Thickness of Rough Lumber

Identifying and sawing for specific dimensions. May 19, 2004

A guy called me the other day about lumber. He said that 4/4 grade lumber is 1 1/8 inches thick. I thought that would be 5/4. Is that right? I have a Wood-Mizer and my understanding of the scale is that it will yield 1 inch lumber when I cut on the 4/4 scales and it will yield 1 1/8 inch lumber when I cut on the 5/4 scale. I don't know why you would make 4/4 lumber actually 5/4 and give away the extra 1/8" every time. When I saw lumber, should I go 5/4 to get 4/4 grade and 6/4 for 5/4 grade, etc.?

Forum Responses
(Sawing and Drying Forum)
From contributor K:
I suggest downloading a copy of the National Hardwood Lumber Grading Rules:

I always have a spare copy with me to give the customer. It will help to educate them as well as hold people accountable. Accountability seems to be lacking when it comes to selling grade lumber.

From contributor C:
1 1/8" thick rough sawn lumber is indeed 4/4 lumber. You need to be at least 1 1/4" rough to be 5/4. I cut all of my 4/4 at 1 1/8" thick, then I skip plane to 1" and sell it that way. As far as grading, I have a $2.00 pile, $2.50 pile and so on. This way I am not selling non-graded lumber as if it is graded. I know the grading rules but I am not a certified grader.

From the original questioner:

Thanks for the info. I'll download the book and print it out. I read a lot of "cliff notes" about grading but did not find anything about thickness. I'll have to measure the gauge on my Wood-Mizer scale. At this point I'll assume that 4/4 yields 1 1/8" rough lumber. I'm interested in knowing the rules but paid a certified grader to grade my lumber.

From contributor K:
I understand that most people have there own way of grading and sell lots of wood, but when a person asks for a grade requirement, I believe we should revert to the accepted standard instead of what someone taught us. I have found way too often bad teaching gets passed on without being questioned regarding its accuracy.

This is directly from the Grading Rules:

13. Standard thicknesses for rough lumber are 3/8", 1/2", 5/8", 3/4", 1", 1-1/4", 1-1/2", 1-3/4", 2", 2-1/2", 3", 3-1/2", 4", 4-1/2", 5", 5-1/2", and 6". One inch and thicker may also be expressed in quarter inches as follows: 4/4, 5/4, 6/4, 7/4, 8/4, 10/4, 12/4, 14/4, 16/4, 18/4, 20/4, 22/4 and 24/4.

14. Standard thicknesses for surfaced lumber is calculated by subtracting 3/16" from standard rough thickness for lumber 1-1/2" thick or less and by subtracting 1/4" for lumber between 1-3/4" and 4" thick as follows:
Rough Surfaced
3/8" S2S to 3/16"
1/2" S2S to 5/16"
5/8" S2S to 7/16"
3/4" S2S to 9/16"
1" S2S to 13/16"
1-1/4" S2S to 1-1/16"
1-1/2" S2S to 1-5/16"
1-3/4" S2S to 1-1/2"
2" S2S to 1-3/4"
2-1/2" S2S to 2-1/4"
3" S2S to 2-3/4"
3-1/2" S2S to 3-1/4"
4" S2S to 3-3/4"

From contributor H:
I have a Wood-Mizer LT40. On my scale, one side is standard thickness and the other is for grade hardwood.

From contributor K:
I think you will find that one side of the scale is for softwood standards and the other is for hardwood standards. That is what WM told me. I'm not so good with the math, so I put on the Accuset. I don't think I could live without it now.

From contributor A:
On your Mizer you should have a fixed scale that reads from the bottom of the blade to the bed. The other scale is a sliding scale marked in 4/4, 5/4, 6/4, 8/4. One side is a standard scale or a softwood scale and the other side is a hardwood scale. Hardwood as a rule is sawed 1/8 inch thicker to allow for shrinkage of the wood. So hardwood 4/4 is 1 1/8 inch. My grade hardwood buyer will take oak sawed from 1 1/16 to 1 1/4 as 4/4 lumber. Less then 1 1/16 and it is culled and over 1 1/4 goes to 5/4. So on hardwood, 4/4 = 1 1/8, 5/4 = 1 3/8, 6/4 = 1 5/8, 8/4 = 2 1/8.

Now for my own use, if I saw oak boards less then 8 inches wide 1 inch thick, they will plane clean at 3/4. On wider boards you need the extra wood to clean up sometimes. Most wholesalers sell dried lumber at 13/16 so that it can be cleaned up a bit before selling at 3/4.

I give them what they want and my wholesaler has never culled one of my boards.

From contributor K:

I think contributor A said it best.
"I give them what they want."

If your customer wants a specific dimension, that is what you have to cut to. If you feel you're giving away too much wood that way, then prior to taking an order, provide them with a copy of the rules with the thickness section highlighted so that they know what the rules are.

The other key is to get to know your customer and what they are going to use the wood for. I know that's not reasonable on big orders, but I bet most of your customers will be more than happy to tell you what they are using it for.

I mention this because I had a local furniture maker that wanted 1 1/4" boards for his projects. When I asked him what final dimension he wanted, he answered that his goal was 3/4" lumber.

It turns out that his past experience with buying from a mill was that the boards were wavy and too many of them would not finish to what he needed, so he simply asked for oversize.

When I assured him I could sell him 1" boards that would finish to his desired thickness, the old timer said prove it! When we were done cutting he became my best friend. You see, he brings his own logs and now he can get more lumber than he could before, and at a comparable price to what he was paying.

From contributor B:
My dad and I made some gauges for various thicknesses on magnetic strips. (I don't have a WM.) This way I can start wherever I want on the saw scale with these adjustable magnetic gauges and get the thickness I want. Really speeds things up for me.

From Gene Wengert, forum technical advisor:
For 4/4, you need to be at least 1.00" thick in the area used for establishing the grade. This is for green or for air-dried lumber. Many mills cut 1-1/16" if their thickness control is very good. This average with a slight variation will assure nothing under 1.00. Other mills cut 1-1/8 average, because their variation is larger. Of course, the thicker, the lower the yield. Each 1/32" is over 2% yield. The idea of 1/8" over the nominal being standard is no longer true.

Incidentally, the idea that the 1/8" allows for shrinkage is not true. The average shrinkage is only 6% or about 1/16". Note that the rule allows KD lumber to be thinner than 1.00".

From contributor A:
What about planing out "cup"? My wholesaler says that if he does not have that extra bit, the wider boards will have to be ripped in half to plane clean.

What do I really lose by sawing 1/8 over? I would have to make 9 cuts to save a board and it would most likely be in the low grade part of the log. If a cant moves on the saw (they do this more than one would think) and I am sawing at 1 inch and now I am at 15/16, my board will be rejected. Only in logs larger than 18 inches would I start to notice any extra wood and it may be of less value and run the risk of a FAS board being rejected for a thin spot due to blade dip (they do that as well) or movement of the mill. My wholesaler has a pile of boards that do not plane clean at 13/16 but do at 5/8. The system is set up for 3/4 and they only want to move a lot of what sells most quickly. I know the math says that I am losing wood, but I am not culling boards and that is what pays. It is a hard call.