Desert Skis Log - Page 2

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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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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New mold design with a bit less rocker

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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)

Latest pair specs:

Core taper: 3.5mm - 10.5mm - 3.5mm

Weight: 1915g

Profile: 187cm 137-105-122 20m radius

Deflection: 45mm

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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.

Finding a base grinder in WA is one of the joys of building skis in Australia!

Howdy all,

Been in the process of designing / building / setting up shop from nothing over the last 7-8 months and figured I should get around to starting a build log. I’ve reaped the benefits of the wealth of information online and find the lengthy build logs full of good information. Hopefully I can contribute in a small way.

To date I’ve pressed two skis (test runs), and am currently in the middle of making my whole setup a bit more ergonomic as well as iron out a few bugs (listed below). Hoping this weeks to get my first pair of ride-able skis out of the press

A bit about me:

Currently I’m based in Perth, West Australia. I decided to start building skis during lockdowns last year as I was unable to spend anytime near snow over the last two years. First time in my entire life I haven’t had “proper winters.” Needing to maintain a connection to skiing in someway (preferably that didn’t involve FOMO) I thought building skis would combine a lot of interests until I could get back to the snow. I used to work winters between USA & NZ grooming/snowmaking/patrolling/maintenance and nearly everything in-between. It’s been tough seeing mates around the world have “lock-in” days/weeks/months with plenty of snow, but hopefully by the end I’ll have the upper hand with piles and piles of freshly pressed skis!

Enough about me...now about my set-up / process (I’m sure y’all will see plenty of familiar processes...)

PRESS

Designed after the Monkey Press and many other I-Beam style presses. Having never used vacuum molding before, I felt more comfortable going this route. Probably a bit more expensive and definitely going to be more of a pain to move, but overall happy with how it has come out. I designed my cavity a bit too short for comfort (2.04m long x 410mm wide), but will have to make that work for now. I'm also considering swapping my molds for the camber-block style with various tip/tail molds. I believe my current molds are too thin and the combination of heat/pressure has deformed the current molds, as well as the first layer of 18mm MDF. It was trashed with about a 2mm "dent" in the middle from pressing a single ski @ 55psi & 80C

Components:

- Molds all made from 18mm MDF. Some "moisture resistant" MDF areas as well.

- 25x3mm aluminum square tubing cat track. Threaded with 2 steel wires and suspended with 5mm shock cord

- Full length upper and lower heat mats

- 400mm HD PVC layflat hose for bladder. About 330mm wide when flat. Some concerns here about not getting a wide enough footprint for the bladder to evenly press a pair of skis. Clamped at ends with angle iron & plumbed in with the "bulkhead" style fitting and rubber washers.

- Adjustable length top mold suspended by angle iron. Slides OK, but a bit annoying to change lengths.

Still to do:

- Swap heat controllers for PIDs. Current controllers have temperature sensor (non-thermocouple) near the edge of the heat mat & is not indicative of the sandwich temp. Plus they gradually drift (overshoot) from setpoint by about 30C

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CORES

I'm trying to build skis using 100% Australian sourced timbers, so using what's available here in WA. Obviously there aren't any "traditional" timbers in an area that hasn't had mountains for hundreds of millions of years. But there are some interesting timbers that I'm going to try out. I'm starting out using a combination laminate of Paulownia & Victorian Ash. It's a bit confusing here as Victorian Ash is 2-3 different species marketed under 2-3 different trade names depending on location and suppliers. It's difficult to determine the exact species from the sellers, and none of it is grown in Western Australia. Trade Names are: Mountain Ash / Alpine Ash and can be Eucalyptus Regnans or Eucalyptus Delegatensis. Then there's Tassie Oak that is sometimes sold as Vic Ash...

I'm using the Vic Ash as the hardwood stringers in my core laminate. Re-sawing the laminated logs into 15mm core blanks. This may end up being a bit thick, but wanted some room to play with this first batch of skis.

I'm creating my cores with a 15mm Jarrah sidewall. Jarrah is a uniquely West Australian timber that is very very hard. Pretty much everyone I've talked to about using it in skis thinks I'm crazy, but it seems to work in the couple of skis I've pressed so far. It's Janka rating is 8.3kN (compared to Maple @ 6.5kN). Its a very durable timber and was used extensively in WA to build houses and is very moisture and rot resistant. It machines OK and oils well. My concerns are it is potentially too brittle, but testing will tell

I cut the sidewalls to be just a couple mm over the final shape to allow for finishing up to the edge. At this point I'm applying an edge rabbet for a rebated space to allow the edge to fit in without creating a gap. I've yet to determine exactly how much this needs to be. I think I've made it a little bit too much on Ski #2 resulting in an uneven base...

I'm thickness profiling using a planer/thicknesser and a sled. Currently I have a sled that is fixed in the middle and using 1mm aluminum shims (offcuts from press mold-skins) as spacers to allow the taper. The few times I've used this I've found it to be pretty cumbersome and not 100% effective. I've got a spiral cutter-head on the thicknesser and have built a large in-feed / out-feed table that fits inside the thicknesser. When getting close to the ends where the taper is ~1.5mm I'm seeing significant tear-out. I'm trying to achieve a uniform thickness with tip/tail fill material, but have yet to achieve this to my satisfaction...

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SHAPES / MOLDS

So far I have created molds and shapes using CAD & by hand. I've used FreeCAD to create mold templates I've had CNC'd out here locally, and my current templates I have made by hand. I'm struggling to suss out an offset function in FreeCAD that will allow me to create a base template (with edge recess). I would like to transition to more CAD design, but you can only bang your head against the wall so many times before needing to get back into the shop and use your hands. I've looked at, and had a play with, SnowCAD & MonkeyCAM and found these quite helpful. However, I would like to find a process that is FOSS and capable. Over the next couple weeks I will take back to the keyboard and mouse and persist...

My shape templates I've made by hand so far have involved CAD drawing, printing paper template, cutting, sanding, finishing. This works OK, but I know is not 100% accurate or symmetrical. The templates look good to the eye & are surprisingly uniform when measured. To transfer template shapes to materials, I've dropped a 1/2 router into a workbench making a large router table. This works pretty good for cores, as I can screw the template directly to the far end of tip/tail in an area that will end up being replaced by tip/tail filler when laid-up. For the base material I'm using spray adhesive to temporarily hold the bottom (non-adhering) side to the template. I like the idea of a vacuum table for this instead, as it would leave less residue.

I'm currently at the sticking point many people have come to it seems. Bending good edges. I've got two pairs of modified nippers (thanks jamesradny). My first two skis were just 3/4 length edges down each side. But yesterday I tried to do a nose wrap and am quite disappointed with the effort required. I've ground away a bit of material to make the nippers a bit easier to use (hopefully) but am reading all I can about the 3-wheeled ring-bender methods here. When you read that guys have abandoned ring-benders to go back to nippers because it is easier, I think my technique is just wrong or my tool is not just right. Waiting another day for some base material to flatten before I go back to re-do yesterdays work.

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RESIN & FIBERS

I've got some West System resin (again from jamesradny), Kirkside K3600 laminate resin, as well as some Surfset Flex resin. Entropy in Australia is not really doable, and will try out a few different locally available resins to see what is preferable.

18oz & 22oz tri-ax fibers are readily available here, as well as carbon / kevlar / flax. Currently just fleshing out the whole process using 22oz triax.

I tried using a machine preservation wax (for woodworking) as a mold release last go & it wasn't very good. Cleaning the resin from the aluminum skins is a nightmare. The first press I used cellophane, for some dumb reason, and lets just say...that was a dumb idea...

I'm going to try a silicone spray this next round and if that doesn't work I'll find a bees wax or carnuba wax or some other heavier wax. Are you guys really lathering it on? Any compatibility issues with resin/base plastic?

Anyways, I think this is a big enough first post, and will continue to add to it. I'm still figuring everything out and looking forward to getting to ski my own skis!

-JP

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What a great first build log!

Regarding your first two pairs, by the look of the photos those were definitely overcooked. You really need to be able to measure your temperature on the laminate as the laminate itself also provides some thermal insulation.

For the edge benders, maybe you could post a photo of your modified tile nippers, so we could check if we see anything wrong with them. Edge bending is always a chore - even after many pairs built.

Thanks, chrismp!

I had been taking heaps of photos and notes over the last few months. Found I kept coming back here for information and though I should get around to making a post to get "caught-up." Hopefully I can post a bit more regularly now

Big shoutout to everyone here that has shared their stories and information so us new guys can get a good start.

> chrismp wrote: ↑Thu Mar 17, 2022 4:15 am
Regarding your first two pairs, by the look of the photos those were definitely overcooked. You really need to be able to measure your temperature on the laminate as the laminate itself also provides some thermal insulation.

I think I agree with you on this & I'll explain below....but first, I gotta ask why do you think they were overcooked? What was obvious to you?

Only during my second press did I remember to get the thermocouple placed near the laminate before pressing. (The first press I forgot to place thermocouple before pressing...) Turns out the controllers I have don't control very well at all. They drift to about +30C over setpoint over the 4 hour press cycle as well as have wild temp swings during the warmup period of about 30-40 mins. This is due to the temperature sensor being embedded into the mats at the end where the connections are. This means the sensor is nowhere near the laminate and mostly inaccurate. I was able to kind of compensate for the big temperature swings by pre-heating the press to 30C prior to placing the laminate in. However I was not on top of the setpoints to accomodate drift.

The resin I was using is Kirkside K3600 with a 4-hour cure time @ 80Ckir (from the best I can tell from the data sheet...)

Currently I'm in the process of putting together a proper PID controller and once I have all the components and build an enclosure I will get that operational. It will be much more reliable and nicer to work with.

Modified Nippers

> chrismp wrote: ↑Thu Mar 17, 2022 4:15 am
For the edge benders, maybe you could post a photo of your modified tile nippers, so we could check if we see anything wrong with them. Edge bending is always a chore - even after many pairs built.

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These are the two pairs of nippers I have. The one on the right (narrow toothed). I took all the factory edge off of to get as flat a surface as I could to allow the contact point of the jaws to get as much of a "bite" as possible. They seem to work OK, but I definitely don't have the touch yet. I'm prepping my next pair and am going for a wrap up both side and around the tip (3/4 wrap??). I was able to get one edge bent pretty good, but stuffed the second. I forced it on whilst gluing and that ended up tweaking the base to where it no longer aligns with the core. I tweaked the narrow nippers a bit more after that and have got a bit better control on some test pieces, and will have another go soon.

Edge Bender (Roller Style)

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I'm going to give a go at building one of the roller style benders as well. I've engaged a local fabrication shop with some drawings and will mount those to a tilting drill-press vice. Tool store had a sale this week and was able to pick the vice up for a good deal. I've added another wider notch on my roller design to run the edge through when it first comes off the spool to take the initial bend out. I achieved this with 3-jars screwed to a board previously

Edge Bender Inspiration from:

- Skevik Skis

- twizzstyle

-JP

The overcooked look is pretty easy to explain: the photos you posted show quite severe print-through of the edge tangs and even the fiberglass. This usually doesn't happen on the base side unless the base material gets too soft from overheating. For the heat cure epoxy I use, I usually stay around the lower recommended curing temperatures as the higher temps only speed up the cure and increase the glass transition temperature, which is not really relevant for ski performance.

The tile nippers on the right look perfectly fine. The ones on the left could maybe do with a deeper cutout, but will still work as is...you just won't be able to bend a tight radius.

For bending edges I found it often helps to overbend the edges a bit on tighter curves and then carefully bend them back to where you want them.

Thanks for the explanation. Two follow-on questions:

- What temperature do you reckon the base material starts to get too soft?

- Is there such a thing as too much pressure?

I know I by the end of the press cycle I was just above 80C. Here's the cure schedule from the Data Sheet:

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I'm interpreting that as:

- Left Column: 7 days @ 25C to achieve properties below

- Middle Column: 15hr @ 50C + 24hr @ 25C to achieve properties below

- Right Column: 4hr @ 80C + 24hr @ 25C to achieve properties below

In trying to minimize my press time I followed the right column (as interpreted). I'm new to working with epoxies so don't know what is a "typical" cure schedule. I agree increasing Tg doesn't make much of a difference for building skis, however some of the other material properties may be desired.

I was pressing at 380kPa (55psi), which for my bladder size (1.9 x 0.33m) results in ~240 kN @ the bladder. This applied across the cat-track (0.41m wide) then onto the ski (0.11m wide average) gives me a pressure of approximately 1300kPa @ the ski (so far I have just pressed single skis, obviously this pressure will half when doubling surface area). I just started at 380kPa as that was what "felt right" after reading through many different posts on here. I've come across people diagnosing problems and referring to "over-pressing" but have also seen posts where people have said more pressure = more good. More pressure will inevitably press more resin out of the fibres and I expect this to be a trial-and-error process to get myself dialed, but can't help but wonder if there are some "unwritten limits" of what is typical?

-JP

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The melting point of UHMWPE (which is what base material is) is between 130° and 136° C. From your description it seems like you might have hit that temperature at least temporarily. It is not advisable to heat UHMWPE to temperatures exceeding 100° C.

The cure schedule for your epoxy looks like it's not really a heat cure epoxy as it always recommends at least 24h at room temperature before post curing at a higher temperature. Real heat cure epoxies can be heat cured right away at high temperatures and usually cure within one hour under pressure (a few days post cure at room temperature is still recommended).

Regarding the recommended pressure, you're right, this depends on many factors. You'll know if your laminate is too dry from too much squeeze out pretty quickly, but yes, it can happen.

PS: I see one problem with your single ski press setup - your bladder is much wider than the ski you're pressing. This leads to higher pressure on the edges of the ski as the cat track gets bent down by the bladder in the areas next to the ski. This probably also contributed to the severe print-through of the edge tangs. So yes, it is definitely better to press both skis at once with your setup or switch to a narrower bladder when you're pressing single skis.

I agree with all you said above. I think it was too hot, and I had concerns about the high pressure zones around the ski edges...Unless you were able to get the ski exactly lined up under the bladder, then it will have a tendency to tilt to one side or the other.

I also learned something about after reading your last comment.

Epoxy Resins can be heat-treated post-cure.

I was unaware of this and just assumed that heat-treating happened during the cure for any epoxy. When reading the cure schedule on my data sheet I assumed it was round backwards because I didn't even think of applying heat after the cure time. In my reading around I also learned about outgassing, particularly around porous substrates (definitely a ski-core). I think I had some issues with this before as well. There were small bubbles and "pockets" for lack of a better word, you could just make out on the top of my last ski.

Just put a pair into the press this morning and will run through the cure-schedule as per data sheet. Going to run the pair of skis @ 30C (ambient is around 23C today) to minimize any thermal difference. Pressure will be at 50psi for the duration. I'm going to leave the pair in the press for 24hrs, but don't feel like this is necessary....

Will post some photos soon.

-JP

I had trouble with the sled and thicknesser when I had a small thicknesser like the one you have. Felt that it just didn't have the roller hold down power or feed through power to push a heavy sled and core. I got a carbatec 15 inch model which was much more heavy duty and it works well.

> falls wrote: ↑Sat May 28, 2022 9:54 pm
I had trouble with the sled and thicknesser when I had a small thicknesser like the one you have. Felt that it just didn't have the roller hold down power or feed through power to push a heavy sled and core. I got a carbatec 15 inch model which was much more heavy duty and it works well.

Yea, I would like to have a bit more robust thicknesser...and planer...and bandsaw

The benchtop thicknesser seems to be going OK. I get about 60mm snipe each end, which is easy enough to account for. But the extended bench is quite handy for running 2m cores + sled through. I coated the table with polyurethane and it seems to slide quite easily. I did have a period where the retaining screws on the cutterhead had gotten out of adjustment (grub screw loosened off) and the boards were coming out with nearly a 1mm difference in thickness from left to right. A quick disassembly fixed that problem. My current thicknesser sled is 2x pieces of 18mm MDF that can handle one core at a time & the thicknesser pulls it through nicely.

I'm looking forward to when I can upgrade a few machines though!