Edge Fall/Fail

[skidesmond]

I've been struggling trying to solve my edge fall problem. I think I finally have it resolved. In short I pre-bent the base/edges to conform to the tip block. Some folks already do this, others don't and don't have the edge fall problem.

Not sure exactly why this problem has been so persistent but my guess is because of the following:
1. I've been using a full wood core tip to tail
2. the tips have been 2 - 4mm thick (too much resistance?)
3. I wasn't using AL sheets for lay up (hard board cracked)
4. FG not wetted out thoroughly (no excuse...)

And probably other causes too. The problem wasn't as bad when I used tip spacers. I did not pre-bend the wood core in my test, although I'm sure that would help too.

Things I did differently in the tests:
1. Pre-bent base/edges to conform to the tip block
2. Wet out FG thoroughly, did not spare epoxy for the tip
3. I'd been doing 3/4 wrap edging and then filling in the gap at the very tip w/ base material. This time I filled it in w/ 1 layer of FG.
4. The test samples were a 2mm core and a 3mm core.

Pressed normally, left test pieces in for 18 hrs. (I don't plan on leaving it in that long in the future, just worked out that way.)

Took the pieces out this morning and they looked much better! I will clean them up over the weekend and post pics.

Here's they are straight from the press:


Edge shot of the 3mm layup. Sorry for the poor quality. Once it's cleaned up I'll post a better pic.


3mm core



2 mm core


Edge fit wasn't the best, no excuse for that. But I think I have the edge fall problem licked.

Thanks for all the feedback and help along the way.

[OAC]

Scientific approach. One step at the time.
Don't you heat up the edges before you bend? To get rid of the temper.

[skidesmond]

No heating involved. They bend pretty easily by hand, only takes a few minutes. I start at where the tip bend should start and carefully bend toward the tip. I over bend it just a bit and then it relaxes to shape. My tip blocks have a radius of 300mm.

[OAC]

Ok.
My tip blocks are under 200mm radius. I calculated with a much bigger "tip fall" when released. They came out alright anyway. I will make a tip block thats around 250mm next time. I'm using 2mm tipspacers. Wood all the way no option for me and "Vaccu-Master 3000".

Hope it works for you!

[skidesmond]

I think it's been a combination of the wood core tip that has been the main root cause and adding to the problem is the 3/4 wrapped edges. When I think about it, that point of the ski is a weak spot, ie at the end of the edge in the tip. Everything wants to bend back to it's original shape and there's not much in that area to prevent it. When I used tip spacers there was less resistance from the P-tex fill pushing back so it wasn't as bad. And when I went to 3/4 wrap that left the very tip area weak and the edges we able to push away. I didn't want to go back to full wrap, even though I think it looks better, just don't have a good tool yet to do it.

Well, that's what I think...

Feeling somewhat relieved now.

[Brazen]

How are you adhering the edges to your base material? I do full wrap edges and tack them with superglue...they always seem to hold really well. Just askin'.

[skidesmond]

I do the same. But I do a 3/4 wrap. When I went back and looked at the skis I made with full wrap, this wasn't much of a problem but I had other problems, namely getting a clean full wrap.

The edges adhere to the P-tex base but pulled away from the upper layers.

[Richuk]

Nice work SD, pleased for you!

[falls]

What specifically are you calling tip "fall". Is it the edges pushing away from the base material when you press? Or is it like OAC seems to be alluding to that your tip curvature relaxes from the radius in the press to a larger radius in real life so you get lower tips?
I think it is that when you press the edges get popped outwards.
One suggestion I could make is to increase your edge setback from the tip. Where they are ending now is on a pretty tight bend in the tip shape. If you shortened your edge length they could terminate on a much straighter part of the tip. I have read a thread on here before that warns against terminating 3/4 wrapped edges on too tight a point in the tip curvature.

The other scenario it sounds like you are describing might be a delamination between the edges and bottom glass layer. I would think this is directly related to having stiff (compared to tip spacer) wood all the way to the end. If it isn't prebent then it is harder for the press to push it firmly against the edges/vds and get a good bond. Plus when you take it out the wood wants to return to it's original shape and this would pull it away from the edges (bond between vds/ptex base and lower glass layer will be the weakest.
Hopefully something useful in that rambling.

[skidesmond]

Falls- Thanks, very useful. The edge fall I'm getting is the edge pulling away from the upper layers of FG and wood core. And I believe the wood core in the tip also played a major roll in wanting to return to it's natural shape, which is flat. In this thread in the bottom pic you can see where the edge pulls away. This has been a common problem in almost all of my builds, except when I did full wraps.
http://www.skibuilders.com/phpBB2/viewt ... c&start=30

As you mentioned also, I contemplated about not bringing the edge quite as high into the tip. I may still adjust my template but for now unless the problem returns I'll leave them as they are.

The tip probably does relax a bit overall also because I'm not using heat but it hasn't been a problem. The skis still perform well. Thanks.

[skidesmond]

Here's some pics with test skis cleaned up. A 100% improvement by pre-bending the base/edge. The bottom ski is the 2mm core the top ski is the 3mm core. Both came out so much better. The 2mm core has a very slight fall but is still far better than I was getting before. It's noticable in the 3rd pic.

Next ski I build I'll pre-bend just a bit more to err on the side of caution.

[falls]

I think if you use tipspacer the problem will go away too.
How come you go with the wood core all the way to the tip?

[skidesmond]

I agree, I think using tip spacers would prevent the problem and give a nice finish as well. I think the tip spacer may provide some dampening too. So I haven't totally ruled out using them. But in the back of my head (way back...), I'd like to begin selling some hand made skis and using the full wood core as a selling point and/or a way to make the skis stand out from the rest in the rack. It's been a headache for sure. Well it's something I'm working towards. Probably only a real ski enthusiast may notice that detail but some day that will be my target audience. There's a laundry list of other minor things I need to start working on as well to get them ready for sale, should the day come. But this was the biggest problem I had to overcome.

[MontuckyMadman]

Hey S, Sfter seeing your vid I think that the use of a thin, 18ga al, instead of the mdf or masonite or what ever could also help.
I think you are getting a pinch because your cassette is extending into the tip area.
I know you have it licked now, but by doing almost a full wrap you are not making it that much easier on yourself.
A 3/4 wrap will terminate much closer to the contact surface and will improve the fit and reduce the edge fall IMO, otherwise go full wrap.

[skidesmond]

MM, I use a 1mm AL sheet now. I'm going to get another set of AL for shorter skis (152cm-170cm). Maybe get a thicker sheet, 1.5mm. Since then I added a center steel support to the press to retain more camber also.

The hardboard cracked right where the tip edges ended so that was a problem. Also I've been more vigilant in making sure the cassettes are not too high on the tip mold. I'm going to adjust my template a bit and bring the edges back another 1cm or so but still prebend the base/edges.

Been toying around with some way to fasten the cassette to the tip mold so it's always placed properly.... but still not interfere w/ pressing... Perhaps add something the the sides of the tip mold and then pin the cassette to it w/ a bolt/screw/dowel/zip tie.... I'll post any revelations


Thanks!