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Thread: Tension logs with a Lucas
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25th July 2010, 09:30 PM #1
Tension logs with a Lucas
So I've been away for a little while slicing timber up at Maryborough. While slicing up there (a heap of spotted gum) I had some long spotty's to cut which had some wicked tension in them, so it got me thinking I'd take some pics and do a bit on it to show you good folks
So when using a Lucas, a log with tension does this kind of thing...
you cut off the top bit and it starts to heave up in the middle, due to the sapwood on the bottom still being fully intact. Sometimes this can heave up so much after slicing a layer off the top and then taking a trim cut off the side, you get something which looks like this...
The kerf mark is for a 3" deep layer. Now remembering the kerf on Bo is 6.1mm, you can see from the pic there is at least 6-8mm above the kerf line. So in this case if I just cut the board off normally it would be around 89mm thick at this point in the middle of the beam and 75mm at each end. Anybody out there want to build with sticks of timber like that? I doubt it Also on a log with tension, we can't do a lot about the log heaving up like this, but I can do something to make the timber much more user friendly...
So you open up the log as normal, once you have the face you are working with,
plan your cuts as normal. In this instance I was cutting 6m long 125x75mm and I want to keep the beam as straight as possible, so I take it from close to, but not in the heart and centered across the face to maximise my chances of it coming out as straight as possible. Cut normally until you are ready to start the beam. Cut the vertical side of the beam and undercut half of the face... (I took my pic before undercutting 2.5" - sorry)
after undercutting a portion of the beam, raise the rails back to the top of the scale, then go back over your beam with the blade horizontally, thus shaving off any 'excess' which has occurred from the log heaving up in the centre. This pic shows half of the face after it was shaved back to dimension - imagine working with beams significantly thicker in the middle than the ends, what a pain...
Hopefully everyone out there using Lucas Mills already do this and therefore give their customers the best possible timber, but for anyone new to milling, I hope it makes sense and gives you a way to produce great timberI love my Lucas!! ...just ask me!
Allan.
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25th July 2010 09:30 PM # ADSGoogle Adsense Advertisement
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25th July 2010, 10:29 PM #2
Thanks Sigidi thats clear as mud . But I think I get it. What caused so much scoring in the timber ?. Might have to come tail with ya for a bit, when ya get an other big job
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26th July 2010, 01:20 AM #3SENIOR MEMBER
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Good pics Alan, being a bandsaw bandit i dont know but, have you ever with small logs like that when you are trying to get 5 by 3s out of it,ever turned the log over onto its flat side and cut back down again just to relieve some stress before you get in near the the heart? Also at 6m long in a log that big you are bound to get some movement bud
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26th July 2010, 05:28 AM #4
Good pics, Allan. Tension is something the Lucas does have trouble with and your method is one way of managing it to produce a consistent thickness. I have to say though, if the log has a lot of stress in it, then the boards will tie themselves in knots regardless and you'll be left with a consistently-thick boomerang.
I recently finished cutting an order for grey ironbark beams, 10 each of 200 x 100 @ 5.4 and 6.4. In order to get enough straight beams, I ended up cutting nearly 50 pieces and rejecting the bowed ones, which then got resawn into smaller stuff, mostly sleepers and posts.
I hate grey ironbark.Cheers,
Craig
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26th July 2010, 08:05 AM #5
Thanks Alan, I have never tryed that before but I will certainly give it a whirl, basicly, perform an under cut on any logs that are showing tension, and then raise mill to go back over the top again then do the second vertical then back down again to finish the horizontal. Can't wait to try that. I do not get a lot of tension in my logs, as I've said before, I try to cut logs that have been down at least 6 months, that is my answer to reducing stress in logs and it does help, not all the time but. I realise this is no good for the type of comercial milling you do but suits me.
cheers
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26th July 2010, 11:20 AM #6
Yeah clear as mud - even with pics it's sometimes difficult to understand what is going on without seeing it/being there.
As for tailing, I'm camped up at Maryborough (not far from Childers, around Bigenden way) most of next week if you wanna visit, spend half a day or more if you want.
Nifty, being a swinger, I never move the log once I start. Only time I've ever moved the log was to make very large posts, bigger than the blade could cut, it worked out well, but was very time consuming. On a bandsaw you have a level bed and can roll the log each board to equalise tension better hey? With the swinger it doesn't matter how level the ground is, or if it slopes etc. the next cut is always reference to the last cut, so if the log stays still all is good, but if the log moves cause it's too light or it's rolled out of supports, maybe the sawyer has driven into it too quick, then you have a lot of messing around to do to get back your levels. I don't like moving the log if I don't have to
Craig, I'm only accepting what falls under grading rules to begin with and then also looking at them from the point of view "would I want to use that stick?" if it passes both tests, then it's in, if it fails one or the other - it's out. I've found long spotty to be the most problematic of all the timber I've cut, some species have 'problem trees', but the majority of long spotty I've cut has been rough on tension.
Not been lucky enough to play with grey ironbark
Johnny, you've pretty much got the idea mate. Next big thing is to be able to judge/identify when you need to and when you don't, without going to the effort and time of raising the mill passing the blade over it to find nothing needed trimming off, then having to come back down to finish your board off. You could measure the board and confirm by way of the result from the tape, but again it takes a bit more time and I like to mill as quick as I can to get more timber done in a day. All these logs have been down and stacked in 2 piles since January this year, I just figure it's long spotty and also taking big layers - 1" feedstock doesn't seem to heave up as much, but taking 3" deep layers over 6-8m tends to allow huge amounts of tension to show up.
On that, I also had a fella once say he put is supports right at each end of the log to try and minimise any counterbalance effect the weight past the supports added to helping the log heave up in the middle, it makes sense theoretically and I do try to put my supports in the last 6" of the log ends, but sometimes this causes loading probs with logs turning and falling off the supports... which increases handling time and slows down timber output anyway that's another threadI love my Lucas!! ...just ask me!
Allan.
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26th July 2010, 04:54 PM #7
Small, sappy logs are always going to be problematic.Maybe slicing them in half is a better option,rather than milling off the excess wood created by the spring.Might be more time consuming but at least the tension in the log will be released.
Mapleman
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26th July 2010, 06:44 PM #8
the idea behind putting the bolsters at the ends is so when the centerer humps up the ends don't go down. and you can run it off
if you have to bolsters 1m from the ends on a 4m log and the center went up 5mm then each end would go down 2.5mm. when you run back over to level teh top you take the 5mm from the center bu the ends are still 2.5mm lower. so u have to drop 2,5mm and run that off aswell.
if the bolsters are at the ends the center would just go up 7mm.
www.carlweiss.com.au
Mobile Sawmilling & Logging Service
8" & 10" Lucas Mills, bobcat, 4wd tractor, 12 ton dozer, stihl saws.
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26th July 2010, 06:56 PM #9SENIOR MEMBER
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Logs heaving
Alan, with the woodmizer we dont get this because the log is clamped in place, not allowing it to move up. We do however get it when resawing cants. I may want to flip the cant over to avoid a shake or whatever, when i release the clamp the cant will spring so i then have to take a trim cut. A customer of mine down south gets me to cut southern blue gum andspotted gum from his plantation. These trees are only about 20 years old so what he does is fall them and throw them into a shallow dam for about 3 months before i get there. We have found this a good way to release alot of tension, and its darn good fun watchin him charge into the dam on the old michigan loader to get em out
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26th July 2010, 07:50 PM #10
Great advice. Also should be followed by people producing feedstock. An occasional leveling cut to reduce the number of boards that are oversize in the centre. It may not be as noticeable in 1" boards but you sure notice it when you put it through a moulder.
My Bandsaw also clamps in the centre so it's not a problem.
I would also agree with shortening the log to reduce the magnitude of the tension but if the customer wants large section pieces in long lengths out of springy logs this is the best way to do it..
Cheers
Steve
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26th July 2010, 08:38 PM #11
i level off every layer as i go. normally its less than 1mm but there is always something to come off.
www.carlweiss.com.au
Mobile Sawmilling & Logging Service
8" & 10" Lucas Mills, bobcat, 4wd tractor, 12 ton dozer, stihl saws.
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26th July 2010, 11:08 PM #12Senior Member
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carl no matter where your supports are under the log the bow in the log is the same , u can also use the log as a bench cut over size ,trim L shape left in the log , reposition timber and trim one side filp and trim the otherside
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26th July 2010, 11:18 PM #13
yes tension is the same.
but if you have bolsters in a long way when u run the top off u have to drop a few mm then run it off or your ends are still low.
www.carlweiss.com.au
Mobile Sawmilling & Logging Service
8" & 10" Lucas Mills, bobcat, 4wd tractor, 12 ton dozer, stihl saws.
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26th July 2010, 11:43 PM #14SENIOR MEMBER
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26th July 2010, 11:46 PM #15Senior Member
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your saw still cuts a straight line from one end to the other no matter where the bolsters are
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