Section 8 - maple pine build

[skidesmond]

I cut out the base material tonight and put on the edges.

I solved an anomaly I had on my other builds that I thought was a template problem. Turned out to be something else.

On this build I've been trying to pay attention to detail and problems encountered in past builds. (No beer until after.... ) In other skis I've noticed in the finished ski that they were not 100% symmetrical to each other. Didn't know why. When I put the bases together the middle of the skis did not match each other. Off by maybe 2-3mm or so in the middle. I thought this was a problem w/ my templates not being symmetrical. So I "tuned" the template. I placed it down on my work table, traced it, flipped it over, traced it again and it was pretty near perfect w/o being CNC'ed. HHMMMM.....

I cut out the bases using the template. Then I placed each one together and they were a perfect match... so far so good. I put on the edges. Then matched them again and they were way off in the middle! I mean by 1/4 inch. I placed each base on the template and only one of them was off.... I thought one had warped somehow.

I carefully peeled off the edges of the warped one. Surprised they came off. I cleaned up the base, took off the super glue, lightly sanded and cleaned w/ acetone, base and edges.

Then I took the base and laid it on the template again and sure enough the base match the template. WTF!?

Turns out it was the edges... i.e. really me. When I bent the edges for the tip/tail I never bent the edges for the middle of the ski. They always seemed flexible enough and contoured ok. So I glued in place. Not thinking I needed to bend them. The tension in the edges must have been causing the base to warp out of shape.

I contoured the edges from tip to tail and re-glued them. After letting them set for about an hour I took off all of the clamps and matched it up to the other base and they match 99.99% perfect.

So problem solved. Bend the edges from tip to tail to avoid this problem.

NOW it's beer time.

Hopefully if time permits I'll lay up the ski tomorrow night. I have a nice sapele veneer for this one.
http://www.certainlywood.com/detail.cfm?ID=2687

[Alex13]

Interesting. I didn't bend my edges for my board along the sidecut either, I may have to test this against another base and see if there was any difference.

What material and thickness is your base?

[Alex13]

I just tested and my base hasn't deformed noticeably. This could be explained by the width of a snowboard vs a ski though, the area moment of inertia in the direction of the edges would be much higher than a ski (goes up by the width cubed, so double the width you get 8x the moment of inertia).

[Dr. Delam]

You shouldn't need to prebend edges in the sidecut area. You just need to put both sides on at the same time as you work down the ski. Equal tension on both sides equals a straight ski.

[skidesmond]

The base thickness is 1.3mm, bought from www.skibuilders.com

Dr.Delam - I glued the edges on at the same time. I even had the clamps lined up across from each other, used about 40 clamps.

I originally thought the base material warped or shifted as I was routing the shape, but after stripping off the edges it matched up w/ my template. Strange the other base didn't do the same thing.

I was going to try to cut both bases out at the same time, but thought the bases may slide against each other. Has anyone else tried cutting both bases at the same time? I just clamp the bases to a work surface.... nothing fancy.

It doesn't take much effort to bend the edge for the sidecut so I'll do it from now on just to avoid future problems.

But I'm still baffled why the other one came out fine.....

[rockaukum]

I'm with Delam. NO need to bend the middle. I have yet to do this and have not had the problem described (others...) When attaching the edges I leave the base clamped to the template. might help...

[skidesmond]

Thanks guys. One thing I should have mentioned early on.... I had the edges standing in the corner the shop so a natural bend was made in the edges. When I laid them on the layup table there was a bend to them instead of laying flat and straight. I'm guessing maybe that was my problem?

On my next order of edges I'll store them on a flat surface to prevent that bend. Just trying to eliminate variables and get a better ski in the end. Thanks.

Hope to layup the skis and press them tonight.

[skidesmond]

Finally got time to do the lay up. Sorry no pics. I was working solo. It was typical layup:

ptex base w/ edges
VDS over the edges
22oz triax FG
maple/pine core
22oz triax FG
sapele wood veneer

I added a pressure gauge to my press. To my surprise I've been pressing at about 30psi. The hoses are rock hard. I wonder if the gauge is accurate. I may buy another gauge to check if it register's the same.

Hopefully by tomorrow night I'll have skis.

[MontuckyMadman]

I found at 30psi and up the hoses feel the same but make a different sound if you smack them. Its very subtle however.

Like checking the tires on yer big rig.

[Alex13]

Your car tyres run around 34psi normally, smack them and see You'll get the same result, they feel rock hard from 20psi or so up.

[skidesmond]

I finally pressed the skis on thursday night. Left them in the press for about 14 hrs. Pleased with the way they came out. Some minor defects to work on but overall I'm pretty happy. The raw veneer looked like it might be a little too dark for the grain to show but grain popped nicely after I put poly on. The sapele veneer looks great.

The skis retained most of the camber out of the press. My goal was to get 1/2inch camber and I got about 7/16inch. So looks like the steam box helped.

The flex is softer as expected, but not too soft. Nice even flex. Should carve nicely w/o too much effort.

Comparison Notes :




Pics from the build:

Base/edge fit for 3/4 wrap


Out of the press. Friday was a warm (90's) day so I let them sit in the sun for the day.




Here's a camber comparison shot.





Defect in the tip where the edge bends into the tip. Not sure why it pulled away. Maybe not enough epoxy during layup? Patched it up afterwards.




Pics of the ski:



Not sure if I'll put the steam box back together. I have some reinforcements coming for the press that may help in keeping the camber. Storing the steam box is a bit of a hassle too.

So looks like I met one of the goals of the build, to add camber. The other goal unfortunately will have to wait until the snow flies..... about 4 months away Maybe 3 months if I get a chance to head to the north country. It will be interesting to get them on the snow and feel the difference.

[Alex13]

They look great. That's a really nice looking veneer. Was your pressing/heating process the same as the first pair?

[falls]

Desmond
I was wondering about a similar problem with the 3/4 wrap. Mine wasn't as severe as yours. On my bottom cassette I can see where the end of the edge pushed into and slightly dented the aluminium. On the finished product the end adhered to the underlying materials but there was a bit of a bump there that was ground off when they were stone ground.
It is obviously the edge not bending to the mould as readily as the plastics and wet glass and will be a high stress point for failure. I don't really know what to do about it.
I have seen on some libtech snowboards that have a 3/4 wrap that they do a scarf-like joint where the base material and edge meets. Basicaly it looks like the edge is ground down to half its thickness and this continues on top of the base material past the notch if you get what I mean.

[falls]

maybe giving the very end of the edge a bit of an upwards tweak before pressing might help too. The radius you bend the tip too is probably not tight enough to cause non plastic deformation of the metal (not sure if that is the right engineering word!). So after you take it out of the press it wants to return to its original flat shape and therefore pulls away from the glass.

Did you use VDS?

[skidesmond]

The pressing process was the same for each. I don't have a heating blanket for the press. Both skis have VDS over the edges.

As for the 3/4 wrap problem.... Falls, thanks for the scarf joint tip. I thought of shortening the length of the edge by maybe an 1/2inch -3/4 inch just where the edge starts to pull away from the rest of the FG layup. I was pretty sure I had enough epoxy put down as this was a problem w/ other builds I had and tried to correct it in this one.

The press/hose had good contact into the tip area. That was another problem I was solving with this build.

I thought of maybe going back to a full wrap but doing it in a different way. Run a metal edge along the running length of the ski, then bend a separate edge for the tip area. Have them meet just after the tip starts to bend up. So you'd have 3 pieces, 1 for the tip and 2 for the running length. I'll go back and look at the skis I did full wraps on. I know bending for the tip is a PITA. I may still have the problem of the metal edge pulling away.

I got some things to fix before make another pair. The hose has a small leak at one of the inlets. I'm going to reinforce the press w/ more steel in the middle to remove some of the flex. Plus I'm out of material... just scraps left for experimenting.