All Mountain Radacoski (AMR-14)

It's been a busy year, but I am currently making a pair of skis for a friend, Matt Radacosky.  I am also in the process of building a new ski press from steel, but will post about that later. This year I am making a pair of eastern all mountain/freeride skis similar to the Aftermath of last year, but wider.  The aftermath is 127-88-109, 53% of the ski is in front of center, and has a turn radius of 17.7m.  The AMR-14 is 128-100-118, 51% of the ski is in front of center, and has a turn radius of 19.9m.  You can see the difference between the skis below.

I am also going with a sidewall design this year rather than the cap design.  I expect the ski to be a little heavier, but should be more responsive in turns. One change I am making this year is using a basalt fiber instead of fiberglass - basalt is made from igneous rock. Here is some info about basalt:

Basalt fiber is a material made from extremely fine fibers of basalt, which is composed of the minerals plagioclase, pyroxene, and olivine. It is similar to carbon fiber and fiberglass, having better physicomechanical properties than fiberglass, but being significantly cheaper than carbon fiber. (http://en.wikipedia.org/wiki/Basalt_fiber)

...the basalt/epoxy sample's strength tested 13.7 percent higher than that of the E-glass sample and exhibited 17.5 percent greater stiffness, although the basalt sample was 3.6 percent heavier than the E-glass sample. Additionally, basalt fibers are naturally resistant to ultraviolet (UV) and high-energy electromagnetic radiation, maintain their properties in cold temperatures, and provides better acid resistance. (http://www.compositesworld.com/articles/basalt-fibers-alternative-to-glass)

 Relative tensile strengths (breaking strength) are listed below:

Steel                  73000 psi  (0.50 GPa)
E-glass            500000 psi  (3.45 GPa)
Basalt              600000 psi  (4.15 GPa)
Carbon Fiber   725000 psi  (5.00 GPa)

After some extensive searching, I found some quad-axial basalt fabric from a company in Germany -iXperial (http://www.ixperial.net/). I highly recommend them; this shipment was fast and the customer service was excellent. Most fiberglass in skis is tri-axial, meaning that it is layered along three axes.  The basalt fiber I ordered is layerd on four.  The basalt will be visible through the topsheet and graphics layer.

 

This year I purchased a new 2.5HP router and a 6 Amp jig saw.  If I could afford a large bandsaw I'd have one.  The extra power in these tools over my past tools makes a big difference in cutting time and surface finish.  The core of the ski is nearly identical to the Aftermath, but substitutes pine for the cedar.  It still uses 3 oak stringers, 5mm wide, along with Aspen and Poplar. Photos of the core in process are below.

 

 

The base material is simlilar to last year and is a 4001 grade sintered P-Tex. This year I was able to get the base template and core member template printed on the same sheet, which saved some time and money.  The base in process is below.

 

 

I did run into a problem this year; after I cut out the base and superglued on the edges, I realized that one base had warped out of shape.  I have speculated that it had something to do with internal stresses in the base material.  When the material was cut, the stresses were relieved and it warped.  It's common in steel and I have seen it in plastic tubing before.  I had to re-order the base material and try again.  This time I cut out the base roughly at first, leaving about 1 inch to the template.  I then took a second pass using the template and it turned out fine.

I am returning to the sidewall design again this year.  The following pictures illustrate attaching the sidewalls to the core, planing the core, and profiling the core.

My friends Matt and Shane;  Shane is determined to make skis with me for a living; I forced them both to wear hearing protection.

 

 

Once the skis were profiled, I used my belt sander and 50 grit sand paper to smooth out the surface after routing. One thing I was worried about, after my last experience with sidewalls, was getting the sidewall to stick to the epoxy.  Ideally, the plastic surface would be very rough with a surface finish that looks like that of the base material.  The 50 grit belt seemed to do the job quite well as shown below.  The surface looks like it does when it is abraded at the factory. This will give the epoxy "hairs" to grab onto as it forms a mechanical bond.  A lesser grit would produce a cleaner looking surface, but would not bond as well.

 



 

The next step is to finish the graphics layer, prep the top sheet and basalt layers, and press the skis.

 

Here is a preview of the new ski press.

http://youtu.be/E45xais1i6o

 



Reinforcement

This year I wanted to make a lightweight ski with adequate stiffness; in order to do this I designed reinforcing rails to mount to the top of the core.  The rails are 5mm tall at the center and taper to 0mm at the tip and tail.  A binding mount platform was also added to the center of the ski (rails would not provide a flat surface on their own).  Adding the rails stiffens the skis by a factor of 2.7 (3.27 -> 8.88 lb/in).

The rails are made from oak to provide maximum stiffness to the core while minimizing the required height.  The rails were trimmed to 5mm thick and 18mm wide.  In order to attach the rails to the core, the outer edge was beveled to 30 degrees from vertical to match the sidewall profile and the inner edge was beveled to 45 degrees.  45 degrees on the inner edge provides a more gradual slope that the top sheet should contour to easier when attached.  The beveling was done using a table saw.

Next, the ends near the tip and tail had to be tapered. In order to do this I set the table saw to 3mm and then 1mm and cut the rails down.  This preliminary cut stepped the ends so that less sanding was needed.  The steps were then sanded to provide a smooth taper.

Once the rails were cut to size, they were sanded with a belt sander.

Next, the rails were glued to the core; the rails were bent to match the edge curvature of the ski and clamped in place.  The ends of the rails extend past the ends of the ski and will be trimmed of when the glue is dry.

Next a binding platform had to be added to provide a level surface to mount the bindings.  This was done by cutting several strips of oak and then beveling the edges to fit together.

Once the sides were beveled, a bevel was added to the ends of the binding platform to provide a smooth transition to the top of the core.

The binding platform was then glued and clamped in place.

Once this was complete, the ends of the rails were trimmed with a jigsaw to match the tip curvature.  The rails were then sanded to provide a smooth transition on the sidewall.  The top edges of the rails were rounded so that the top sheet would more easily fold over the sides.

 

The skis are nearly finished now; the final step is to design the graphics and press the fiberglass, graphics, and top sheet onto the ski.  Once done, the bindings will be mounted and the skis will be grounded, waxed, and sharpened.

AMH-12 Core

As mentioned in my last post, I am making the cores for this years skis out of aspen, poplar, and oak. A core set of wood is shown below.

 Similar to years past, I am using what I call a pre-tensioned core design.  Rather than laminating thin strips of wood into a rectangle and then cutting the shape out of it, I cut two inner core members to a curve which allows for uniform wood strips in the center and on the sides of the core. Uniform strips on the ski edge  allow for even edge pressure.

The first step is to rip the core members to the predifined widths.  The three oak stiffeners are 5 mm wide.

Next, the shaped core members can be cut using the core member template.

Once this is done, the core members are sanded and can be glued together. A single core set is shown below consisting of 11 pieces.

This year I applied glue with a roller which improved the process over past years.

 

Once glued, a planer is used to create a smooth surface on both sides of the ski and to create the maximum thickness of 12 mm (binding platform).

The core template is then used to cut the shape of the tip and tail into the ski.  A jig saw works well for this.

The next step is to set up the ski profiling jig and cut the ski thickness profile with a router.

 Once profiling is complete the core is again sanded.  Once sanded, the core is complete and ready for layup.