Rotating Logs to Avoid Sawing Through the Bark

      Sawmillers discuss ways to handle wood to avoid sawing through the bark, and other issues relating to bark and blade dulling. November 12, 2008

Question
I recently received help here on this forum solving a blade wear problem, the cause turned out to be multiple cuts through the bark. My band blade would be dull after the four bark cuts! I looked for a thread on this problem but could not find one so I decided to post this. I mostly cut softwood, so my solution to this problem comes from cutting that type of wood.

My solution is to cut through the bark only one time for each log. I do this by rotating my logs towards the blade. I considered adding a de-barker but have not used that option since my current solution is working without it.

My mill manufacture did not know that the blade "sharpness life" would be shortened by rotating the log the way they teach their customers, and the subsequent four cuts through the bark. My hydraulic mill has an offside adjustable fence, log dog, and two rotational drives with clamps. I use the fence and log dog together to rotate the log, making the final adjustments using the rotational drives.

Is your mill maker aware of this issue, have they covered it? (Certainly if you have a de-barker they have). Is this a hardwood issue? (I did read a posting about 180 degree rotation, which gave me the impression of sawing through the bark multiple times).

Forum Responses
(Sawing and Drying Forum)
From contributor R:
The Turner Mills have that problem figured out by reversing the blade and cutting in the opposite direction of most mills.



From contributor S:
What brand blades are you running?


From contributor R:
I see, you are wondering how blades cut in the opposite direction of most mills.
Simple - you grab the blade wearing gloves and turn the blade inside out.


From contributor O:
It's a lot easier to do on some mills than others. Most log turners work much better going in one direction than the other. It depends on how your mill is set up from the manufacturer - the relation of the fence arms, the turner, and the blade direction. I seem to remember from a couple times running a Woodmizer, and due to their design it is much more natural to turn the log into fresh bark every time. My Baker is set up opposite Woodmizer, and it is natural to turn into a square cut edge.

You asked if mill manufacturers know about the dulling effects of bark. They certainly should. Blade life is the primary reason of debarking in the sawmill industry. No full time production sawmill in the country, soft or hardwood, runs without debarking. We are running a much different machine, and have much lower expectations, but it does make since to absolutely minimize blade exposure to bark, and mill makers should account for this in their designs, and in the education of their customers.



From contributor G:
There are benefits to be had in both situations. It was mentioned that Woodmizer utilizes a design that puts you into bark on each cut. The benefit is that the log/cant is being held against a fence of dogs and clamping pressures are minimized, as well as secure clamping being maximized. The band is pulling the cant into the fence. In order to accomplish this secure clamping, the moveable guide must be on the idle side which makes it more important for blade control and might make it more prone to maintenance.

The mention of Baker's and others methods of cutting into clean wood require that the log or cant be held against the idle side of the mill bed. While it means that you are cutting into fresh wood (usually after the first cut), clamping is minimal.

These mills are using only one clamp, which means that the log or cant is being pulled away from the fence by the band. Torque at the ends of the cant can be enough to actually roll the cant out of its clamped position. The fence has minimal use on this style of mill.

The fixed guide is on the idle side, input side, and the more maintenance prone moveable guide is on the power or output side; an argument that the guides can do a better job with less maintenance. So, “'better” is really in the opinion of the user.



From contributor J:
I sympathize with the dulling the blade with bark trouble - I've had the same problem, but not as badly as you seem to be. I'm wondering if the trouble comes from the bark or from dirt in the bark? In white pine or cedar I seem to be able to make quite a few cuts through the bark as long as it's clean They both have fairly coarse bark that would hold a lot of dirt so I check the logs quite carefully and clean (quickly) where possible. When I am able I try to make only two cuts through the bark by rolling 180' after the first cut. Unfortunately on a large log this method creates some big slabs.


From the original questioner:
FYI, I use Uddaholm, Banso blades. Yes they (the manufactures) should know, but it took bring my problem to you guys to find out my problem. My turners do work better in the other direction, hence the use of the fence and log dog for the bulk of this rotation.

Yes my sawmill is layout to have the fence supporting the log for the entire cut. I did look at my turners and decided not to redesign them. They do help keep the log on the table, which for me is very important. I do recall wondering why all the turns I have observed use chain and not a set of rollers, does anyone use rollers?



From contributor O:
You're right about the Baker and clamping, and the reverse setup. That's been my only real complaint with this machine. There really should be two clamps. 99% of the time, one is fine. There is more than adequate pressure to hold the wood stable, but on some logs, especially longer ones, it would really be nice to have a second clamp.


From contributor A:
Cutting into clean wood does help with blade life. WM made de-barkers for their mills and have the blade pulling the cant into the backstops. It keeps the boards straighter and truer. My LT70 has a chain turner and it will roll the log in either direction so it is no problem to roll to clean wood.

The problem comes when you have one flat face and then clamp a round face to the back stop and a flat face to the clamp. It is harder to keep the faces perpendicular to each other. When rolling the flat face 180 so that it is now laying on the deck or 90 so that it is against the backstop helps keep the cant more square. When making timbers I always flip 180 so I can keep them really square. To say that cutting into clean wood is the best way is not so true if you cannot hold the cant square. Trees near dirt roads are really hard on blades.



From contributor S:
If the Udaholm blades get dull too fast, I think you should try some different brands of blades. Take a close look at the logs as well, you can’t expect a blade to last long if the log is encrusted with mud and small rocks. I use various hand tools to clear a "path"
for the blade on real muddy logs. If you have water and electricity, you can get an electric power washer at discount stores and websites for $100 or less.


From contributor N:
I cut for 1 or 2 hours on a band 300 to 600 bf and don't worry about cutting though the bark. On smaller logs I take the slab and one or two flitches, rotate 180 then the same which is 4 to 6 cuts through the bark. As far as cutting straight keeping the blade clean, set and hook angle make all the difference.


From contributor W:
I get about 200-300 bdft out of a blade before changing sometimes less. I saw mostly western juniper which has lots of taper, bark pockets and limbs so it’s not wood that you can debark easy and no way can you saw without being flat and tight to the log posts so changing blades often is just part of the costs.


From the original questioner:
Thanks everyone for the info, it is a big help. Contributor A does bring up the issues that can occur with this type of rotation. It really occurs on the second cut because the log/cant does not lend itself to clamping, since the first slab will not reach the table with a 90 degree rotation, but it is a good point that it will lay nicely on the table with a 180 degree rotation (there will be two cuts through the bark on each log this way).

I have been handling the problem of setting a 90 degree angle with the use of the fence and log dog (I could also use the two log turners but normally I don't find it necessary). I do find that I can easily see the right angle by sighting down the log (the log and table are both visible).

I wish the bark on the DF logs did not dull my blade but they do. I have taken a blade and cut through the bark four times, then I have taken the blade off and you can feel how dull the blade is, it does not feel sharp. If I were to continue to cut I must slow the feed speed down. The blade will not last two hours and it will likely break if kept on the machine that long.

In contrast, rotating the log so that I only cut through the bark one time per log and then removing the blade after two hours the blade has that sharp feeling to it. I was able to continue to cut at a good speed. The blade may not be razor sharp, but plenty sharp, the teeth and gullet look sharp too.

I am switching at two hours too. I am assuming that it is better to switch a blade while it still works like a fresh blade, and the two hour run time appears to be a common best practice. I do keep track of my production rate, which commonly runs between 250-300 bf/hr.



From Gene Wengert, forum technical advisor:
The bark itself is not dulling the blade. Rather, it is the grit in the bark, probably from logging. Have you considered power washing the logs prior to sawing? It works well indeed to remove grit and small stones, etc.


From contributor W:
As Dr. Wengert stated, pressure washing is a good solution to dirt under the bark. I have had tandem dump truck loads dropped off to be sawed that came from job sites that had bulldozers shoving them through the mud and dirt. I loaded these logs on the tow motor one at a time, pressure wash it while on the forks and then set it at the mill to be sawed. I charge $.10 per BF extra for this pressure washing service.

You may as suggested before try different name brand blades and sharpening service. Feed rates and surface footage on the blade also has a huge effect on blade life and you may want to recheck this again. If you are only getting about 4 cuts when starting on a new log, then I feel it may be more than a dirt problem. When I get burned out on a problem, I just regroup, go back through the basics and usually find my problem.



From the original questioner:
I agree that there is an abrasive dulling my blades. I would offer that the problem I am observing is in the content of the bark and the way it is pulled through the saw cut. Many of my logs have not been "logged". I have picked them up with my all-terrain forklift, or the tree service's mini excavator.

I had guessed that the "grit in the bark" has been added by mother nature over the course of many years of wind and rain. I have noticed that cutting bark doesn't seem to produce a chip like cutting wood; it may therefore present a better environment to help keep the abrasive media on the saw blade. If so then it would take a lot less of this grit to dull a blade.

Often DF bark is very thick (2-4 inches), and the angle the blade travels through it can make it seem even thicker. The big mills remove the bark, why do they do this if not to lengthen the blade sharpness?



From contributor S:
The big mills de-bark the logs for 2 reasons: One is to get rid of dirt, rock and ice that might dull the blade. Reason two is so they can run their waste through a chipper and sell "clean" chips to the paper mill. Wood chips with bark mixed in are pretty worthless. I still think, after all this, that you really have a blade problem.

My opinion is that you should try some blades that are specially made for cutting softwood. The hook angle and set will be different. If the bark is really causing you problems, get a de-barking attachment that fits on the end of a chainsaw. You can remove a strip of bark when you have to.



From Gene Wengert, forum technical advisor:
Contributor S has indeed stated the facts correctly and I am with him on trying a new blade design. (Please note this agreement between us - it may be an historic moment)!


From the original questioner:
I took a look on the internet and found a vintage paper that cover the abrasive properties of bark. Here is a copy of that part of the paper that covers Silica, it naturally occurs in bark:

Insoluble silicates are naturally occurring minerals that are commonly found in soils. They include not only extremely hard and abrasive types of minerals but silicon as an element in clay minerals of soils. Silica (SiO 2) levels are of interest because, in the form of minerals, they represent the principal acid insoluble fraction in bark and, as such, are expected to remain as one possible abrasive contaminant in pulps.

Again, as with ash and calcium, softwoods are much lower in inherent silica than hardwoods. Averages for the two groups were 0.10% and 0.23%, respectively.

By percentage there is more Silica in hardwood bark than in the DF. The DF bark would need to be four times thicker to match the value for white oak. Sounds to me that the Silica in the bark in not this issue.



From Gene Wengert, forum technical advisor:
Thanks for tracking down that paper. Note that white oak (northern and southern respectively) has 0.29% and 0.42% silica, while Douglas-fir has 0.06% or 5 to 7 times less. This is for bark that did not get contaminated from logging. In either case, the amount of SiO2 is very small.



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