So, it's been a pretty busy couple of months since my last update.
I have pressed 4 pairs of skis! Each pair has gotten a bit closer to my desired shape/flex/weight. And I've learned & refined on my process heaps. Again, this site continues to be a huge resource and I thank all my priors!
Turns out, my previous single ski presses were definitely too much pressure & probably too much heat. I've since only pressed pairs of skis & have incorporated PID controllers for top & bottom heat blankets. Upon inspection of the MDF in my press taking up space for the bottom half, I found I had compressed the middle of the board!
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So after replacing the bottom supports in the press with a drawer slide setup & replacing the crap controllers that came with the heat blankets with proper PID controllers. I was in a much better position! I even used some scrap cores for part of the PID controller box. It's attached to the press with high-strength magnets so it is easier to remove if necessary.
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Last edited by verticalwhiteout on Tue Jul 19, 2022 3:18 pm, edited 2 times in total.
After upgrading the heat control and feeling confident enough in laying-up materials. I went on to press the first pair.
I tried using hot-glue to attach some alignment tabs to keep the core/base in place during layup/inserting into the press. This worked OK, but was a bit of a hassle & I wasn't very accurate with this. Later attempts I was able to do away with this step & keep aligned without adding the tabs.
This being my first "Success" I was pretty f**kn stoked! Even though I think they deflect too much & will probably ski poorly, I gotta try out the first pair.
Paulownia core with Vic Ash stringers. 15mm Jarrah sidewalls. Single layer 22oz triax above/below core. VDS along edge. Plastic tip/tail fill.
Core taper is roughly 2mm - 10mm - 2mm. Profile is 137-105-121 & 186cm. Weight once cleaned up is 1820g/ski.
Again, I think these are waaaayy too soft and will bounce around too much, but had to put a set of bindings on because they're the first real pair I've made
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A few problems I noticed after the first pair was:
Flex was too soft
Topsheet had pitting
Slight ding in top of one ski due to thermocouple placement
Tip/Tail filler to core interface wasn't made with great tolerances
Rocker was too aggressive, not leaving enough effective edge
My attempts to fix these, with varying success...
Increase core thickness
Keep my molds well waxed and free from dust. This has proved to be more difficult to achieve
Place thermocouples on the outer layers of the heat blankets
Swapped to straight edge tip/tail interface. I still think a V or angle is better to distribute the forces from a flex across a join rather than all at the single point, but that can be future problem...
Updated mold to decrease rocker amount
Quick comparison of deflection of all skis in my shop. Supported at 2 points at a distance of 1400mm. 25kg static load placed at the waist. Easy to see My first pair (S3) was much softer than anything else...
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Can see the pitting in the epoxy on the top coat. I'm skimming the veneer with resin during the layup. I was hoping to get away with a decent finish this way, but I haven't had much luck yet. The overall finish is 95% good, but there is pitting throughout. When I've been more diligent and clean I think there is less, but I haven't got it properly sussed yet.
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Can see the ding in the top of the ski from the thermocouple placement. After moving the thermocouples to the outside of the heat mats I haven't seen this problem again.
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After going too thin in the core and producing a very soft & floppy ski. I went the complete opposite direction. Kind of on purpose, to "set my limits" so to speak. I was hoping to go just beyond what I considered "reasonable" for thickness of a ski. And this pair was stiff!
I also used a resawn piece of Vic Ash for tip/tail spacer as I had no material thick enough to accommodate.
Core taper: 5mm - 12.5mm - 5mm
Weight: 2150g/ski
Deflection: 30mm (less than anything I owned)
These came out of the press nicely, but they're basically two-by-fours...However it was good to make an adjustment in core thickness, keeping everything else the same & see how they compare. Having previously made a "too soft" ski I'm happy I have now made a "too stiff" ski...
What I'd like to improve:
Topsheet resin pitting from straight out of the mold. This pair was less so than the previous pair.
Reduce weight
[*}Use better tip/tail filler. Maybe keep it wood, but Vic Ash is too heavy (but durable)
Cleaning up is a chore, and my big belt sander does OK job on bases, but need to find a better method. Preferably base grind machine. Those are pretty rare in Western Australia...
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Latest 2x pairs are getting real close to what I'd like to call an "enjoyable ski"
I haven't had the chance to ride any of the pairs yet, but I reckon the first couple pairs would be a real chore to ski. Now I've got something that I REALLY want to ski!
Dialed in the core taper to get a flex I think is pretty nice feeling and simple deflection measurements that compare to some production skis (although they are old skis)
I've always sanded the topsheets back and refinished afterwards with sprayed on polyurethane. Don't think you will get perfect results out of the press with waxed aluminium cassette. You could try a release film used in vacuum bagging, but I reckon it would be hard to prevent folds in this when pneumatic pressing. Some people sand their tops back then get a clear coat done at a spray shop for cars. I have refinished with epoxy also but found I got pinholes a bit with this too. Perfect finishes require a specialised environment like a spray booth I think, but you can get it pretty good with a spray gun at home if you hang some plastic tarps and don't have sanding dust etc in the air.
I set my thermocouples at the centre of the cassette and run the wire along the middle between the skis - stuck to the aluminium with tape used for sublimation printing (on the outside of the sheets between the aluminium and heat blankets). I don't know that this is any better than just attaching it near the periphery. Definitely don't want them placed over the ski even with very thin wire.
