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Tuesday, August 3, 2010

The flat truth about milling stock

As I got to the point where I needed to do some additional dimensioning in the sideboard project, I recalled a recent blog post by Glen Huey from Popular Woodworking.  He submits that the whole idea of letting wood acclimate to your shop is nothing but hogwash.  He suggests there is another force at work, and it has nothing to do with loitering lumber.  Well, based on the insanely warped poplar I got when milling up my cabinet partitions, I was willing to listen.  Glen insists the key to achieving flat stock nirvana is to remove the same amount of material from both sides of a board.  So I put that theory to the test using more stock from that same batch of poplar that produced stock only fit for a Pringles can.


12 comments:

mdhills said...

Thanks for running the experiment. Think the original blog entry was by Glen Huey (although my feedreader lists Chris as the author of the feed as a whole--have to check the byline at the end of each to know which editor I'm reading. Although Chris' recent set of disturbing images definitely make his pretty obvious)

I did want to ask about your thought on how evenly wood is being removed. For flattening (especially with some twist), I'd expect the wood to get removed in localized spots.

Rob Bois said...

Thanks to mdhills for correcting me. The PWW article was indeed by Glen Huey, and not Chris Schwarz (I have gone and edited my post accordingly). As for the question about flattening with a twist, yes there will always be spots where you are removing more stock from one side than the other, but the idea is to minimize that if at all possible. I also haven't gone as far as disproving Glen's notion that proper acclimation can also help. I've just shown that proper milling definitely works (and that bad milling does not)

TheWoodWhisperer said...

The proof is in the pudding....or pringles....as the case may be. Nice demonstration and thanks for the real world experiment Bois.

Larry Marshall said...

Rob, it's somewhat 'old school' thinking that if you flatten one side of the board (jointer or hand planes) and then bring it to thickness by flipping the board with each pass, you'll end up with stable boards. I've always done it that way and it seems to work just fine.

I think the real problem comes in flattening one side of 4/4 lumber and then taking all of the thickness down to 3/4" (or even 7/8") from one side of the board.

Cheers --- Larry "aka Woodnbits"

Anonymous said...

Rob, nicely done. Interestingly Norms video on The Shaker wall clock on his website this week makes the same point near the beginning. He planes alternating sides to allow moisture to leave equally to avoid cupping.

Runningwood

Dyami said...

Rob,
nice posting & video. I'll certainly be trying that method out myself, once I get my jointer set up.

Bruce said...

Rob,

Another great production. When one considers the reason behind the premise, it's evident the moisture content in the center of a board is the highest, with lower moisture content exiting at the exposed surfaces relatively lower. Hence when removing equal amounts of material from opposing surfaces, one reduces the tendency for more moisture to escape from one side. Thus, less warpage occurs. Keep up the good work you do. Bruce

Rob Bois said...

Exactly right Bruce, it's all about keeping moisture loss equal on both sides. That being said, I wonder how long you would need to keep stock acclimating to your shop to the point where there is an equilibrium throughout the stock, and milling alternate sides wouldn't matter? I pose this question because my first batch of stock had been acclimating for almost a month and still warped on me. I wonder how often those bad experiences are really due to case hardening or poor kiln drying versus moisture loss. I don't have an answer, but maybe someone else out there does...

Anonymous said...

Doing anything one time and taking the results as law doesn't prove anything. I think a better experiment would have been to take an equal cut from the other side of your original board and milled it mostly down on one side. That way if IT warped and your original experimental piece did not, you could have made some valid judgment about what conditions really produced the end results.

Rob Bois said...

This was, in fact, a two part experiment. In the Taking Shape episode (http://theboisshop.blogspot.com/2010/06/taking-shape.html) I showed how by removing more stock from one side of the partition pieces caused some fairly severe bowing. This most recent episode used stock from the exact same board and milled to the exact same thickness, with very different results. So I do believe this proved the milling has a dramatic effect, and was not just an anomaly.

Eric Madsen said...

I enjoyed the video, but please lower the guides on your bandsaw... no reason to leave enough space in there to saw off a thigh.

Tom Buhl said...

Hey Rob,
Great post/video on this vexing subject. Always glad to see thoughtful, in-depth examination of positions put forth by others.

I have a number of observations which may temper the enthusiasm for following good practice being a cure-all, or even close.

First, this material from the same batch, was in your shop longer than your initial work which caused trouble. Unless you had it stored off-site, but even then, perhaps some benefit accrued by the passage of time.

Also, you mentioned localized differences in removal due to twist. Removing the cupping also removed significant amounts non-uniformly. The outer portion of the board its entire length had significant "extra" material removed on the concave side and much more material removed the entire length on inner portion of the convex side.

Just a point of procedure: once you have the board flat and parallel, going between jointer and planer was unnecessary. Flipping the board while making identical changes to blade height on planer would accomplish the same thing, and probably more accurately. As the gauges on the jointer and planer may not be totally accurate (identical).

Bottom line, very happy whenever I see well-behaved material and would like to think our good practices made it happen. But I believe we have to accept that some days, some woods, some conditions beyond our doing, will kiss us some times, and bite us others.

Thanks and see you at WIA 2013. Yeah!