New press bladder design

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RYM Experimentals
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Post by RYM Experimentals »

I think its a great looking press but have you had any blowouts using wood on the top? Your concept is sound but I worry that if it lets loose you could have some safety issues with splintering of those top boards pressing down. Does that make sense? First look to me is that top side might blow apart under the force. If its holding then you have a cool new way of doing things.
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falls
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Post by falls »

I don't know that you will gain anything by using a laterally oriented hose in there that you won't achieve with some wood shims or a better designed top mold that dips down in the tip/tail (other than it is inflatable and can be deflated to allow loading more easily).
I think our trouble is trying to use one top mold and one length of hose for all camber/rocker profiles and lengths. I guess it's unrealistic to make a matching top mold for every profile.
The longitudinal hoses do work fine especially on long rockers that don't have any tight radii. Tight radii need better top mold shaping and hose length choice. SHIF had some nice pictures of his setup with a perfect hose length and recessing of the pneumatic connectors and a really well matched top mold. Think he was only doing one length though which is really the key for why the OP was innovating.
I think diam of your cat track pieces and whether they have rounded corners is important in a tight radius too
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falls
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Post by falls »

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SHIF
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Post by SHIF »

Hey Falls, glad you remember my set-up. I've used this same technique of having matched upper and lower press forms to make skis having conventional tip rise radii with no issues. The key is to keep the bladder hose as flat as possible. No cat track required. In fact the advantage of having no cat track is the top of the ski can conform to the composite layers and is not forced to be flat (across it's width). If you place strips of unidirectional carbon down the middle, the top sheet bends down over the strip and results in squeezing out excess epoxy and making a lighter and better structure.

These ski press photos are quite old. Since moving to Utah I've replaced my bottom steel beam with one having a much larger cross section. It's flatter and deflects very little under pressure.

Cheers...

-S

Brotherboard
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Re: New press bladder design

Post by Brotherboard »

So I just built a pneumatic press and have been trying to stop leaks for the past week before I actually press a board in it. I am dealing with leaks at both ends of the tube and at the valves. What order do you have your valve set up in Falls?

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chrismp
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Re: New press bladder design

Post by chrismp »

Leaks at the ends are usually due to your clamping material deflecting too much. At certain pressures you will need a pretty beefy piece of steel to hold the force created by the bladders.

As for the connectors, have a look at the Happy Monkey Wiki. His method has proven to be somewhat of a "best practice" for hose connectors on here: http://www.happymonkeysnowboards.com/Mo ... onnections

Brotherboard
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Re: New press bladder design

Post by Brotherboard »

Thanks Chrismp but I did follow thier build and I'm still having leaks. I am going to try folding each end of the hose back on itself and then bolting it all down. As for the valve leaks, I decided to try an automotive gasket to make it airtight. I am inflating tomorrow to check again.

mammuth
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Re: New press bladder design

Post by mammuth »

If you have leaks at the clamps your clamps are not strong enough ;)
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fred
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Re: New press bladder design

Post by fred »

you also might want to put a small piece of the hose outside the outermost screws, to prevent deflection:
Hose_small.PNG
Hose_small.PNG (395.75 KiB) Viewed 687 times
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barnboy
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Re: New press bladder design

Post by barnboy »

Just wanted to add a little weight to what Shif and Falls have mentioned above. Having been at it for 15 years now, and having skinned the cat over and over again, I can wholeheartedly support their notion of matching forms and full-length hose "trapping". About 4 years ago (I think?) I started making A / B matched forms for all my varied lengths and the difference in press behavior is 100% worth the extra hassle of loading/unloading multiple top-forms, as well as figuring out where the hell to store them all. Shif is dead-on, you want to keep that hose as flat as you can to ensure as much equal pressure throughout the entire length of your shape as possible. You can take in to account the varying thickness of your ski, all of your press layers, etc... and then design an offset spline in whatever design suite you're using and you're off to the races... like everything else, you'll need to fine-tune it all, and figure out your own "rules". I always use the 10psi test as a general rule when testing the quality of a new form set. At 10 psi you should have full compliance through your full shape, meaning you cannot squeeze a zip tie or plastic wedge underneath your aluminum cassettes anywhere from tip to tail... If you need to crank the press up to 30 or greater to get there, you no longer know what pressure you're really seeing at any given point in the press... Of course, you're still going to press at whatever level of pressure you've decided upon (and safety-factored for in your press design/build), everyone has their number, but a good goal would be to reach full compliance at 10 psi.

Besides A/B'ing your forms (with an offset) another good "trick" is to build all your forms long enough to trap the majority of your hose... if you have 12 inches of hose hanging out one end of the press, that's going to really hinder the presses ability to reach the "bottom" of your tip/tail closest to that excess hose. Further, having it run through a flat section first, before diving, will also help a lot. Of course, you can make a very ski-able ski without doing any of this, this is more for the folks who are trying to achieve an "at market" level of quality and/or consistency. Not suggesting you're doing it wrong, or wasting your time if this isn't what you're doing, just adding some support to the matched form theory based on my experience.

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