Swinger cutting thick in the middle

[brdmkr]

I was cutting some 20' oak for trailer decking today.  I was cutting 2x6s, cutting 6" in the vertical.  I noticed that the boards were coming off about an 1/8 thicker (maybe a little more) in the middle.  Anybody have any idea what was going on?  I had a true 8/4 on each end.  This was a pretty big log (probably 30" diameter).  I really didn't notice the saw bogging down.  I thought it was really weird.  After I noticed this, I skimmed the vertical edge, taking 1/4" off and everything was fine from that point on. 

Oh, I did have my middle upright in place.

On the plus side, cutting 20 footers was cool 8)

[Tom]

So typical on a bandmill too.  When you relieve the internal pressures off of the top of the cant/log the log will rise.  Opposing parts of the bottom of the log will rise too.  On a bandmill, you can look under the cant/log and see daylight increasing.  I'll bet you can on the swingmill too.

I don't care what kind of mill you are using.  When you take boards from only one side, you will get movement as a result of relieving the internal stresses.  On  a Bandmill, you turn the cant 180° and take boards off of the opposing side untill the cant begins to move the other way.  I've heard swing-sawyer's talk of the tension on their logs and their solution is to do just what you did, take an adjustment cut.

[LOGDOG]

At first glance I wondered if maybe your rails needed re-enforcing in the middle. I've experienced that from time to time. But you said your middle brace was in place so maybe not. The circle saw really isn't one to wander per say so I'm guessing it could be stress like Tom said.

LOGDOG

[getoverit]

if it was doing it in a horizontal cut, I would say that the log sagged in the middle.. I'e seen that a few times especially when there isnt much of the log left...

When it does it on a vertical cut, you can bet that the culprit is tension in the log. Sounds like you did the right thing to relieve it.

[brdmkr]

I pretty much can count on sagging if I don't leave a thick vertical edge, but this was cutting vertical with 10 - 12" of log underneath the cut.  There was even 10 - 12 " of wood that I was cutting vertically into.  As much wood as was there, I would have thought it would have held still for me ;D, but I am going to take Tom's explanation for this.  I noticed that some of the cuts wanted to close up on me and others wanted to open up.  So, I know there was tension in the wood.  I just never would have guessed wood that thick could flex 1/8" or more.  I am just glad that the adjustment cut seemed to have corrected things.  In the future, rather than scratching my head and wondering what is going on, I'll make that adjustment cut as soon as I notice someting is 'off'.

[Part_Timer]

I'm with Tom and Ken.  I've had several do it to me.  Especially the ones that have set in someones barn yard for a year or so.  : :  The top part of the log is super dried out so it pulls funny when it is cut depending where it lands when you roll it onto the bunks.

When I notice the log moving I will make a correction cut then make several of the vertical cuts before making the horizontal cut.  Then make another correction cut if needed.  This seems to help.  I do the same thing if a log is wanting to roll on me as Imake the vertical cuts on the right side.

Tom

[woodbowl]

That's what happened alright. From time to time on my bandmill, I get disobediant logs that force me to flip the cant on every board because it crowns up on every cut.

Another strange happening has been when I had to saw boards on a side bow cant. As the first cut was made, you would expect to recieve a bowed board. Not so, as the cut was being made, (2 X) the board straightened up and the cant remained bowed. The second board was cut and it did the same thing. Two straight boards from a bowed cant!      Figure dat! When the third board was cut ........... It went crazy! It bowed in the same direction as the cant and more so. Now the cant has straightened up considerably. The next board was slightly bowed and the rest of the boards were straight. It seems that there was only a few inches of wood in the cant that was responsable for bowing the whole cant.

After I noticed this, I skimmed the vertical edge, taking 1/4" off and everything was fine from that point on.

Sounds kinda' like the same thing. I've been wondering if it ever happened on a swingblade.

[jack]

I have had that happen also,  'cept i put a floor jack under the log middle, and gave it a slight boost. 

I have also noticed that once, when i was tired, I and moved the upright supports to the rails too far to the ends,  that there was a little SAG in the Middle.  not as much as in my middle,  but when the carriage went down to the middle of the rails it dipped.

Once, i had set up the frame on some really soft punky forest soil,  when the weight of the carriage went to the end of the log,  the rails settled down and caused the blade to DIG in to the log. 

them are the only things that i can recollect that would cause that much dip..

Jack