Ski Builders Forum

Mechanical Properties of Wood - the book has been posted, but comes up with these search terms : )

Experience and testing have proven that a smooth, knife-cut
surface is best for bonding.
...

Abrasive planing with grit sizes from 24 to 60 causes surface and subsurface crushing of wood cells. The adhesive
industry typically recommends 60–80-grit sanding as acceptable for wood bonding as this equates to 24 to 30 knife
marks per inch when planing. Generally, anything above
200 grit fuzzes the wood surface and is not recommended ...
...

Figure 10–3. A simple water drop test shows differences in wettability of yellow birch veneer surface. Three drops were applied to surface simultaneously and then photographed after 30 s. Left drop retained
a large contact angle on aged and unsanded surface; center drop had a smaller contact angle and improved wettability after the surface was renewed by two passes with 320-grit sandpaper; right drop showed a small contact angle and good wettability after four passes with the sandpaper.
...

A surface with good wettability and penetrability will absorb the drop within 20 s. If the drop spreads out but some water remains on the surface after 40 s, then the surface has good wettability and poor penetration, and may be difficult to bond. If after 40 s the water drop retains much of its original shape with little spreading, then bonding problems from surface inactivation (poor wettability and penetrability) is a certainty.
...

So the industry recommendation of 60 - 80 grit is questionable and a simple water test is a tool for understanding/comparing wettability and penetration.

Good! I will remove the abrading chapter. :-)

Richuk - Good info thanks! http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf


I think this info helps explain why my "Going Old School Ski" build failed with epoxy the first time. Although I know I didn't prep the epoxy well either.... The poplar veneer I used, I did not do any sanding of it prior to laying down the epoxy. I used the veneer right out of the box, so to speak. That probably contributed to bonding failure.

When I re-did the layup using Gorilla glue, I sanded all the surfaces to remove the left over epoxy, which more than likely help the Gorilla glue bond. Had I sanded the wood at first the epoxy may have bonded properly.

hey OAC! Im researching on building a bladder press like yours. How did you mount the rubber sheet to your top frame? Double sided tape? contact cement? or is it clamped together? Maybe some close-up pics would answer my question. Thanks!

Coming up! I'm out traveling... :-)

Dear OAC... I want your job and vacation time!!!

Yeah...you wish!


On the frame and under the silicone membrane, windostrips/sealer(?). I used a couple of flat head screws to keep the membrane in position. I started to use nails to fastened it on the outside, but got bored and used staples instead! Not so important.
The important part is the sealer. So you are sure that the membrane get a super air tight "connection" with the table.
I will change the table surface before next pressing. For the moment I use foamed PVC. Ok in room temp. but NOT ok with heat above 60°C. I will switch to "paper laminate" a.k.a. bakelit.



My new experiment! Tyre warmers for racing MC's! It will go up to 80°C. And it "only" draws 400W, compared to the "Grill-Master-3000"
But I need to work with the insulation.

man. Awesome. I hope so much it works for you, you're very inventive

The best part, since they are used, when heated my garage smells like a racing pit!! Formula 1 !

Do you think it would be possible to put the warmer under the membrane to get a tight fit?

Cheers, Christoph

Not with these, it's not a mat or blanket, it uses a wire, (in a pattern) which I don't think can handle that much pressure(even vacuum). Maybe I test someday

2 point for OAC for thinking outside the box. Great idea!

Thanks SD! Sometimes I surprise myself!
(I have to see if it works first before I shouting too loud...)

Two new cores ready for process. One with poplar and Ash, around 50% each. And one core with Poplar, Ash and Paulownia! Around 30% each. It feels very soft, but light!
To compensate that I'm going to use a Quad CF! 600g/m². This was a wrong order I did a couple of months ago. I thought it would be thinner, but its not. Big mistake...
But anyway it's worth the test. The biggest issue, I think, will be how to wet it thru with epoxy? There are fibers everywhere! Dispite that, it will be very light core. The rolls I cut out only weighs 115g!



To be continued...

Some kind of heated layup table will do the job for you OAC!

Dry the CF in the airing cupboard overnight - can't hurt. Layup table at around 40 - 45 degrees, allow the fibre and epoxy to warm gently - apply epoxy when ready. You can increase the temp for a minute or so when actually wetting out the fibre - but I'm not too keen, as you are pumping in energy and a process needs to be repeatable.

Result: saturated fibre, less epoxy used (20 - 25%).