OK - it sounds like a contradiction, but the whole high pressure press thing has me a bit wigged out so I have been thinking up better ways to do it and I think that I have the solution:
I can't post pics 'cos I am too useless, but imagine the following:
2 large area 'plates' which have a vacuum bag around the outside. When you apply a vacuum the force between the plates is 15PSI * the area.
Now take our standard firehose bladder that we use for the high pressure rigs and put it between the 2 plates semi inflated. The bladder is much smaller in area than the plates, so when plates come together due to the vacuum, the pressure in the bladder becomes:
Pressure = 15* Area of Plate/ Area of bladder.
So to get 45PSI in the bladder then we need a plate that is 3 times the area of the bladder. We now have the same pressures as used in high pressure presses, but without the structural elements (although the bladder is still seeing the same loads).
Whadyathink?
Sorry for the lack of piccy,
B.
Vacuum press that can generate 50 PSI
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Well, it sounds pretty clever to me. I'm sure that you have this worked out, but if the plate surface area is 3 times the surface area of the bladder, is there a problem keeping the plates from slipping off to one side or another of the sandwiched bladder? I suppose that you could have spacers at the really distal ends of the plates (so the spacers wouldn't interfere with the compression of the central plates) that would keep the plates from tipping. Then again, maybe a little tipping isn't a big problem?
G-man
G-man
hardy har.Bambi wrote:Through the hole in the end?
:-)
B.
Isnt that gonna be a pretty heavy set of plates and a huge bag? Its hard enough to get my mold into a vacuum bag without moving the materials and i dont have any huge plates. To get the entire force applied downward onto the ski you'd need to have the plate not bend much.
I dunno maybe im not seeing it right. show us a pic!
yea def incorporate it into the top mold that would be the most sensible way to tranfer the force.
I mean in principle it shoudl work if you can effectively get it into a bag and pull a vac. - edit see below
cant wait to see pics if you do it.
I mean in principle it shoudl work if you can effectively get it into a bag and pull a vac. - edit see below
cant wait to see pics if you do it.
Last edited by beansnow on Wed Mar 14, 2007 3:13 pm, edited 1 time in total.
I've been thinking about this because the idea of getting decent results without having to build a press is very apealing.
For the spacers on the sides, it would be easy enough to build your core wide, profile it, and then take a rip to use as a spacer. You'd have to pad it out with a piece that is a little thinner than the total thickness of your base, glass, and topsheet, but this would be a constant thickness and easy enought to make up in a thickness planer.
You could most likely use a light weight cat track on top instead of a plate to transfer the pressure to your lay-up. You might even be able to use wood for the track. Underneath would be whatever you would normaly run under the track in a pneumatic press.
If the width is what's causing problems getting the whole rig in the bag, press one ski at a time and only make alpine snowboards.
Vaccum bagging film can easily be found large enough to lay a sheet down, set your mold on top (assuming you want the mold in the bag as opposed to a single skin sealed to the mold surface), do your lay-up, and lay another sheet on top, seal the whole mess up and turn the pump on.
Or, if you're fortunate enough to have a bag large enough, an easy way to get obnoxiosly large and heavy objects into it from the end is to slide a pice of thin MDF in first and then slide your rig in on top of it. At the shop I work in we use a platten made of 3/4" particle board with 1/8"wide by 1/8" deep saw cuts making a grid of 2" squares (Super fun cutting the grid on a 12'x4' platten ). This goes in the bag first and everything slides in on top of it. Makes for good vaccum everywhere.
I haven't built any skis yet so please forgive me if I've looked over some obvious reason that this wouldn't work.
This is a great site by the way!
It's answered a lot of my questions and got me thinking I can realy do this.
For the spacers on the sides, it would be easy enough to build your core wide, profile it, and then take a rip to use as a spacer. You'd have to pad it out with a piece that is a little thinner than the total thickness of your base, glass, and topsheet, but this would be a constant thickness and easy enought to make up in a thickness planer.
You could most likely use a light weight cat track on top instead of a plate to transfer the pressure to your lay-up. You might even be able to use wood for the track. Underneath would be whatever you would normaly run under the track in a pneumatic press.
If the width is what's causing problems getting the whole rig in the bag, press one ski at a time and only make alpine snowboards.
Vaccum bagging film can easily be found large enough to lay a sheet down, set your mold on top (assuming you want the mold in the bag as opposed to a single skin sealed to the mold surface), do your lay-up, and lay another sheet on top, seal the whole mess up and turn the pump on.
Or, if you're fortunate enough to have a bag large enough, an easy way to get obnoxiosly large and heavy objects into it from the end is to slide a pice of thin MDF in first and then slide your rig in on top of it. At the shop I work in we use a platten made of 3/4" particle board with 1/8"wide by 1/8" deep saw cuts making a grid of 2" squares (Super fun cutting the grid on a 12'x4' platten
). This goes in the bag first and everything slides in on top of it. Makes for good vaccum everywhere.I haven't built any skis yet so please forgive me if I've looked over some obvious reason that this wouldn't work.
This is a great site by the way!
It's answered a lot of my questions and got me thinking I can realy do this.