Shifting during pressing

[doughboyshredder]

be careful!

If you have any thing holding the edge from the side it has to be continuous along the entire edge, or you will get unintended magnetraction. I know it's hard to believe but the base expands and contracts along with the metal edge during pressing. Gluing the base down allows it to freely expand and contract. Having a shaped cassette allows it to expand contract equally. Having it only held in from the sides in a few places forces it to expand and contract in varying degrees, resulting in wavy edge.

[SRP]

Doughboy, Thanks for the info. I have actually been gluing down the base as well. I am thinking the magnets will be used more for core alignment so I don't have to drill a hole in the core for the dowels. I think I will continue to hold the base to the skin/cassette with the glue. I'll just have to see how it works.

[falls]

I like this magnet idea!
Instead of puting them on the outsides of the ski attached to the steel sheet you could incorporate them in the actual core! If you drilled out a recess in the core for the magnet to fit in snuggly you could drill out a recess in your bottom mold at the right spot for core alligmnet and mount a magnet in the opposite polarity there.
Going further if you mounted them the opposite way in the other ski once the pair was finished the magnets would hold the bases together when you were carrying them!
Going even further imagine the marketing gimmicks you could create when you had magnets actually inside your skis!!

[chaka]

ummmmmm.... tele skis holding together?, ski tips holding together when you carry them strapped in your backpack?. That sounds really nice, lot of work to do, but nice.

[CFO]

Hey Crew,

This is not exactly about the core shifting, but matches the topic. Has anyone experienced floating laminates? Used some uni carbon under transparent top sheet and when the board came out of the press, the stringers had floated all over and did not resemble straight lines even approximately. Is there a solution to this apart from using less epoxy?

Cheers,

[CFO]

The carbon stringers were above the top fiberglass layer.

[doughboyshredder]

Hey Crew,

This is not exactly about the core shifting, but matches the topic. Has anyone experienced floating laminates? Used some uni carbon under transparent top sheet and when the board came out of the press, the stringers had floated all over and did not resemble straight lines even approximately. Is there a solution to this apart from using less epoxy?

Cheers,

not that I can think of

[skidesmond]

I like this magnet idea!
Instead of puting them on the outsides of the ski attached to the steel sheet you could incorporate them in the actual core! If you drilled out a recess in the core for the magnet to fit in snuggly you could drill out a recess in your bottom mold at the right spot for core alligmnet and mount a magnet in the opposite polarity there.
Going further if you mounted them the opposite way in the other ski once the pair was finished the magnets would hold the bases together when you were carrying them!
Going even further imagine the marketing gimmicks you could create when you had magnets actually inside your skis!!

The magnet idea sounds interesting. You'd have to be pretty precise with the placement of the magnets.

And yeah, the marketing B.S. could be crazy funny!

I thought I saw somewhere in the forum that a ski manufacture (Elan?) uses magnets to keep the edges aligned on the base. They did they layup right in the mold in the press. They layed down P-tex base then the edges w/o any glue to attach them to the P-tex, then fiberglass, etc. Someone commented that the used magnets to keep the metal edges in place. The entire lay up is done in a mold in the press, once all the layers are in place they close it like a big waffle iron. So, not sure if the magnets is true or not. I'm sure the mold was CNC'ed to account for all the materials.

I guess if we had the big bucks we could do the same... but that would take some of the fun out of it.

I like the way skevik does his layup. ( viewtopic.php?t=2016 ) basically make the base and core longer than needed, drill holes in the extra material in the tip/tail sections and pin it altogether with the sheet metal mold.

I've also thought about drilling alignment holes in the tip block so the pins (actually a small bolt) would go through the top of sheet metal mold, ski layup, bottom sheet metal mold and into the tip block, so the placement into the ski press is always in the exact same spot. Just a thought right now. I'll try it over the summer.

[falls]

Yeah that video looks like the bottom mold has been milled out of metal. Once the base is in the edges are just dropped in next to it. The edges are pre bent exactly to shape and therefore fit nicely between the wall of the mold and the base. You can't see it but if a magnetic force was applied from beneath it would hold them there nicely. Everything else is then added all having been cut to size. It looks like prepreg glass.
Like doughboy said they get support of the edge for it's whole length so there is no waviness developing.

The only thing I see as a problem for drilling right through skins, materials into molds is that epoxy may seep through your hole. If you have a very tight bolt fit you would need to account for the angle of your tip and make sure the bolt goes through everything at a perpendicular angle. Again a fair bit of precision, but I suppose that is what you are looking for in an allignment system.

[falls]

I looked at some rare earth magnets on eBay. There are some 18mm diam and 10mm tall. I think they were about $1 each. Each one had a holding force of about 12kg. Interesting stuff!

[skidesmond]

....
The only thing I see as a problem for drilling right through skins, materials into molds is that epoxy may seep through your hole. If you have a very tight bolt fit you would need to account for the angle of your tip and make sure the bolt goes through everything at a perpendicular angle. Again a fair bit of precision, but I suppose that is what you are looking for in an allignment system.

Good point! The angle would have to be just right and I'd have to be careful about epoxy leaking into the hole and on the bolt, otherwise I'll had a tip mold permantently attached to my skis . That will make skiing difficult.

Also the way things are now there's not a lot of space between the forms (hose and cat track) in the ski press to fanagle with a pin into the tip mold so I'll have to work on that also.

I'll give it some more thought.... a hefty dose of car wax or butcher wax may prevent the epoxy from sticking where it's not supposed too.... Thanks.

[MontuckyMadman]

I have spoken to some industry folks that say the cnc cassette layup is done with a magnetic layup table hence no pre stuck edges. The core in that system only fits in the cnced cassette so core shift is not an issue.

There's a million different ways to do all this stuff.

[falls]

I bought some magnets on eBay. I think 50 of them for 25 bucks. Just going to have a play around with them and see if they can be of use. I like the idea of a force rather than physical constraints holding things. If nothing else the magnets are fun to play with. Apparently you can put one on your palm and another on the back of your hand and they will stick!

One idea I have is for cassette allignment. I might mount 4 or 5 recessed in the running length mdf board right at the periphery (so not where the ski actually sits). Then allign my cassette exactly and clamp it in place. If I then put magnets on the top of my bottom skin they will auto allign with the magnets underneath. If I then put superglue on the magnets and let them auto align they will be stuck on the cassette. Next time I put the bottom skin in the magnets should lock it in the right allignment a bit like those magnetic clasps on some ski jackets.

How much force does the cassette need to resist to stop it shifting side to side or front to back? The magnets I got have a 5kg holding force. So 4 on each side would give 40kg holding? Reckon it will work? I'm looking forward to this particular experiment!

[redbull]

I also want to find a better way to position the bases/edges. Right now we currently super glue the edges to the base then hold the base/edges in place on the cassette with temporary clamps until the cassette is sandwiched together (as shown in our layup video).

Magnetic cassettes are my dream but would guess they are very expensive! Anyone looked into how much it would cost? Anyways I came across this video:
Check out 0:34. It looks like they use the excess base material as alignment/holding. Find a bit that has a diameter of the edge width and puzzle it together with the edges? Any thoughts? I would like to get the process down to not pre-attaching the edges to the base, but would guess the edge may pop out of place when my flat cassette is placed in the mold for pressing. Magnets a must when not pre-attaching them??

[doughboyshredder]

my press has became slightly magnetic. I assume from the voltage leaking from the heat blankets, but have no idea. It's almost strong enough to hold a screw.