are all nice and uniform. The side rails are no problem but I wasn't really sure the best way to form the rails around the tip.

ABS is a thermoplastic so heating it up makes it go very pliable but at what temperature is it workable and at what temperature does it burn. Rather than google (cause I dont' have a thermometer to do anything precisely) I experimented on a number of ABS strip offcuts. The approaches I tried were

i) Use a propane torch to heat the plastic through fibreglass matting to minimise the direct contact with the flames
ii) place the rail material inside a narrow metal pipe (and on a bed of fibreglass to keep it from direct contact with the metal to avoid burning it
iii) Use a multiple quick passes of the flame directly on the plastic

Pipe Oven.
On balance (iii) turned out to be the best approach. I simply held the rail by the short end, passed the torch under it back and forwards quickly at a good distance so it was the hot gases and not the flame warming it up and as soon as the plastic started to bend under its own weight it was in the right state to be formed.

ii) Has promise and will probably be the best approach if I can get a temperature probe to monitor the heat. Alternative I could just look up the require temperature and see if our kitchen oven an provide the right amount.

UPDATE: The magic number seems to be 234 degrees f or 112 degrees C. Should have just backed them in the oven!

In the various attempts I scorched the plastic. It didn't burn it but there was brown discoloration on the outside. When it cooled I tried breaking it and the scorched plastic was definitely more brittle - it broken rather than deformed elastically before separating. When I examined inside there was clear small bubbles in the plastic which no doubt would account for some of the reduced strength.

Once I had worked out the approach to softening the plastic I used the board template and the plastic mould pieces to press the rails into shape.

Used the core template and the mould pieces to force the rails into shape. Word like a charm

So, the final piece of the puzzle left to solve is how to be secure the mould piece onto the rocker table surface. One approach would be to just to bolt it in place but I'm reluctant to drill holes in the table surface because it will mean drilling a new set of hole for each mould and template.

I have been wonder if, once its in the vac bag and clamped then this might be enough to hold them in place ( the idea will be to assemble and vac bag the the lot including the rocker table when flat and then bend it in the jigs. So everything will be clamped before bending on the jigs. I' wondering then if the clamping pressure from the vacuum will be enough to hold the mould pieces in place. I think it will come down to how much tension the bag can hold without stretching. I don't think that proper vac film will be very good at this cause its design to stretch over the surface and not bridge. So, I think that using thick PVC film like table protectors might be the way to go.

Saturday, January 21, 2012


I really like the look of narrower planks of wood in cores. Ken from South Africa recently sent me some photos of the board he had just been working on with his brother in NZ. They did some really great work with laying out the grain pattern of the wood. narrower strips but also laying them off axis and it looked awesome.

I had tried to cut the 100mm planks I've got into 50mm by hand but the limes weren't straight enough and there was gaps all over. So I thought it was worthwhile to spend sometime making a hobby sized table saw to cut the 100x6mm planks. I bought a very handy HandyCut by Worx tool a while back. it's a single hand controllable circular saw with 100mm blades on it. Very very useful for all manner of things.

I used scrap bits of mdf and just clamped the table top to the work bench. worked like a charm and so now if planked the wood into 50mm strips ready for cutting out the template.
Side view showing the HandyCut saw mounted underneath and the surface clamped to the workbench
HandyCut Bench Saw set up to mill 100mm Paulownia planks
Showing good OH&S practices in action
Planks all cut into50mm strips ready for cutting out with the template.

Thursday, January 19, 2012

Production Improvements - Moulds and Inserts

So, the other part to this board is an attempt to improve the speed of production. I've blogged about this before and come up with a few different ideas but I keep coming back to the general approach that Brokite use. There setup lets the make a kit of all the pieces and so when the board is made the core and inserts, rails, laminate all go in at one time so no waiting for epoxy to cure time and time again before getting the board done.

Eliminating waiting this way is the low hanging fruit in improving the speed that a board can be made. To date I've had to wait for epoxy for the core material (planks of layers), inserts, rails so at least 3 x 10 hour waits.

This time I'm going to try to kit it Bro-style

First things first, the templates for the board and the rocker table. I used 16mm MDF cause its cheap and dense.

Rocker table jigs
Board Jig surrounded by perspex sheet to be used for clamping
I had some 4mm perspex that I bought from our local recycling center and so once I'd cut out the board template from MDF I placed it on the perspex and used the 9.5mm inverted flush trim router bit to cut out the outline of the board with the 9.5mm channel all the way around. These pieces will ultimately be used to hold all the board pieces together once they are assembled and layed up. I haven't quite worked out how to secure under the vac bag but all in good time.

The core is going to be 6mm thick so the 4mm perspex will ensure that these mold pieces done' interfere with the glass bonding to the rails.

Next up is prebuilding the inserts. Again recycled perspex to the rescue. I cut a piece of 6mm perspex lengthways, pushed them back together and clamped them in place then used 16mm and 25 speed bores to drill the holes centered on the lengthwise split. But  'gluing' pieces back together with silicone sealant I created the moulds for pouring the inserts. I used a bit of mould release but it probably wasn't needed.

I mixed up 40gms of epoxy and but a very small amount of q-cell in it just o discolour it because I am using the M6 stainless steel locking flange nuts for the footstrap inserts and I didn't want them to be too visible. I filled the nuts with wax and washed them in isopropyl alcohol to get any contaminants off.

I need to use these nuts as the board is only going to be 6mm thick and so the bolts will need to go all the way through the board to avoid the risk of delaminating the glass underneath the inserts and to provide enough thread for the bolts to get a good grip on.

Then I placed masking tape on the underside of the mould plastic to create the complete mould and poured the footstrap inserts and also the fin inserts all in one hit.

M6 Stainless Locking flag nuts encased in epoxy in the mould

When it had all cured the inserts popped out easily and the mould is entirely reusable after a bit of fresh silicon is used.

There is some extra meat on the inserts  ( I purposely over-filled them) so that then can be sanded back to rough them up for better bonding. The wax stops the epoxy getting into the thread and avoids the need to re-tap the thread.

So now I've got the inserts that can be placed in at layup time and I can make them whenever to build up a stockpile.

Net step will be cut the core pieces and the rails.

Light Wind Board underway

I'm going to have a try for a light wind board as around here we get a lot of low 10's knot days. Fellow board builder Jorge in Argentina built a great looking 147x43.5 wood core board that gets him up in going in 9- 11 knots on an 11 meter. That adds up to a lot more time on the water

In part because the planks of wood I have are just 140cm long and partly a desire to test out the idea the the width has a more important effect than the length when it comes light wind performance I've gone for a 137x44cm design. Here's the BoardOff Plans.

BoardOff Plans incl. rocker jigs

I made the mid section much longer this time at about 400mm and let it taper just 1% of the width between the middle and the end of the mid-section. The straight rails will help up wind in the light conditions. Tips are 375mm wide (355mm+20mm) rails.

I've tweaked the concave/rocker a bit this time. I'm planning on making it from 6mm wood planks. When you run the numbers this roughly doubles the maximum stress in the outer layer of glass. So to improve things I changed the rocker and concave in two ways:

i) Included 6mm of concave at the middle but have it reducing much more rapidly so that its relatively flat just after the footpads. This should stiffen the middle but let the tips flex a bit as I am not going to thin them out.

ii) Used the NHP style rocker line that is curved through the mid-section and relative straight to the ends. However, because I'm building it thinner this time and its likely to flatten in middle when water pressure is on it, I kicked the tips up a bit so that when the mid section is flattened completely the will still be about 10mm of rocker in it to help ride over the chop which plagues us here in DY. This also makes it easier to get the rocker table surface to conform to the jigs as it was a bit easier to avoid introducing kinks.

Overall the board has 30mm of rocker which I'm feeling is a bit too much for really good light wind performance because rocker = drag but the trade of is spray in the which I am thoroughly sick of. This is a bit of an unknown so only time will tell.

In terms of layup, the plan is 2x200gm e-glass top and bottom with 2 x 65mm uni direction carbon tape strips along the length top and bottom which will cover about 30% of the top and bottom of the deck. Uni directional reinforcement is about twice as strong and stiff as woven cloth because of the absence of any crimp in the threads that delays the fibres bearing the load. I've run this through BoardOff's flex model and AEBE the stiffness profile is about 10% less that the same as the 9mm concaveless board from my last attempt. The maximum stresses are still about double, there is no getting away from that as the stress accord to the E-B equation is only a function of the geometry of the cross-section and the distance of the outer layer from the neutral axis of the cross section. It doesn't depend on the elastic modulus of the material. The strain will but the stress won't. So hopefully using the carbon whose elastic module is about 210 GPa compared to e-glass 80GPa will provide the extra strength required to avoid breaking it.

Rails: I bit the bullet and got our local plastics shop to cut the ABS plastic off cut that I had into 10mm strips for using as rails. This time around I'm going to flame treat it properly as last time I used it it was the cause of the delamination that cracked the board under my heal.

The other thing I want to work on is improving the speed of production...