Dressing Stock, Stress, and Movement
A discussion of planing and jointing techniques: Does wood need to "rest" between passes? April 30, 2009
Question
I have recently taken a position as a 'bench carpenter' with a local shop. It has been a long time since I have been on the production floor as I have been managing and consulting for more than seven years now. I recently had a disagreement with the owner on how to go about flattening (jointing) and planing solid wood for face frames and doors.
I was taught way back when to face joint to the depth needed to flatten all cupping, twisting and warping (if the jointer is long enough or the board short enough) and then plane to a similar depth to remove equal amounts of shell. I usually remove all but 1/16" to final dimension to allow for sanding, etc.
While doing this recently the owner got all upset and told me that he only wanted me to take one pass on the face each day and let the board 'rest' in between passes in a stickered pile. Then once I have the face flat to run the board through the planer in a similar schedule (he figures it will take five days) until all boards are done. He claims this is so the wood can 'acclimate' slowly. He says that he always has to 're-joint' boards that 'move' so this is the best way to get flat lumber.
Not wanting to argue with a new employer I did the next batch as he wanted. Sure enough it had 'issues' with staying straight. The boards I did previously had some of them move but most all of the ones I did stayed straight. The owner claims it was a different batch.
Not for nothing, I have been doing this for 30 plus years and have never heard of this practice. Truth be told I believe that this method is causing him problems. I know the moisture content of the shell is usually different than the core. If you remove one side of the shell and not the other (for a period of time) it seems intuitive that the board will at least warp and possibly cup, to the dry side of the board (moisture expands a board). So help me out here folks. I need some other 'authority' to back me up here.
Forum Responses
(Solid Wood Machining Forum)
From contributor J:
I am no "authority" by any means but have been in the industry for some years. I have never heard of your boss's way. I kind of see where his thinking is coming from, but I don't believe his way is doing anything. It sounds like a humidity problem in the shop that he is trying to get around on the cheap.
From contributor R:
You are both right. On poorly dried boards with more extreme cup, twist or bow it is better to allow the board to rest between flattening joints. This is because previously stressed wood is being removed unevenly and any resident stress will release accordingly. With most boards that are reasonably straight and flat you can save a lot of time and joint perfectly your way.
From contributor U:
My experience was all in the high production plants. We hit it top and bottom one time and that was enough because when you rip it and then do the re machining in moulders, panel gluing and re planing, etc., any remaining cup is removed during those subsequent operations.
In other words, if a rough board is 5.5" wide and has 1/8 cup after planing and you rip it into a 3" and a 2", each piece would have the amount of cup proportional to its width vs. the width of the rough board. So the 3" piece would have only 55% of the original cup. Certainly little enough to be removed in subsequent operations. For my reasons stated above, we felt that jointing and planing until a board is perfectly flat in its rough width wastes thickness and lots of it. Thin lumber is not much use.
From contributor J:
It seems like "rough ripping" and then flattening the smaller strips would be the way to go but I'm not sure how your shop runs. It is easier to flatten wide strips ripped a little over sized than the whole board and then rip. Throw that one at your boss and see what he has to say.
From contributor J:
Have him buy a little digital gauge that measures the humidity and temperature .Just stick it somewhere in the shop. It is a cheap way to find out if you’re fighting unknown demons.
From contributor T:
I am lucky if I have that much time to finish the project. Five days to prepare the stock! I have found that if you can get good materials to work with, they are stable. However much of what you have to work with is only sawn for yield and no matter what you do it will do its own thing.
From the original questioner:
To answer some questions: yes, I use our slider as a 'chain rip' to get one straight edge then rip to oversize. This last batch I was doing mahogany door jambs (all exposed, no casing and two integral stops, so I needed to do 8" widths on a small 72" x 8" jointer).
Contributor U – I ran a moulding shop for some time. Also, doing figured maple for doors the face does need to be absolutely flat. Yes it wastes wood, but a callback wastes more than wood.
Contributor R: my understanding for more than 30 years is that stressed wood is stressed wood. You can fix some of it all the time and all of it some of the time, no?
Contributor J: the humidity gauge was provided by me, as was the moisture meter.
Regarding removing the shell unevenly - I was always taught that this introduced problems with movement. I was taught to remove equally from both sides at the same time, then let it sit stickered for a time if needed, before doing final prep.
From contributor D:
I have always worked somewhere in between production and one-offs, and much of our work needs to stand straight on its own. Almost all work goes through the joiner - first cut to rough length, then rough width, then faced and edged, then planed or molded. The stuff for doors that needs to be straight of its own free will is stickered for a day or two after width and length, facing and edging, then run back over the joiner if needed, then finished off to width and thickness. The material that will go to a wall or other members and held straight goes right on thru to S4S. We have almost no problem with things moving after production or in service.
The notion of shell and core is somewhat accurate only if the wood is not properly dried. Conditioning in the kiln is a strategy to relieve internal stresses and even up the MC through the thickness. Properly dried lumber reduces the need for a 5 day voodoo exorcism.
Long ago, I learned to cut out a 1-1/2" long section from the center of a board in an arriving load (typically 8/4 or 6/4), and turn it 90 degrees and saw out a section to leave a U shaped piece. If the legs of the U stay straight, it is properly dried, able to be ripped, re-sawn, planed, whatever. If the legs bend towards each other, the MC gradient between core and shell is too great and we would consider returning the load.
From contributor A:
If your boss enjoys wasting his time and money, then it's hard to argue with "his way". I just pray for your sake there is no profit sharing. We are talking faceframes and cabinet doors. Faceframes get fastened to an immovable box with fasteners, glue or both. The entire face frame can be warped twisted and it will still straighten out when applied to the box. Cabinet doors are small parts that you are running thru a wide belt sander. It will flatten anything you throw through it. If I was building a really, really, fancy piece of furniture, I would only let the door panels "sit" for a couple of days. There is a better chance that you will mess up clamping a door than the wood will move due to stress relief. The vast majority of woods that have so much internal stress that they need to sit for days to re-warp, will likewise warp again, as you continue to stress relieve on your next facing.
From contributor H:
I'm not married to the concept of removing exactly the same amount from both faces. Very often, you don't have that luxury. As stated above, faceframes and similar work that will be secured to a rigid assembly you can take liberties with. Doors are another matter entirely.
For doors and other such "stand alone" items, I rough mill the stock to about 1/16th inch over the final dimension. Then sticker and stack it. Overnight minimally, but a couple of days is better. The material will "relax" after having removed some. Then it can be re-milled exactly as before, but now to final dimension. This method has never failed me unless the wood was badly dried to begin with. When your boss says that you don't have time to prep it properly, then remind him how much time re-making the doors will take. If he can't listen to that sort of reasoning, maybe you need a new boss.
From contributor J:
Bring the subject up to your boss. Let him know your trying to improve things (time, material and etc.) and have him rough out a few boards his way, and you do your way. See what boards move and maybe take it to the final product. You could make it a fun experiment and save the shop a boat load of money! But like posted above, if you had properly kiln dried lumber, you shouldn't even have to worry about this unless the climate in the shop is doing you harm.
From contributor U:
I could never work in a plant, so I am not talking from experience, only from my gut feeling. Any contest between a supervisor and his boss is going to end up with the supervisor losing. It is what you call a lose-lose situation. If you lose, you lose. If you win, you lose big time. A contest with your boss is not going to end happily. You need to figure out how to get him to think he thought of your way before you thought of it.
From contributor E:
The old adage; "the boss is not always right but he is always the boss" works out most of the time. What contributor U said is very true. Arguing with the boss seldom is a win situation. When one works for someone else he is going to have to do things that may not make the least bit of sense.
From the original questioner:
Well, interestingly enough I have spent so much time 'in the big chair' over the years that I am painfully aware of all this! Thanks for the advice anyway, it is good and sound! I have also been woodworking for 35 years. That does not make me an 'expert', simply an 'advanced student' in my thinking. I know most of this stuff-never question it in my own shop or when I am the big cheese or whatever you want to call it. Today, as I was explaining why there is so much water in the compressor lines (another subject entirely) the owner says; "it's nice to have a 'wood geek' in the shop", so, there are happy endings.
I did do the '2 leg test' for him when the material came in (thanks to WOODWEB for learning that a few years ago) but my experience is that this only indicates that board is either good or bad.
I did prepare the wood both ways - his and mine. Both worked well and mine took less time. The comments on frame vs. door wood are spot on. I usually use over-size lumber as well if the doors are particularly large (tall-wide) so I can process twice if needed.
Thanks to all of you for your comments. You guys are all a bunch of pros and I consider WOODWEB to be an incredible resource to me and whomever I happen to be working with.
