Hi Buuk,
Yes, 3,5 bar squeezes out a lot of resin. I try to conserve on the resin that I use in the initial lay-up... I ususally get by with using about 550ml per ski. I still get quite a bit of resin running out all over things when I pressurize, so, I put down a lot of newspaper to protect the press table and floor. I really don't know if 6 bar would cause the ski to become too 'dry', and subsequently weaken the bond strength , or not. I have noticed that at 3,5 bar, a 22 oz. triaxial fiberglass layer ends up being about as thick as 3 or 4 pieces of paper. I can't imagine squeezing it too much thinner than that. Your question is one that could probably best be answered by experimenting with some small test samples. Who knows, maybe 6 bar would make both a lighter and stronger ski.
I hope that you post a picture of your 6 bar rated press when you get it finished. That's a lot of total pressure.
Sorry that I can't readily translate into Euro/metric equivalents on the 22 oz. fiberglass for you. I'm always impressed that you European builders can bounce back and forth between systems so well.
G-man
G-man's skis and press
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
Hi G-man,
Thanks for your reply!
Of course I will post a picture of my press under 6 bar pressure.
And it's a good idea to create some test pieces, although this might be quite hard, because the edges will close in the epoxy when the system is closed. So I have to build a fully closed test piece I think.
About converting units:
I always use a nice program to convert all values into each other, it's called convert
and it can be downloaded at www.groene-engel.com/Buuk/Skibuilders/Convert.exe (size:568 kB) and it's free to distribute.
So 22 oz is about 600 grams/m^2.
Buuk
Thanks for your reply!
Of course I will post a picture of my press under 6 bar pressure.
And it's a good idea to create some test pieces, although this might be quite hard, because the edges will close in the epoxy when the system is closed. So I have to build a fully closed test piece I think.
About converting units:
I always use a nice program to convert all values into each other, it's called convert
and it can be downloaded at www.groene-engel.com/Buuk/Skibuilders/Convert.exe (size:568 kB) and it's free to distribute.So 22 oz is about 600 grams/m^2.
Buuk
I am using West Systems epoxy for laminated plywood runners on Komatik cargo sled I designed at work, and in talking to the engineers at West Systems they told me that overpressuring the laminated pieces is bad. A thin layer in between each piece is desirable as the modulus of rigidity doesn't change on that stuff until -125 F (-88 C). That might just be for West Systems though, so the best bet is to call up resin suppliers and ski companies and get info on press pressure from them. I am an engineering student right now, and I got in touch with several companies and told them about my design project so they were happy to give me info. Hope this helps.
Hey hafte,
I see what you mean... some of them are gone. I'm currently on the road and won't be back home for about a week. The pics are on my other computer, so I'll have to wait till I get home to repost them. Right now, I'm using my wife's laptop at a KOA campground... they have wireless! Great sunset on the Front Range tonight.
G-man
I see what you mean... some of them are gone. I'm currently on the road and won't be back home for about a week. The pics are on my other computer, so I'll have to wait till I get home to repost them. Right now, I'm using my wife's laptop at a KOA campground... they have wireless! Great sunset on the Front Range tonight.
G-man
hafte,
I'm able to view the original picture post now. I don't know why I couldn't see them a few days ago. I'm presuming that you can also see them at this time and that the disappearance of the pics was just a temporary glitch. Let me know if you still don't get them and I'll try something different.
I like my press pretty well, but there are a few changes that I'm currently working on. I got some different ideas from the ski press in the Kingswood video: www.skibuilders.com/phpBB2/viewtopic.php?t=388. I like the idea of having more of a 'cassette' type system where one can lay up the ski on a work table, then load the relatively lightweight assembly into the press. Since I presently lay up my skis directly in the press, I have to wait in between pressings for the press to cool down. If I used two cassettes, I could remove one pressed ski and imediately load the next cassette into the press. I could then press one ski about every 30 minutes. I'm also installing a top heating unit so that heat will be applied from both sides, thereby reducing the time that it takes to heat the ski through and through. It will be interesting to see how heating from both sides effects the camber.
G-man
I'm able to view the original picture post now. I don't know why I couldn't see them a few days ago. I'm presuming that you can also see them at this time and that the disappearance of the pics was just a temporary glitch. Let me know if you still don't get them and I'll try something different.
I like my press pretty well, but there are a few changes that I'm currently working on. I got some different ideas from the ski press in the Kingswood video: www.skibuilders.com/phpBB2/viewtopic.php?t=388. I like the idea of having more of a 'cassette' type system where one can lay up the ski on a work table, then load the relatively lightweight assembly into the press. Since I presently lay up my skis directly in the press, I have to wait in between pressings for the press to cool down. If I used two cassettes, I could remove one pressed ski and imediately load the next cassette into the press. I could then press one ski about every 30 minutes. I'm also installing a top heating unit so that heat will be applied from both sides, thereby reducing the time that it takes to heat the ski through and through. It will be interesting to see how heating from both sides effects the camber.
G-man
Just out of curiosity...are you building skis for yourself or starting a business??G-man wrote:hafte,
I'm able to view the original picture post now. I don't know why I couldn't see them a few days ago. I'm presuming that you can also see them at this time and that the disappearance of the pics was just a temporary glitch. Let me know if you still don't get them and I'll try something different.
I like my press pretty well, but there are a few changes that I'm currently working on. I got some different ideas from the ski press in the Kingswood video: www.skibuilders.com/phpBB2/viewtopic.php?t=388. I like the idea of having more of a 'cassette' type system where one can lay up the ski on a work table, then load the relatively lightweight assembly into the press. Since I presently lay up my skis directly in the press, I have to wait in between pressings for the press to cool down. If I used two cassettes, I could remove one pressed ski and imediately load the next cassette into the press. I could then press one ski about every 30 minutes. I'm also installing a top heating unit so that heat will be applied from both sides, thereby reducing the time that it takes to heat the ski through and through. It will be interesting to see how heating from both sides effects the camber.
G-man
Hi Mike,
Don't know for sure, yet. If I'm going to sell anything, I want to really be sure that it is going to perform well. I just don't have the delamination issue solved yet.
The two outdoor activities that I enjoy most in this life are bike riding and backcountry skiing. What greater way to make a living is there than to make and sell a product that plays a main role in activities that you love. I made a pretty good living building bicycle frames for 12 years in the 70's and 80's. I have dreamed of making skis for many years, but it just seemed out of my reach... until I discovered this website. I learned from building bikes that a business that you initially really enjoy can quickly turn into an out-of-control activity that you really dread.... maintaining promised quality, keeping up with delivery times, maintaining reliable sources for raw materials, the guilt of having failed customer's expectations in some way. So, I'm proceeding really slowly and I'm mostly just going to let the ski building flow on it's own, with maybe just a gentle nudging towards being a business. Even if it works out to be a business, I don't want to build more than one or two hundred pairs a year... only what I can handle by myself and leave plenty of time for skiing and riding.
By the way, I've seen your website. Very nice. You're an ambitous and talented guy. I hope things go well for you this winter.
G-man
Don't know for sure, yet. If I'm going to sell anything, I want to really be sure that it is going to perform well. I just don't have the delamination issue solved yet.
The two outdoor activities that I enjoy most in this life are bike riding and backcountry skiing. What greater way to make a living is there than to make and sell a product that plays a main role in activities that you love. I made a pretty good living building bicycle frames for 12 years in the 70's and 80's. I have dreamed of making skis for many years, but it just seemed out of my reach... until I discovered this website. I learned from building bikes that a business that you initially really enjoy can quickly turn into an out-of-control activity that you really dread.... maintaining promised quality, keeping up with delivery times, maintaining reliable sources for raw materials, the guilt of having failed customer's expectations in some way. So, I'm proceeding really slowly and I'm mostly just going to let the ski building flow on it's own, with maybe just a gentle nudging towards being a business. Even if it works out to be a business, I don't want to build more than one or two hundred pairs a year... only what I can handle by myself and leave plenty of time for skiing and riding.
By the way, I've seen your website. Very nice. You're an ambitous and talented guy. I hope things go well for you this winter.
G-man
G-man, I'm getting block at work. I tried to look at the pictures directly and the flicker site is blocked due to "graphic or adult content". 
I'll have a look from home.
I was really impressed with what I was seeing before. Hope you don't mind if I borough a few ideas when I get ready to build a pneumatic press. I couldn’t tell, but what are you using for a connector when you drop the top down into the working position… if you don’t mind me asking. I could see the bar that you lift into place, but couldn’t see how they were fastened to the top. It seems like that would be your weakest link.
I like the cassette idea too. There is another factory tour from the graf snowboard site that… well it was there. They just made a major change and I didn’t see the links page anymore. But they were using the cassettes in a hydraulic press. Looked like they had a top and bottom as I remember with locator pins to keep things from moving around.
You mention delamination problems. What kind of issues are you running into, or have you brought them up in another thread?
Thanks for the great Journal thread.
Hafte
I'll have a look from home. I was really impressed with what I was seeing before. Hope you don't mind if I borough a few ideas when I get ready to build a pneumatic press. I couldn’t tell, but what are you using for a connector when you drop the top down into the working position… if you don’t mind me asking. I could see the bar that you lift into place, but couldn’t see how they were fastened to the top. It seems like that would be your weakest link.
I like the cassette idea too. There is another factory tour from the graf snowboard site that… well it was there. They just made a major change and I didn’t see the links page anymore. But they were using the cassettes in a hydraulic press. Looked like they had a top and bottom as I remember with locator pins to keep things from moving around.
You mention delamination problems. What kind of issues are you running into, or have you brought them up in another thread?
Thanks for the great Journal thread.
Hafte
hafte wrote:
About the press, the removable vertical 2x2 square tubes are secured in place by two 1/2 x 3 1/2 inch grade 8 bolts at both top and bottom. I actually don't use nuts on the bolts that pin the removable members, I just slip the bolts through the holes and inflate the bladder. All of the vertical members have the same number of grade 8 fasteners. You may be right, though, regarding the center verticals being the weakest link because the verticals at the ends get loaded from only one side, where the middle sets of verticals are loaded from both sides... I actually just now realized that fact... oops. The press is way overbuilt, though. I think that I calclated that the double shear value for a 1/2 inch grade 8 bolt was 4,000 lbs or more, and there are 32 of them that pin the verticals in their brackets and 32 more that fasten the brackets onto the longitudinal press members. Maybe I should double check my calcs anyway.
The only delamination problem that I have had is on one pair of skis in which the top and bottom layers of fiberglass delamed where they were supposed to have bonded to the top and bottom surfaces of the sidewall strips. I initally noticed just a small area of delamination (the second day of sking on them), and I took the point of a knife, stuck it in that spot and easily ran the point all the way down the length of the ski, separating the layers as I went. The condition was pretty much the same on both top and bottom of the ski. Inboard of the sidewall strip, however, the laminations held very solidly. None of my other skis have had any problems, even with 30 or more days on them. Subjectively, I performed the flame treatment operation exactly the same on all of the skis, but obviously, the level of surface treatment varied quite a bit.
Oh, by the way, I was just kidding about posting my wife's pictures... even though they are pretty good.
G-man
Dang, must have been those nude pictures of my wife that I uploaded... don't worry, she's MUCH younger than I am and quite a hottie.I tried to look at the pictures directly and the flicker site is blocked due to "graphic or adult content".
About the press, the removable vertical 2x2 square tubes are secured in place by two 1/2 x 3 1/2 inch grade 8 bolts at both top and bottom. I actually don't use nuts on the bolts that pin the removable members, I just slip the bolts through the holes and inflate the bladder. All of the vertical members have the same number of grade 8 fasteners. You may be right, though, regarding the center verticals being the weakest link because the verticals at the ends get loaded from only one side, where the middle sets of verticals are loaded from both sides... I actually just now realized that fact... oops. The press is way overbuilt, though. I think that I calclated that the double shear value for a 1/2 inch grade 8 bolt was 4,000 lbs or more, and there are 32 of them that pin the verticals in their brackets and 32 more that fasten the brackets onto the longitudinal press members. Maybe I should double check my calcs anyway.
The only delamination problem that I have had is on one pair of skis in which the top and bottom layers of fiberglass delamed where they were supposed to have bonded to the top and bottom surfaces of the sidewall strips. I initally noticed just a small area of delamination (the second day of sking on them), and I took the point of a knife, stuck it in that spot and easily ran the point all the way down the length of the ski, separating the layers as I went. The condition was pretty much the same on both top and bottom of the ski. Inboard of the sidewall strip, however, the laminations held very solidly. None of my other skis have had any problems, even with 30 or more days on them. Subjectively, I performed the flame treatment operation exactly the same on all of the skis, but obviously, the level of surface treatment varied quite a bit.
Oh, by the way, I was just kidding about posting my wife's pictures... even though they are pretty good.
G-man
Hahaaaa, I really don’t think it would have been anything you posted out there. They block almost everything here… total paranoia.
I don’t know if this would help your side wall situation, but I found in my boat building manual that using a bit of colloidal silica in the epoxy will increase inter-laminar bond strength. It sounds like there is a shear between the materials as the ski flexes causing the separation. I use the stuff for bonding almost everything and in my lay-ups with fabric. It just made sense that increasing the strength of the epoxy with the silica would make the bonds/shear strength between the layers better. It’s kind of like little micro hooks in the epoxy making a better connection between materials. Silica is cheap and may be worth a try. I add just a few grams for this use, enough to make the epoxy cloudy. I don’t want to lose the wet out characteristics of the epoxy by occupying it with too much filler. The biggest problem with this stuff is getting the lumps out and it’s hard as nails when cured. It needs to be run through a screen before adding it to the epoxy, and add it to the epoxy after it has been thoroughly mixed. It also makes a great thickener to set your inserters, so the epoxy doesn’t run out of your holes.
I don’t know if this would help your side wall situation, but I found in my boat building manual that using a bit of colloidal silica in the epoxy will increase inter-laminar bond strength. It sounds like there is a shear between the materials as the ski flexes causing the separation. I use the stuff for bonding almost everything and in my lay-ups with fabric. It just made sense that increasing the strength of the epoxy with the silica would make the bonds/shear strength between the layers better. It’s kind of like little micro hooks in the epoxy making a better connection between materials. Silica is cheap and may be worth a try. I add just a few grams for this use, enough to make the epoxy cloudy. I don’t want to lose the wet out characteristics of the epoxy by occupying it with too much filler. The biggest problem with this stuff is getting the lumps out and it’s hard as nails when cured. It needs to be run through a screen before adding it to the epoxy, and add it to the epoxy after it has been thoroughly mixed. It also makes a great thickener to set your inserters, so the epoxy doesn’t run out of your holes.
G-man, I just had a thought. I may have this sidewall thing backwards. The silica will make the interface of the two materials stiffer/harder and possibly prone to failure under shear forces. Are you using VDS strips in your lay-up? Wouldn’t the VDS rubber allow for a slight shear movement between the glass and the sidewall material… maybe enough to keep it from failing? Sounds like you plan to do some testing. One more thing to try. I would still use the silica in the rest of the layup.
Hafte
Hafte