I wasn’t able to find much in the archives or on the web. All I could find was that end grain is slightly heavier than long grain, and that long grain is more flexible than end grain. From this I would think that long grain is better suited for skins, but I’m not sure how the two grains compare in regards to strength. Any tips?
End grain is a whole bunch of little chunks glued together. Its heavier because of the glue and also exposes open grain to your resin and soaks it up. But it makes good filler between skins and in a sandwich I’m learning that the strength of the filler material isn’t all that important. Platty did a marvelous job with end grain balsa, but I think that board ended up fairly heavy.
I guess if you can get sheets of end grain in the 1/4" thick range, it would save some time in ripping balsa or taping together small flat pieces. Thicker than that and you’re looking at a lot of weight.
Sheets of end-grain may be a suitable alternative for rail layup.
its good for core applications.
but i’m not so sure it would be a very good choice for the deck and bottom sandwich.
-bill
The first couple vac boards I’m going to do will be balsa over urethane. Rather than dive into the shallow end from the 20m, I’m going to slip myself into this one and just get my feet wet first. I have an ultralight clark blank that I’ve already shaped into a 5’0" fish and I’ll be picking up some RR epoxy this weekend. My plan was to use 1/32" - 1/16" balsa sandwiched between two layers of four oz e (I’d prefer to use S but I’ve still got a whole role of e laying around). I’m not expecting it to do much in terms of performance (especially since I won’t even be attempting perimeter stringers on this one), but it should get me familiar with the bagging process.
Knowing that much, does it really matter which grain of balsa I use for this one?
Quote:
Knowing that much, does it really matter which grain of balsa I use for this one?
As far as I can tell, you can’t buy end-grain balsa thinner than 1/4" so the choice is really pretty simple.
Hey Losos,
Agree with Benny1, as it’s the sucking action of the end grain that takes on the resin and adds weight. To clarify endgrain and sidegrain: Generally speaking, a board weighs what a board weighs no matter how you rip it into lumber flat sawn, quartersawn, end grain, side grain, etc.). Nutrients flow up through the trunk of a tree from its roots through millions of vertical capilaries much like straws as you suck up through one. Open a box of straws and look at all the round holed ends, and imagine similarly, the end of a board.
When you cut the tree down and rip wide boards the length of its trunk, the long boards have side grain on their surfaces (sides of the straws). The two very ends of the board show the end grain (microscopic openings or holes of the straws). Imagine looking at the the “stump” of the tree at the ground where the trunk was sawn through horizontally, and you’ll see a slab of all endgrain lumber. Since felled trees are ripped into long boards from the trunks, all commercial lumber is side grain (flatsawn / quartersawn). You would get end grain if you sawed off the end of the board repeatedly into slivers all the way down its length. This is what Platty did and glued the little pieces all together to make a surface (lots of work).
Very long answer, but just trying to make sense of an actually simple topic, though not widely understood when terms are bounced around.
Thanks trent - I didn’t realize end grain could only be ordered in thicker sizes.
RichardMc - That was a great explanation. I had glanced at a diagram that was trying to explain the same concept and couldn’t make sense of it. After reading your post, it’s all clear.
Losos. I was in the process of replying last night when things went pear shaped at my end. Ben and Richard pretty much summed up what I was going to say. I might add if you do use end grain balsa to form a panel as you describe. Do not use a high amount of vacuum as you will end up with all the resin in the bleeder. You only need enough vacuum to bond the balsa to the skin. To much and all the resin will get sucked through the straws as Richard describes into the bleeder blanket.
The board I built was made from 2" end grain milled into 6" by 6" blocks. Then glued on the end grain to form four 6"x 6"x 10’ 6" logs. It weighed in at 24kg finished.That is about 50 Lb. To heavy really but it does surf far better than I ever expected.platty.
you could also seal the grain with a mix of resin and microballons.
spread it on, scrape off all the excess.
allow the surface to start to kick before you add any additional glass and vacuum.
-bill