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Cant stress. Swing and Band Mills

Started by solidwoods, October 19, 2003, 07:00:56 AM

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solidwoods

Hey everyone.
This has to have been asked but I havent seen it (if you know of a post/thread about this,please post us a link).

I see pics of swing type mills 1blade and 2 blade, cutting a log where (how do I say this) END VIEW,,, 1/4 of the log  has been milled away, but removed in a pie shape (90 deg sides).   Not slabbed off  around the center,, like band mills  do.
It looks to me, that if you remove a pie shape piece you would have stress relief or stress creations in the cant (more than milling arround ctr).  Not all logs but more than sawing strictly perpendicular around the center.  I have seen logs that as I saw them, they bow (some durring cut and I mean prety quick).  Even perfectly "boxing the heart" turning each cut, same thickness cuts, each side never more than one cut from being the same as the other sides from the ctr.
I know someone would have to have been around both type of milling to be able to compare the rate of cants that have stress releasing problems durring cutting,  to tell if opening logs pie vs. flat faces
And no I don't think a mills hyd dog system can hold a cant against the back fence and prevent the cant from rising in the middle (re-saw hold-down is different)

Thanks
JIM
Ret. US Army
Kasco II B Band mill
Woodworking since 83
I mill & kiln dry lumber, build custom furniture, artworks, flooring, etc.
If you mill, you'll be interested in some of my work in one way or another.
We ship from our showroom.
N. Central TN.

Captain

Hey Jim, I'll take a whack at explaining the experiences that I have had with stress in cants.  For the record, I have run a couple of Woodmizers, and owned a Logosol chainsaw mill, so I know about the presentation of stress in cants while cutting.  I now own a Peterson WPF, and speak from experience of making boards WITHOUT making cants first.

When cutting oak, especially quartersawing logs of smaller (16 to saw 24") size with some spiral growth patterns I had the most difficulty.  It was a common occurrence when making the heavy slabbing cuts necessary to quartersaw with the Woodmizer or the Logosol to have the slab start to lift - sometimes as much as a foot - before the cut was complete.  I knew I was in trouble with the log...there was little way possible to make straight quartersawn lumber of consistent thickness and width.  You are reduced to turning the cant for every cut to minimize the variation in the boards.  The process is more labor intensive and long, and the product is not as good off the mill as I would like it to be.

Now for the Swing blade style of mill.  On the same type of log, There is nothing I can do to stop the board from twisting and turning after it is released from the cut.  However, there is no turning of a cant to minimize variation (there is no cant) and the lumber that comes off is consistent in width and thickness.  How is this?  The future board is being supported by still being attached to the rest of the log, until the cut is completed and the board released.  It works great.  This is true until you start getting tho the bottom of the log that may have stress.  Stress in the bottom of the log is combatted by proper cutting, and using a support "spine" to keep the remainder of the log from reacting to the stress.

Undoubtedly, many of you have seen the pictures of how a swing blade mill progresses down the log.  Typical designs enter from the left of the log (as the operator is standing) and finish on the right.  When the log is flattened on the top, the operator returns to the left and starts the process over.  When approaching the bottom of a log that has been presenting with stress, I am careful to leave some support on the right side of the log of the log, rather than just cleaning off the top.  This is a picture of a Maple I finished last night just to give you an idea.

In this example, you can see I was going after maximum recovery.  On a "stressful" log, I would have left a bit more on the right, a bit taller for additional support to keep the bottom of the log under control until I was done.

I asked the folks at Peterson about stress in logs before I bought the mill.  Their answer was "due to the way that this mill cuts, stress is not a problem"  they were right.  Again, there are times that I get boards that are not straight, but that is not the mill's fault.  At least they are consistent in thickness and width, and that is more than I can say for my experiences with bandmills and my chainsaw mill.  Plus no turning cants!!!

Hey, all mills have their place.  Honestly, there are times that I think I want a small bandmill basically to resaw cants and have kerf savings.  Last night in that big maple you see the remainder of, the log scaled 280BF and I got 272 out of it.  Not too bad for a circle mill cutting 1 1/8 inch stock.  Maybe I don't need one.

Captain

Fla._Deadheader

  FINALLY 8) 8)  This is the problem I have encountered with that DanG Aus. Pine. The smaller logs will be tough to get real good lumber from, but, anything over 16" should get some nice yield.  Thanks for splainin that, Cap. 8) 8)
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

Gus

"How do I know what I think unless I have seen what I say?"

DanG

Good job of 'splaining, Captain. :)   That "attached slab" on the off side of the log would tend to hold the original shape of the log. Liken it to the difference in rigidity of a piece of angle iron to a piece of flat stock.

To be honest, I hadn't thought of leaving it attached for that purpose, and I usually knock it off, but I will use it in the future when it seems warranted. :)

Chalk up yet another advantage we enjoy as dimension mill operators(I consider swingers to be dimension mills, along with the multi-blades).
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Captain

Thanks DanG, "attached Slab" is a great way to term the piece on the offside.  I'ma gonna use that if you don't mind....

Captain

DanG

Shucks, Cap'n!  You can HAVE the term. I'll take the technique! ;D
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Captain

I took the opportunity before I declared this afternoon a rainout to take a series of photos illustrating another little understood characteristic of swing/dimension mills.

I was quartersawing a 4 foot long low quality oak log this afternoon, and I wanted to show how defect can be removed from the product in the sawing process.  I had already started the log, taking vertical boards off the top, and was into the low grade section in the middle.  The log was about 24" in diameter.

Next, the edge is cleaned up

Next I removed a board until the edge of my substantial defect, the board only ended up 3 1/2 inches wide, and did have a knot on the close end.

Now, I removed a larger board to remove the substantial defects in the middle of the log.  All of the defects are in one piece.  Sometimes, I'll take a couple of stickers out to remove small areas of defect.  I can literally cut out as much or as little as necessary.

Now the remainder of this layer yielded two fine 6" wide quartersawn boards with nice ray pattern.

I always found it frustrating when cutting with bandmills or my Logosol to open up a cant and find defects inside it.  With a swing or dimension mill, you have better opportunities (in my opinion) to control your defects and maximize your high grade yield.  

Hope the rain stops soon.

Captain

ARKANSAWYER

   I have a real problem with someone telling me that as a swing mill cuts from the top that the log will not move under the saw.   I have split several 24 inch logs in half and watched them bow.  I split 12 inch erc's for benches and they bow.  
   Now if what you say is true then I can sit a log on the deck and clamp it and start sawing from the top and when I hit the middle I can flip it 180 degrees and it sit flat on the deck of my mill and then saw it to the deck and it stay flat. ???   Not going to happen.   As you remove part of the wood the log is going to move.   Smaller logs will move more.  I will grant you that most of the time it will not be noticable and some times alot.   I have had hickorys jump from my hydralic clamps so I know about stress.  I have sawed with a swing mill and the oak log did bow up and we went to sawing vertical boards.   Since each cut was just a little off it did not matter much.  
   Even when I ran a big circle mill the logs would move some if I took to many cuts from one face.  But maybe they just do this in Arkansas where trees grow on the sides of hills.
ARKANSAWYER
ARKANSAWYER

Jeff

I didnt read that they dont move, what I was reading was a way to saw lumber while minimizing the movement using that side slab technique. I imagine once the top is leveled off ya get a rocker.
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

Captain

That's right, Jeff.  Toward the middle (in a small log) or bottom (in a big log) I start to leave the attached slab on the side.  Sometimes I go back after the log is nearly done and recover a board out of the side slab or two out of it if it is worth it.  I try not to do it when quartersawing, as these boards are recovered vertically out of the side slab and therefore are flat sawn.  In a big log, that slab starts to look like a miniature stairway as I reduce the cut width to follow the log (see the first pic I posted).  I also get an early warning that the log has stress.....if I start pulling boards off that are curved and spring as they release, I definately leave a substantial side slab.   In my bandmill experience. sometimes stress snuck up on you and you were reduced to turning constantly and making thin cuts to get lumber of consistent thickness/width.

If I plowed the whole thing off flat, you bet it would move.  If I do not leave a substantial thickness in the side slab (substantial thickness is relative to the original size of the log) it will still move, but not as much as without that support.

Awful hard to make an attached side slab with a band mill.

Anyhow, I will repeat, the boards sure will bow and twist ONCE THEY ARE RELEASED if there is stress present.  

I can honestly say that since I've been sawing this way with a swingblade mill, I've not had nearly as much trouble with stress.  (In sawing that is :-/)

Captain

Bibbyman

Very good question Solidwoods,  and very good answer Captain. I was expecting to see a swinger at the Mid-West Forestry show but none were there.  

It's true,  with band and circle mills,  'boxing the heart' only releases the stress on one side at a time – thus only approximates keeping the cant square and straight.  Some times the stress variation cancels out and sometime it accumulates.

On our old manual Wood-Mizer, the clamping system only held the cant against the back supports.  It didn't really hold it down.  The older style hydraulic mill with the flap clamp,  didn't really have any hold down force either.  You pretty much had to turn the cant to release the stress evenly.   You could saw right down and have relatively even thickness boards until you got to the last one that would be minus all of what the other boards gained.  

The new style WM dual plane clamp does hold the cant down and can to some extent pull some of the bow out of a cant that is already bent.  

When sawing dimension lumber 'thru and thru',  I'll often block out the cant and then clamp the cant and saw all the way to the bottom without re-clamping or turning.  This has proven to provide boards of true thickness.  When sawing for grade,  we turn the cant anyway.  When the grade is gone,  I clamp and saw all the way to the bottom.

The hickory that jumped out of ARKANSAWYER's new WM dual plane clamp is a rare exception in my experience.  Cants have sprung free of the clamp on our Wood-Mizer but I've suspected I neglected to get it clamped tight enough to start with or I've pulled the HD lever by mistake and released it.

Logs is logs – no matter what blade cuts them.  I suspect bigger logs tend to show less stress because proportionally less material is removed with each cut.  Taking a 4/4 cut off a log 24' in diameter is a relative small amount of it's total volume.  Cut the same amount from a 6" log and it's the majority of one half the log.  SPRONG!
Wood-Mizer LT40HDE25 Super 25hp 3ph with Command Control and Accuset.
Sawing since '94

Percy

Attached Slab...I get it. The "L" shape is much more resistant to flexing than a simple square/rectangle. Ill have to spalin this to the local swingers as Ive worked on one(Lucas 8/25) and the guy running it never used that technique. Learn somthin new every day..Thanks Captain.
GOLDEN RULE : The guy with the gold, makes the rules.

Bibbyman

Now if could just invent a process to core a log like an apple,  we could saw it inside out.  

Make you wonder what new technology will evolve.   I know just a few years ago we were arguing about band saws vs. circle mills.  But when you look back at history, circle mills are relatively new.  Band saws probably date back as far if not further.  Even the pit saws are really a band blade that doesn't go all the way around.  

What's next?  Laser?  High-pressure water?  
Wood-Mizer LT40HDE25 Super 25hp 3ph with Command Control and Accuset.
Sawing since '94

DanG

Hmmmm! Sawing inside outards, huh?  Sounds like a job for Deadheader. :D  Actually, I was thinking more of a climbing sawmill, so's ya could just send it up the tree an it would just drop the boards back down to ya.  8) 8)

Oh well, it would probably turn out like my telephone co. career. Fiber optics came along and stole my thunder just as I was making some real headway with my "modulated steam" idea. :-/ :'(
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Bibbyman

How about getting a tree to grow up inside of some square tube mold?  When it gets to be say 16"x16"x20' long,  cut it and pop the mold off?  

It'd make everything run more efficient except rolling it. :D
Wood-Mizer LT40HDE25 Super 25hp 3ph with Command Control and Accuset.
Sawing since '94

KiwiJake

Hey Arky, about that super swinger you were looking for a while ago, met a guy in gisborne, his Peterson mill is three years old and his son has put out 12 00000 board foot with it in that time. :o  He's trading in for an automated.

KiwiJake

I just did my math and it works out to average out at 5200 board foot a day, 6 days a week @ 640 board foot an hour, with no holiday! Something seems terribly wrong with these figures. Or he needs to lay off the steroids. ???

HORSELOGGER

My take on reading Captains excellent replies and pics is that he is trying to say that even though there is stress in a log , the swing mill deals with it better and still cuts dead on lumber. If that is what I am understanding you to say Captain, I am thinking you maybe have'nt sawed a whole lot of lumber on that thing yet. If a log wants to relax to the left or right , or bow up or down int center, it will typically do it as you release a board. When you finish a 6 or 8 inch deep vertical cut, and remove the board to stack it, by the time you go for the next cut, the log will have bowed, and your next board will be a thick/ thin torpedo special.Aint nothin a swinger can do about that. I am only adding this comment in the interest of clarity for those reading who dont have a mill yet or might read your comments and get the impression that swingers never miss cut a board. They certainly do.I love my Peterson mill, but logs are logs and stress is stress, and you can only do so much.
Heritage Horselogging & Lumber Co.
"Surgical removal of standing timber, Leaving a Heritage of timber for tommorow. "

Captain

Hey Horselogger,

Agreed, agreed, agreed.  There was (and still is) a learning curve involved for sure...how to bunk to logs and dog them properly to prevent miscuts from log rocking was the biggest part.  Properly wedging the slab to prevent rolling from the weight of the "attached slab" another.  Still a third, properly supporting the bottom slab as it becomes thinner to get that last board out of the log...probably the hardest and least accurate operation on a swing blade mill.

Sometimes the swing blade mill is limited by its virtue of being easily transported.  Others have made permanent sets of tracks and sawbeds with more cross rails and dogs - I have thought of the same to setup here on the property and go portable with the alumininum track setup.  The permanent set with more positive dogs in theory should cut down on operator induced miscut variables, such as the log shifting or rolling.

BTW, another tactic that Vermonter taught me on smaller logs to help relieve stress is this:
Cut the boards vertically.  Instead of cutting one board at a time, make a series of vertical cuts across the log defining the thickness of each board.  When the vertical cuts are finished, make a horizontal pass to undercut all of the boards at once.

This helps the problem of smaller logs bowing as each board is released

Thanks again, Horselogger

Captain

ARKANSAWYER

KiwiJake,
  If a fellow saws 1.2 million bdft in 3 years that is not bad.  That is just 400 mbdft a year, or if he saws 300 days a year then it is just shy of 1,400 bdft a day or 2.5 hours of sawing with a swing mill.   I would call the man who does that a Stud Swinger for sure.   But if a Stud Swinger could put out 1.2 million a year then he for sure would be my hero.  They say a swing mill can put out 600 bdft an hour so if he sawed 8 hours a day and 300 days a year then he would put out 1.4 million bdft.   Not bad.
   Captian,
   Dave and I soon picked up on the vertical cuts and then release horizontal after the mid point to get better boards.   In that side piece is seems like you are leaving some of the best wood.   After all FAS comes from the first and second cut on the log. ;D  I saw that on TV.
   I am glad that Horselogger and I agree that them DanG logs willl move on a man no matter what.   Captian I get some hickory that you can swing on and you will think that you are sawing a snake.
ARKANSAWYER
ARKANSAWYER

Tom

Have you tried pouring a little Alka-Seltzer on the log to relax it and leave the truck door open with some soothing country playing on the radio?

Kevin

Try sitting on a carpet and playing a flute.  :D

HORSELOGGER

That just makes the snake come outa the basket
Heritage Horselogging & Lumber Co.
"Surgical removal of standing timber, Leaving a Heritage of timber for tommorow. "

KiwiJake

I think I muddled up the numbers, 1500 board foot a day is around what he's been putting out. I kinda thought I was telling a fib at first, I guess it was a practical number.

How about this... a lady named "Teressa", bought one of Carl Petersons first mills, a chainsaw powerhead type, she did 320000 board foot in her first year. The next year she upgraded to a hydraulic type and produced 600000 board foot. I could probably post some pics of the write ups a magazine did on her. Does a  "SHE STUD" count? 8)

Hey man I've cut logs that have folded inside out with it's first slice, it still got cut.

ARKANSAWYER

  If she can cook I might think about moving :o :o :o :o
   I just can not find any one here in the States that wants to work one that hard.
ARKANSAWYER
ARKANSAWYER

HORSELOGGER

Ultimately, the impressive swinger output numbers , at least that I have seen, are always in big softwood. I wonder if there might be some guys in the Pac NW that are sawing all day , every day with a swinger? If a guy ( or gal ) wants to saw, and saw only for a living, I dont beleive a manual mill of any kind is gonna get the job done. Especially if they have to buy logs competitively and sell on the green wholesale market. The margins are just too slim for a lower production manual mill. In hardwoods, with log prep, loading logs to the right face, and all the general and usual stuff that goes with a day of milling and keeping things organised, an average day of sawing 4/4 material for me , working alone would range from 800 bft in small logs, to 1200 plus in 18 to 20" plus logs. I have almost tripled those numbers, though when sawing dimnesional lumber out of pine logs, and having a helper. The opening face is nowhere near as critical to me on a pine log as it is on a nice cherry or red oak. Also I have the Hydraulic version Peterson ;) ( in other words, I usa a skid loader to load logs, move lumber , slabs and sawdust.) In the old days, when everything was a hand job, the material handling took up more time than the sawing... Anyway... Arkansawyer, the guy who runs a buy logs/ saw for the wholesale market with a swinger is maybe not out there, but the people who have include a swing mill as part a diversified and creative overall business plan are using it as a very effective tool , but only as one faccet of there operation. I saw untill I dont need any more lumber for the kiln or for an order, then go do something else.After abou a week of just sawmilling, I am ready for something else to do, as I have ADD and get bored easy :D I would not want to do any of the things that make up my business exclusively, as any of the can become a drag in large doses. I enjoy the overall diversity, but some would not be able to enjoy the constant change and varying problems and challenges that come with the territory.So... I am not a super swinger , I guess, but the swinger is a super part of my operation!
Heritage Horselogging & Lumber Co.
"Surgical removal of standing timber, Leaving a Heritage of timber for tommorow. "

KiwiJake

Horselogger, are you form the states? I did'nt even know we exported the hydraulic type over there, when did you buy it and whats powering the hydraulics? Just curious.


Jeff

He told ya Jake. :D

( in other words, I usa a skid loader to load logs, move lumber , slabs and sawdust.)
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

KiwiJake

Carls mark2 mills were powered through a tractor PTO or a trailerised 50hp hydraulic powerpack (still the push pull version). But I get it... ::)

Horselogger, given a forklift and an automated swinger and a good load of logs, at the end of the day on my own I could have some real production figures. If I was on my own with a manual mill those figures would be reduced by half to a third I would think. Terresa's production rate was just a little over amazing I wreckin (2500bf a day). I've cut a lot of hard wood and our 27hp 6tooth blades love the stuff. What size horse power are you running on your mill?

HORSELOGGER

Jake, I have the 24 Honda, 8 tooth blades. Regarding the daily production numbers.... This is something that would be good to clarify, as it comes up from time to time on the forum.I personally dont put a lot of weight on raw bft per hour or day numbers any more, unless the person talking can be more specific about what a "day" of sawing includes.A sawyer with help, hydraulics, deadpiling for shippment to a wholesale yard etc... are going to get more boards a day than me. My day of sawing starts with a clean work area , because moving slabs, shoveling out the sawdust from the work area and piling with the skid loader was the last thing done the night before. That was after all lumber was stickered and put away or covered from the elements.In other words , a "day " of sawing for me is a lot diferent than a full out production operation would be.If you looked at the actual minutes spent sawing lumber, the Peterson mill is very fast and impressive, but because of the other parts of how I manage my sawing day, the overall numbers are not very impressive to someone keyed into that only. On the rare occasions that I do a portable job my production goes up noticeably, as I will have help, and the lumber stickering and clean up are not my problem. 8)
Heritage Horselogging & Lumber Co.
"Surgical removal of standing timber, Leaving a Heritage of timber for tommorow. "

KiwiJake

Yep your right in saying that theres alot more to processing than just milling for sure.
Chears

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