best PSI to use

mrobyrne · Post by **mrobyrne** » Tue Oct 21, 2008 11:20 am

hi
i am just about to make my first board.
i have made a fire hose press but am unsure what pressure to operate it at.
i am told too much pressure will leave the board with too little epoxy.
after speaking with a local company on how to set the pressure i was told of a formula that will can take into account the parameters of your press and output the correct pressure.

any thoughts would be greatly appreciated
P.S i am making a snowboard if that makes a difference

MontuckyMadman · Post by **MontuckyMadman** » Tue Oct 21, 2008 12:00 pm

Please tell us what your experts told you.

Most people here I believe are between 50 and 75 psi. for a pneumatic press
Room temp cure or heated?

mrobyrne · Post by **mrobyrne** » Tue Oct 21, 2008 12:24 pm

unfortunately the formula has been missplaced. essentially i was told too much pressure will remove too much epoxy from the snowboard, making it light but also very weak.
i also do not have a heated press, i am thinking that a room temp press should operate at a lower pressure, as the epoxy will be weaker than heat cured epoxy.
is this correct?

MontuckyMadman · Post by **MontuckyMadman** » Tue Oct 21, 2008 12:30 pm

I don't see your logic. Its more about set time than it is strength and weakness. I figure you think it will be weaker so you want to leave more epoxy in the ski and not sqeeze it out? In a heated press temp and pressure is ramped to achieve the best balance. ( I think)

I would test your epoxy and observe how its sets over a room temp cure.

rockaukum · Post by **rockaukum** » Wed Oct 22, 2008 7:39 am

I press at about 40psi on my skis. I have used a pellet stove in a small room to heat the press (and everything else in the room) to about 125*. I have also done without the heat. Follow what the epoxy states for the cure time and then let the ski sit for a few days before flexing. Should be fine.
rockaukum

SHIF · Post by **SHIF** » Wed Oct 22, 2008 9:34 am

I have pressed several pairs of skis so far and experimented with bladder pressure and temperature parameters quite a bit. My lower press form is a heated aluminum sheet based on the construction described in the “articles” section of this great web site. My press frame is steel I-beams with a 88” long opening span.

I’ve settled on 35 psi in the bladder. Much more than this and two negative things happen to the ski:

• Too much epoxy (QCM) gets squeezed out of the ski lay-up resulting in sunken bases, and every tab on the steel edges making bumps in the base.
• The ski camber gets flattened a bit due to press frame beam bending.

I just pressed a perfect pair of skis this past weekend using 35 psi. I let them sit in the press under pressure for half an hour prior to turning on the heater. Then I warm them to 150F for 30 minutes, then 190F for two hours. Finally a long bake at 160F for three hours. After all this, I turn off the heater and let them sit under pressure all night long.

I believe a heated press is essential and well worth the expense and effort. I don’t recommend using thermocouples embedded into the heater blanket. For more accurate results I simply tape a type K thermocouple from Omega:
http://www.omega.com/Temperature/pdf/5TC.pdf
directly onto the aluminum sheet covering my silicone heater blanket. It responds very quickly and my heated ski press is very stable.

Cheers,
-S

rockaukum · Post by **rockaukum** » Wed Oct 22, 2008 3:00 pm

Shif,
A couple questions for you...
On your bases, do you route out a recess for the edges? On skis that I did not do this I had the concave base effect you described and when I routed, the skis were flat.
The second question has nothing to do with this topic but I would like to know the height of the press cavity (without mold, blatter ect) and how much room do you leave for the layup (measurement between the top of the bottom mold and the cat track, if used)?
Thanks for the help
rockaukum

knightsofnii · Post by **knightsofnii** » Wed Oct 22, 2008 4:37 pm

we're going to get some TC's like the one SHIF described, to put on the top side of our "cassette" just to gage what it is doing during pressing.

I'm under the suspicion that the heat blanket does not like to heat up when at 60+psi, it took 35-45minutes for our probe to get the controller to shut off when set to 180degrees, then after baking for half hour was still not enough to kick the top layers.
Though i later found out the QCM formula I have has a 45minute cure time at 180.

I'm using EVH 0043 and ECA 408. There are MANY different QCM formulas and combinations of resin/hardners within these, and I bet no two of us are using the same.

And now I forgot what my point was, ...oh...
Rockaukum, what do you mean by putting a recess in the base? Do you mean recessing the SIDEWALL or the CORE, to account for the edge tooth thickness?

We just pressed at 65psi for what I described above, then when we pulled it out early and saw it was all bubbled, threw it back in real quick and ramped the psi up to 70psi and 180degrees.

Heat DOES make a stronger board. Read the Q&A with Roy from QCM. I've cured at room temp and at 160+degrees, and so far the results are boards that you can really BEND the snot out of before you hear any kind of cracking.

Also get resin that's designed for ski's and boards: QCM, Jeffco, some Huntsman formulas, I think one or two more. West System and other "marine epoxy" formulas are diluted versions of the above. They are designed for bonding wood to wood, and for laying up fiberglass over wood, not really built for "compression molding", though they seem to do ok with it, there's better stuff out there

. QCM doesnt cost any more than west system from what I've seen.

rockaukum · Post by **rockaukum** » Wed Oct 22, 2008 7:01 pm

Yes. My bad. I do mean the core to account for the edge thickness.
rockaukum

SHIF · Post by **SHIF** » Wed Oct 22, 2008 7:13 pm

knightsofnii wrote:...I'm using EVH 0043 and ECA 408...

Exact same epoxy and curing agent that I use. Seems to have the longest pot life of any combo QCM offers. I transfered the corrosive curing agent into a one quart rectangular tin can having a screw-on cap. That stuff is really nasty and I don't like its original shipping container.
I use a standard pump made to screw onto quart cans (TAP Plastics sells these for a couple bucks) to dispence the curing agent. I weighed the amount dispensed during one full pump action to be 26 grams. Therefore I measure 104 grams of resin into each of several 5 oz. paper cups prior to a building session. This way I can easily mix up a mini batch of epoxy as needed. I have a couple extra resin cups ready just in case. So far I've only needed six such mini batches per ski build, using about five and a half in the actual lay up. Unmixed epoxy resin gets dumped back into its gallon container.

Hey rockaukum, as for routing a step into the core assembly to accomodate the edge tabs, I've not tried this. My cores of choice are now vertically laminated bamboo with UHMW side walls and P-tex tip filler. I can envision creating such a step using my router table, just need another template and a bit set for a shallow cut. Ya, that will work...next time I'll try it!

I just wet belt sanded and stone ground my latest skis today on my local Wintersteiger. There is definitely minor base "sinking" evident near the edges, especially near the front contact point of the ski. This may clean-up with multiple passes over the stone. I don't think its really that bad however, especially since I expect to peg a few stumps and rocks with these puppys anyway.

Speaking of my latest skis, I added a three inch wide strip of 9 oz. unidirectional carbon fiber above and below the core. This in addition to my usual 20 oz. triaxial E-glass layers top and bottom. I expect this carbon to really add some "pop" to the ski. Plus it was really fun to work with.

Good luck to all...

-S

bigKam · Post by **bigKam** » Wed Oct 22, 2008 7:44 pm

This is just a thought and I don't think anyone is doing this, but locating the sensor (TC) far away from the heat source could present a challenge for the controller, unless the controller gains are properly tuned to limit the heat output.

doughboyshredder · Post by **doughboyshredder** » Thu Oct 23, 2008 6:00 pm

SHIF,

Why do you do the temp ramp up and press for such a long time? Is this your formula, or did qcm suggest this? I am curious because some manufacturers use qcm and cook their boards for 12 minutes or less at 175. I am especially curious about the first half hour with no heat. I don't get the benefit to this, can you fill me in?

Seems like we may have discussed this somewhere already, but what is everyones opinion on whether the press should be preheated or not.

knightsofnii · Post by **knightsofnii** » Fri Oct 24, 2008 8:42 am

per Roy @ qcm, using evh0043 and eca408, requires 45minutes of cure time AT 175 to 190ish degrees.

Blanket takes time to heat up, then heat needs to get through board entirely.

Ramping the thing up slow allows more uniform heat....heat gradient?...through the board. I mean you wont have the bottom at 180 and the top at like 100 still. But ours just never even hit 180 for like 45minutes.

Other epoxies take less or more cure time at different temperatures.
There are definitely epoxies out there that you can heat for 15minutes and they cure fine.

SHIF · Post by **SHIF** » Fri Oct 24, 2008 10:19 am

doughboyshredder wrote:SHIF,

Why do you do the temp ramp up and press for such a long time? Is this your formula, or did qcm suggest this? I am curious because some manufacturers use qcm and cook their boards for 12 minutes or less at 175. I am especially curious about the first half hour with no heat. I don't get the benefit to this, can you fill me in?

Seems like we may have discussed this somewhere already, but what is everyones opinion on whether the press should be preheated or not.

I don’t turn on the heater right away because I want the excess resin to flow through the fibers and out of the ski. At ambient room temps most of the excess resin is expelled. A slow warm-up lets thing equalize. An hour or so after starting my composite lay-up, the epoxy starts to exotherm on its own and curing begins. This is when I turn up the heat and let ‘em cook.

If you have a dual heater press, one on the top and one on the bottom, then I think you can cure the ski much faster as Roy suggests. I only have a lower heater. On my first few builds I attached thermocouples to the top surface of the ski so I could measure the heat transfer up through the ski lay-up at a couple locations. At the thickest part of the ski I always measured a delta of 20 degrees F. Therefore I cook at 190F which results in about 170F in the coolest part of the ski, still hot enough to fully cure the epoxy. I cook them for several hours because it takes time to fully equalize and simply because I can. Longer is better, right? I made up the temperature recipe myself after discussions with the chaps at QCM and building several pairs of excellent powder skis.

Hope this helps…

-S

doughboyshredder · Post by **doughboyshredder** » Fri Oct 24, 2008 8:42 pm

Makes sense, thanks for the well thought out response.

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best PSI to use

best PSI to use