Flattening boards with a planer

Methods for planing warped wood flat. September 25, 2002

I need to flatten some boards that are too wide for my 6" jointer. It seems that if I could support a twisted, cupped, bowed or otherwise warped board from below, using a fixture, I could get one side of the board flat with repeated passes through my planer. And once one side is flat, the planer can make the opposite surface parallel to the first.

Has anyone built such a fixture? The boards are, for the most part, less than 6' long and less than 12" wide. They can be a half inch or more out of flat.

Forum Responses
From contributor J:
I had some 5/4 maple that had quite a bit of twist that I was able to flatten without having to resort to a hand plane on the opposite corners. I made "running boards", say 1 x 3, out of pine. I then propped the maple up on the bench so the maple was higher than the 1x3 on edge and the maple was approximately even in the amount of twist in all directions. I then screwed the running boards to the maple and then could run the whole works through the planer for as many passes as needed. One disadvantage is that all the finished maple boards had screw holes on the edges, but in my case they hadn't been jointed anyway, so it wasn't a problem for the most part.

From contributor W:
The runner solution is a good one for twist. For the cupping, I take very light passes, less than a 64th if possible, to minimize the pressure. That is, don't have the planer pressure flatten the board. That is why I decided to not get one of the big planers for my shop. I stick with my portable unit that can't take gobs of wood off in one pass.

From contributor F:
Just curious... Is good lumber so hard to find or so much more expensive than your labor, that you can afford to devote endless amounts of time to produce a product from otherwise rejected material?

From contributor W:
In my area of NE Tennessee there are few local hardwood dealers, a number of sawmills but few drying kilns. I'm large enough to have 500 to 1000 bd ft shipped in. (In reality I don't want to be that big.)

On a given day I may have a total of 400 bd ft of the five species of lumber I use most. So when I do get a stock of lumber I get the best I can at the time. That may mean taking good 5/4 or 6/4 when the 8/4 I would like is a mess. Plane, stack, laminate, rip to the 1 5/8 or 1 7/8 I want.

I avoid rough boards with more than 1/2 inch twist in an 8-10' length no matter the thickness or width (ie. 6" or more). I make chairs and wood is the frame for weaving the seats and backs. Cupping is easily dealt with by selecting 5/4 or thicker stock, planing lightly until I get a reasonable flat area over the total length and then taking thicker cuts until both sides are flat and parallel. I usually set aside 2 hours to get 100-200 bd ft ready for upcoming orders.

From contributor J:
I live in WY and it is really tough to get any quantity at reasonable prices. For lots of species I would have to go out of state to purchase them. Now that I'm mostly retired, time is one thing I have a lot of.

From contributor A:
My shop is in southern New Mexico, where good wood is very hard to find. We buy all of our wood rough to gain a little more thickness. We make a lot of 7' moulding and warp is a big concern. We chew up a lot of labor preparing wood. I believe the shops in the southeast have access to better wood. Our humidity averages less than 15%. Any wood that has been stored here for any length of time meters less than 6%.

I really can't understand why you would go through all of this trouble to get your material flat when you are talking hundreds of board feet at a time. It seems to me that using jigs or shoring up corners to run through your planer is asking for trouble if not just plain dangerous.

I also face the problem of not having a large enough jointer to straighten my cups, bows and twists on stock wider than six inches. However, I believe my health as well as yours is much more important than the time it takes to split the stock, machine it safely and then reorient the grain and glue it up. Very few laymen would ever notice and your body and equipment will remain intact until you can purchase a larger jointer, better grade of lumber or, as I did, buy a wide belt sander. You know that you want one anyway so you might as well go just a little deeper in debt. At least you'll still have all of your body parts intact so you can feed that twisted stock into your new sander! Stay safe and it will continue to be fun.

If a board is too twisted, cupped or crooked, we don't take it off the truck. And if by chance we find a mother load of free or really cheap wood, the bad stuff gets converted into BTU'S instead of SKU's.

From contributor W:
I guess it is a matter of degrees. What is too much cup or twist? I assume that we are all talking about rough lumber here. And I assume that we are making panels for tables, doors, etc. I can work with cup of less than 1/4" across a 10" plank and 1/2" twist in 8 to 10 feet on 5/4 or thicker lumber.

Part of my view is my customers (before I moved to chairmaking) wanted figured woods showcased in their custom furniture. Otherwise they would go to some big furniture store. Highly figured stock most times is not from trees that grew 'straight as an arrow', so we have to do some work. Our customers need to know how difficult working in wood is at times.

From the original questioner:
The story of the wood I am working with is as follows. I start with local windfall hardwood trees, mill them with a chainsaw mill, resaw them with my bandsaw, then sticker and dry them. Why go to all that trouble for something you can buy down at the local wood store? That's the thing - I am getting things like red mulberry slabs, black walnut crotch sections, curly white oak, red oak boards up to 40" wide (which I flatten on my CNC machine), paulownia, holly, dogwood, elm, flame beech, eastern red cedar, and a lot of true quarter sawn red oak boards. I am also working with reclaimed heart pine beams which are 12" wide, and resawing those into flooring and furniture boards. The problem comes with boards that are too small to mess with on the CNC but too wide for the jointer. So I would like a safe way to hold boards so they can be run through the planer until one side is flat.

I can understand that the economics of sawing trees, slabbing them, hauling the slabs out of the woods, resawing them, stickering and drying them may not (almost assuredly do not) make sense, but there you go. I am an amateur woodworker with a day job, so I have the luxury of being able to track down boards with 4' long feather figure and the like.

From contributor J:
I wasn't sure if we were talking a couple of boards or a lot. I had over 250 bf of 5/4 maple shipped to me from WI that had a lot of twist, but not severe. As for the local lumber yard, the few sticks they may have will bend like a pretzel as they lay loosely piled. That's why we go out of state.

A 6 inch jointer will cut 12 inches. Just make a table to support the edge of your board, then after the first cut turn the board. This will not be perfect but it will make a base you can start to work with your planer without the risk of an accident.

From contributor C:
Cup can be minimized on the planer by taking light cuts on the convex side of the cup on the first pass. If too much feed roller pressure is used, you flatten the board, then it cups again or splits, which is why a couple light passes are better than one heavy pass.

I have been using a simple method which works well on cupped yet untwisted stock. I use lengths of 3/4" MDF and select from a variety of thicknesses to install a shim under the board at the maximum cup height. This shim minimizes any of the boards' tendencies to deform from contact roller pressure. You can usually reduce the board's curvature by 90% in the first pass.

From contributor D:
Come on, all of us have ordered 100 bf for a mold or s4s run and had a few lemons we had to use because of time. I have joined one side, then turned 180 to do the other, but for twist I have had better luck with a trusty 3 inch electric hand plane. Eyeball the high spots until the plank doesn't rock on your bench. I also have an 8 foot box beam bed that slips into my planer that really helps with the long stock. My 13 inch planer is 600 lbs but 12 and 16 foot lumber is way easier this way. Also, if you shift your fence past blade on jointer and join the hump side to the blade, you can usually pick up 2 to 3 inches of capacity.

The truth is that when lumber is graded, it must be flat enough to surface to standard thickness. The area considered is the clear area used to determine the grade. This is the NHLA rule for hardwood lumber. Pieces that you bought with more warp should possibly be returned to the seller (for a refund) as being "off grade." Why should you lose money due to someone trying to sell off-grade lumber? In other words, be assertive when you are right.

Gene Wengert, forum technical advisor

From contributor D:
Gene, I don't know about your neck of the woods, but in mine I'm lucky to find FAS in most species. Wholesalers like to stock S&B. I supply materials to DYI and small pro shops. They call for 50 of this rough, 200 running feet of that s4s, oh and can I have that in 48 hours. I can see it now. I order, it comes in, I reject, I lose 2 days, I lose sale. Resupply comes in, I have dead inventory. In a perfect market, suppliers would follow NHLA book. Show me where is says in that book that dealers can charge for shrinkage. I have to figure into my costs 7 to 8% margin for shrinkage or I eat it on the resale. I just look at shrinkage, bad counts, warp and waste, etc as the cost of doing business.

99% of all hardwood lumber dealers and suppliers at the wholesale level will follow the NHLA rules if they sell using the NHLA rules and grade names. This is throughout the US and I suspect Canada, too.

The rules are very clear that you cannot charge for shrinkage - you must sell and measure the lumber as it is and cannot add back 6% or whatever for shrinkage. This is in the Rule Book and also is in every state Weights and Measures law, as this was adopted by the National Weights and Measures years ago. There are still a few people that sell 1000 BF and then add 8% (it used to be 6%) to the footage to account for shrinkage. In other words, 1000 BF is sold as 1080 BF. Illegal, unethical, and just plain cheating. Most folks do not do this, so if you use the prices in the Hardwood Market Report, these people who add 8% are just charging 8% more than the HMR values!

You are correct in considering the loss of a sale due to delays in getting the correct lumber. But maybe you need to visit your supplier or try a new supplier. I have been in many disputes of this sort (one over $3 million) and there are some lumber folks that cheat and really do not care about their customers. I suggest finding one who does. (I work throughout the U.S. and not just in Wisconsin.) Some suppliers actually have their grading inspected every month to make sure they are accurate. These folks can display the CERTIFIED NHLA inspector logo.

Gene Wengert, forum technical advisor

From contributor C:
It is all relative, isn't it? If you know you are paying for gross board footage, that's okay. If you know you are paying for net board footage, that's great, too. Very few of our suppliers sell by NHLA rules. I do not care if someone calls it "Wausau select", if I can process this grade and make a profit, everyone is happy. Buyer beware.

From contributor D:
I'm in south Florida and have been buying wholesale and selling lumber, plywood, and veneer for 15 years. I have not met a supplier yet who doesn't charge for shrinkage. We have at least 10 that I can think of and all add a 7 or 8% margin. It's obvious and blatant even without the net count I do every load. Only once did I get 100 feet for a 100 foot charge, but it came in 1 board (16/4 pattern mahogany). Took a forklift to get it in my shop. I agree that it's relative. Every supplier does it, every customer knows it, it's accepted as the cost of doing business.

Many of the companies I work with do not do it.

Gene Wengert, forum technical advisor

From contributor A:
To get back to the original question... There are two ways I have used to flatten wood (before I bought a 25" jointer). Build a sled and shim to provide a stable bed for the wood. Take light cuts on the planer until you have a flat surface. The other method is similar. Build a router fixture to allow surfacing with a router. This works best with smaller pieces of wood.

From the original questioner:
I have used the router method in the past, and that has worked well. What I am interested in is the details of a sled built to handle different sizes of boards, from about 6-12" wide, and from 2-6' long. Something like that. I have used sleds purpose built for specific boards in the past, but I am faced with a larger selection of boards that need attention right now. How do you get the shims to stay in place? I am leaning towards double sided tape - ever tried that? Heck, that might even work to hold the board to the sled. Hmm...

From contributor W:
If you go with double sided tape, use the fabric type because you are trying to hold on to a pretty rough surface. On surfaced boards I use the cheaper film tape that doesn't 'squirm'. On rough boards the thicker fabric tape will compensate a little for the roughness.

Base sled with a back fence to hold the piece from slipping off the back. I use a few small tacks through the fence to hold the work in place. Lay the twisted board on the sled and shim with playing cards every so often. Simple tape to hold the cards in place, light cuts on the planer and voila, a flat face!

I've seen a number of different sleds in the woodworking magazines. You might want to search their archives. This is the simplest and easiest I've seen and used though.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor P:
Build a sled of appropriate length and width. I used two pieces of 3/4 MDF glued together. This ensured flatness and rigidity. At the tail end (the end which enters the planer last), screw on piece of wood 2 1/8" tall, 3/4" thick and as wide as the sled. This allows for 5/8" to protrude above the surface of the sled (this won't interfere with the knives assuming you're sizing stock down to 3/4"). The stock butts up against this protusion. To prevent slippage, I drilled a row of screws along and just sticking through the protusion to "grip" the tail end of the stock. Now, along the near end of the sled (the long edge nearest the operator), on the surface and 3/4" in from the edge, I drilled and countersunk a row of 1" flat head screws, spaced about 1 1/2" apart. Install all the screws flush with the surface. Now, to use, lay stock on the sled and unscrew whichever screws you need to to support any 'high' spots. This jig works well. The only disadvantage is that it is heavy if you make it 6' long. I also made a 3' one for ease of handling on shorter stock.

Comment from contributor B:
I use a flat sled made of laminated particleboard with melamine surfaces on both sides. Lay the twisted board onto the melamine, and mark the high spots with a pencil. Lay strips of masking tape on the underside board surface at these pencil marks. With the board upside down, put blobs of hot melt glue onto the masking tape, and quickly flip over the board and stick it to the melamine. Don't let it rock until the glue sets up (about 15 seconds). The glue acts as shims when it cools. Pass the whole thing through the planer until it's flat, then pry off the board (the glue won't stick to the melamine), pull off the masking tape along with the now-hardened hot-melt glue, and you have a flat side.

Comment from contributor E:
I recently flattened a few pieces by gluing them to a piece of particleboard with urethane glue and running them through the planer. The glue expands to fill the gap, so shimming is unecessary and particleboard makes a cheap and flat base. This is economical for wood that is valuble enough to justify the effort.

Comment from contributor S:
I do woodworking as a hobby and have developed a way to flatten boards that are too wide for my 6" jointer. Well, I shouldn't say I developed it, but I have tweaked it a little.

Basically I use a sled like others have mentioned. Mine is about 11" wide by 4' long. It's made of particle board with a melamine facing. I hot melt glue the warped board, bow side up, with tacks of hot melt at each corner. Then I hot melt shims under the bow on both sides about every 6 inches.

That's it I run it through the jointer taking light passes until flat. This isn't a perfect system - wide boards will still deflect some in the center as there is no support there. But for stuff under 6-8" wide, it works well most of the time.

To remove the board from the sled, squirt alcohol on the hot melted areas. With a small amount of force the board will pop off the hot melt. Apply alcohol to any hot melt still stuck to the board or sled and it will come right off with a chisel.