Softwood
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
You don't need to pressurize gradually. Just pressurize to what ever psi you are using, and hold it there for a few min before hitting the heat. A gradual increase in pressure is not needed.
Fighting gravity on a daily basis
www.Whiteroomcustomskis.com
www.Whiteroomcustomskis.com
It is quite possible your Ipe is flexing depending on how much it's over hanging you layup. That would definitely cause the rounded over top sheets.
Not sure how rigid Ipe is compared to aluminum but it would make sense.
sam
Not sure how rigid Ipe is compared to aluminum but it would make sense.
sam
You don't even have a legit signature, nothing to reveal who you are and what you do...
Best of luck to you. (uneva)
Best of luck to you. (uneva)
Sam, I think you are on to something. Thinking back on the three presses we've done the first had the layup more equally spaced over the width of the cat track and the top is virtually flat. The second and third press had the slight crown and the skis were closer together, 1" spacer block separating them. Never thought the ipe could bend, but there's a whole lot of force at play here. It's hard wood and so dense it sinks in a bucket of water. I will space the lay up more evenly in the future.
Here are some pics of our 4th pair.
What we learned-
applying (new to us)nylon top sheet upside down doesn't stick too well.
MM's advice on re pressing right side up worked very well.
I really like the nylon compared to the Duravision 5050. Harder and clearer. Took some work to ease the edges.
Top and base are very flat. We moved the layup outwards on the cassette to more evenly distribute the pressure and lowered the psi to 45. I still don't understand the wide range of pressures used by different builders?
Also waited 5 minutes before turning on the heat.
Seems like we're using more epoxy with each pressing. I tend to worry there is not enough, while my son says there's plenty. He says I worry too much, I told him it's a conditioned response learned while raising a teenager...
He's excited to try them out.
What we learned-
applying (new to us)nylon top sheet upside down doesn't stick too well.
MM's advice on re pressing right side up worked very well.
I really like the nylon compared to the Duravision 5050. Harder and clearer. Took some work to ease the edges.
Top and base are very flat. We moved the layup outwards on the cassette to more evenly distribute the pressure and lowered the psi to 45. I still don't understand the wide range of pressures used by different builders?
Also waited 5 minutes before turning on the heat.
Seems like we're using more epoxy with each pressing. I tend to worry there is not enough, while my son says there's plenty. He says I worry too much, I told him it's a conditioned response learned while raising a teenager...
He's excited to try them out.
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twizzstyle
- Posts: 2207
- Joined: Tue Mar 07, 2006 8:25 pm
- Location: Kenmore, Wa USA
There's an easy explanation for that: none of us have a clue what we're doing.bhenry wrote:I still don't understand the wide range of pressures used by different builders?
True story.
I think it's just a matter of the TLAR approach - That looks about right.
I think most of us have narrowed down to a pressure that works for each of us based on end results we've achieved over many builds - base flatness, flex, durability, etc. We all do things slightly differently so there are too many variables to say one pressure works for everyone. It's a more empirical approach to data on the end results, and then again... TLAR.
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skidesmond
- Posts: 2338
- Joined: Tue Apr 07, 2009 3:26 pm
- Location: Western Mass, USA
- Contact:
TLAR - I call it "eyeball engineering"twizzstyle wrote:There's an easy explanation for that: none of us have a clue what we're doing.bhenry wrote:I still don't understand the wide range of pressures used by different builders?
True story.
I think it's just a matter of the TLAR approach - That looks about right.
I think most of us have narrowed down to a pressure that works for each of us based on end results we've achieved over many builds - base flatness, flex, durability, etc. We all do things slightly differently so there are too many variables to say one pressure works for everyone. It's a more empirical approach to data on the end results, and then again... TLAR.
There are a few right and wrongs for ski building, the rest "depends" because of all the variables. Once you find something that works, stick with it. Then make 1 or 2 changes at a time to find out if the change works or not.
For a 4th pair they look darn good!
You are looking for a laminate thickness calculator: http://www.saertex.com/materialrechner/ ... echner.php The proof is maths heavy, so don't worry if you ignore it.
What resin ratio you use is something you will need to research further and discuss within the forum. It will vary according to the materials being used and between manufacturers. You may find that your material supplier have provided the data in published research or that they provide access to online tools.
Once you have defined the resin ratio, you will need to factor in the amount lost to waste e.g. tooling, penetration into the core material (not waste) and flow. This is a really important thing to do.
After a number of trial pressings, you should be in a position to identify how close you are getting to the target figure. Just try to ensure that you are clear about the moisture content of the materials you are using.
Reaching this target figure won't mean that you have optimised the mechanical properties of the materials you are using. So I would suggest you stay a little resin rich compared to the absolute values recommended by online tools. Optimal is not real life. Manufacturers etc will have systems and controls in place that you do not.
The above is broadbrush and doesn't comment on issues such as ramp rate, variation of temperature within the ski press, application of pressure and void content. All these things will affect the overall quality of the laminate to a greater or lesser degree.
What resin ratio you use is something you will need to research further and discuss within the forum. It will vary according to the materials being used and between manufacturers. You may find that your material supplier have provided the data in published research or that they provide access to online tools.
Once you have defined the resin ratio, you will need to factor in the amount lost to waste e.g. tooling, penetration into the core material (not waste) and flow. This is a really important thing to do.
After a number of trial pressings, you should be in a position to identify how close you are getting to the target figure. Just try to ensure that you are clear about the moisture content of the materials you are using.
Reaching this target figure won't mean that you have optimised the mechanical properties of the materials you are using. So I would suggest you stay a little resin rich compared to the absolute values recommended by online tools. Optimal is not real life. Manufacturers etc will have systems and controls in place that you do not.
The above is broadbrush and doesn't comment on issues such as ramp rate, variation of temperature within the ski press, application of pressure and void content. All these things will affect the overall quality of the laminate to a greater or lesser degree.
Interesting stuff.
For the skis pressed so far we lay up on a separate table and work the Entropy into the fabric until it appears uniformly saturated.
I'm guessing that with the "proper" amount of epoxy, uniformly applied, full saturation may not take place until the skis are in the press with pressure applied? If true, layup time could be much quicker.
More research..
For the skis pressed so far we lay up on a separate table and work the Entropy into the fabric until it appears uniformly saturated.
I'm guessing that with the "proper" amount of epoxy, uniformly applied, full saturation may not take place until the skis are in the press with pressure applied? If true, layup time could be much quicker.
More research..
It's easier to think in terms of wetting out the fibre rather than saturation. On a layup table, the fibre will just look a little more resin rich with the viscosity of the resin holding everything together.
If you are using the Kingwood video as your frame of reference, it's important to note that the core material is bamboo. Wood continues to draw epoxy away from the fabric during pressing, so whether you build using partially saturated fibre is judgement based on results. Results will vary according to species.
How quickly or completely the fabric wets out on a table depends on the manufacturer and the materials (it varies), presence of any grease or moisture (its worth thinking about how you store or preprocess your fabric) and the temperature of the materials when they are brought together. Temperature is the factor that effects the viscosity of the resin, reducing surface tension. Repeatable results depends on setting good process conditions and not press pressure. You should be careful about raising the temperature of the epoxy much above 20oC before pressing, it's volitile stuff.
You may take the view that while the epoxy is sitting on the fabric, that you have time to take a small amount of epoxy and coat the core. The wettibility of the core is the issue worth concentrating upon i.e. moisture content and surface preparation.
If you are using the Kingwood video as your frame of reference, it's important to note that the core material is bamboo. Wood continues to draw epoxy away from the fabric during pressing, so whether you build using partially saturated fibre is judgement based on results. Results will vary according to species.
How quickly or completely the fabric wets out on a table depends on the manufacturer and the materials (it varies), presence of any grease or moisture (its worth thinking about how you store or preprocess your fabric) and the temperature of the materials when they are brought together. Temperature is the factor that effects the viscosity of the resin, reducing surface tension. Repeatable results depends on setting good process conditions and not press pressure. You should be careful about raising the temperature of the epoxy much above 20oC before pressing, it's volitile stuff.
You may take the view that while the epoxy is sitting on the fabric, that you have time to take a small amount of epoxy and coat the core. The wettibility of the core is the issue worth concentrating upon i.e. moisture content and surface preparation.