Pre-Surfacing Lumber Before Drying
Planed green lumber dries with significantly less checking. March 3, 2006
Question
Is it best to joint and plane boards to remove saw marks before drying? Why or why not?
Forum Responses
(Sawing and Drying Forum)
From contributor A:
In general, it is not best to joint and plane boards to remove saw marks before drying. During drying you can get cup, warp, etc. that will have to be taken out by jointing or planing after drying anyway. If you try to plane away saw marks prior to drying, you will still need to plane off roughly as much after drying as you would even if the saw marked material was still on the board. Therefore, after jointing or planing after drying, you will have a thinner board than if you had not planed before drying.
From contributor B:
The dimensions of the wood change when it dries, so you might plane the wood to 3/4" or whatever dimension, then dry it, and have a thinner piece coming out of the kiln. The pieces won't all shrink the same amount, so they won't be 100% uniform. Also, the grain will stand out a bit on some woods when it is dried, so a smooth planed surface may have raised grain after drying.
From Dr. Gene Wengert, forum technical advisor:
Planing of oak lumber to remove the saw marks before drying is a great idea. It is called presurfacing. By removing the saw marks, you actually increase the surface strength and make the wood much less likely to check, with perhaps 15 times less checking. This is written up in DRYING OAK LUMBER and DRYING HARDWOOD LUMBER. With planing, the lumber is thinner and therefore dries a bit faster with less energy use and high kiln capacity. There are many positives and a few negatives.
Typical green thickness after planing is 1-1/32. There is less planing required after drying, so you can actually save wood, contrary to the other posting. Also, with all the lumber being uniform in thickness, you will better control cupping. In short, it is a great idea and is practiced in the industry at a few locations. Merillat, a very large kitchen cabinet manufacturer, uses it 100%, as do several other companies.
From contributor C:
I’m not quite sure what Dr. Wengert means when he says you'd actually save wood. If your wet off saw target is the same and your dress/dry target is the same, you're not saving anything. Also, he mentions typical dress green thickness of 1-1/32. With attention to sawing, that is my rough target on 4/4 lumber off the saw, which means if I dressed saw marks on both sides I'd be a little under an inch, which would still probably work out fine, but it's a lot of extra work. Merillat or a few other specialized lumber consumers may use this process, but the big boys of hardwood processing (wholesale-concentration/drying/processing) such as Baille, Atlanta Hardwoods, etc. don't fool with it.
From Dr. Gene Wengert, forum technical advisor:
Almost all hardwood lumber producers of 4/4 use a target of 1-1/16" or even 1-1/8", so there is plenty of wood to remove to get a green target after planing of 1-1/32". It is rare to see someone producing 4/4 hardwoods to 1-1/32" initially, except for a small producer, as the lumber will be under 1.00" thick after drying. Further, at 1-1/32 inch target and the normal thickness variation (rarely under 0.15), there will be some pieces produced when using a target of 1-1/32" that have a green size under 1.00 which means that they are not 4/4.
When lumber is sold as planed lumber after drying, the finished, dry planed thickness is typically 15/16" (often hit-and-miss) although some companies go as thin as 25/32".
Note - if a green piece is under 1.03" initially, it is not planed then. Once green planed, there is no need to rough plane before it is cut up. Further, the lumber is flatter, so the warp allowance mentioned earlier is not as large. After planing and drying, there is only a molder allowance left or perhaps a slight planing allowance.
Incidentally, Merillat is the largest kitchen cabinet manufacturer in the US, if not the world. The companies you cite are all lumber companies and not users. Presurfacing is typically done by the user of lumber and not the producer. This is mainly because of the grading rule issues on planed lumber. Some companies plane lumber on one side only to a given thickness to eliminate the thicker pieces. This process is called blanking. The thicker pieces will be planed heavily after drying if not planed green, so why not remove the extra thickness before drying? Which piece takes longer to dry - thick or thin?
By eliminating the thick pieces, overall the lumber load will dry about 8% faster, use about 8% less energy, increase kiln capacity by 8%, dry flatter, and cost less to dry overall. Over the past 25 years or so, there has been a lot of published information about blanking and presurfacing.
Let's not lose sight of the main reason for presurfacing - 18 times less surface checking in circle-sawn oak. In the South, surface checking can be quite a problem with the normal air drying weather and the higher risk of checking in species like cherry bark oak and in thicker oak. I believe that the US Forest Products Lab estimated that the losses to checking in oak in the South were 7%. A study in WV a few years ago came up with similar numbers. That is quite expensive for the ultimate user (not the sawmill) and could easily justify using a slightly larger target size if needed. Reducing checking losses to under 1% would save huge sums of money. It would not involve increasing lumber green target sizes at most mills.
From contributor C:
To Dr. Gene Wengert, forum technical advisor: I agree on the blanking. It is a very, very good thing to do for sawmillers who can't seem to saw without thick pieces. You state that the checking in the south on circle sawn lumber is due to stress concentrations around sawing variations, and possibly sawing grain angle difference between band and circle. I would think this should be significantly less on thin kerf band lumber. I believe that band produced lumber, correctly produced, would not benefit from presurfacing as much as circle sawn. What do you think?
Are there studies comparing drying of rough and dressed lumber of the same thickness? I would think, with all else constant, that a rough piece with more surface area would dry quicker than the planed piece.
From contributor D:
I agree with Dr. Wengert on this, particularly when handling extreme widths of QS Oak. When I quartersaw a 50"-60" oak, I saw on my Mizer's 5/4, 6/4 or 8/4 scales and target my widest widths (free of pith or sap) at 15" (capacity of my current planer). Since the lumber comes off my Mizer perfectly straight and flat, it doesn't take more than one 1/16" pass on either side to get the boards clean. Since I'm not selling by NHLA grade, it's the figure and quality that sets my price so I don't worry a whole lot about whether my end product is a little thin.
Besides, I believe that the end woodworker does end up getting thicker yield from pre-dressed lumber when rough cutting before jointing and planing. It definitely cuts down on surface checking and I've found that it has helped in pre-selling air-dried lumber as the customer can better see the product's potential.
From contributor E:
I dried some 8/4 fiddleback hard maple. Few boards would have easily made instrument grade if not for the checks. Would presurfacing have worked on the maple?
From contributor C:
Maybe planing would have helped but I doubt it. There are too many other variables to consider - kiln schedule, handling and drying rates early in the drying process, and many others. It is hard to pinpoint after the fact, but you dried an extremely difficult item. Were there other defects such as case hardening or honeycomb, or just the checking?
From Dr. Gene Wengert, forum technical advisor:
Presurfacing works because the saw (especially a dull saw) actually tears the fibers and leaves a lot of small checks and fractures that can develop into checks when drying. A sharp saw (bands have to be sharp or they will not run) has much less of this effect, hence we often hear that band sawn checks less than circle. In one study, the smoothness or roughness did not seem to appreciably affect drying rate. I do not know about maple. As this wood checks so little, I would look for some other variable that was out of control.
From contributor F:
I am about to mill some oak logs, so this is interesting information for me. My suspicion is that planing reduces the effective surface and porosity of the wood, so that it dries more slowly and thereby gets less checking. Is this correct? If so, it would mean that it would dry more slowly, too.
From Dr. Gene Wengert, forum technical advisor:
In comparisons of equal thickness wood, we have never seen any difference in drying rates. Because planed lumber no longer has the thick pieces, it will dry faster overall.
From contributorG:
Do you have any tips on planing green lumber? I know when we have tried to plane green or wet lumber, it is hard to feed. Any tips?
From Dr. Gene Wengert, forum technical advisor:
When you plane green lumber, it is common to see quite a bit of spring back, which means that the pressure bar must be a little bit more open than for dry lumber. The bed plate should be smooth. Exhaust system must be strong to remove chips that are twice as heavy as dry chips.
