Awesome site, I'm looking into building my own pair and I have a quick question...
The size of the wood core, should it be cut to exact size before glueing/shaping? I was planning on eproxy sidewalls which would have to be between the 2 layers of composites. If I cut to size after I'm done shaping, how will I add the sidewalls? It's a bit confusing, seems like a dumb question...
Thanks.
-Jesse
Core Size?
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
Depends onwhat exact size you're shaping to. First, you have to shape the core for the flex you want. Easier said than done if you're a perfectionist. You'll also have to have a base profile template for cutting your bases, routed or cnc'd out of MDF. You can use the template dimensions to help you ascertain the contour of the core sides, which will be vertical. The core should fall inside the edge teeth (where the edges are glued to the base) to prevent base concavity. UHMW sidewalls can be routed with same jig as your core shaper, then ripped on a table saw for width. But subtract 1/2 mm in height for the edge teeth that the sidewalls sit on. A good 2-sided tape will hold the sidewalls to the core, but allow it to shift enough under pressure to align for height without getting pushed outwards by resin flowing during the pressing. This is for a vertical lam layup.
Kalisto, if you make a base template you can use that for shaping the core. The trick would be to change out the baring size on your router bit to offset the sidewall thickness. It’s ok to have extra material overhanging the edge during lay-up, you remove this after the ski is pressed. Woops just reread your post,
“Epoxy sidewalls“. Maybe shape your core first but under size it, then figure out how to dam the core and fill along the edge of the core with epoxy so that it will overhang the ski edge. After you do this, profile the core. Honestly I’m talking out my ass on this, I have no experience with epoxy sidewalls
.
Splat-
Why not glue the sidewalls to the core before profiling, after shaping? Then profile and rout the recess. I know the Bro had problems with sidewall blowout and to me the tape method is asking for problems, if not a full blowout then the possibility exists for slight horizontal movement resulting in week voids, bubbles or relying on the epoxy that fills a possible gap. If your going to have a floating sidewall I would think it would be smart to have some side force incorporated into the cassette. Interesting process.
“Epoxy sidewalls“. Maybe shape your core first but under size it, then figure out how to dam the core and fill along the edge of the core with epoxy so that it will overhang the ski edge. After you do this, profile the core. Honestly I’m talking out my ass on this, I have no experience with epoxy sidewalls
.
Splat-
Why not glue the sidewalls to the core before profiling, after shaping? Then profile and rout the recess. I know the Bro had problems with sidewall blowout and to me the tape method is asking for problems, if not a full blowout then the possibility exists for slight horizontal movement resulting in week voids, bubbles or relying on the epoxy that fills a possible gap. If your going to have a floating sidewall I would think it would be smart to have some side force incorporated into the cassette. Interesting process.
A lot of guys glue or staple the sidewalls to the core. Hard to do if you are trying to keep the bottom of the sidewall 1/2 mm higher. We had sidewall blowouts and some concave bases because that 1/2 mm had not been taken off the sidewalls. Building a wall to hold the sidewalls in is a hard thing to do unless you mill a mold out of aluminum, which is costly. If the layers are precisely milled, they'll hold their position during pressing. Epoxy in the voids is the glue that holds it all together. You just don't want big voids.
Great info on this thread, thanks to everyone for contributing.
Our last few pairs have had wood sidewalls since it is quick and easy and we are not expecting them to last forever. We don't put a rabbet for the edge thickness and our bases our a litttle concave. A good base grind gets rid of most of it. The only time I notice the concavity of the bases is in really hard conditions, then the skis are a little squirrley. Maybe I'll try putting a rabbet for our next pair.
For the epoxy sidewalls, you would first cut the shape of the profiled core about 1/4" smaller than the base using the method fiddled described. Then sandwich the core between some smooth UHMW and make a little dam. You can then pour epoxy into the dam and make sure you pour enough to overhang the base. Once the epoxy cures, flip it over and do the other sidewall. Take the plastic off and a little sanding should finish it up. That being said, epoxy sidewall aren't all that great, they tend to chip and look like crap after a few times. If you're looking for a quick method, go with wood sidewalls; something more durable, go with abs or ptex sides.
-Kelvin
Our last few pairs have had wood sidewalls since it is quick and easy and we are not expecting them to last forever. We don't put a rabbet for the edge thickness and our bases our a litttle concave. A good base grind gets rid of most of it. The only time I notice the concavity of the bases is in really hard conditions, then the skis are a little squirrley. Maybe I'll try putting a rabbet for our next pair.
For the epoxy sidewalls, you would first cut the shape of the profiled core about 1/4" smaller than the base using the method fiddled described. Then sandwich the core between some smooth UHMW and make a little dam. You can then pour epoxy into the dam and make sure you pour enough to overhang the base. Once the epoxy cures, flip it over and do the other sidewall. Take the plastic off and a little sanding should finish it up. That being said, epoxy sidewall aren't all that great, they tend to chip and look like crap after a few times. If you're looking for a quick method, go with wood sidewalls; something more durable, go with abs or ptex sides.
-Kelvin
Kalisto,
I think the best way to make epoxy sidewalls is to use your router to create a channel in your laminated blank core along the perimeter of your intended ski shape. It's faster and cleaner to do it this way. More details and pictures are shown on the sidewall construction page. When I make my next one I'll try to shoot some video so it's easier to understand.
I used to use the "dam" method that Kelvin and Fiddle described but I found that's extremely tedious and very messy. Kelvin is right about epoxy sidewalls. They're weak and tend to chip. I'm still a fan of it, however, because of the wide range of color options from dyed epoxy. But I think using fiberglass strips with the epoxy instead of just pure epoxy will make a more durable sidewall. I'll try this on one of my upcoming skis and let you know how it works.
I think the best way to make epoxy sidewalls is to use your router to create a channel in your laminated blank core along the perimeter of your intended ski shape. It's faster and cleaner to do it this way. More details and pictures are shown on the sidewall construction page. When I make my next one I'll try to shoot some video so it's easier to understand.
I used to use the "dam" method that Kelvin and Fiddle described but I found that's extremely tedious and very messy. Kelvin is right about epoxy sidewalls. They're weak and tend to chip. I'm still a fan of it, however, because of the wide range of color options from dyed epoxy. But I think using fiberglass strips with the epoxy instead of just pure epoxy will make a more durable sidewall. I'll try this on one of my upcoming skis and let you know how it works.
- Kam S Leang (aka Little Kam)
I was also thinking of going with the routered channel and placing mold releas on the outside edge except for a few spots to hold it in place during profiling. That way the outside edge of the channell should define the outside edge as accurately as the cut can be made. I just got in a bag of phenolic microballoons and microfibers to use in the mix. I hope to use a flexible epoxy (TBD) in combination with them to create a light and tough sidewall. Does anyone know of a good, tough, and somewhat flexible epoxy system? Room cure? Temp cure?
Fiddled wrote: .
Splat-
Why not glue the sidewalls to the core before profiling, after shaping? Then profile and rout the recess. I know the Bro had problems with sidewall blowout and to me the tape method is asking for problems, if not a full blowout then the possibility exists for slight horizontal movement resulting in week voids, bubbles or relying on the epoxy that fills a possible gap. If your going to have a floating sidewall I would think it would be smart to have some side force incorporated into the cassette. Interesting process.
Don't waste money to buy UHMW for a dam when you could put it or abs on your core for sidewalls. Fiddled, you're right...
You can shape a piece of UHMW by router using the core profiler to get shape and then glue them on the core or...You can cut the sidecut into your core blank and glue UHMW or ABS right onto the curve - then rout for core profile. 8 mm is the standard for rough sidewall thickness, but if you want to be sure, you can go 10-12 mm easily. If you slope your sidewalls beyond 10 degress, it can get thin at the top when finishing with only 8 mm thickness to work with. Whatever is hanging over the edges gets trimmed with the excess glass, then rout or sand to finish. UHMW takes the router better, ABS finishes with a sander to perfection. Rout that sidewall bottom to compensate for the added height of the edge teeth. .5-.7mm will do fine to ensure a flatter base.
Last year we had a cnc sander to profile cores. It allowed us to glue sidewalls to core blanks and then profile both together at once. That's really sweet. This year, we're getting profiled (cnc'd) cores and profiled sidewalls shaped in sheets which will be ripped to 8mm, tben glued together before pressing. A little more tedious, but it's all about the machines we have to work with and the adjustments that get made accordingly.
From an engineering standpoint and for more precise references - the view from above looking down on your core is the Plan View. Looking from the side to see the tapering is the Core Profile view. Using this language will help you communicate about your projects more effectively.
Building skis is really all about cutting and shaping a bunch of component parts that must all fit together with very tight tolerances. So each piece and part of the process must be as close to flawless as possile.
Splat,
Good idea about using a more consistent language. I've noted a number of instances where differing use of descriptive terms has led to confusion.
Reading your post brought up two questions that I'm hoping you have time to answer.
You mentioned that you have previously used a cnc sander to profile cores with the UHMW side walls attached. I understand, of course, how a cnc sander would work well for profiling the wooden core, but the UHMW portion of the core assembly is so resistent to abrasive machining, how did you pull off that part of the operation?.. what type of sanding belt did your sander use, and what grit? So far, I have found that silicon carbide sanding belts work the best for removing UHMW, but only in really small amounts. My bases come out of the press really quite flat, but they always need a little material removal to get them just right. I've used a 6" wet belt sander set-up with a 60 grit silicon carbide belt to clean up the bases, but it still takes a lot of work to remove that little bit of material. I really don't understand how a couple of passes through a commercial base grinder can get the job done (I've never actually seen one up close)... just what kind of grinding medium does a base grinder use, anyway. As you can probably ascertain, I'm trying to avoid having to buy a real base grinder.
Here's my second question, and it's one that I've pursued a lot through this forum. You indicate that you use UHMW for your sidewalls. Do you have any secrets that you can share regarding surface treatment techniques for increasing the bond strength of the UHMW side wall to the top and bottom composite layer. I abraid the surface, clean with acetone, flame treat (using very well tested and specific parameters), dyne test... supposedly all of the right stuff... and the sidewalls are still getting small areas of delamination after a little abuse. My Durasurf UHMW tip spacers (surface treated before they leave the factory) are quite resistent to delams, so, my best conclusion is that my surface treatment is not as good as the factory treatment... so there is still room for improvement.
Lastly, thanks so much for sharing your ski building knowledge with all of us on the forum. Your information is clear, concise, and very helpful.
G-man
Good idea about using a more consistent language. I've noted a number of instances where differing use of descriptive terms has led to confusion.
Reading your post brought up two questions that I'm hoping you have time to answer.
You mentioned that you have previously used a cnc sander to profile cores with the UHMW side walls attached. I understand, of course, how a cnc sander would work well for profiling the wooden core, but the UHMW portion of the core assembly is so resistent to abrasive machining, how did you pull off that part of the operation?.. what type of sanding belt did your sander use, and what grit? So far, I have found that silicon carbide sanding belts work the best for removing UHMW, but only in really small amounts. My bases come out of the press really quite flat, but they always need a little material removal to get them just right. I've used a 6" wet belt sander set-up with a 60 grit silicon carbide belt to clean up the bases, but it still takes a lot of work to remove that little bit of material. I really don't understand how a couple of passes through a commercial base grinder can get the job done (I've never actually seen one up close)... just what kind of grinding medium does a base grinder use, anyway. As you can probably ascertain, I'm trying to avoid having to buy a real base grinder.
Here's my second question, and it's one that I've pursued a lot through this forum. You indicate that you use UHMW for your sidewalls. Do you have any secrets that you can share regarding surface treatment techniques for increasing the bond strength of the UHMW side wall to the top and bottom composite layer. I abraid the surface, clean with acetone, flame treat (using very well tested and specific parameters), dyne test... supposedly all of the right stuff... and the sidewalls are still getting small areas of delamination after a little abuse. My Durasurf UHMW tip spacers (surface treated before they leave the factory) are quite resistent to delams, so, my best conclusion is that my surface treatment is not as good as the factory treatment... so there is still room for improvement.
Lastly, thanks so much for sharing your ski building knowledge with all of us on the forum. Your information is clear, concise, and very helpful.
G-man
First of all, I have found ABS much better to use as a sidewall material. It bonds better (has to be flamed) and sands better. You can also buy it in 2.35 mm sheets for tip spacers.
As for the cnc sander - in one pass it profiles a core with sidewalls, whether durasurf, abs, or uhmw with a grit of 60-80. But that belt is almost 4 feet wide. And that machine is costly.
If you have a core that you're running with on a consistent basis, and you can be consistent in construction with regards to core size, you can rivet blocks into the aluminum that will hold your sidewall in. You'll have to cut out your glass cloth to accommodate the blocks, but to keep your sidewalls on, it is much better.
As for the cnc sander - in one pass it profiles a core with sidewalls, whether durasurf, abs, or uhmw with a grit of 60-80. But that belt is almost 4 feet wide. And that machine is costly.
If you have a core that you're running with on a consistent basis, and you can be consistent in construction with regards to core size, you can rivet blocks into the aluminum that will hold your sidewall in. You'll have to cut out your glass cloth to accommodate the blocks, but to keep your sidewalls on, it is much better.
Wow, Splat, that was a fast reply.
The cnc sander does sound quite amazing... and expensive.
Some builders are reporting problems with ABS getting brittle and cracking in the cold. Have you experienced any such problems? Maybe it's just in situations where it gets 'really' cold. Now-a-days, we don't often get very cold around here, and maybe ABS would work just fine for me. I think I'll get some and give it a try.
Again, I can see where my question has not been very clear. My delam problems have not been with the sidewall delaminating from the core. My delaminations have occured in the bond area between the sidewall top surface and the top sheet. The top sheet bonds well to the top glass layer, but the top glass layer does not bond well with the top surface of the sidewall (arrg... this descriptive language can get difficult). Basically, I can take a knife point, stick it in between the top sheet and the sidewall (2-3mm in penetration depth), and run it down the length of the ski test samples and separate the bond area between the sidewall and the top fiberglass layer. When he knifepoint reaches the depth of the wood core, it will not penetrate any further because the bond between the glass and the wood is very solid.
Going with ABS may solve the above problem. It seems that a lot of builders are using ABS and pumping out a lot of skis. I just got cold feet about using ABS after reading this: www.compositesworld.com/ct/issues/2004/December/687/
Thanks again,
G-man
The cnc sander does sound quite amazing... and expensive.
Some builders are reporting problems with ABS getting brittle and cracking in the cold. Have you experienced any such problems? Maybe it's just in situations where it gets 'really' cold. Now-a-days, we don't often get very cold around here, and maybe ABS would work just fine for me. I think I'll get some and give it a try.
Again, I can see where my question has not been very clear. My delam problems have not been with the sidewall delaminating from the core. My delaminations have occured in the bond area between the sidewall top surface and the top sheet. The top sheet bonds well to the top glass layer, but the top glass layer does not bond well with the top surface of the sidewall (arrg... this descriptive language can get difficult). Basically, I can take a knife point, stick it in between the top sheet and the sidewall (2-3mm in penetration depth), and run it down the length of the ski test samples and separate the bond area between the sidewall and the top fiberglass layer. When he knifepoint reaches the depth of the wood core, it will not penetrate any further because the bond between the glass and the wood is very solid.
Going with ABS may solve the above problem. It seems that a lot of builders are using ABS and pumping out a lot of skis. I just got cold feet about using ABS after reading this: www.compositesworld.com/ct/issues/2004/December/687/
Thanks again,
G-man
Gman - do remember that many companies have and still do use ABS sidewalls on their skis.
K2, older igneous (althought they did switch to ptex later), ninthward, Kingswood.
My understanding of the reasoning igneous switch was the Ptex was more impact resistant. It would take blows better than the brittle ABS.
BUT - I honestly don't think ABS is that bad. I've skied on many skis with ABS sidewalls and never had a problem.
Does anyone know how much harder it would be to use P-tex instead of ABS though? My understanding is that it is a bitch to finish Ptex sidewall once you are done with your skis.
K2, older igneous (althought they did switch to ptex later), ninthward, Kingswood.
My understanding of the reasoning igneous switch was the Ptex was more impact resistant. It would take blows better than the brittle ABS.
BUT - I honestly don't think ABS is that bad. I've skied on many skis with ABS sidewalls and never had a problem.
Does anyone know how much harder it would be to use P-tex instead of ABS though? My understanding is that it is a bitch to finish Ptex sidewall once you are done with your skis.
Iggyskier,
Check out www.priorskis.com and www.slouchsnowboards.com. They both also use ABS for sidewalls and tip spacers and both seem to put out a good product. I know a number of snowboarders who really think highly of Prior boards. There is no question that UHMW is more impact and abrasion resistent than ABS. I'm just having such trouble getting, what I consider, an acceptable bond with it. I want it to be bomb proof... maybe I'm asking too much of a material that was originally developed to be slippery... although, the base and topsheet material bond well, so, it must just be my inadequate surface treatment technique.
As far as any difficulty with finishing/sanding UHMW is concerned, just take a piece of UHMW and hold it against a belt sander for awhile... a long while... and see what happens (or doesn't happen).
Later,
G-man
Check out www.priorskis.com and www.slouchsnowboards.com. They both also use ABS for sidewalls and tip spacers and both seem to put out a good product. I know a number of snowboarders who really think highly of Prior boards. There is no question that UHMW is more impact and abrasion resistent than ABS. I'm just having such trouble getting, what I consider, an acceptable bond with it. I want it to be bomb proof... maybe I'm asking too much of a material that was originally developed to be slippery... although, the base and topsheet material bond well, so, it must just be my inadequate surface treatment technique.
As far as any difficulty with finishing/sanding UHMW is concerned, just take a piece of UHMW and hold it against a belt sander for awhile... a long while... and see what happens (or doesn't happen).
Later,
G-man
sidewall material and groove for edge teeth
G-man
I hope my article didn’t cause you undue frustration. I have been looking into the issue of sidewall material a little more and have boiled down the pro’s and cons as follows.
UHMWPE- More durable of the two materials, much harder to work with and proper bonding is harder/more complicated.
ABS- Less durable but much easier to work with, also easier to get a strong bond with the core and composites.
As splat noted, although many companies have “upgraded” from ABS to UHMWPE there are still plenty of good companies using ABS. I think if I have to pick between a stronger material and a stronger bond, at this point I go for the better bond since the seam is the failure point in the majority of the blowouts I have seen. Looking at it this way I think that ABS is my current pick although it might be an interesting future project to try and figure out how to make UHMWPE work. I know a good bond is somehow possible with UHMWPE sidewalls, nine seasons of torture testing my Winterstick have proved that.
Here is something that I haven’t been able to figure out. There has been some discussion (splat, hoseman) about routing a rabit groove around the edge of cores to fit the edge teeth and avoid concave bases. Are the people doing this using dampening rubber around their edges? It seems to me that the rubber strips plus lower layer of fiberglass placed in-between the edges and the core would mask the profile of the edge teeth and cancel out any benefits to shaping the base to fit the teeth. Are the edges/base being placed directly against the core? Is the bump from the edge teeth transferred that cleanly through the rubber and glass?
I hope my article didn’t cause you undue frustration. I have been looking into the issue of sidewall material a little more and have boiled down the pro’s and cons as follows.
UHMWPE- More durable of the two materials, much harder to work with and proper bonding is harder/more complicated.
ABS- Less durable but much easier to work with, also easier to get a strong bond with the core and composites.
As splat noted, although many companies have “upgraded” from ABS to UHMWPE there are still plenty of good companies using ABS. I think if I have to pick between a stronger material and a stronger bond, at this point I go for the better bond since the seam is the failure point in the majority of the blowouts I have seen. Looking at it this way I think that ABS is my current pick although it might be an interesting future project to try and figure out how to make UHMWPE work. I know a good bond is somehow possible with UHMWPE sidewalls, nine seasons of torture testing my Winterstick have proved that.
Here is something that I haven’t been able to figure out. There has been some discussion (splat, hoseman) about routing a rabit groove around the edge of cores to fit the edge teeth and avoid concave bases. Are the people doing this using dampening rubber around their edges? It seems to me that the rubber strips plus lower layer of fiberglass placed in-between the edges and the core would mask the profile of the edge teeth and cancel out any benefits to shaping the base to fit the teeth. Are the edges/base being placed directly against the core? Is the bump from the edge teeth transferred that cleanly through the rubber and glass?
powdercow,
No undue frustration experienced here... all info is good info when it comes to ski building. I agree that a good bond is possible with UHMW... eventually. I haven't been able to spend as much time this summer doing surface treatment/bond strength testing like I'd hoped, so I think that this season's skis are going to be built with ABS sidewalls. I'll just pass them around to friends and tell them to beat the crap out of 'em. Then I'll see what they look like in the Spring... if my friends will give them back. So far, they've been reluctant to do so, but I've eventually managed to pry their fingers away by whacking them with a stick so I could get my skis back.
I do rabbit a .030 inch deep groove in the core (actually ends in the sidewall strip) for metal edge clearance. I also use VDS rubber foil. Your question/concern is a good one. I get around your suggested problem by making the groove a little wider than the metal edge so that there is room for the foil and the glass layer to conform into the groove, along with the edge. I use a 7/16 inch straight cutter for the rabbit which results in a groove that is .030 x 7/16 inch. My bases come out very flat. In the lay-up, the VDS goes on top of the base/edge assembly, then the glass layer, then the core. I don't know if you have gotten you hands on a piece of VDS yet, but keep in mind that it is very, very thin... like paper thin.
I hope that helps.
G-man
No undue frustration experienced here... all info is good info when it comes to ski building. I agree that a good bond is possible with UHMW... eventually. I haven't been able to spend as much time this summer doing surface treatment/bond strength testing like I'd hoped, so I think that this season's skis are going to be built with ABS sidewalls. I'll just pass them around to friends and tell them to beat the crap out of 'em. Then I'll see what they look like in the Spring... if my friends will give them back. So far, they've been reluctant to do so, but I've eventually managed to pry their fingers away by whacking them with a stick so I could get my skis back.
I do rabbit a .030 inch deep groove in the core (actually ends in the sidewall strip) for metal edge clearance. I also use VDS rubber foil. Your question/concern is a good one. I get around your suggested problem by making the groove a little wider than the metal edge so that there is room for the foil and the glass layer to conform into the groove, along with the edge. I use a 7/16 inch straight cutter for the rabbit which results in a groove that is .030 x 7/16 inch. My bases come out very flat. In the lay-up, the VDS goes on top of the base/edge assembly, then the glass layer, then the core. I don't know if you have gotten you hands on a piece of VDS yet, but keep in mind that it is very, very thin... like paper thin.
I hope that helps.
G-man