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excess tip/tail epoxy vacuum press

 
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Wvmtnbiker



Joined: 28 Jan 2014
Posts: 17
Location: Greenwater, WA

PostPosted: Fri Dec 01, 2017 2:55 pm    Post subject: excess tip/tail epoxy vacuum press Reply with quote

Ok so I've made 10 or so skis thus far. On most of them I get quite a bit of epoxy around the tip and tail edges that's a pain to grind off - it usually works out ok but I want to fix the problem.

I use a vacuum table for pressing and get good pressure- the most I can get out of it 25inHg at 2000'. i think that part of the problem is that i'm not rabbeting the tip and tail fill so where the tip/tail fill meets the core(which I do rabbet) is where i'm having the problem. The edges are not flat with the base, lots of epoxy and thus all the grinding to get them flat. Probably wouldn't be a problem with a steel press with more pressure??

Anyway I'm planning on rabbeting the tip/tail fill on my next pair so I assume I'll have to flame the rabbeted tip/tail fill to get good adhesion ?? Or can I just sand the newly exposed tip fill? Anybody else using a vacuum press have this same problem - OAC ??thanks for any help
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Akiwi



Joined: 15 Jan 2015
Posts: 366
Location: Olching (Near Munich) Germany

PostPosted: Sun Dec 03, 2017 11:38 pm    Post subject: Reply with quote

Yeah, I know what you mean. Pre bending your tip and tail helps so the edges sit flush to your mould, and rabbeting also helps, but I don't have a perfect solution for you.
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24Dave



Joined: 03 Oct 2011
Posts: 96

PostPosted: Mon Dec 04, 2017 11:53 am    Post subject: Reply with quote

I vacuum press now only. A general concept for vacuum I think is to have all your pieces fit as perfect as you can have them and don't count on a lot of excess resin being squished out the same way as a pneumatic press.

Try to use laminates that lay flat. spread resin on your fabric on a separate table and let it stand for a minute, while it is sitting, brush a thin layer of resin on the base and core and scrape off excess hard. Then scrape excess resin out of the fabric, lift it and place it on your base and assemble. You need lots of flat table space and baking paper, but it gets your laminate free of a lot of excess resin from the start.

Pouring resin on your laminate while it is on the core surfboard style invites having too much resin that needs to be squeezed out, a press does this fine, vacuum-not so much unless your pieces fit perfect and your resin is pretty runny. plus it is just a mess.
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Wvmtnbiker



Joined: 28 Jan 2014
Posts: 17
Location: Greenwater, WA

PostPosted: Tue Dec 05, 2017 7:24 pm    Post subject: Reply with quote

Thanks for the advice. I just pressed another pair and it looks like rabbeting the tip and tail fill helped some. The tails and one of the tips has less epoxy than before but one tip on one side still had more than i would prefer. The next pair I'll try to prebend the tips and tails. Do you guys anneal the edges prior to pressing or do you just prebend? I'll also try do wet out the fiberglass on a separate table - thought about that but didn't do it. I did try to use less epoxy on the base - filled the edge recesses and scraped the base pretty clean - definitely no excess epoxy on the base but probably still used too much epoxy wetting out the glass. Guess i still err towards a little too much rather than not enough?? I mixed 1100g of entropy and used maybe 900g to 1000g for a ski thats 180 cm 127/97/112. Do you guys go straight to heat in the press or wait a bit?? - is it possible that i need to wait till glass transition stage before adding heat? It takes me about 45 min for layup so it should be close - i keep the epoxy in the house at about 67 deg and where I press is heated but probably in the low 60's with low humidity.
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kit



Joined: 07 Aug 2015
Posts: 17

PostPosted: Thu Dec 07, 2017 11:34 am    Post subject: Reply with quote

My $0.02: For a lot of reasons, I think vacuum is the way to go; you're on the right track.

For sure, pre-bend tips and tails of base and core. Per above, all the pieces need to be really right before vacuum. Don't expect a vacuum press to set the shovel and tail curves. You don't want that tension built into the ski anyway. Rabbet the cores and tip and tail fill pieces - .6 to .8 mm to accommodate the edge tangs just as you would normally for your cores. If you have a flat mold, the skis will come out flat. The tip/tail fill material at 2mm that I use comes sanded and flamed. I don't worry about re-treating the rabbets and haven't had any problems. I do sand to 80 grit the cut edges that join with the cores so they stick with superglue.

I don't use a separate table for fabric wetting any more - tried it and didn't like it. Rather, I wet the base/edge unit generously, drop the pre-cut vds onto it, wet it on top, flip vds, locate, and touch up. Then lay dry fabric onto the base unit and press by hand to start wet out. I then wet the fabric from the top and work it in with a short bristle brush. Same with the layer on top of the core. Overall it seems way less messy and more efficient of epoxy and time. A little too much resin is ok - like with wood glue, some squeeze-out (or suck-out, as the case may be) is good. It lets you know that the internal surfaces will bond. You'll get no voids in a vacuumed layup if it's wet enough. Too dry is fatal.

By using a non-heat curing epoxy, I avoid having to use heat to cure the ski - why bother? There are great 2 hour set laminating epoxies out there in the boat building world that work brilliantly. I have never used a heat-cure epoxy and have had zero delams. Some of my skis have >60 days under the feet of aggressive young skiers. You might have to wait a bit longer for cure, but with a vacuum rig, that's no problem.

Grinding off excess epoxy? Well, you have to cut the ski out of the flash somehow anyway. I use a jig saw with a zero-kerf blade and cut flush to the edge, then sidewall bevel with a router jig to 14 deg +/- with the bit bearing riding on the edge. It's quick, comes out slick, and makes the whole cutout/cleanup phase less of a pain.

The general rule of thumb for vacuum for veneering in woodworking is less than 25 and I honor that - I usually go 22 or 23 or so for skis. Use breather mesh (over a waxed release platen), even an extra layer or two at the bag nipple to avoid getting resin into your tube.

Hope this helps.
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Gilo



Joined: 03 Feb 2013
Posts: 57
Location: Somerset - the flatlands

PostPosted: Fri Dec 08, 2017 2:52 am    Post subject: Reply with quote

Interesting thread - I use only vacuum and have bought a commercial vacuum table - big platen with a hinged frame on top that houses a natural rubber membrane.

I use a separate wet lay table and wet out the layers in reverse order and then put them to one side as I work my way down the stack. I then use a brush to put epoxy on the bases (pre-located in the mould) and layer everything up. I don't rabbett the cores but use a thin cork infill to level everything out. It helps with damping also. I have various lines etc drawn on the mould to help me centre things up and the cores are kept in place by small blocks fixed to the mould surface. The cores are held to the mould using double side tape. So far so good.

I have encountered a problem which is almost the exact opposite of the initial question on this thread. I can press at 28, but have ended up pressing at 17 because at pressures higher than that the epoxy is drawn out of the laminate, especially at the tips and tails leading to delaminations in the mould - it has been a pain up the arse to work out what was actually happening - the consensus was that because I use a slowish cure epoxy at quite cool temps (typically 50-55f in the workshop) the vacuum was drawing the still liquid epoxy from the tips and tails before it had time to go off. I now use heat to speed the curing process in the form of an electric bed blanket over the top of the membrane. 4 hours to cook under vacuum and then a further 2 hours under vacuum to cool before demoulding.

In all the skis I have made that haven't delaminated in the mould due to the tip and tail problem (took me 4 pairs to work out the problem- grr) I have never had any delams - most pairs have had at least 30 days on them.

it has been a bit of a journey to be honest and I got a bit demoralised, not to mention the cost.

If anyone has any thoughts I would welcome your input. I don't think that pressing the ski at 17 has any impact upon the performance, but having to turn the pressure down goes against my nature!

Gilo
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kit



Joined: 07 Aug 2015
Posts: 17

PostPosted: Fri Dec 08, 2017 9:50 am    Post subject: Reply with quote

Delam in the mold?! Hard to imagine. Maybe try a different epoxy? I use System 3 Silver Tip - never an issue, even at 27. Maybe the rubber is focusing pressure on the tips and tails because of leverage or something? Sounds very strange.
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Wvmtnbiker



Joined: 28 Jan 2014
Posts: 17
Location: Greenwater, WA

PostPosted: Fri Dec 08, 2017 10:15 pm    Post subject: Reply with quote

Thanks for all the info Dave and Kit. So i just finished the skis i pressed last week and the excess epoxy on the one tip ground out in two passes so it was a lot thinner than it looked so the tips conformed to the mold better than i thought. The tails were better than before but took a lot more work to grind out so I will definitely prebend tips and tails next time.

Im assuming you are pre bending edges for the tips and tails by hand after they're glued to the bases or are you using some sort of jig. I've seen the line skis video where they prebend using two big what look like steel rollers?? Are you heating/annealing the edges first or just bending them? Thinking i could get a smooth bend around a big PVC pipe or a small bucket. I remember seeing some bending jigs people came up with on this site in the past but i'll search a bit for them.

Gilo - in the past I have had something similar to what you're talking about. I use entropy resins which the cure time is 20 min at 180 degF. Anyway I pressed the skis for 45min and pulled them when they had cooled to 140 deg
F. When i started to pop the skis off the cassette i could see the layers slightly pulling apart - and the excess epoxy was pretty soft still. I think this is what your referring to as your skis delaminating in the press. I my case my heat thermo coupler was way off so the temp was too low and so the epoxy hadn't cured yet. I put them back in the press and used a kitchen thermometer and ran the heat blanket manually and the skis came out fine. I don't think your epoxy is fully cured?? When I first started building I didn't want to pay a lot for a MEI heat blanket ($500) so I found one through Alibaba (china) for around $150 which included shipping. Took a couple of weeks to get and it works great - you just send them your specs and they make what ever you want - mine is
110 and 1200W 190cm x 34cm and it looks just like the MEI blanket. Ill look and see if I can find the info on the company. Wasn't as easy as dealing with MEI but worth the extra effort IMO - hope this helps
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kit



Joined: 07 Aug 2015
Posts: 17

PostPosted: Mon Dec 11, 2017 1:24 pm    Post subject: Reply with quote

I do a really standard routine - heat the areas of the edges that will get bent to yellow hot with MAP gas torch and clean off the debris with a dremel and 80 grit sanding wheel. I use a pair of modded nippers as documented on this site for tip curve bending and do a full wrap of the tips with a joint at the center line. I extend the edges a little bit into the curve of the tails, so I bend them slightly for that too. Then the edges get super glued to the cut-out bases.

I built a shovel and tail bender and mounted it to a bench but I don't use it any more Very Happy Now I simply quick clamp a foot-long piece of 5" PVC to the edge of my worktop and free-hand the shovel bends on it - faster and more accurate than the darn tool I spent time on. . . The upturn of the tails I bend with a pair of sheet metal vice grips.
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OAC



Joined: 23 Jul 2009
Posts: 945
Location: Sweden

PostPosted: Tue Dec 12, 2017 5:25 am    Post subject: Reply with quote

Pro tip:
(Just kidding, more of a 10y experience of pressing w. vacuum)

Annealing the tip and tail of the edges, pre-bend the tip (and if neceesary the tail) of the edges. Makes life much easier. Especially if there are "steep rise" on tip and tail. Even if the vacuum is strong enough for the rest of the pressing it has difficulties to press down an edge to the mold. Even a full woodcore(when no tip and tail fill).
Also there is a known fact that the resin/epoxy find it's way out of the laminate on the shorter sides (i.e tip and tail). I don't know way, I've been told, but I can definetily see it!
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Wvmtnbiker



Joined: 28 Jan 2014
Posts: 17
Location: Greenwater, WA

PostPosted: Tue Dec 12, 2017 8:22 pm    Post subject: Reply with quote

thanks kit and OAC. Ill anneal and prebend the next pair for sure. Now that i look back on all the pairs i've made the tips and tails that came out the best were the ones that have a very gradual bend and low rise - the ones with more pronounced bends not so much. Kit I'm buying a pair of the pliers - thanks for the tip - looks like they should work great for bending the tails with out twisting. Thanks again for the responses.
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OAC



Joined: 23 Jul 2009
Posts: 945
Location: Sweden

PostPosted: Wed Dec 13, 2017 9:15 am    Post subject: Reply with quote

Just a thought about pliers. If one not doing a full edge all the way to/around the tip and tail and just doing a 3/4, annealing the edges, there is no need for pliers. Just a "light" bend by hand is usually enough. I found it even better than using pliers. I get a much smoother/better follow between the edge and base.
Again, this is just my experience and works fine on my models.
Don't miss the fun part where you experimenting and experience your own building!! Very Happy

Ski season is about to begin....!
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Wvmtnbiker



Joined: 28 Jan 2014
Posts: 17
Location: Greenwater, WA

PostPosted: Wed Dec 13, 2017 9:32 pm    Post subject: Reply with quote

thanks OAC. I greatly appreciate your advice. you and sammer were the journals i looked at the most when i started to build. the vacumaster 2000 or 3000 ?? was my blueprint for my press and I learned a ton from all the pictures/videos of your workshop so thanks for taking the time and effort for posting all the info! Maybe some day Ill sub my own top sheets and have 100 plus pairs under my belt. If you have time I think everyone on the boards would love to check out any of your new additions etc to your ski building. Since I started building five years ago I haven't skied on anything but my own skis - even my twelve yr old son and my wife love their home made skis - Im addicted!
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24Dave



Joined: 03 Oct 2011
Posts: 96

PostPosted: Fri Dec 15, 2017 5:49 pm    Post subject: Reply with quote

Wvmtbiker-
To answer your questions a bit back. I only do 3/4 edges, so just an inch or two beyond the contact points. Bends are so easy you could do with hands, I use the standard modified end cutters. I don't heat treat the metal at all.

I superglue edges to base then bend over different radius PVC to get the curve just right.

Heat curing resin doesn't have to happen right after lay-up, so you can definitely wait for your resin to gel under vacuum before beginning the post cure or heat cure. You can watch a thin layer or drops of resin on your lay up table, when it gets pretty thick then you can add heat if you are concerned about resin getting more runny in your part and leaving a void.
Ski mfgs add heat right away to speed up press turnaround and increase daily production. I've been advised that for some aerospace parts, they are pretty much brought to full pressure pretty quick and the post-cure temperature is ramped up gradually. My understanding is that longer times at slightly lower temps ending in full cure temp. can cause the resin molecules to link up into longer chains which improves toughness as compared to a full temp short cycle which is probably almost as good.

Heat adds to the adhesion properties of epoxy, but more importantly adds to the toughness of the cured resin. This helps in preventing compression failures on the deck side of a ski or board in a deep bend. The less fabric reinforcement you use, the more you ask of that bond and proper heat cure matters more and more.

Laying up fabrics on a table might be more of a technique for trying to get your resin/fiber ration as low as you can for weight savings. It is also useful under a veneer or topsheet where you are more likely to get a lump of resin trapped if you start with a lot of excess.

I use fabrics like Textreme and uni-carbon that are super thin and a little hard to confirm the fabric is saturated compared to fiberglass. Using these fabrics and taking advantage of how little resin they use, it only makes sense to let resin sit on them and really saturate, then scrape them hard to minimize resin content. I do this on two full length strips of baking paper, then just roll the paper up to clean up-it's pretty tidy. Baking Paper-best skibuilders tip ever!! If weight is not a target, it certainly isn't necessary. I get about a 1/4 to 1/2 inch flange of resin out of the edges of a ski or splitboard half.

I use snowboard materials.com epoxy at about 85-90 degrees F before I mix it or Resin Research at at least 75 degrees F, but again I need it pretty runny to laminate fabric that is not very porous.
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