using m + f molds

jwahtera · Post by **jwahtera** » Tue May 24, 2011 9:33 am

Hi!
I have acces to a lot of machinery viá dayjob and I'm currently in design stages to building a few skis as a side project.
We have a large oil-heated hydraulic press used to glue veneer sheet to mdf sheets forexample, and a nice CNC machine. Seems to me it would be most practical to model the ski in CAD, make fairly thin (20-30mm) male and female molds and a casette-sheet using the CNC and then press the ski in the heated hydraulic press without any bladder. Absolutely everyone seem to use bladders here though, so is there some profound problem with "hard" molds?

Thanks, great info and inspiration here!

JV

skidesmond · Post by **skidesmond** » Tue May 24, 2011 10:24 am

I suppose since you have access to such equipment that can make super accurate molds, etc using CNC it will work. I'm assuming this press can exert plenty of pressure.

One thing the bladders and cat tracks provide is to distribute the pressure equally to account of inconsistencies in the molds.

But sounds like what you have will work.

Brazen · Post by **Brazen** » Tue May 24, 2011 1:41 pm

"I just happen to have a Ferrari, but I notice you're all driving Chevy trucks". Is there a reason all of you prefer trucks? Is there a profound problem with Ferraris?

Really? No. Go ahead on with the beautiful equipment you have available.

novaskis · Post by **novaskis** » Tue May 24, 2011 4:31 pm

my truck feels like a Ferrari to me

it how ever it looks like the beater car i used to drive

COsurfer · Post by **COsurfer** » Tue May 24, 2011 7:43 pm

Ferrari's dont make it to powder days.

OAC · Post by **OAC** » Tue May 24, 2011 8:33 pm

Brazen wrote:"I just happen to have a Ferrari, but I notice you're all driving Chevy trucks". Is there a reason all of you prefer trucks? Is there a profound problem with Ferraris?

Good analogy!

richie · Post by **richie** » Tue May 24, 2011 9:39 pm

http://www.topspeed.com/cars/car-news/l ... 87270.html

crikey even has a roof box, hope he drives this thing like its meant to be , can you get chains on those tyres without ripping all the carbon out with one loose link?

cool, sort of

think I'll stick to my Nissan anyway!

cheers, Richie

twizzstyle · Post by **twizzstyle** » Wed May 25, 2011 9:15 am

That's why I have the Lotus for summer, and Subaru for winter

CNC'ing molds opens you up to proper cap-construction. People have tried doing cap-construction with various other methods with varying levels of success, but you really can't get a perfect cap without a CNC'd top mold. If you've got access to machines that large - go for it!

Keep in mind that while the "big guys" use CNC'd molds, they still use firehoses and air!

jwahtera · Post by **jwahtera** » Wed May 25, 2011 11:56 am

I ride a Buell but otherwise I see your point... Didn't mean to brag, sorry

I found older threads about this, even with exactly the same kind of machinery we have in pics, but they weren't very descriptive about what the outcome was. I'm concerned about uneven pressure distribution. Part of it might be fixed with a layer of rubber in top mold but it's not the same as a bladder, it definetly has a function in there like stated above. Also measuring the pressure will be more math and guessing and less "check the meter in the bladder"...
I think for now I'm gonna start with hard molds with maybe 3-5mm rubber somewhere in between and press a pair of skis. I could split one ski in the midlle to check layer thicknesses. Then build a bladder if I'm not happy, this way I'll lose nothing.

Another idea is to use the press as a clamp and heater for an autoclave. The idea would be to lay a sheet of silicone on the bottom mold with the ski, then put a box on top of it and clamp it down in the press. The press would heat the mold and air inside the box. Pressurised air would be fed to the top "box" and a vacuum pump would suck air from the bottom mold. This would have no disposable parts as silicone sheet won't stick to epoxy and no vacuum-tape is needed since basic silicone insulation-tape can be used between box and silicone sheet. Well , suction pipes will be lost to overflooding epoxy but that's not much.
This has one problem: I have no idea of the amount of force 4bars really is, considering the press and the conclace box. I don't wan't to blow the press up nor make a steel box if don't have to (I was thinking mdf+laminate, or mdf+velcro).

twizzstyle · Post by **twizzstyle** » Wed May 25, 2011 10:00 pm

4 bars is about 60psi. That would be equivalent to pressing with a firehose at 60psi (that's around what I've pressed at with my firehose). Without the autoclave you're only getting about 14.5psi (1 bar, duh) which works, it's just not ideal.

jwahtera · Post by **jwahtera** » Thu May 26, 2011 2:02 am

Yeah, I get that but putting a pressure inside a pres is a risk to the pressing machine. And I don't really get if 4bar/60psi is a lot of force or not, I think it's pretty much... 4kg/cm2 is 40'000kg/m2 inside the press with 1m2 mold area. Does that mean it's equal to puttin 40t of mass in the press?

The autoclave is > work than making a top mold anyways so I'm starting with molds. A working autoclave would be sweet for a lot of different stuff we build here though.

OAC · Post by **OAC** » Thu May 26, 2011 11:22 am

Don't loose it! You had it all in the first post!

Check this one:
http://www.bumtribe.fr/fabricant-artisa ... =fr&pg=185
In terms of hydralic press and molds.

Damon · Post by **Damon** » Thu May 26, 2011 7:47 pm

Obviously an autoclave is overkill for skis, I'd hate to pay for all that material just to press a ski.

You could test the uniformity of the press pretty easily. Lay up some test panels (maybe 6 plies thick) in an arrangement under the press and measure the thickness of the panels after cure.

jwahtera · Post by **jwahtera** » Fri May 27, 2011 12:36 am

Thanks OAC, what Bumtirbe did was damn clever. Only problem with using PVC foam as a mold is that it won't rebound, so the top mold will lose shape after a while. I would definetly recommend checking that wid out for anyone who is only looking to produce a couple of pairs, like me. For now at least

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using m + f molds

using m + f molds

maybe not a Ferrari but check this guys Lambo out!