Log Tension by Timboz

**John.G** · 12th March 2014, 01:01 AM

I'm going to add a few thoughts I had about that report here... was having PC issues last night and couldn't.

1. The writer knows a lot about theoretical sawmilling... but I didn't like the breakdown patterns he was suggesting in the latter part of the report. I particularly thought that his section on twinsaws was out. I'm not an expert on them but i've been around a few and as a miller armed with one I wouldn't be taking my first cut based on small end diameter... rather I'd be taking it based on the first saleable length of timber I could get out... back to our theoretical 5.7's from before I'd be chasing a 3.0m 4 x 1.... or even a pallet board. But I do the same with a carraige mill or a Lucas too.

2. I really think you can't lump drying stresses in with growth stresses. Growth stresses are a tree thing... but drying stress is a sawmill issue. My experience tells me that it's a far bigger issue then it gets credit for. My gut tells me that (having sawn a log or two) there is a noticable difference in how they cut if end sealer has been applied immediately after felling rather then on the ramp hours later, and that there is a marked difference in how they cut if sawn immediately (as in a day or two) against a week or two later. My theory... and i'm nothing but a sawmiller... is that sapwood is more porous then heartwood cause it's supposed to carry water. But that also means it drains water faster then heartwood which is why you get a steep moisture gradient. Smaller logs have a higher proportion of sapwood to heartwood then mature trees... so this means the drying of the sapwood has a greater effect on heartwood movement. When wood dries it shrinks so it has to pull towards the dry side. If you handle your log properly: prompt application of end seal, dont damage the bark, apply end seal immediately after crosscutting, and don't let it lie around the mill yard it cuts straighter... Pretty obvious huh? I noticed that over a few years and changed my practices to suit and believe I'm getting a better product with far less need to oversaw and straighten. Prompt milling is now my standard on logs I expect to be problem children.

3. A lot of that report really doesn't help the portable sawmiller or the guy armed with a CSM directly. (Understanding the issues of course helps indirectly.) If I've got a log that has a bend in it...armed with a lucas mill... I set the log so the bend is "banana up" but with the ends of the "banana" at either 10.30 or 1.30. This means I'm cutting stress from two faces as I go, whereas if I'd position it at 12 or 6 (banana down) I'd only be dropping stress from one face. Banana down is both the easiest way to set up a log like that... and the worst. As you saw and the log "humps up" you're actually decreasing your recovery because you're making the bend worse.

4. The major difference between working a fixed mill and "livesawing" with a portable is the inability to turn the log. General opinion is that a Lucas or similar is no good on small tensioned logs, and there's a reason it's said so often. However it's not the saws fault... its the inability to roll the log to reduce tension in an efficient enough manner to mill productively thats the issue. Take a third off, take one vertical slice to trim the sapwood off the middle third and "upturn" your log like you would on a carraige to get the top to the bottom and the trimmed side away from you... and there is a huge difference in how that log will cut. The issue is whether you can set up to turn like that efficiently enough to make money as compared with losing recovery but not spending time doing the turn. I didn't put in a deck for my lucas for nothing.

My $0.02.

**rwthom279** · 20th November 2014, 09:13 PM

Originally Posted by John.G

4. The major difference between working a fixed mill and "livesawing" with a portable is the inability to turn the log. General opinion is that a Lucas or similar is no good on small tensioned logs, and there's a reason it's said so often. However it's not the saws fault... its the inability to roll the log to reduce tension in an efficient enough manner to mill productively thats the issue. Take a third off, take one vertical slice to trim the sapwood off the middle third and "upturn" your log like you would on a carraige to get the top to the bottom and the trimmed side away from you... and there is a huge difference in how that log will cut. The issue is whether you can set up to turn like that efficiently enough to make money as compared with losing recovery but not spending time doing the turn. I didn't put in a deck for my lucas for nothing.

John,Is there chance of getting a few pictures of your deck?? It would be MOST helpful. I have been scratching some ideas down on how to incorporate log handling (maybe hydraulic) so I can deal with tension in a similar fashion like I do on my bandmill. Sounds like you already have a good handle on it. Thanks in advance

Also, Thanks to all who have put this info and more on here. MANY hours of reading/learning, has taught me more than I could have learned on my own or elsewhere.

**John.G** · 20th November 2014, 11:38 PM

Originally Posted by rwthom279

John,Is there chance of getting a few pictures of your deck?? It would be MOST helpful. I have been scratching some ideas down on how to incorporate log handling (maybe hydraulic) so I can deal with tension in a similar fashion like I do on my bandmill. Sounds like you already have a good handle on it. Thanks in advance

Also, Thanks to all who have put this info and more on here. MANY hours of reading/learning, has taught me more than I could have learned on my own or elsewhere.

I'll grab some pictures if you want but basicly it's a copy of a bandmill deck, more or less. It's fixed rather then mobile... if I want it moved I pick it up with a forklift and load it on a truck. Infeed is by loader or forklift. Width is about 5' or so... the lucas blade isn't on the deck if its wound off to the operator side. Got a couple of popups down that inside to stop logs rolling right through, and a chain style turner under it. I've got a piece of timber that can be inserted into the infeed side to work as a linebar but... it's more trouble then it's worth ATM. I will eventaully get around to making that hydraulic raise and lower so I can feed logs in over it then pop it up when I need the linebar thing.
The deck portion itself is raised 8" - just below saw blade height. It's 6" channel with 2"x3" on the crossbars so if I do cut in well... its just a bit of wood not steel.

pretty basic, but it works. I am able to mill straight spring free boards from small eucalypts, to a level comparable or better then anyone in the industry regardless of the equipment they have. Slow though, but still faster then cutting bent boards and resawing them.
The current one was just the proof of concept machine. Next one will be elevated and fully hydraulic, with attention paid to dust extraction etc. I need the elevation to get straight feeding into the greenchain system and I've figured out how to fit a pretty efficient sawdust removal system under there by going that way. I am satisfied that a swingmill is capable, given the ability to roll the log to counter stress, to cut timber as consistently straight as anything else out there.

**rwthom279** · 21st November 2014, 01:23 AM

John,

Sounds like what I've had in mind. You must be really geared up for production without sacrificing quality

My goal as well.

PM sent

Thanks again

Thread: Log Tension by Timboz

Thread Tools

Search Thread

Similar Threads

Belt Tension

blade tension

tension again

Tension measurement?

Tension OFF?

Tags for this Thread

Posting Permissions