One of the first things I needed to figure out when I started cutting rough lumber on a sawmill was what thickness to make it. I could generally determine if I wanted it to be thick or thin, but just how thick or thin? 4/4 lumber is 1″ thick, so it should be rough cut at 1″ thick, right? Not exactly. For hardwoods, the commercial target for 4/4 lumber is actually 1-1/8″, which allows enough margin to produce dried and planed lumber at a thickness of 13/16″ or 3/4″ (3/4″ is acceptable, but the extra 1/16″ of thickness in 13/16″ material allows room for additional planing or sanding after panels or doors are glued up).
The crazy thing is that back then I couldn’t find solid information on lumber thicknesses anywhere and when I referred to the NHLA (National Hardwood Lumber Association) guide, the thicknesses didn’t match up with what I was finding from hardwood producers. The NHLA guide doesn’t include the bonus 1/8″ of thickness – 4/4 lumber, for example, is specified at a minimum of 1″.
In my experience, 4/4 hardwood lumber cut at 1″ is too thin to consistently produce flattened and planed lumber at 13/16″ thick and will even have trouble producing 3/4″ thick unless the boards are very flat. The only way 1″ thick rough-cut hardwood lumber can plane out completely to 13/16″ or 3/4″ thick is to skip the flattening and just plane the lumber. This will produce thicker finished lumber, but it won’t be flat and straight since the planer will simply follow the curves of any crooked boards. From a woodworkers perspective this is a horrible practice and makes woodworking much more difficult. For this reason, I cut my 4/4 hardwood lumber like all other quality producers at 1-1/8″ thick and don’t accept anything from other sawmills or wholesalers at 1″ thick.
Starting with the lumber measurement and adding 1/8″ for the final thickness is how all of the hardwood measurements go, with a target for 4/4 lumber at 1-1/8″, 5/4 lumber at 1-3/8″, 6/4 at 1-5/8″ and 8/4 at 2-1/8″. These are the commercially accepted numbers, and except for 8/4 lumber the ones that I shoot for. The problem with 8/4 lumber is that since there is more wood it shrinks more than thinner lumber and 2-1/8″ thick just isn’t enough thickness to flatten and plane lumber to consistently finish at 1-3/4″, which is the target for 8/4 lumber. When I flatten and plane batches of 8/4 lumber milled at 2-1/8″ thick it isn’t uncommon for half of the lumber to finish at 1-5/8″ thick instead of 1-3/4″.
Because I think 2-1/8″ is a little thin, I commonly cut 8/4 lumber at 2-3/8″ thick. 2-3/8″ thick is twice that of 4/4 lumber, plus the 1/8″ saw kerf that would have been between the two imaginary cuts. The extra thickness not only impresses the ladies, but it assures a final dried and planed thickness of at least 1-3/4″ and officially uses no extra wood when compared to cutting 4/4 lumber (to keep things simple, a friend of mine simply calls it “double four quarter” lumber). As I mentioned though, 8/4 is commercially sawn at 2-1/8″ thick, so if you cut it at that measurement it isn’t wrong, 2-3/8″ is just better for the end user (none of my customers have ever been upset that the wood is a little thicker).
The previous examples were for hardwoods, but softwoods, like white pine, can be cut thinner since they shrink less and dry straighter overall, plus softwoods are commonly used for construction purposes instead of furniture, which don’t need the extra thickness for secondary planing or sanding, so 3/4″ final thickness is common for 4/4 softwood lumber. For 4/4 white pine for example, I cut 1″ thick, which will finish at 3/4″. And, for cedar, which shrinks very little and is very straight and stable, I will go even thinner, down to 7/8″. In general though, softwoods are cut on the standard quarter scale with 4/4 lumber measuring 1″.
The scale below shows the target hardwood lumber thicknesses for commercially produced, rough-cut lumber and their planed thickness counterparts. These are the sizes you should expect to find when shopping for hardwoods.
Hardwood Lumber Measurements
Quarter-scale measurement Rough cut thickness Planed thickness
4/4 1-1/8″ 13/16″
5/4 1-3/8″ 1-1/16″
6/4 1-5/8″ 1-1/4″
8/4 2-1/8″ (or 2-3/8″*) 1-3/4″
*2-3/8″ is a better thickness to consistently finish at 1-3/4″ thick, but 2-1/8″ is the norm.
I have been on a sycamore kick lately, and this sycamore slice keeps my streak going. There are three stacks of these rough sawn slices for sale in my shop, and though I have sold a few, this is the first one to officially get finished and installed.
The slice is 3″ thick and is a cross cut of a 48″ diameter hollow sycamore log that had the added benefit of having a long open wound that didn’t quite seal up. In the tree’s attempt to close the wound the new wood took on a curl shape on both ends that make the slice look more like an artistic expression than just a hollow log.
Since the tree was standing dead all of the sapwood is consistently spalted and marbled in appearance. There is some solid heartwood in the piece which isn’t spalted, but has a beautiful rust color.
I was planning on ditching this tree since it was hollow and didn’t seem to have any millable lumber in it, but when I saw the curl shape on the inside of the log I did a u-turn on my way to the dump. Solid logs with complete centers that are sliced like this tend to crack and fall apart because of the drying stresses in the log, but in this case all of the drying stresses were relieved since the center was gone. When the outside wood wanted to shrink it wasn’t restricted by wood on the inside and could freely reduce in diameter without any problems.
I installed the slice on the wall with two lag screws, just like a mantel. I drilled matching holes on the back of the wood and just slid it on the wall (with the help of my customer). This system works great since it allows the piece to get flush to the wall and enables it to be removed without tools should the need arise.
Overall, I am ecstatic to have one of these completed and out the door. Next up is to finish at least one extra to keep in the shop to show off. You wouldn’t believe how much faster they sell with a finished sample around to seal the deal.
This week I picked up a sycamore log at Grant’s Farm for a local woodworker. He has been commissioned to build a round table from the tree that has stood on the property since the time of Ulysses S. Grant.
Because the log was too heavy to load in one piece and was going to be cut into round slices anyway, I cut it in half to make it easier to handle. The log is a minimum of 60″ in diameter on the skinny end, and should make a few nice table tops.
I jokingly complained to my wife that I drove all the way to Grant’s Farm only to pick up two 3′ long logs – that, by the way, filled up the truck.
Recently, I set up three large hollow spalted sycamore logs to cut in the Lucas mill. They are all in the 48″ diameter range and most were cut 3″ thick. I see future tabletops (with glass) and wall decorations. Out of all the logs I had on the lot, these were drawing the most attention, so they got cut first.