Ski Builders Forum

what methods do people use for alignment of their core during pressing?

I hear people talking about having excess sidewall that is trimmed with the flash, and others talking about cutting it precisely to the dimensions of the ski before layup.

Which method is better and how do you align during layup and pressing for each method?

I'm going to use a vacuum bag mould and have inserts, so i need the core to be aligned perfectly

you need to cut your sidewalls to the exact dimensions of the ski before layup only if you plan on creating a capped ski (one where the topsheet wraps around the sidewalls and meets the metal edges). if you plan on building a ski with exposed sidewalls like the enemies, armadas, etc. then you simply leave excess sidewall material over the ski's edge during layup and trim the sidewalls off after the pressing.

i've never vacummed bagged my skis before but here's how i align my cores for my pneumatic press. after i've layed down the base and bottom layer of composite into the mold i align my core on top of the composite. i then secure it into place by nailing the core directly into the mold. the nails go into the excess sidewall material that overhang the ski's edge. i'm not sure if this method will work with vacumm bagging though. you may have problems getting a good airtight seal.

another method is to create a simple "cassette". you can cut out some small wooden blocks (maybe 1/2" x 1" x 2" in size). secure these blocks onto your mold around the perimeter of your core to keep it from sliding around. this is just a thought. i've never tried it before but i'm sure something similar will work.

For the jib skis we made at the U of U, we used a similar method to what kam suggested, you don't want your core shifting and rendering the skis useless. We took small cylinders of ptex and superglued them to the aluminum of the mold near the tips, tails and underfoot portions of the skis after lining the core up on top of the base and composite. It was also practical for us to superglue the sidewalls to the core before layup so that when lining up the cores the sidewalls would stay put. Afterwards we could just chisle off the ptex alignment nubs so that they could be repositioned for the next layup. I would suggest leaving excess sidewall material and trimming afterwards in case you do get minimal shift it won't affect the final product as severely.

i'm not sure if i described the nailing method well enough, but there are some new photos that were just added to the layup preparation page in the how-to section.

In the snowboardmaterials.com video they use the binding inserts to align the core. Two are placed in the core with some superglue and then the core is aligned on the base and held in position until the glue sets. The core is then carefully removed leaving the inserts.

Has anyone ever done this with skis and just leave them buried?

Cheers!

dbtahoe,

In order to use the 'insert bonded to the base material' technique, you have to create little holes in the bottom layer of fiberglass cloth so that the cloth will fit around the inserts. It seems to me that this would result in corresponding weak areas in the bottom glass layer... maybe not a big deal in a snowboard (due to the greater width), but, I'm not so sure, myself, that it's a good technique for a ski... although, in practice, it might work just fine. Just my two cents worth.

G-man

i have a patented alignment process. actually, it's mickey-mouse. i only say patented to make myself feel better.

if you look at the photo in this thread:
http://www.skibuilders.com/phpBB2/viewtopic.php?t=754
that shows my headless body pouring epoxy, at cord center, there are four strips of wood that run lengthwise relative to the base material -- two for each ski. the "rails" are hotglued to the top of a thin sheet of uhmw and they act to align the wood core relative to the base material. the bases (with edges) are also hotglued to the uhmw. notice in the photo that the rails are blue -- they are covered with masking tape to keep epoxy off. when i'm ready to add the wood core, i remove the tape, then put the wood core in place, followed by applying a small bead of hot glue to secure the core to the rails. since the rails are aligned with the base that's hotglued to the uhmw sheet, everything pretty much lines up.after the topsheet, i wrap the sanwich then shove it into the press. the rails keep the cores from shifting relative to the base material.

does this make sense? i plan to either write this up and make a movie of it to better illustrate. it's somewhat complicated to describe.