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excess tip/tail epoxy vacuum press

 
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Wvmtnbiker



Joined: 28 Jan 2014
Posts: 15
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: 355
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: 88

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: 15
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: 12

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: 53
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: 12

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: 15
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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