Quantcast

tunable board

classic Classic list List threaded Threaded
28 messages Options
12
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

tunable board

mattma
Administrator
At last! After being the longest serving non-contributing member of the forum I'm happy to say that I've turned the first sod on a new board project.

I going to have a go at making the tunable board that I've been thinking about. The idea is a board that you can change the concave and rocker in the mid-section by tightening and loosening differently shaped jigs that will be bolted in place. For freestyle in flatter water the idea will be to increase the concave to stiffen and flatten the mid-section and for riding choppy conditions or surf I'll loosen the mid section so that it is more flexible and makes for a softer ride.

One small hitch is that a few of the key shops I need are shut and I'm going to reuse the template I cut for my last project which is a Lunacy like outline. 134x41cm, 6mm wood core, 450gm stitched e-glass + 120gm woven glass top and bottom. Additional stiffening under the footpads plus some additional support where the tuning jigs will contact the board.

The first step was to cut the 100mmx6mm paulowina planks into 50mm widths, shuffle them around so the imperfections get distributed and glue them. I'm trying a new polyurethane glue called Purbond. It reacts with atmospheric moister and foams up so that it fills voids well. Its also really bloody strong as I found out after sticking the core to a sheet of perspex and breaking then end of the core when I tried to remove it.....

Gluing vertically

I only glued the end quarters so that the mid section planks aren't bonded. This will make it easier to add some 'default' concave to the middle without any spring back. The epoxy from the fibreglass will be squeezed in through the gaps and lock it in the concave (that's the hope anyhow).

A few strips of double sided tape down on the core to hold the jig in place



And then route around the jig and I drill the insert holes this time with a 20mm and 25mm Forstner bits for fins and footpad+tuning inserts. I used a hand drill rather than the drill press just to keep things moving along. Note the 3 insert holes between the footpad inserts. Really there is only one more than if you were including inserts for a handle. The placement of the tuning inserts is a shot in the dark. Hopefully the first prototype will shed a bit of experience on the subject.



I've still got some 4 mm abs plastic strips left over so I'm going to use them for the rails. I routed around the template to a depth of 4mm. I only have a 9.5mm router bit and the strips are 10mm wide so I had to freehand it a bit to make them wider. The idea here is to use the channel as the jig for forming the ABS rails.

The new tool in the kit is a heat gun ( cheap one for removing paint) and it works like a charm for heating the ABS plastic so it can be formed easily. Previously I was trying to use a benzene torch for both shaping and heat treating but the heat gun avoids the scorching of the flame is generally just easier to handle.



After shaping the rails I sanded them with 40 grit sandpaper and then hit them with the benzene torch to heat treat them. I'm using the Purbond again after the core breaking experience of sticking the wood to the perspex I am pretty confident it will hold the rails in well.





Now, I need the damn shops to open so I can get the glass.

Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

Wolfie
Quick work there Matt, I see you have drifted away from the 1 shot process on this one.  Are you still going to use a mould for the default shape or a conventional rocker table and half bag?
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

downunder
We are in Sydney for AU day!
Will u finish it till than?
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

mattma
Administrator
In reply to this post by Wolfie
Hey Wolfie,

Yes, I need to fine tune the one shot processes some more. One of the biggest time wasters in assembling it all in one shot is the poor tolerances on everything ( the template, the channel for the rails, the insert holes) meant that it was sufficiently asymmetrical that everything had one and only one place it could go. Having not foreseen this i needed to work out on the fly where everything went. As a result the time to get the whole think under the bag was too long and it left bubbles and excess resin (especially on the underside) because it had started to go off before getting everything in place. I think with foam cores this is not such an issue because the core has more give in it that the wood and so you can put a slightly square peg in a round hole so to speak. However, wood is not so forgiving.

The mould pieces that pushed in on the rails were there to hold all the bits in place while it cured but with the core 'par-boiled' they aren't needed any more.

This one thing I'm hanging on to it to make a uniform thickness core and use the placement of the reinforcement material to control the flex. Shaping the top surface was such a pain in the past I'm keen to avoid it.

I'm really keen to see what's need to make the tuning work so I'm not going to spend a lot of time making this one pretty. This is also a chance to use some of the scrap that's been accumulating around the place.

First things first though I've got to build the work area!! That's tomorrow job!


Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

mattma
Administrator
In reply to this post by downunder
Hey Dean

Yes. I hope so. I'm hoping to have it finished by the end of next week. Where are you staying in Sydney?

Cheers
matt
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Inserts

mattma
Administrator
 I managed to get half an hour today to do something on the new board so I started the inserts.

Only thing a bit new here is that I drilled the 20mm and 25mm holes in a bit of 6mm ply wood using the same bits I used to drill the holes in the core. Then I put tape on the underside and then put cling wrap in the holes. What I'm hoping is that the cling wrap a) keeps the resin in and away from the wood and b) keeps a bit of clearance between the wood and the resin inserts.



Is seems that the 'stand-off' from the holes (between the cling wrap and the holes) was helped a bit by the creasing and doubling up of the cling wrap when I pushed it into the holes. This is ideal because the creases will create channels around the insert that, when inserted into the board, will let the resin flow from bottom to top and glue the inserts in place.

Still using the 6mm stainless steel locking flange nuts. Filled the centers with wax and just poured the resin in around them.

Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

downunder
In reply to this post by mattma
mattma wrote
Hey Dean

Yes. I hope so. I'm hoping to have it finished by the end of next week. Where are you staying in Sydney?

Cheers
matt
Excellent!

I'll be in Darling Harbor. Caffe time?
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

mattma
Administrator
Done. I live in Dee Why which is not far from town. I'll send you my mobile number and we can organisation a time to catch up. Will be great to meet up!!!
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Core pretty much ready

mattma
Administrator
I had some spare time today after working on the work area that will be used for working on thing:) so I managed to do a bit of work on the core. I cut out the core and routed around it to expose the rails. I used my newly acquired multi-tool (or sonic tool) which has a cutting blade that oscillates rather than rotates. Worked well and make me wonder whether it could be used for cutting off the excess after putting the firbreglass on.



The shot below shows the non-bonded middle of the core. I only glued the end 25% so to reduce spring back in the concave.



The insert experiment seems to have worked. I ended up with lots of channels around the insert that will let resin flow from top to bottom and any insert fits in any hole so no messing around like I did in the one shot construction where I had to work out which one went in which insert hole.


Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

downunder
In reply to this post by mattma
mattma wrote
Done. I live in Dee Why which is not far from town. I'll send you my mobile number and we can organisation a time to catch up. Will be great to meet up!!!

OK no probs! See you there than
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

mattma
Administrator
Have maxed out on the workshop renovations so decided to do some work on the board. There's still a few things I need to do so get the new pump and controller ready so I used the equipment I had planned to retire.

Old faithful



The layup I'm using this time is top to bottom

180 gm/m2  plain weave e-glass
graphics
450gm/m2 stitched eglass
core + inserts
450gm/m2 stitched eglass
printed surfboard inlay
180gm/m2 plain weave

perforated release film
breather cloth
single layer nylon vac film.

So, the whole process was 1 hour. Still too long. By the time it was going under the vacuum I am sure that the resin on the bottom side was not mobile. I used release film which holds in more resin so my guess is that its going to come out very resin rich so probably weaker that hoped.

First layer and graphics down. I miscalculated the amount of resin and so had to remix another batch. Doh.



Core and inserts went in. The inserts , now sanded where slightly undersized, dropped through in  a couple of places. But fortunately they stayed in the right spot.

I used pleats in the vac film to help it conform around the edges of the rails which are sculpted.




Under the pump now @ 55 mins. Its a cool night so that hopefully mains it still mobile. vac pump is holding 26 inHg.

26 inHg Vac. on Old Faithful.

Going....



... going ( 1 min after pressure starts to fall )



... at about 3 mins after pressure starts dropping.



I think that there was too much excess resin. In my haste I poured on loads of resin at the end but put the extra reinforcement at the footpads and tuning inserted on top of that. This meant that it was too hard to squeeze out all the resin without moving the extra reinforcement. So it was pretty soaked. tomorrow will tell.


So for next time, things to try

i) mix all the resin upfront and maybe chill down the half not needed until later so that it does not start curing to fast.
ii) See if I can get 1 layer of 650gm/m2 + glass to avoid working 2 layers per side.
iii) extra reinforcement for footpads etc to go down first.






Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

simona
Matt

how long will you have to keep it under vacuum? does that depend on the power of the machine?
mine will be 60 L/min
Did you apply release wax or release film on the plexiglass? i guess epoxy should not stick to plexi (am doing the same table with plexiglass)
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: tunable board

mattma
Administrator
Hi Simona

I keep it under the vacuum for 24 hours. Once the initial vacuum has been pulled the pump only comes on every 15 mins or so and runs only for about 30 seconds or so. That's why a pressure switch of some type or a timer is a key bit of the setup.

A couple of bit of info that might be helpful when you're thinking about vacuum bagging is that the all the work of squeezing the excess resin out and bending it over the rocker table is done by the atmospheric pressure outside the vacuum bag squeezing down on it. The volume rating of the pump only changes how quickly it can remove air from inside the bag. If you have a good seal around the vac bag then once the air is removed from under the bag there should only be a very, very slow rise in pressure so the pump will only need to engage every 5-10 minutes and only for a few seconds because there is almost no air in there.

In the video where the guy uses a standard vacuum cleaner, it runs continuously because he has a hole in the  hose so that the vacuum cleaner has some air passing through it all the time to help reduce the chance of overheating. However, running it all the time isn't needed.

With 60 L /m the air will be removed very quickly. Maybe even a bit too quickly to give you time to remove wrinkles or fix anything. You might want to stop part way through, fix anything you need to attend to and then continue.

The power of the pump I think will mostly determine how close to a full vacuum you can pull and maybe the longevity of the pump. No matter how strong a pump is the best you can do with vac bagging is 1 atmosphere pressure. I just checked my pump and it 1/15 hp ( 50 W). It has been comfortably holding 26 inHG  (85% of a full vacuum or about 12.5 psi).

If the plexiglass is brand new ( no scratches) then mould release may not be necessary. However, after a couple of uses or if the surface has scratched on it then the epoxy will stick to it (the epoxy will set around the scratches and hold onto them tightly). As a matter of course now I always put down and wipe back 2 layers of mould release. Its a good insurance policy.

Cheers
Matt

Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Post curing

mattma
Administrator
Yeeehaaaa. I had a chance to try out the controller and heat blanket that I'd worked on a few months back. The controller was a side project built around a microcontroller kit called the Maximite and the heat blanket was made following a very long thread on skibuilders.

I didn't have the opportunity to try it out before but today I decided to bite the bullet and use it to post cure the board while it was still on the vac table. The resin I use calls for 50 degrees for an unspecified number of hours.

So here it is in all of its overkill glory



On top of the board I put a layer of carpet felt underlay, then the heat blanket, reflective film, another layer of felt and then some weights. I put the 3 temp sensors on top of the board and then one underneath. I put the pressure sensor in as well and rigged it up to the vac pump but because everything was being powered through the same extension board the startup power spikes from the vac pump caused everything to reset. For the sake of seeing it all in action I just used it to monitor the pressure after an initial pull down.



A few interesting things came out of it.
i) The thermocouple wires I bought are long ( about 2m) and then picked up a lot of inteferance from the heat blanket (+/- 5-10 degrees C). This meant that using the instantaneous temperature readings to turn the blanket on and off had the relays cylcing on and off every couple of seconds as the temperature reading oscillated. I did a bit of tweaking on the software to convert it to a running average of 10 seconds and that helped a lot.



ii) once at temperature the blanket only came on about every 5-7 minutes and was on only for about 30 seconds. After switching off the temperature continued to rise for another couple of degrees, I guess while the heat off the blanket made its way through the felt.
iii) The blanket is only running at about half power to get up to 50 degrees which as about 400 W.
iv) there is about a 10 degree temperature difference between the top and the bottom of the board. This narrowed slowly over time to this level, I guess as the setup all warmed up.


Its been under for about 4 hours so hopefully tonight I'll take it off the table.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Off the table

mattma
Administrator
Whoa Hooo!!!!!

7 hours baking in the oven and she is cooked just fine:)






The resin on the underside was more mobile than I thought and bottom finish is great. The top is a bit patchy but a vast improvement over my lightwind board. The perforated release film definitely held in more resin. There were very few dry fibres visible compared to the results I got with peel ply directly on the surface. Adding the extra reinforcement on top of the deck was a mistake as I realised after I did it. The edges and loose fibres off them are quite visible. The stitched e-glass also has wider bundles of fibres compared to plain weave and pattern of it is also quite noticeable although it looks good in a rustic way.

The idea of the resin pushing up around the inserts was mostly successful. It did push through but it also pushed the inserts themselves up about a millimeter about the deck. Not entirely sure if it was the partly cured resin draging the insert up on the way or just the pressure over the underside of the insert. I suspect more space around the inserts might help but would need to make sure they remained centered.

Overall very happy. Haven't checked in the light for finer details but feel good about the progress on this one over the last couple of boards. The process highlighted a couple of things to work on (especially around the speed to get in under the bag).

Next chance I get I'll write up my learning log for it.

Cheers
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Off the table

downunder
She does look good hey!

What's the meaning of Japanese characters?

And, it looks quite a spring back?

Btw I decided to strip the topsheet off the board. Interestingly, this will be quite easy...Maybe around SS inserts not so. Will see.

Cheers
D.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Off the table

mattma
Administrator
Hey D

Cheers. The characters say Kamikaze which literally translates to God Winds which I thought was very fitting.

Almost zero spring back. I'm no suprised with this for the concave because with the planks not being glued in the mid section prior to glassing it they are glued and not bent into place. I guess the thin woodcore (6mm) means not much spring back.

Have you pulled to topsheet off already? Did Mirsad have any ideas?

Matt
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Off the table

downunder
This post was updated on .
Excellent,

Didn't know Kamikaze means God Winds! We always related Kamikaze to something else, WWII etc...

So not gluing mid section is a go. Good to know, thanks.

After I removed the protective plastic and the shine almost blinded me for good, decided to leave it as is.

D.

P.S.

The information I've got is that a loads of filler should be used with FG before rolling a topsheet. After glass the epoxy should be left to "breath" for even 2 hrs letting the air out. Than roll topsheet. However, I don't like using fillers, makes everything cloudy.

I would say than we should be using slow curing epoxy and not flame at all. Didn't flame it anyway.
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Off the table

mattma
Administrator
Hey D

The story of the word alway stuck with me since high school Japanese classes. On two ocassions in the 13th century when the Mongolian fleets where smashed by a Typhoon as they attempted to cross and invade Japan. The Zen Buddhism samuri's said the winds were stirred up by the gods to protect Japan. This is where the suicide pilots got their name from.

Letting the FG breath for 2 hours is a strange one. Does that mean most of the air is coming out of the core and not because it wasn't able to be squeezed out from under the topsheet?

What is the filler supposed to do?
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Off the table

downunder
The info is from an kite board builder here locally and he says it can be 3hrs process leaving FG to breath. Duno.

My bamboo is sealed anyway I wouldn't say the air is coming from the core. But sometimes when I use a spreader with epoxy I see heaps of small air bubbles on the spreader, which stays on FG.
This is not a  problem when using perforated layer. Air goes away. I’m guessing perforated core would eliminate topsheet problem. It would be even possible to do everything in one go with perforated core, top and bottom Providing plastic is only at the bottom.

I forgotten what he said about a filler. I hate using it

Might be nicelly filled FG threads? They are visible now under the topsheet, something I never seen before.

I've just had a look at Mirsad prod. photos and it does look like heaps of filler, like really heaps....
12
Loading...