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Author Topic: Size does matter  (Read 3997 times)

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Offline GeneWengert-WoodDoc

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Size does matter
« on: March 03, 2013, 09:13:04 PM »
Consider that you have to saw 500 2x6s.  What green sizxe should you use so that when dried and planed, they will (except for warp) clean up at 1-1/2 x 5-1/2"?  A suggestion was to add 1/4" to the thickness, which is a good value.  A similar suggestion for the width would add 3/8".  So, the target green size is 1-3/4" by 5-7/8".  The cross sectional area is 10.28 square inches. 

(CAUTION:  Do not misread this and think that I am suggesting these sizes are correct for your mill.  This is only an example to illustrate what excessive oversizing costs in terms of yield.)

Now, let's assume that just to be sure, you add 1/16" extra to the width and thickness, but you really would not have to.  Now, the area will be 10.76 square inches.  The area increase is 5%.  What this means is that the overall lumber yield from the log will be decreased by around 4% (it is under 5% due to saw kerf).  You will have to saw 4% more logs to get the 500 pieces you need.  (Of course, with trees being so plentiful, we really do not have to worry about conserving our resource, do we?)  Plus, the larger pieces will take longer to dry and use 5% more energy in kiln drying.  And the will be 5% heavier.

BOTTOM LINE:  Excessive green lumber size does matter.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline GDinMaine

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Re: Size does matter
« Reply #1 on: March 03, 2013, 09:41:30 PM »
Doc Gene,  Your posts are always very interesting to read.  You explain, that things are not nearly as simple as they seem.  I wish some customers would read them too. :P
It's the going that counts not the distance!

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Online Jeff

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Re: Size does matter
« Reply #2 on: March 03, 2013, 09:59:24 PM »
And sometimes things are made much more difficult than they need to be. I was told one time that I didn't need to know how to rebuild a trasmission in order to drive a car. That advice can free your mind and allow you to accomplish things you may never have done if you stayed mired in the details.
Just call me the midget doctor.
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Offline GDinMaine

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Re: Size does matter
« Reply #3 on: March 03, 2013, 10:23:11 PM »
You are right. I don't need to know how tires are made to drive a car.  But it is still interesting how they are made, even tho it helps me none that I know.
It's the going that counts not the distance!

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Offline Magicman

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Re: Size does matter
« Reply #4 on: March 03, 2013, 10:50:31 PM »
I regularly saw 75+Mbf of framing lumber from SYP every year which ain't bad for a peckerwood sawmill and an ole man.  That is also probably much more than most other members here saw.  Over 15 entire homes and many more sheds, barns, and utility buildings have been built using my framing lumber and I have never been asked to return and resaw or resize any lumber.  I can assure you that I do not saw 1 3/4" X 5 7/8".  (And by the way, there is a problem with the {now corrected} 7/8" figure used in the 4th sentence.)

Members here have watched me felling, skidding, sawing, drying, and using my framing lumber on this Cabin Addition thread.
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Offline hackberry jake

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Re: Size does matter
« Reply #5 on: March 03, 2013, 11:54:29 PM »
Yep I saw em at 1.5 x 5.5 and screw em up green, or sticker em till I have enough to start building then screw em up.
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Offline Brucer

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Re: Size does matter
« Reply #6 on: March 04, 2013, 01:31:47 AM »
Interesting.

I will only saw an entire log into 2x6 when someone is prepared to pay me 8x8 and 8x12 prices in order to fill a 2x6 order in a hurry. It happens but not often. Even then I keep my really big logs for the big, high priced timbers.

So I worked Gene's numbers into the logs I would normally use (if I'm paid for them) and I found ... absolutely no difference in the number of logs I would have to saw ::). At best I might get an extra 1x4 out of the odd log.

Now some of you don't bother with going down to this level of detail, and I usually don't either. But I have a program in my calculator that will give me a sawing pattern from a given sized log just in case someone wants to get that detailed (it happens once in a while). That's what I used just now to find the 1/16" makes no difference in the yield of 2x6's on my logs.

I'm very wary of blanket statements like that. It will probably work out in some situations but in others it won't.
Bruce    LT40HDG28 bandsaw with two 6' extensions.
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Offline woodyone.john

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Re: Size does matter
« Reply #7 on: March 04, 2013, 01:54:59 AM »
brucer tell us more about your calculater and program please? cheers john
Saw millers are just carpenters with bigger bits of wood

Offline Kansas

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Re: Size does matter
« Reply #8 on: March 04, 2013, 03:39:35 AM »
We don't cut softwood so I don't know if inspectors or builders require it to be dried and planed when being used in a house or building. And I suppose all the rules and regulations vary by state and/or local ordinance. On occasion, I have someone inquire about using hardwoods for framing lumber in a house. I always try to steer them away from that. For beams, a timber frame, kiln dried wall or floor covering, that is fine. But a conventional stick house, I would be very leery of it. I know old houses around here that were done in hardwood. But there are some places pine just lends itself to being easier to work with. I know there are guys on here that cut pine and built houses with it. Magicman, you seem to have done a bunch of it. Do you have problems with shrinkage on pine? Does it become an issue on framing lumber? Just curious.

What the wooddoc says makes sense if you were going to try to produce a lumberyard 2x6, surfaced all 4 sides. I don't know if that is necessary. I know if I tried that with oak or cottonwood, I would have to oversize the width and probably skim off both sides after air drying. Realistically, probably a full inch. Both for straight edging and allowing for shrinkage. Thickness would not matter.

Offline stavebuyer

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Re: Size does matter
« Reply #9 on: March 04, 2013, 04:32:52 AM »
Excellent point on extra thickness; but I think it would apply more to hardwoods cut random width. A market that will accept well manufactured boards green at 1 1/16" vs 1 1/8 will net additional lumber yield.

Offline red oaks lumber

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Re: Size does matter
« Reply #10 on: March 04, 2013, 07:27:41 AM »
first thing its cheaper to go buy 2x6's at the lumber yard. i saw everything full 2x6 dry it then plane it to size, it cleans up 100% and i'll be able to saw alot faster without worring if my cut is real accurate.so the little extra material am using its still cheaper because of the speed i can saw, also when planing i sell my shavings for added value aalso my slabs, so this topic is a mute point for me. just my opinion.
the experts think i do things wrong
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Offline GeneWengert-WoodDoc

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Re: Size does matter
« Reply #11 on: March 04, 2013, 07:36:29 AM »
the point I was trying to make is that a small extra thickness or extra width (1/16") makes an important difference in yield.  I was not trying to suggest that 1-3/4" x 5-7/8" is the correct size.

Actually when you saw a log into lumber with a decrease in size, a simple computer program for yield will not show any yield difference.  The reason is that we will only once in a while  get an extra piece of lumber by saving 1/16", instead of having a thick outer waste slab piece.  Brucers' test showed that.  Rather, what happens more often  is that we get an extra two feet in length in a piece or an extra 2" in width.  This effect has been shown in the more complex log yield programs that include length and taper.  It is included in data and discussion from the US Forest Products Lab.  A large softwood mill today scans the shape of the log and then uses complex algorithms to solve for the best solution, including the price of various sizes of lumber.  It is amazing to see and it is possible to increase or decrease the size, saw kerf, etc. to see the effects.  And it is not just theory, as the results when sawing do indeed match the predictions.

Let's consider hardwoods.  One key for hardwood lumber is that after drying, the customer needs the thinnest piece to be 15/16" thick.  (Whatever value the customer wants can be used.  this is just an example.)  Due to sawing variation, and shrinkage, we would add 1/4" to the thinnest to get the green average target for the sawmill.  (Again, add whatever actual number is correct for your mill.  If we know the species, final MC, sawing variations and grain (Q or F), the calculation is easy.)  So, the green thickness in order to keep the customer happy is, in this example, 1-3/16".  However, if a mill is cutting 1/32" thicker than 1-3/16" and giving the customer 31/32" minimum thickness, that extra 1/32" is translated into just under 3% yield loss.  Again, the piece count will not often change, but many pieces of lumber will be a little bit wider.  A few of those wider pieces (maybe five or so out of a hundred) will have an increase in width that gives an extra BF.  (example:  4/4 x 6-7/16 x 12 is 6 BF, while 4/4 x 6-9/16 x 12 is 7 BF)

The idea of having planer shavings (or other offal) offset the extra thickness losses is indeed valid and should be seriously considered.  In many cases, however, a ton of lumber is worth 50 to 100 times more than a ton of planer shavings.  If this wasn't true, then we would chip a sawlog into shavings instead of worrying about lumber and get more money. 

BOTTOM LINE:  A little bit here and there when sawing adds up to a 3% more dollars over a week or month.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Magicman

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Re: Size does matter
« Reply #12 on: March 04, 2013, 08:04:24 AM »
My problem is the posting of an absolute figure that may be written down and used by a new sawyer.  This exact figure was obtained using facts, figures, and formulas that may not always be applicable when used on an inexact "green log".

The logs that we encounter out here in the real world are not all created equal.  Some may have been felled and bucked the previous week.  Some several weeks and even months.  There also may be some beetle killed logs in the mix.  Then a log from a tree with " to " growth rings will shrink much more than a log from a tree with " growth rings.  When sawing framing lumber, some boards will be flat sawn, some QS, and some rift.  Each of them will shrink differently and different amounts.  That also is a fact.

It is the sawyers responsibility to judge the logs in the whack and adjust the oversize amount accordingly.  I will never ever post or suggest absolute oversize figures to someone because doing so would be a disservice to them and their customers.

Now with all of that being said, certainly the framing lumber that I produce has variations.  Carpenters often ask me if I have ever measured "store bought" lumber?  Yes I have and the variations are sometimes astounding.

There was a home being built close to me using my framing lumber a couple of years ago.  I often stopped by and the carpenters would remark about the quality and consistency of the lumber being used.

BOTTOM LINE:  Framing lumber with some variation is of no ill consequence in the real world.
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

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Offline 1woodguy

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Re: Size does matter
« Reply #13 on: March 04, 2013, 08:36:56 AM »
   I think that everyone should explore different ways of looking at everything
In any business we make a lot of decisions . Lots  of material cost ,time,quality quanitity,and we all decide to do it like we want to.
  sometimes you gain in one area at a cost in another
Here is an example lets say wife and I are talking and....
     Coffee is$11.99 a can nearby store ,and its $9.99 five miles farther
Or I can drive 25 miles and get it for $8.00
Hmmmmm...... Do I take the toll road or the old highway.  Do I drive my truck that fits me or wife's lil car that gets better mileage
  We still have several cans in stock ,should I wait till I am going that way anyway,
wait to see if it goes on sale?
what if the price goes up tomorrow?
Should I go or her?

I think a lot of ideas are worth looking at everyone sees things different
  a friend of mine always eats the specials at the restaurants even when he doesn't  like the choices :D to save afew coins.
 Another always hits the drive thru  to save a minute
Another takes thirty minutes to decide what he is getting and sometimes changes his order after he tells waitress

   so today I may eat what I want to eat and don't care about time or money.
But tomorrow may be different  cause of other circumstances.

 :)
Experience is a rough teacher first you get the test later comes the lesson!

Offline 1woodguy

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Re: Size does matter
« Reply #14 on: March 04, 2013, 08:42:28 AM »
  Magicman,
I posted before I read your post,
And I got to say Yours was well worth reading Once ,Twice!!!
  And then again!

Experience is a rough teacher first you get the test later comes the lesson!

Offline Kansas

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Re: Size does matter
« Reply #15 on: March 04, 2013, 08:43:09 AM »
Concerning hardwoods. We cut, for the kiln, 1" thick lumber. We don't cut on the one inch mark.. We allow 1/8 for kerf. Yet the blade doesn't really take out 1/8 inch. So you have slightly thicker than one inch. Not often do we get a board that will not plane out at 3/4. Some wide boards, with a little cup, need to be ripped in half first. And on occasion we have someone wanting stuff planed thinner, or they will themselves. The only exception we do to this is quartersawn sycamore. Where we true quartersaw every board, sycamore shrinks thickness wise. We will up the thickness there. Quartersawn oak does the same thing, is a bit iffy, but usually have no problem getting 3/4. We did learn one lesson though. We hit extreme curl in a couple of oak logs we quartersawed. Then you could not get 3/4 out of them cutting one inch thick. We can get away with cutting 1" because we do not cut for the commercial markets.

Offline Tree Feller

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Re: Size does matter
« Reply #16 on: March 04, 2013, 08:47:57 AM »
There seems to be some animosity towards Gene and his post that I find puzzling. His point was that sawing excessively oversized lumber was wasteful, produced less usable material, increased costs and was heavier to handle. 

That seems like a perfectly valid observation to me.

Cody

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Online terrifictimbersllc

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Re: Size does matter
« Reply #17 on: March 04, 2013, 08:51:08 AM »
Doc, what I have thought before when I have read this analysis, is that it ought to be qualified for the situations where it works.  It seems to suggest that thinner is better in all sawing situations. For example the analysis must assume that thinner lumber remains 100% useful to the customer because it  doesn't include any amount for losses when it is not. These losses would be weighed against the 4-5% increased yield. 

I often find myself recommending thicker lumber to customers depending on their project needs.  Explaining to them why 1/8" extra is fine for pencil boxes but not for most small-medium size projects.  Why 1/2" extra might not be enough extra for table tops or bed members.  How trying to get an extra board here or there might be a false economy.  Your analysis is obviously mathematically correct including conclusions about minimizing waste. But there can be the situation where none of the lumber is useful because it wasn't cut thick enough.    And even if the 4% extra is delivered off the saw, what good is it if the customer throws the jacket sapwood boards, made wider by cutting the rest of the lumber a bit thinner, onto the slab pile?   And the backdrop to the waste consideration, is that even with cutting thicker lumber, a huge amount of waste is prevented by the sawing done by members of this forum.






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Offline Kansas

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Re: Size does matter
« Reply #18 on: March 04, 2013, 08:53:18 AM »
Magicman, you obviously know what you are doing. I guess the thing that always worried me is such issues as sheetrock. Maybe it has more give in it than I realize. Most of my experiences with sheetrock, well, have been less than wonderful.

Offline 1woodguy

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Re: Size does matter
« Reply #19 on: March 04, 2013, 09:09:05 AM »
  We put up a lot of non load bearing walls that were 2x6 last year
customer supplied  junk materials from lowes and it sucked but he wanted to use it anyway

   Later got talked into the Sheetrock
Used lil power hand planer cardboard and wood shims
Then lots and lots of mud to finish it right
And his comment was that I didn't need to try to get it perfect :D it's just a wall

     
Experience is a rough teacher first you get the test later comes the lesson!


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