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

 



Press Stage 1

The skis I am designing this year use a cap rather than a sidewall.  Eliminating the vertical side wall creates a lighter ski with no reduction in strength or stiffness in addition to a ski that is less susceptible to top sheet damage.  In order to create a cap I have to press the ski in two stages.  The first stage attaches the base, edges, rubber foil, and fiberglass to the core.  Once these are connected, the flashing is trimmed and the sidewall is beveled to 30 degrees from vertical.

The first step is to attach mounting hardware to the core; this will ensure the core doesn't shift during pressing.  This is done by super gluing blocks on either side of the center line and drilling a hole through each block into the mold.  This allows a nail to be passed through into the mold.  The base is held in place by the fixture already attached to the mold.

 

A piece of plastic (2 mils thick) is cut to place between the ski and the mold.  This prevents excess epoxy from sticking to the mold.

 

The base is placed on the mold using a pre-attached alignment guide.  This guide is made from excess edge material and prevents the base from shifting forward or backward.

 

Once this is done, all material is staged.  This includes the fiberglass, rubber, core, base, reverse mold, and bladder.  The air compressor is also charged so that it will be ready to inflate the bladder.  At this time, I mix 1.25 cups of epoxy.  I use a west system two part epoxy (105 resin, 206 hardener) to make my skis.  Marine supply stores such as www.go2marine.com are great places to get epoxy.  http://www.go2marine.com/product/97792F/slow-epoxy-hardener-206.html

 



Once staged, the epoxy is applied to the base, rubber, fiberglass, and bottom of the core using a foam brush.

The press is then pressurized to 23 psi.  The pressure is checked periodically to ensure the pressure is maintained.  The epoxy has a pot life of 20-25 minutes and is hard within an hour.  The ski will remain in the press for roughly 12 hours to ensure the epoxy is fully cured.

 



 Once cured, the ski is removed from the press.

 

 

 

After the skis are removed, a jigsaw is used to trim the flashing from the edges.  The saw was set to a 30 degree angle and the cut was made from the bottom of the ski, using the edge as a guide.  This year the wood at the edge of the ski is aspen, which is a softer, lighter hardwood; this wood allowed the skis to be trimmed faster than in years past.

 

 

Once trimmed, the edges are sanded smooth with an 80 grit belt sander.

 

Typically, I would round the sidewall into the top of the ski to remove the sharp edge and allow the top sheet to easily bend over the ski.  This year I am adding "rails" to the top of the ski to add additional stiffness and will round the top of the rail.