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some More skis
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Joined: 04 Jul 2012
Posts: 112

PostPosted: Thu Aug 30, 2012 2:40 pm    Post subject: Reply with quote

Alright, can I bounce a design off you guys?

I'm about 191cm (what's that, 6'3"?) and don't get much change out of a 100kg. looking for an all mountain charging kinda vibe from this first pair. Local snow conditions are pretty variable. generally quite hard, lots of crud with the occasional day on fresh which is generally a pretty wet snow - we don't get dry powder. So I'm looking for something pretty stiff and stable.

Here is where I'm at.

sketch is top down of the finished ski - not a flattened image.

The camber profile is 5mm of early rise over 170mm, 7mm camber over a running length of 1500mm, then 3mm of early rise over 100mm of early rise in the tails.

Construction is going to be bamboo, full width, full length. Planning on 600g triax top and bottom, with some undetermined (200g? full width?) carbon uni on top of the core.

Where I'm a bit stuck is the core. Seems like this is where art meets science.... So let me just throw some numbers out and you guys can tell me if I'm way off.

how about 1.7mm in the actual tip radius, linear taper to 2.8mm at the transition from camber to rise, linear taper to 11.5mm 7cm in front of boot center, then tapering back down with the same numbers from 10cm behind boot center (2.8mm; 1.7mm).

Am I way off? I know there is a certain amount of build it and see here, but I'd love to get some days on my first pair before they're superceded Very Happy

Thanks in advance for any advice.
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Joined: 04 Jul 2012
Posts: 112

PostPosted: Thu Aug 30, 2012 3:41 pm    Post subject: Reply with quote

One other question - there's pretty much no point looking beyond a linear taper until I know what the hell I'm doing, right? I have the capability to do a parabolic or splined taper, just no idea if it is of any benefit.
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troublemaker



Joined: 22 Jan 2012
Posts: 217
Location: The Dalles Oregon

PostPosted: Thu Aug 30, 2012 10:04 pm    Post subject: Reply with quote

Nice looking heat mats! Love the thermocoupler idea, I buy K couplers for a $1.50 U.S. each, how much does thermo wire cost? Also what kind of solder are you using on the NiChrome?
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Joined: 04 Jul 2012
Posts: 112

PostPosted: Fri Aug 31, 2012 2:11 am    Post subject: Reply with quote

We're somewhat less fortunate with supplies here trouble Smile I think the reel of extension wire was like 40 bucks? themocouples locally were going to be a tenner each or something, and then be too short.

Just standard electrical solder on the nichrome. probably got lead and all sorts of other yummy stuff in it...
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skidesmond



Joined: 07 Apr 2009
Posts: 2283
Location: Western Mass, USA

PostPosted: Fri Aug 31, 2012 10:52 am    Post subject: Reply with quote

Looks like a pretty beefy ski design. Tip/tail core thickness are typically 2-3mm. I make my binding area ( the area in front and behind boot center ) bigger. I have a fairly flat area in front of boot cent that's 130mm and 230mm behind boot center.

So you're not far off, and the ski design you have certainly will work.
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troublemaker



Joined: 22 Jan 2012
Posts: 217
Location: The Dalles Oregon

PostPosted: Fri Aug 31, 2012 12:27 pm    Post subject: Reply with quote

More wrote:
We're somewhat less fortunate with supplies here trouble Smile I think the reel of extension wire was like 40 bucks? themocouples locally were going to be a tenner each or something, and then be too short.

Just standard electrical solder on the nichrome. probably got lead and all sorts of other yummy stuff in it...


I tried some 60/40 rosin core solder and counldn't get to stick. Is your rosin core? Found 50 feet of thermocoupler on ebay for 20 bucks shipped. I like the idea of having thermo in bulk and not have to wait on shipping.
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Brazen



Joined: 25 Nov 2010
Posts: 840
Location: San Bernardino, CA

PostPosted: Fri Aug 31, 2012 12:30 pm    Post subject: Reply with quote

I believe you'll want more rise. I've been working with rockered early rise tip and tail and you actually have to build your forms with a bit more rise as they drop. Where does your tip height sit on your drawing? Those look a bit like the Armada JJ's , nice design.
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MontuckyMadman



Joined: 20 Jun 2008
Posts: 2348

PostPosted: Fri Aug 31, 2012 3:47 pm    Post subject: Reply with quote

camber and tip and tail will all fall around 1cm, not more than this.
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Brazen



Joined: 25 Nov 2010
Posts: 840
Location: San Bernardino, CA

PostPosted: Fri Aug 31, 2012 3:55 pm    Post subject: Reply with quote

Right, he's going for 3 and 5mm rise over 100mm and 170mm respectively. I believe he'll want to raise that a bit. Just my opinion.
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Joined: 04 Jul 2012
Posts: 112

PostPosted: Fri Aug 31, 2012 5:14 pm    Post subject: Reply with quote

Awesome, thanks for the feedback guys.

Tip and tail height after the early rise is ~60cm over that 70mm at the front and 65mm at the back. I'm on the wrong computer right now, without solidworks, but I'll post a mould sketch later which should show the elevation profile.

So Montucky and Brazen, I should expect a drop of a cm towards flat even if I've got evenly controlled heat top and bottom? I might have to remake some moulds... well... the machine might have to remake some moulds I guess Smile the mould material is all free so not a biggie to redo. I can keep these ones for making something flat and playing around with heat induced shape later.

Des, thanks for that, Yeah I'm certainly after beefy and burly, being a big heavy bastard. Reckon I should drop that core thickness at the contact point at the tip to 2.5? I quite like stiff tails so I might make that marginally thicker by .1mm or so. I was thinking (please correct me if I'm wrong) that a reasonably thick tip would be key for smashing through crud ?

I'll stretch out the flat to 200 aft and 100 fore of boot center.

Thanks again for the advice everyone - it's awesome, I go to bed and there is all this information waiting when I wake up Very Happy

Trouble - I'll check the solder but it definitely had a flux core. the thin wire we used certainly wasn't a good option though. wouldn't use it again.
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skidesmond



Joined: 07 Apr 2009
Posts: 2283
Location: Western Mass, USA

PostPosted: Fri Aug 31, 2012 6:06 pm    Post subject: Reply with quote

I make my wood core tips about 3mm maybe 2.8mm. I use 2 layers of 1/16 wood veneers which is about 3mm or just under after I sand them a bit. Same with the tail, I like the tail of my skis on the firm side. I'm about 195lb, and yes they will plow through crud very nicely.
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Joined: 04 Jul 2012
Posts: 112

PostPosted: Fri Aug 31, 2012 6:13 pm    Post subject: Reply with quote

Excellent, looks like we're back to 2.8-9mm tip and tail Very Happy
Thanks again. This is all getting a bit exciting... I'd better order some glass and carbon!
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Joined: 04 Jul 2012
Posts: 112

PostPosted: Sun Sep 02, 2012 4:21 pm    Post subject: Reply with quote

Routed up a top mould extendy thingie on cnc in the weekend. Took WAY longer than it should have due to some suprises from the machine... probably just should have done the job by hand instead of setting up the machine, ah well.



(pay no attention to the ruined workpieces on the floor.)



I decided instead of using metal pins and glue I'd thread the ends and bolt it together. Mounting it in the press tonight.



Falls, this is the mounting method I was trying to explain. Basically amounts to a threaded rod sticking up out of the moulds so they can attach to the press like this - loosen the nuts and it can slide along, then tighten to clamp.



So I'm getting fairly close to layup now... I've searched around looking for detail on mould relaxation coming out of the press... everyone seems to have different experiences. Hope I'm searching with the right keywords. Sorry if this is a stupid question and pretty please correct me if I'm wrong here:

Assuming I can get perfectly even heat top and bottom (I think that should be fine - independent PIDs, and I can change the duty cycle on each mat if/when the top one needs a bit more relative love) I won't get any heat induced camber gain / camber loss. HOWEVER there will still be a relax back towards a straight core as the fibers have to absord the tension / compression of the bent core. Yeah?

Then I get to the amount to expect, which I'll want to compensate for in the moulds. I would have thought this effect would be more pronounced in the middle of the ski where the core is thicker? And less so in the tips / early rise? But from reading the experiences of others, the effect ranges from zero to ~10mm. I suppose that it would be better to compensate high than low - so I should redo my bottom moulds and build an extra 10mm into camber?
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vinman



Joined: 09 Nov 2007
Posts: 1301
Location: The tin foil isle

PostPosted: Sun Sep 02, 2012 5:10 pm    Post subject: Reply with quote

10 mm is huge. I press my powder skis with 4mm of camber. In general they come out nearly exact to the mold, maybe 1mm either way with using equal heat top and bottom.

My mold is a 4 mm over the lenght of a 185 cm ski.

I tend to increase 5-10 deg of bottom heat to account for skis shorter than 180cm to account for this smaller span on the camber block. This goes for skis with a very short running lenght also.

I'd say press a pair with equal heat top and bottom and see where you are at. Then compensate with heat to get your desired camber on your next set.
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Joined: 04 Jul 2012
Posts: 112

PostPosted: Sun Sep 02, 2012 5:54 pm    Post subject: Reply with quote

Suck it and see, ok Smile

I suppose worst case is I have a set of skis to do some destructive testing on, which sounds pretty rad anyway.
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