Pith in pine lumber/beams

customsawyer · February 14, 2016, 10:16:47 AM

I wasn't sure which thread to put this in so I just started a new one. I was sawing pine lumber for a customer on Friday. There has been several post recently pertaining to the pith in pine lumber. Well one log I was sawing was a perfect example of what I am talking about when I say center the pith in the log and not the pith on the ends.
In this pic I am sawing 2x4 lumber and when I cut the 12" cant into thirds to make the 2x4 lumber I had to keep a close eye on the pith in the log. The pith on the end was in the wrong spot to have made decent lumber out this log. If you look at the end of the log one of my cuts is splitting the pith. If you look about a foot into the log you can see where the pith curves over and is running in the center cant. This is what I am referring to when I say center the pith in the log and don't worry so much about the pith on the end. ;) This log had sweep in two different directions so it was a challenge to get strait lumber but as you can see the 2x4 on top are not moving very much.

drobertson · February 14, 2016, 10:20:10 AM

good pic, what happens if the pith gets split?

Magicman · February 14, 2016, 10:24:16 AM

With a wandering pith, you may loose a few, but most of them will be OK. The log is always the boss, so we read it as best we can and work with what the log gives us. You did good.

customsawyer · February 14, 2016, 10:37:51 AM

If the pith is split the lumber tends to warp more do to having mature wood on one side and juvenile wood on the other side. If it is warping coming off of the mill it will usually get worse as it dries.

Magicman · February 14, 2016, 10:42:26 AM

Mature trees such at that are "usually" more stable than 14" - 16" ones.

customsawyer · February 14, 2016, 10:54:45 AM

These trees were the exception to that rule MM. They had seeded in naturally and were spaced out so wide they had grown really fast with lots of large limbs. I advised the customer against cutting them into 2x lumber as I knew many were going to break just coming off of the mill but he said he didn't care as he would just scab them together. I even offered to let him have some of my better logs I had on the yard but these had come from his parents place and he wanted the wood to remember them by. Not much I could say after that other than "yes Sir" and start cutting. He left happy as could be and that pleased me.

drobertson · February 14, 2016, 10:58:10 AM

Thanks, and I had forgot about the juvenile growth thing, but will admit to splitting it more than once,, for no other reason than the center was plum retarded, no way to keep from it that I could see, I've seen crazy behavior and good stuff as well,

dean herring · February 14, 2016, 02:47:56 PM

The 2x4's your cutting actually measure 2 full inches x 4 full inches .How much do you add to the width of the cant for blade thickness loss?

drobertson · February 14, 2016, 02:59:43 PM

It looks to me like for two pieces one kerf, add a kerf for every additional piece to be sawn, hope this is right.

kelLOGg · February 14, 2016, 10:16:22 PM

Quote from: customsawyer on February 14, 2016, 10:16:47 AM
If you look about a foot into the log you can see where the pith curves over and is running in the center cant. This is what I am referring to when I say center the pith in the log and don't worry so much about the pith on the end. ;)

I see the peak of the "cathedral" grain curving over as you describe. Is that an indicator of the pith path? :P
Bob

scsmith42 · February 14, 2016, 10:41:21 PM

Good thread Jake.

GeneWengert-WoodDoc · February 14, 2016, 11:21:20 PM

From a strength point of view, load bearing lumber cannot have any pith. The pith is extremely weak and actually is not wood. The area right around the pith is also very weak. For this reason, we like to keep the pith in one piece (box the heart) to minimize low grade lumber losses. Plus, the pith piece can be ripped to provide one or two pith-free pieces. Secondly, there is lengthwise shrinkage in the region near the pith, so if the pith is on one face or edge, the lengthwise shrinkage in the region will cause bow and side bend. If the heart is boxed, this warp is minimized.

Upper · February 14, 2016, 11:40:23 PM

So a 6x6 with the pith centered can not be used as a load bearing beam?.

GeneWengert-WoodDoc · February 15, 2016, 07:28:09 AM

A 6x6 is a timber, while my comments were for lumber that is graded by the softwood grading rules.

Upper · February 15, 2016, 07:57:41 AM

Got it,thanks

Sixacresand · February 15, 2016, 08:14:56 AM

If you are sawing for pith free lumber, and you don't have a need for a boxed in pith timber, what generally happens or should happen with this timber? What do you guys do? BTW, I think CustomSawyer did the right thing to warn his customer that his lumber might be inferior due to the log condition.

Magicman · February 15, 2016, 08:33:19 AM

Jake did what we sometimes have to do. Logs with "traveling" piths and limbs should not be used for framing lumber, but there are times when the customer makes the call because he knows that he will need "shorts" for bracing, corners, and T's. Nothing is wasted. The customer also makes the call whether he wants full sized or "factory" dimensional lumber.

customsawyer · February 16, 2016, 08:00:33 PM

Quote from: dean herring on February 14, 2016, 02:47:56 PM
The 2x4's your cutting actually measure 2 full inches x 4 full inches .How much do you add to the width of the cant for blade thickness loss?

These 2x4 were full size. Some customers want the store bought size and others want full size. If you want full 4" width the cant needs to be 12¼" to account for the 1/8" kerf. Basically you need to add a 1/8" for your kerf with a band mill.

Quote from: kelLOGg on February 14, 2016, 10:16:22 PM
Quote from: customsawyer on February 14, 2016, 10:16:47 AM
If you look about a foot into the log you can see where the pith curves over and is running in the center cant. This is what I am referring to when I say center the pith in the log and don't worry so much about the pith on the end. ;)

I see the peak of the "cathedral" grain curving over as you describe. Is that an indicator of the pith path? :P
Bob

Yes the cathedral grain pattern is the indicator of the pith.

This is only to reference what the pith indications are with in a log. When it comes to what you actually do with the pith is up to you. When you are cutting for a customer sometimes you have to do what they want. By paying attention to the pith in the log you will be able to produce better lumber than if you are just paying attention to the pith location on the ends of the logs. I know that most of the box store lumber I see has some pith in it so I am not sure how it passes the grade that Gene is referring to.

Magicman · February 16, 2016, 08:08:36 PM

It is my understanding that a certain % of below grade is allowed, which takes care of the sawmill. I would imagine that they are for sure that whatever amount is allowed is in the bundle. :-\

GeneWengert-WoodDoc · February 17, 2016, 12:03:08 AM

Just to make sure we are all on the same page, pith is the exact center of the log as defined by the growth rings. The pith is about the same diameter as a small pencil.

Sixacresand · February 17, 2016, 10:58:35 AM

Quote from: GeneWengert-WoodDoc on February 17, 2016, 12:03:08 AM
Just to make sure we are all on the same page, pith is the exact center of the log as defined by the growth rings. The pith is about the same diameter as a small pencil.

I guess I been out in right field and on the wrong page, as usual. I had assumed the pith was lots bigger than that. If you let a pine log set a couple of weeks the center few inches will turn a dark brown. For some reason I assumed that was the pith. Shoot, if the pith is only as big as a pencil, I'm not going to worry about it, strength wise, especially for the stuff I build for myself.

beenthere · February 17, 2016, 11:20:23 AM

Six
Not out in left field...
Pith-associated wood is the juvenile wood laid down in the first few years of tree growth.
Some call it the "pith" but that is "technically" not correct.
The juvenile wood can have some very strange behavior, one of which is weak strength properties and more longitudinal shrinkage which leads to warping frustrations.

In the OP pic, the juvenile pith-associated wood is very fast grown so the diameter of that abnormal wood is several inches. If the first 7-8 years of tree growth were slow grown, the diameter of that abnormal wood could be much smaller. Some try to manage for slow growth the first several years, but hard to accomplish. Just deal with it later.

Magicman · February 17, 2016, 11:26:53 AM

This is not Pine flooring, but the long dark streak on the right side is pith showing. I personally do not have any problem with it. Matter of fact, I like it in some instances.

Clevelander · February 17, 2016, 12:31:07 PM

Is the pith in hardwood as much a concern as in softwood since it is seldom used as structural? If so, what is the formula for determining the proper size cant around the pith? I will be predominately milling red oak, white oak and maple over 36" in dia.

beenthere · February 17, 2016, 12:36:42 PM

Pith associated wood is not as finicky as in softwood, as well there are differences between wood species.

My understanding is that growth stresses that build as the hardwood trees lay on new layers each year which have more tension have the effect causing warp if those stresses are unbalanced. Busting a log through or near that pith center releases these stresses in the most dramatic way, most often causing banana shaped products.