2x6 studs

[astidham]

I called the lumber yard today and asked about their 2x6 stud grade, they say they are stud grade. the plans require #2.
is stud grade #2? the place was 84 lumber if that helps.

[Don_P]

No, stud is its own grade...basically a #3 structurally with #1 edges.

The maximum slope of grain in #2 is 1 inch in 8 in a stud it is 1 inch in 4... twice as steep. The maximum allowable centerline knot is 2-7/8" in #2, maximum knot at edge is 1-7/8". A stud max centerline knot is 3-3/4" in a 2x6, 2-3/4 toward the edge.

To relate this to the nails and screws thread, think about where the stresses are carried in a piece of lumber and the reason for the difference in knot size in the neutral plane or near the edge (the extreme(outermost) fiber) should become clear. The load is primarily carried on the outer edges. An I beam has that shape because it is efficient. A knot in the middle does less harm than one on the edge.

Basically a stud is a compression only member, it cannot take much bending at all. You never want to walk into a house and see stud stamps on horizontal members. You don't want studs subject to bending.

[astidham]

Thank you Don_P

[bayview]

   Hand pick you lumber!   Seems every lumber yard has their own grading system . . .    Not every #2 seems the same . . .


/

[Don_P]

Hogwash... to an extent.
A true #2 is not a pretty piece of lumber. The rules governing it are standardized by law. As the grading instructor told us "We want for you to get every single #2 out there, just no #3's by mistake". You may see varying amounts of Better, but you likely are not seeing much below grade. If you do report it, a grader needs a dope slap.

The public has in their mind what they think a SS or a #1 or a #2 is... but they really don't know what makes one or the other. The big boxes realized this when people came in and hand picked lumber. Much of what they picked through was well within grade but not up to the "eye candy" specs people expected. The big boxes invented a new grade "Prime". It means nothing structurally, there is no adjustment to published engineering values, but the Prime stamp and pretty edges gets them business.

We had a delivery by 84 a couple of years ago and we were pretty unimpressed by the quality. I was ready to turn it around but we decided to grade our way through it and keep anything that was on or above grade and return the below grade stuff. It was all hugging the line but I wanted to shake the graders hand by the end of that exercise. He had a tough job, I imagine a crappy run of logs and I had nothing that missed grade. It was not pretty but it was to spec and structurally up to the strength designed for. Ultimately that is what grading is, it makes sure the wood is up to the engineering needs.

I can also change the grade at the cutting bench.

[DirtyLittleSecret]

Dang Don, that's some great info.  I wish we had a "lumber grading tutorial".

[Don_P]

I wouldn't normally do this... but this was such a neat message I hope Rick forgives me;

First off thanks for your posts they are very informative.

Don a question I would like to pose on this subject.  I do know when  I was around lumber mills up to age 22 or 23 from the tender age of I just remember they were always just there.  I am 58 almost 59 now so a lot has occurred that I am not aware of.  In fact not until I read some of your posts on this subject did my interest peak again in grading.  Anyway back then there was associations the saw and planer mills belonged to.  They were required to grade to that associations standards.  IE Western White Pine Assn.  which also set standards for Ponderosa Pine, Doug Fir, White Fir and I think Tamarack out here in the west.  Now days is grading actually set in stone via law or actually by association.  Are they actually codified by Federal Law or some interstate commerce regulations?

I do remember when the grader inspector arrived at the mill every couple months he would tell the usually the head fork lift driver,  "I want to see so many different units of lumber.  Might be a unit 5 quarter shop, a unit of one by ten boards and two or three units of dimensional inventory.  They would set them out for him and then he would grade the grader or graders.

I use to love to watch the graders at work.  They had computer brains. Scan the front side, flip it look at the back side and scan the edges and on went the stamp.  Or he would stamp it mark it with a crayon for the trim saws.  Usually a line and a number.  Or which saw he wanted the trim sawer to drop.  This was all done in seconds of course.  Back then with the planer screaming behind him.  The trim saws were ahead of him along with all the air rams on them popping and making all kinds of noise.  No wonder none of use can hear today.

           

That is pretty much exactly how it works. The American Lumber Standards Comittee was empowered by congress to come up with standards for softwood lumber. They in turn recognized industry grading associations, some of which wrote rules, all of which fall under the NGR, Nat'l Grade Rule. These are voluntary product standards. They are called a quasi government agency. You're in the grey area, it is called voluntary, it is effectively law. By the time I get to building with a stick, those laws do codify that it be graded by a recognized agency... there is where it is really codified. The congressional mandate said they couldn't step on the little man, and so nobody seems to be doing so. It is all voluntary, I don't have to comply. But if I don't join the club I surely can't play.

Now I'll look at that from the other side. If you stamp something #2, in most places you had better be a member of a recognized grading association.  I do have a pic of a bootleg stamp here somewhere, we got a whole load in on one job. The ALSC website used to have a section on enforcement, haven't been over there in several years. I'm trained but the dues are out of reach. If I need grading done I have to bring in the grader's inspector.  ... The nice young college boy that trained as my table partner left class to become an auditing grader, I went back to work with no ticket (Violins in the background  )

The sawmill grader must be within a very small percentage of the auditors calls or they start pulling more of his crayon colored packs. If he is consistently off the auditor leaves with his card. He can be retrained and slowly let back in. It is not an easy job and one of the highest paying in the mill. The guys I trained with had about 3 seconds to scan all 4 sides, pick the controlling defect, assess it and make the call. The instructor was on me the entire final test "make the call, make the call". Our class did post the highest scores that agency had ever recorded. They had specialized to just grading, A carpenter in their midst was a learning opportunity they had never had. They have advanced things a great deal by specializing but somehow we need to learn to share what we all know better, it advances us all.

These are some pics from the agency lab, we were having some concepts proven on the killing floor.



This was a borderline #2, and broke very close to #2 design numbers

This is a tension test machine. There is a 2x10 loaded flatways between the orange jaws that will be pulled apart lengthwise.

And our instructor with the damage;

[Don_P]

Is Mike holding the tree rightside up or upside down? 

[bayview]

   Thanks Don_P   Very informative.

   I purchased and had delivered #2 2x6s from our local lumber yard sight unseen.   They probably were of grade but barely.   Some were very crooked, some with excessive knots and some still had bark on them!   I ended up taking about 1/2 of them back.

   I purchased the rest at a "big box" store.   They also were #2s but a whole lot prettier.   And cost less, too. . .         

/

[dougpete]

Thanks Don -

So I got some 2x6's at the big box store which are very pretty and say "Premium" and "Stud", but do not have a no 2 stamp - are they then not up to no 2 spec? Am I being fooled into buying less than true quality by a pretty face?

DougPete

[Don_P]

Premium is a sales grade rather than a structural grade.
Stud is a structural grade, all studs of the same species carry the same design values whether stamped "stud" or "premium stud"... same allowable loads. The premiums will normally have tighter wane restrictions (no bark) and may have tighter warp restrictions.
A #2 is another structural grade that is higher than "stud". It carries tighter restrictions and is given higher strength values. In SPF (the species grouping containing Spruce, Pine and Fir) The grade is actually #1/2... both grades have been rolled into one grade. In SYP (Southern Yellow Pine, 5 species) #2 is broken down into more grades, #2 non dense, #2, and #2 Dense, each with different allowable loads. #1 and #2 in SYP spans 6 grades. These show how the rules writing agencies have tailored the national grade rule to fit the species those agencies specialize in.

I am not opposed to hand picking. I went to the big box and hand picked stuff that was obviously below grade and carried them into class...junk does get through. The instructor graded the pieces for us and then looked at the stamp to see if it was one of his graders. He would have been scheduling a pop inspection if it had been. The system is not perfect but it is better than the days before standardized grading, that is when indeed each seller made up his own grade rules. That made safe engineering impossible. With the current system I can check a load, determine through tables or calculation what dimension lumber is needed and order that species and grade. The worst stick in the pack should be at least that strength with the others being above that. The ultimate strength on the weak stick in the pack should actually be 2.1 times stronger than the base design value when we break it. The strongest members in a grade may be 5 or more times the allowable strength values for the grade. We are segregating into groups of strength and allowing loads not to exceed the weakest members of that group. You can hand pick the "cherries" from the group if you know what to look for. I tend to order a bit heavy and put the best wood in the highest stress areas while putting the middle of the road stuff in lower load areas. The stuff that is barely on grade is cut down when possible for lower loads or shorter spans and then for blocking.

I'll try to scan in and post the stud and #2 grade pages from the NGR
NeLma also has grade books for download on their website. It isn't all in the books though.