Cassette Design

[camhard]

I've had a look through previous topics, but most of what I could find is quite old and doesn't show photos anymore or isn't particularly detailed.

I'm looking to use a cassettes with tabs to prevent core shift. I've built two pairs, this way, but neither was perfect. I used spare sidewall material for the tabs, which were fastened using rivets (attempt no. 1) and then screws (second try). I will probably try the Loctite product mentioned in another thread on the next iteration. The tabs were tight to the base w/ edges attached; do most people allow some wiggle room? I trimmed the core with the sidewalls to match the base, exactly, so that it would fit in the tabs. Unfortunately, things seemed to relax/move ever so slightly between prepping the cores and the pressing, so it was always a challenge to seat the core in the tabs properly (it wanted to pop out). one solution I was thinking of would be a stepped tab, which is tight to the base, then offset above that (for the core), and trimming the core with a little (1-2mm) tolerance, which would then be trimmed off post-pressing. I also ran into the issue of the fibreglass running out from under the base and up the tabs (the small added thickness made fitting things in even trickier); do most people try to trim their fiberglass exactly to the ski shape, if they are using a tabbed cassette?

I'd like to do a partial top cap in the future, but I'll sort that out once I get good results with the bottom only.

[Dr. Delam]

A technique that I have used with success is using the sticky foam squares to keep things in place. A stepped setup with thinner ones tight to the edges and thicker ones outside of the sidewalls. I usually give myself a couple mm of extra sidewall and cut my fiberglass to the width of the sidewalls. Even if the glass comes up between the sidewall and the tab the foam compresses a little to compensate.

[falls]

If you are doing metal pieces to keep the edged base in place keep in mind that people have had issues using just occasional pieces to support the edge when doing a heated cure. They have found that the base and edges expand with the heat and the supports end up creating a dimpled edge after cure (sort of like magnetraction) because the edge and base weren't able to expand in that spot.
Either support the edges the whole length with a metal strip sut to shape, or scribe a line where the edged base goes and stick it to the cassette with spray glue in the same spot each time. Either way you can then use occasional supports for the core without ill effect with heat. I don't trim my glass and have about 2mm of extra sidewall material overhanging the edges, then a 0.8mm offset on the support to allow the glass to fold up and over.

[vinman]

I hot glue small squares of MDF in 3-4 locations along the length if the ski. I leave less than 1 mm of room to allow the glass to fit. These hold in the press well but pop right off after pressing. They cut off in the flash.

For location I measure in from the edge of the aluminum sheet 3.25 -3.5 inches and make a line. This is the center of my base. I spray adhesive the base to the parchment covered alu sheet. Place the cores over the base. Then hot glue the squares in place. Remove the cores and lay up.

I don't trim my glass to shape. I use 13 inch wide glass and just roll it out and leave it full width.

[camhard]

awesome. thanks for all the info. I'll put together a new cassette and post how it works!

[NinetyFour]

To keep my bases from shifting in my cassette, I've just masked off 4 sections, one for the tip and tail of each ski, with 2" wide tape, 24" long, to prevent me from getting any mold release on my cassette when prepping it for a layup. Then I remove the tape, spray the area's with 3M super 77 spray adhesive. Then with my bases masked off with vinyl application tape, I just stick them to the cassette. Have had 0 trouble with a base shifting in the press.

I also use core locator pegs glued to my bases to stop the core from shifting, and the rabbet effectively assists them in this function to if done precise enough.