So many problems.

[chrismp]

1. Check your thermocouples and heat blankets for faults. I've had a fried circuit on a heat blanket with the TC right on top of the broken circuit which caused the heat blanket to get way hotter than the second one. If you're using a PID make sure it's calibrated properly.

2. How do you make your cores? Any stress in the wood itself can be exeggerated by heat.

3. Is your fibre weight equal on both sides of the core?

4. Do you pull your boards out of the press when still hot? I usually press at 80-90°C, then I let the press cool down to about 70°C and pull the board out. If you do this you need to put the board on its side (rails) immediately and let it cure like this at least for another day to keep it from warping.

I don't think the base material is the culprit here. If it was, how could any one of us press a flat board (my boards come out almost perfectly flat)? I even pressed a board at 130°C because the base had warped so badly from sublimating it under too little pressure. Still, the board came out flat.

[SleepingAwake]

Carbon fiber has a different cte in different directions, so it can be pretty tricky to have a flat part.

First of all, do you have a layup with the same fiber orientation on both sides?

Do you use a symmetrical layup in terms of fiber weights as well?


If both of the upper points are true, I would try to put a thin carbon fabric with 90° fiber orientation on the bottom side to "pull this side together" while cooling. I know that there are ski manufacturers doing that to get flat bases (sometimes on top, sometimes on the bottom, depending on the rest of the layup).

[Dtrain]

The above is true. I have put a 90 degree carbon Layer on bottom and created a concave snowboard base. Sucked to base grind, but what a sweet ride it was.

Wish I could be of help. We mess shit up all the time still. Just need to sell a pair of nice ones once in a while to keep the experimentation funded.

Good luck

[Richuk]

Hi,

Is the core dried using a separate heat cycle prior to use?

Your boards come out concave, but flattern out when subject to a second cycle. Does this mean the topsheet is flat and become concave?

Could you provide a sense of the width of the edge rebate and how the core is held within the cassette.

Are there problems with camber, is it correct or exaggerated.

[BLOODTYPEZX10R]

MM I have had no problems with carbon fiber in my boards, either uni or 2x2 or 4x4, a combo of fg, and cf with multiple layers.

Yes metal cat track (steel 1x1 .065 wall). Never any issues at tip and tail upcurves with flatness after completion (of course this is a compound area and would not expect distortion to happen there).

I am sorry that I cannot explain exactly my cores but I can say that at the point that I am assembling base etc. the core is flat across its waist and profile matches mold 95%+.

Carbon fiber has a CTE relatively close to glass fiber depending upon which end of the scale you look at (cf -1 to +8, glass +7). If this were and issue it would have presented itself in my core construct.
Heat has been applied top, bottom and top and bottom. I have worked with ramping temps with again no differential in results.

Now, the elephant in the room. Thermal expansion of the base. If the base expands thermally then the base expands thermally, period. In all directions and at a proportionate or somewhat exponential rate. The waist of my boards range from 17mm-22mm using racing base material. I would suspect that different base materials would expand at different amount due to additives.

These problems only happen after the final assembly is cured.

[BLOODTYPEZX10R]

Richuk, only flat if the heat is applied, if the heat is close to pressing temp. the board is flat as it cools again the base will go right back to concave.
concavity comes thru as convex on top. The entire core is being pulled in at he base.

[Richuk]

So you have no lateral shift of the core. You have looked at a faulty board in cross-sections?

[BLOODTYPEZX10R]

I have used two heating processes one hydronic and silicone heating mats, both have been closely monitored for actual temp compared to pid temp. For our purposes the temps are within a few deg. C.

Uni-carbon is most likely to expand along its length since the fibers are not common to each other in their width. I do not use top sheets and the board is wrapped with carbon fiber twill. In the final process all materials are held in place with vacuum bag and pressed.

I have tried a core with just heating from top and the result is a convex base (without the base applied); however given a few days the wood will stabilize and will return to flat. Is does effect the camber (relaxes) and tip and tail curvature (relaxes) and is not effected by moisture content.

I believe top heating only and the changes that occur is because naturally heat rises and the thermal pressure going into the board is being dissipated by a poor thermal conductor (wood) and eventually absorbed by the aluminum liner of the mold and drawn away from the core.

[BLOODTYPEZX10R]

Dtrain I would have to say that there advantages to having a base that is concave in the case of corrugation. It is much stiffer for the given thickness, but impossible to grind-unless it is kept at a constant 170* during the grinding process.

[BLOODTYPEZX10R]

So you have no lateral shift of the core. You have looked at a faulty board in cross-sections?

There is no way it can shift- core is done before it goes in the press for final stage assembly.

[BLOODTYPEZX10R]

First of all, do you have a layup with the same fiber orientation on both sides?

no, but neither does the core and it is perfect.

Do you use a symmetrical layup in terms of fiber weights as well?

no, but neither does the core and it is perfect.


If both of the upper points are true, I would try to put a thin carbon fabric with 90° fiber orientation on the bottom side to "pull this side together" while cooling. I know that there are ski manufacturers doing that to get flat bases (sometimes on top, sometimes on the bottom, depending on the rest of the layup).[/quote]

I may try one with no cf between base and core, if this is true then we would expect the result to be a convex base due to cf on top of board.

[Richuk]

Do you know how much epoxy you are losing to the core. Are the core materials top and bottom the same? Have you measured for consistency in the thickness of the laminate?

[BLOODTYPEZX10R]

So lets assume there is no lateral shift and that the lower laminate is not affected by a kink over the edge set. Do you know how much epoxy you are losing to the core. Are the core materials top and bottom the same?

How much epoxy I am losing to the core? I am not sure what you are asking but I will say given a board that is 179cm overall and a waist of aprox 19cm with a side cut (general) of 12m. One layer of 4.5oz uni-carbon it take about 60mg? to wet out, I cannot say to any precise measurement because all residual is absorbed by mat.

I present this too you, if the rebate is an issue would you expect the concavity to neutralize when the board is brought back to curing temp and if so why? I do not use sidewalls but what I have coined as a consumable above the edge. The only portion that is in contact with the core are the teeth of the edge and the concavity would represent the entire thickness of the edge. All measurements of materials and edge teeth are accounted for, rebated in depth and width. Checked prior to assy.

If there were a shift then it would only effect one side of the board as the other would be off and low. The final measures identical from side to side core thick. including base.

[chrismp]

I think it's kinda weird that you suspect the base material's thermal expansion to cause the uneveness of your boards. You claim you've had no issues whatsoever with your process in the past, but all of a sudden it's a soft piece of thin plastic causing your problems?! Did you change anything about your base material compared to your previous builds that went well? If not, the bases are probably not the issue.

My guess is that a combination of your core wood (which can behave differently depending on which part of a tree it came from) and your fibers is causing your issues. Try pressing a sample with base, edges, core and even fibre layout and see how that goes.

[chrismp]

What Richuk refers to is the fact that different types of wood and wood fiber orientations can soak up different amounts of resin which need to be accounted for.