Troubleshooting a Diving Cut on a Swing Blade Sawmill

Swing-blade owners run through the usual suspects trying to find the source of a hard-to-explain blade-diving problem. February 12, 2007

This is a first for me. I have a Lucas 825 and suddenly the blade is diving, but only when I take a full cut. 2x4 cuts are not a problem, it's only when I cut 6 or 8 inch that the blade dives, and sometimes it moves up. It's very frustrating. I have checked for loose bolts, alignment, etc. Any ideas?

I had a flat decked log, and by moving the power head back and forth, I was still getting sawdust off the flat of the log. I thought that it would have cut once and then not cut on the second or third pass. If the saw is in one place too long, it will leave the circular cut in that one spot. Go figure.

Forum Responses
(Sawing and Drying Forum)
From contributor P:
Without knowing more, I am suspicious of your blade's tension. Have you swapped blades to try to solve it? I have six blades for my Peterson 10" and one of them is contrary right now. It needs some special attention.

From contributor M:
If I understand correctly, you had a flat-topped log and with the blade horizontal, you removed wood every time you skimmed the top of the log? If this was occurring in the middle of the log, I would suspect that you have tension, causing the log to rise up after you took some wood off to flatten the top. If it was occurring on the ends, I would suspect that the log was sagging or tension was causing the middle to drop down.

If the log is not sagging due to its own weight, you may want to make a thin adjustment cut. Band mill operators would flip the log and take a cut off of the other side to relieve stress.

Finally, I never take a full bite with the horizontal cut. When I do, the mill often tries to move side-to-side. You may want to try cutting half of the horizontal cut on the first pass. Pull the blade out of the cut, return to the starting point, and cut the remainder of the horizontal cut. I hope I understood your question.

From contributor U:
I'd guess the problem you're having is due to the weight of the cut lumber deflecting the blade toward the end of the cut. Using wedges to keep the kerf open will alleviate this problem (if I'm right). Every so often, I have the same problem, and it's almost always due to my forgetting to use a wedge to keep the weight of the board off the blade.

From contributor S:
What I found that causes that on my 825 was having 2 or more of the teeth with the corners off. That's 40% of the teeth not cutting on one side. The saw should give you shavings from all the teeth, not just some and not sawdust. A chainsaw will cut circles if only one side of the chain is sharp and I think it's the same thing.

From contributor P:
All the last three responses are legitimate suggestions. I have seen these situations (tension in log, log sag, kerf friction, dull tooth corners) The way you started this thread, I assumed you had experience enough to have already suspected those types of problems, so I went a less likely way (blade tension).

Let me throw one more at you: In the past, I have had a log set on scrap, wedges or what have you, which was on a thick layer of saw chips - on a spongy layer. As I cut off the weight of the log, the log was actually rising up. The "ground" was springing up, as the weight was reduced, lifting the log. Since you are probably set up on some fine bunks, this is not a probable cause, but I did have it happen. (Now I try to act like I know better.)
Now, however, I am curious. You have the full gamut of possibilities. What turned out to be the real issue ? Inquiring minds want to know!

From the original questioner:
Well, having installed some fresh grey hairs.... I first thought it was the chipped teeth on the blade, then went to look at the spongy ground (been there, done that before), then I changed blades, and it still dipped, but not as bad. Then I stuck a 4' level on the blade to measure against the frame. Everything is in order, 1/16 difference, front aims down a bit. I called Baileys, and after our discussion of all the below mentioned items, Sam suggested that I look at the bolts that hold the gearbox to the frame. They were tight, but the bolts that hold the front of the swiveling piece that allows the blade to swing were a bit loose. Maybe that was the problem.

I will know more when I get back to the saw on Tuesday. I adjusted it a bit and it still dipped, but not as bad. My next adjustment is the front slide block and the roller. Thanks for all the input. One of the logs was way tensioned, so I tossed it off to the side until I get this adjusted correctly.

Do you have any of the heads of the bolts that hold the saw blade to the hub? Do any of those heads protrude just a smidge? I replaced those bolts and I have two of them that are protruding a smidge. They are not flush. I cleaned and inspected the bolt holes and surfaces.

My thinking is to buy a new blade and save it as an inspection/standard to insure that the blades aren't out of tension or whack. My 5 blades have been re-tipped say 12 or so times.

From contributor B:
I always check the simplest things first, and you have probably checked this, but are your rails and stabilizers on solid ground? I've had this problem from setting the mill on soft ground.

From contributor D:
I think just about everything has been covered except your kerf. If your teeth are worn back, you are running a narrower kerf. Not so much of a problem if your blade is properly tensioned, but as they get used, they loosen. Also, if the grain of the log runs all over the place, it can give you fits. I make full 9 inch horizontal cuts all the time with my Lucas when everything is right, but still run into the odd log that won't let me do it. What kind of wood are you cutting?

From the original questioner:
Yes, I have experienced that, but with the urban lumber I'm cutting, teeth don't exactly wear out before a bolt, bottle, or any other item that was stuck in the tree gets discovered and teeth fly off. The blade had maybe 6 hours on it.

I'm cutting Monterey pine. I tried an experiment - air dry the logs and see how much lumber I get after a couple years. Interesting that on some logs, which have been down for 3 years, I get about 75% of the good wood out of them, and some logs are less than fire-feeder. I have determined that with proper air flow around the log, without the bark on them, the 2-3 year old trees are still of some value. If they have bark and are closer than 6 inches to the soil, then the tree is junk.

From contributor D:
One other thing that just came to mind. I bought my Lucas several years ago (820 Briggs). It seemed to cut not bad, but being new at it, I had nothing to compare it with. I then bought some 23" saws so I could cut ties. What a difference. I spoke once with Rex Lucas and he said that they did have a really bad bunch of saws. I believe they were made by IKS. I've since bought new 21" saws made in Australia and they work great. IKS made my 23" saws and they're fine, so I'm not trying to disrepute them. Maybe you just got a bad blade. If you're hitting a lot of trash, make sure you haven't bent the blade, but I'm sure you've already done that. I've never cut Monterey pine, but the pines I have cut (lodgepole, western white and ponderosa) saw really nice.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor J:
The biggest problems I have run into with climbing or diving blades is how sharp the blade is. For some woods like oak or ash, you need to touch them up after a couple of logs, especially if they are knotty. I know it sounds excessive, but believe me it works. I was first told of this by a friend of mine. I refused to believe it at first as well, until the mill would bind so much after a couple 16' oak that I couldn't even push it forward and it actually jumped off the rails. After a couple of minutes of touchup, she was cutting clean and straight again.

For all you guys looking for a saw doctor, we quit sending them off at $40 a pop and now we re-tip our own. A soldering kit to do this doesn't cost a whole lot, and tips are only a couple of bucks. Just make sure you get the right solder or the blade tips will instantly come off. Now we only need two blades to keep sawing all the time instead of the four we used to have on rotation to and from a saw doctor.