Author Topic: Boxed heart beams or not? (Read 28180 times)

Jim_Rogers · « **on:** October 10, 2003, 05:05:46 PM »

The other day, at the beginning of a timber framing workshop, we needed to get some timbers out of the pile for the frame we’re cutting.
I had cut out all the timbers for this frame quite a while ago and had them stacked up on 4x4’s in one tall pile. The 4x4’s were 4’ on center and each row of timbers weighed about 1000 lbs as that’s the limit for my forklift.
When we removed the lift of 2” stock that was on top of the pile of timbers, working as a weight to hold them straight and flat, we found one of these timbers had “taken off”. Shown here, it’s the one on the left:

Now you can see the heart of the timber in the center on the end facing us, as it’s marked with a red lumber crayon, as a plus sign (+), or cross hairs for you hunters. But this heart wandered a bit as it traveled down the timber from this end towards the other end. And about where the forks are it came out of the top for about 3” and then went back in. It was centered on the other end. This wandering heart of the tree, I believe is what caused it to not stay straight. The other two next to it were in the same row under the same load and are very straight. The middle one is a hemlock and the right one is an eastern white pine same as the bent one.

While doing another job, cutting up some dunnage blocks, for a customer who was going to use them to block up his cottage while they dig out a cellar, I decided to try cutting some 6x6’s in different patterns to see what would happen to them.
Years ago I saw this photo in the Kiln Dryers handbook and it’s been used many times by many people:

As you can see by this photo if you were to mill timbers that weren’t boxed heart you could expect some distortion when they dry. You can see the one that’s in the upper right side that looks like it’s a diamond shape. But it appears that if the timber were milled out in the right spots you might be able to make straight timbers that won’t distort much as they dry.
So I tried, with a very large log, to mill out some 6x6 timbers in a pattern like this:

I thought that if the timbers where in the 12, 3, 6, or 9 o’clock position as well as one in the middle that they might not move much when they dry.
Well I cut this very large log into nine 6x6’s. Three across and three high, like a tic-tac-toe pattern.
These three timbers are the ones from the 9, middle, and 3 o’clock positions.

The nine o’clock timber has my left glove on it, the three o’clock timber has my right glove on it and the middle one is in the middle.
You can see that the 9 o’clock timber has “taken off” and bent quite a bit. (You can see the opening in between the timbers as the ends touch each other). I knew it had because it did as soon as I released it at the mill. It almost sprang off the cant.
The middle one is some what bent also, and the heart doesn’t truly run down the center of the beam. The 3 o’clock one seems to be the straightest of them all.

These bent timbers were not wasted as the customer just needed them 3’ long so they were all cut up and sold. And they were straight enough for him to use.

I’ve set aside the 3 o’clock timber for the next workshop and also milled out a boxed heart replacement beam in case it moves before we get to use it.

This was kind of an experiment in milling timbers for a timber frame. And I thought I’d show you what happened.
You should always “box heart” your beams as they are the straightest and strongest. I hope this experiment has been helpful to you.
Jim

ohsoloco · « **Reply #1 on:** October 10, 2003, 05:28:45 PM »

If the pith isn't in the timber, it is also possible for a knot to run the entire way through a timber which would not be good for the strength of the beam.

Greg · « **Reply #2 on:** October 10, 2003, 07:32:10 PM »

Quote

snip...

This was kind of an experiment in milling timbers for a timber frame. And I thought I’d show you what happened.
You should always “box heart” your beams as they are the straightest and strongest. I hope this experiment has been helpful to you.
Jim

Excellent writeup Jim. Thanks for taking the time to share your experiment. Good to see real life experience back up the book diagrams.

BTB, in your milling how quickly do your customers typically cut the joinery and assemble?

I think thats the big reason to cut and assembly quickly green, to help stabilize the beam, right? If it can't move, it can't bend!

Greg

Oregon_Sawyer · « **Reply #3 on:** October 10, 2003, 11:07:08 PM »

I took my builder to see the beams I had cut for the timberframed trusses and perlins for my log house. He hadn't seen them before as I had them stored off site.
I believe he was concerned they would be good enough until he saw them. Most were box heart doug fir. 7x7 and 6x7. But the one he commented about was a free of heart almost clear 7x9 that was as straight as the day it was cut. These were cut oversize but he didn't want me to trim the two biggest ones at all.

These aren't quite true timber frame as we are using plates and bolts to make the connections. My welder is making the plates up tomorrow.

Jeff · « **Reply #4 on:** October 11, 2003, 05:46:34 AM »

Thank-you Jim! Great demonstration. We get comments all the time about boxing the heart and you have just create the "go to" post for discussion examples.

Jim_Rogers · « **Reply #5 on:** October 11, 2003, 06:12:03 AM »

Ohsoloco:
Your right about the through knot. You can mill a 6x6 with a four inch knot in it, but it won't be strong. Whoever mills timbers should understand the grading rules for their area and understand what a grade 2 or better timber looks. And what size knots can and can't be in order to comply with the rules.

Greg:
I've cut beams for barns that have sat for a couple of years before they were assembled.
I've cut beams for a timber frame thatched roof house in Maine, where they received the timbers in January and they assembled the frame in July.
Each customer has their own time table and every one is different.
If timbers are cut correctly, and stacked properly they should be OK for a while. Maybe I should have blocked my timbers at 2' centers instead of 4' centers. That may help prevent bending next time, I don't know if it will or not but I'll try it with the next frame.
One reason the joinery is cut while the timbers are "green" is that the wood is easier to work than when dry. Another reason to assemble as soon as possible is to not allow the timbers to "take off" and bend. They are some what restricted as they are being held in place at several different points, and hopefully these will keep the timbers "in line".

Oregon_Sawyer:
If I understand your intended assembly, that is using bolts and steel plates, that type of heavy timber construction is called "Post and Beam" construction.
When you build a timber frame building you use posts and beams by all the joinery is wooden. Using mortise and tenon joints held together with wooden pegs is called "Timber Frame" construction. That is the definition of both terms, although most people don't always understand the difference in the names there is a major difference in the type of construction and methods used to build each type of building.
Some times in timber framing we'll use a steel plate or other types of steel fasteners but we always try to hide them from view.

Jeff:
Thanks for your comments.

Jim

ohsoloco · « **Reply #6 on:** October 11, 2003, 02:56:27 PM »

Jim, I'd also like to add that you did an excellent write up about boxing hearts on beams...nice examples too

You mentioned grading beams, could you tell us a little about that, or show some examples of different grades of beams?

Jim_Rogers · « **Reply #7 on:** October 11, 2003, 05:06:06 PM »

ohsoloco:
Well, understanding grades of beams can be a difficult subject, as there are different lumberman assoications around the country and I'm only familiar with the one in my area.
I'm not sure if all the "grade rules" are the same with each association.
Hopefully they are, maybe other can comment on whether they are or not.

ohsoloco you're from PA what organization controls your area? In the northeast it's NeLMA, are you under those rules where you live?

Here is a shot of the cover of the grade rule book:

Opening the book to section 6, Beams & Stringers, Posts & Timbers, the grade rules take up the next 12 pages.

It could be a little difficult to explain it in this forum, but I'll work on it a little.

First, let me tell you a story about having a traveling inspector come here to my mill yard, to inspect some timber for a barn, being build in a neighboring town.
The building inspector require these timbers to be inspected as they were milled from recycle beams from some huge factory that had been torn down.
The customer had his carpenter/house-wright give me a list of what he wanted milled out of the large 12"x16"x22' timbers. The list included things like posts, beams, rafters, girts, purlins, and such. Which I did my best to box heart the post as then needed to be the strongest. The rest of the parts came off the sides of this timbers. These timbers were fir but I'm not sure what type, but old growth as the inspector knew by the number of rings per inch, about when they were milled from trees.
One of the first things he asked me when he was ready to start inspecting was "what is this timber going to be?" He wanted to know whether it was a post or a different timber. That's because the grade for posts can be a little lower than the grade for a horizontal beam or something like a rafter.
Horizontal beams or rafters come under the "stringer" category, which require a higher grade.

Posts are strong as they are used in compression.
I'm trying to find a good example off the difference between a grade 2 post and a grade 2 beam.......
I seem to remember, for example, that a grade 2 post, say a 5"x6" can have a 2" knot in the middle of one side face. Where if this was a beam or a stringer there couldn't be any knots at all at the ends or along the center line of the wide face except in the middle third of the timber.
It's very hard to describe as there are so many rules.

When I went to a grading workshop they told us to get a rule book and read a section at a time. Learn that section and then when you're looking at timbers remember the grade rules for that size and see how it applies. Then when you understood that section, read another sections and do it again.
Well if you read the section on beams and stringers, posts and timbers, and you understand what a grade 2 timber beam or stringer is, then you should make all your timbers that quality or better. The reason for that is that you can't be sure that this low grade post you just made will be used as a post. The customer might change his mind and use it as a beam, and if he does then it doesn't meet the grade rule for a beam.
So I try to make all my timber meet the grade rule for stringers and then if the customer changes his mind and makes it a post, who cares, it's strong enough for a stringer so it great for a post.
I've tried to make all timbers whether they're posts or beams grade 2 or better using the stringer grade 2. Then it doesn't matter where they are used in the frame.
By doing that I just have to understand what the rules are for grade 2 stringers. Not all sections and all 12 pages of this section.
Now when the code say grade 2 or better that just means if grade 2 will allow a 2" knot and you've got 1" knots well then it's better than grade 2. And it complies with the code.

I'll try and think up some stories and see if I have some pictures to show you different grade timbers.
Jim

beenthere · « **Reply #8 on:** October 11, 2003, 06:27:27 PM »

Jim
The grading rule you referred to can be picked up on this link, for anyone interested in looking at it further.

http://www.nelma.org/graderule.asp

From there, the section referring to the posts, beams, and stringers can be seen.

Oregon_Sawyer · « **Reply #9 on:** October 12, 2003, 11:35:52 PM »

Jim: I learned something today. So my constuction would be post and beam.

My builder builds log homes and had metioned he would like to someday do a timber frame home. I told him we could use some ideas in my home.

It was the engineer that came up with the post and beam design.I did some checking into actual timber frame trusses but would have had to reengineer the system because it was going to change the weight carry points which would also have changed the way the logs were going to go up. Next building maybe but not this one.

My welder got the plates made Sat. He said it took him 5 hours to drill the holes there were over 100 in the 32 plates.
Sunday I resawed the truss beams the most any were out was just under 1/2 in of sweep in a 20ft beam. They all came out quite nice. One beam did have a fracture in it but we will use it for a shorter member and cut it off.

Jim_Rogers · « **Reply #10 on:** October 13, 2003, 07:57:10 AM »

beenthere:
Thanks for that link.

Oregon_Sawyer:
Good luck with you're project. Sometimes you have to use steel to satisfy those engineers.
If possible post some pictures sometime.

Jim

ronwood · « **Reply #11 on:** October 14, 2003, 12:16:35 PM »

Jim_Rogers,

What would happen if you made the post say 7x7 in, let them dry and then recut them down to a 6x6 in. post to get some of the bend out of them. Would the post be stable once it dried out some?

Ron

Squirrell_Boy · « **Reply #12 on:** October 14, 2003, 12:43:55 PM »

Jim: Just wondering did that timber bow in the direction of the bark side? Did you cut down the tree of those timbers so that you knew how they were growing? Could this be due to reaction wood or spiral grain?

Minnesota_boy · « **Reply #13 on:** October 14, 2003, 04:52:36 PM »

Ronwood,
I once cut a couple 3/4 inch strips off the side of a nice straight 2x6 bur oak to get nice straight strips. The oak was air dried for at least a couple of years inside a barn loft. The strips bowed about 2 inches in a 6 foot cut.

If the beam has a bad bow, I'd expect it to bow some more if you cut the sides off.

Jim_Rogers · « **Reply #14 on:** October 14, 2003, 05:00:38 PM »

ronwood:
I'm not sure if that would help. If I understand it correctly, it takes about a year to dry 1" of lumber so a 7x7 wouldn't dry that much in 6 months and then you'd be milling it off to make it a 6x6.
But, I haven't tried that experiment yet.
The timber pictured above was in the pile for over a year and as you can see it "moved" quite a bit. Looking at it I'm not sure if I cut off 1/2" whether or not it would straighten it out.
I think it all has to do with tension in the tree/timber. If you have a straight log and you mill it with the heart/pith in the center on both ends, hopefully without the heart/pith wandering around much, it should stay straight.
A year ago April, I took a course through the guild, where we took apart a barn that had been together since 1856. Now those timbers were dry.
When we went to put it back together again a 36' plate had a twist in it. We had to induce a opposite twist to get it back together. It, the plate, went together again with no problems, other than that twist.
I wasn't near the plate when they removed it from the tops of all the posts so I don't know if it was twisted in place or whether they had to put some pressure on it to get it apart or not. But it was something to watch the masters put a twist in the plate in order for all the tenons to line up and slip into their mortises again. There are tricks to each trade, some you only see at a raising.
You should try to go to every raising you can.

Squirrell_Boy:
As you look at the picture above the bark sides of the left beam is on the left, the bark side of the right beam is on the right, 9 o'clock and 3 o'clock. The left hand, 9 o'clock, beam bowed toward the middle, as shown by the gap between the left hand side one and the middle one.
I didn't cut it down, it's been in my yard for some time, as it had a rotten spot on the butt end, and I was waiting for some shorter product that I could make from it.
I would assume it was reaction wood or just tension in the log. I don't believe it had any spiral grain.

Jim

Jim_Rogers · « **Reply #15 on:** October 14, 2003, 05:05:51 PM »

Minnesota_boy could be right. How do you know you're cutting off the correct side to relieve the stress? You might cut off the wrong side and create more.

It's hard to tell what's going on in there.

Jim

SawInIt CA · « **Reply #16 on:** October 15, 2003, 08:06:28 PM »

Hmmm. I sell a lot of Doug-Fir timbers and most of my customers want FOHC....free of heart center. they dont check as much as boxed heart. It does take a big tree thou as they seem to twist or bend if either side is too close to the pith or the bark. If they are not they almost always stay straight. I guess both ways have their positives. I cut some 24' FOHC 8x12s the other day and all seem straight.....I sure hope they stay that way.

Dave

Mark Gillis · « **Reply #17 on:** October 16, 2003, 05:33:11 AM »

Hi All,

It seems to me that the reason some FOHC timbers and Boxed Heart timbers do not move as much has to do with the presence of sapwood. If the 9 o'clock piece in Jim's photo had more sapwood than the 3 o'clock piece, I'd expect the left face of the 9 o'clock piece to shrink more than the rest of the piece, resulting in either twist or bowing (as seen).

Just my two cents ($Canadian = 1.5 Cents $US)

Jim_Rogers · « **Reply #18 on:** October 16, 2003, 07:01:11 AM »

Dave is right FOHC beams won't check as much as boxed heart beams.
As to why they stay straight, Dave's Doug-Fir, could be the quality of the tree and the amount or not of sap wood as Mark has mentioned. It could be the type of wood. Wood is very variable, and each tree is different, depending on where it grew, on a hill side or on flat ground, for example.
My experiment log may have grown on a hill side and therefore have some tension and compression wood in it. Or the bowed timber could have more sapwood in it.
It's hard to say, why one my 9 o'clock timber bent and the 3 o'clock timber didn't. And I've had boxed heart timbers bend.
Jim

SawInIt CA · « **Reply #19 on:** October 16, 2003, 11:45:21 AM »

Thanks for all you input Jim. I will do a little testing as well next time I cut beams.

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Author Topic: Boxed heart beams or not? (Read 28180 times)

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