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How Rough (Dimentionally) to Rough Cut?

Started by abosely, July 26, 2015, 01:49:41 AM

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abosely

I mean how much bigger than finished/planed, final dimension do I rough cut lumber?

Boat lumber in particular, it will be mostly 1"x 2", 3" & 5". But some up to 1"x10" finish planed dimensions.

So I mill the lumber over sized, dry it, then plane to final dimensions.

But how much bigger than the final planed size? I want to have enough material that I can run it through a joiner if needed then the thickness planer.   

I'm  planning to use full comp chain, even though it will cut a little slower, to get smother initial finish, if that makes a difference.

The wood will be Rainbow Eucalyptus, Kamarere if that makes a difference.       

Cheers, Allen

beenthere

You'll need to know what the shrinkage is for that species.

This link gives you the percent shrinkage, and I'd calculate based on the radial shrinkage of 3.8 %.

http://www.wood-database.com/lumber-identification/hardwoods/deglupta/
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

abosely

Wood Database lists Radial shrinkage 3.8% - Tangential 8.5% - Volumetric 15.5% T/R Ratio 2.2.

I don't know what to do with these numbers tho. Lol

For the boat lumber I'll be cutting it for vertical grain, if that makes any difference.


Cheers, Allen

dboyt

For quartersawn, the thickness will have radial shrinkage.  For oak, I'd mill 1-1/4 for up to 6" wide boards, and 1-3/8 for wider boards, since they'll tend to warp more (even quartersawn).  How stable are your woods?  If they have a reputation for warping while drying, you may need to go even thicker.  Love to see some photos!
Norwood MX34 Pro portable sawmill, 8N Ford, Lewis Winch

longtime lurker

I'm not intimately familiar with Warrams designs though there used to be quite a few Pahi's about here when I was a kid. I have however been involved in a few other marine ply on frame builds, and as a business we target that market.

You need to look hard at your plans before you buy or saw a board. Ply on frame is not as critical as plank on frame in terms of how important the frames are to total structural integrity but they still matter. Less so if you're going to use the hull as a plug for a GRP coat, more so if you're going to use something like dynel sheathing.

There's a couple of things to consider here. Stringers and frames carry fastenings differently. Grain orientation needs to be maximized around nail retention ability so while the normal orientation is rift, you need to look at which way the rift has to run as its nailed in service. That's one of those read the plan with care things... Work out whether it's the face or edge of a board that's carrying your fastenings and orient grain to that.

Secondly you need to figure out how your frames are bent, if they are indeed bent. I have no idea if Warram cuts curved frames from wide straight boards, or laminates thinner sections together, or if you need to steam bend your members. if laminating or steam bending you don't want dry timber. Dry timber will crack when forced to bend, or need to stay in the steam pot forever until it's wet enough to bend... Timber needs to be wet to bend so the cell walls can stretch and compress rather then cracking.
If the bents are sawn from straight timbers that's different, but even then you don't want bone dry framing as its going to take up moisture and swell a little in service. That's more a fairing issue then a strength one as it'll just grip the fasteners better but might as well give the girl curves instead of cellulite.

So basicly figure out your ideal orientation of grain in various bits, cut them oversize, dry them to 18 to 20% unless the plan specifies otherwise, then dress them back. Shrinkage isn't really an issue as there's no real shrinkage happening at that point. But check the plan... If it says dry timber or KD then that's what you need. Add 10% to everything when cutting green anyway. It's waste but better then not enough.



The quickest way to make a million dollars with a sawmill is to start with two million.

PC-Urban-Sawyer

I don't know anything about boat building but it's obvious that Longtime Lurker does...

Good luck with your build.

Pictures or it didn't happen!

Herb

GeneWengert-WoodDoc

Quarter sawn lumber has the growth rings running from face to face (sometimes called vertical grain).  This means that thickness shrinkage will be the tangential number, as thickness is parallel or tangent to the rings.  The width shrinkage would be 90 degrees to the rings, so width shrinkage is radial.

Flatsawn has the growth rings running from edge to edge.  This means radial shrinkage is the thickness and tangential shrinkage is the width.

Note that radial is always smaller...in your case, 3.8%.  Tangential is 8.5%.  You do not need volumetric, which is essentially the sum of these two.  Lengthwise, or longitudinal shrinkage is 0% mostly.

If you divide these numbers by 28, then you will get an estimate of the size change per one percent moisture content change for dry wood.

Perhaps you have heard some people say quarter sawn is more stable than flatsawn, as indeed the width shrinkage is about half, but thickness shrinkage of quartersawn is double flatsawn.

Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Brucer

And one secret for getting a smooth cut with a CSM is to insert kerf wedges behind your saw as you cut. They should be just a hair thicker than your kerf. You can get a smoother rough cut than with a bandmill (I have a piece of 0.02" x  8" x 8' Birch to prove it ;D).
Bruce    LT40HDG28 bandsaw
"Complex problems have simple, easy to understand wrong answers."

scsmith42

Quote from: dboyt on July 26, 2015, 08:51:03 AM
For quartersawn, the thickness will have radial shrinkage. 

Dave, I think that you meant tangential shrinkage - not radial for QS.
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