When to Change Band-Mill Blades
Long, thoughtful thread on cost-effective ways to manage the timing of blade changes and blade re-sharpenings. August 8, 2008
Question
I know folks have discussed band saw blade sharpening and how much use you can obtain from a blade. I have read about folks recording information about each blade and keeping track of the run time results. My question is about a universal measure of blade sharpness and use. Many folks talk about the number of board feet per blade but this can be misleading. What would be a more consistent way to measure how much a blade can cut? I will start by suggesting linear feet of cut, even though I know it is flawed.
Forum Responses
(Sawing and Drying Forum)
From contributor A:
I don't go by the number of board feet cut - I go by the way the blade cuts. I use a blade until it starts cutting badly or I hit something. One day cutting softwood I used a blade 1-1/2 days, almost 1800 feet, but that's rare. Never push a blade so hard that it takes all day to sharpen it or it's junk. As long as you keep it cool as you cut and the logs are clean, cut as long as the cutting is good.
From contributor B:
When most companies give blade life information or board feet per hour sawn they are talking about 4/4 lumber. This is the best information possible and many are cutting pine when they give it. But that is the problem. I get 800 board feet on average per blade use on my LT 40. I may even get 1,200 cutting good pine and only 400 in hickory. The size of the log cuts down on the blade life. Whether you edge on the mill or with an edger makes a difference. Very large logs tend to heat the blade which may lessen life. A debarker and coolant also make a difference. If everyone posted their results all cutting 16" 12' clean green SYP or red oak into 1 inch wide boards then we could really tell something about blade life.
From the original questioner:
Yes it would be nice to have a standard. It would certainly help folks diagnose their equipment. I can see the point at which my blades cut slower but my cut quality is rarely changed. I mostly cut DFir. The blades seem to keep going at a slower rate for quite some time. I am not effective at picking the time to change blades, unless I pull the blade at the first sign of it slowing down.
From contributor C:
To get the best blade life, I change the blade every 2 hours. I don't worry about board footage too much. Sometimes I'll push it to 3 hours if the blade is still cutting well. Changing and sharpening the blade often is easier on the blade and it is easier to sharpen. I've had as many as 24 hours running time on a blade. Most blades give me at least 10-12 hours running time. That would be 5-6 sharpenings. In 2-3 hours I average 400-500 board feet depending on log size and lumber size (4/4, 5/4 etc.).
From the original questioner:
I have decided to try the 2 hour swap out. I first tried using my hour meter but found that the hour meter factors in rpm so 2 hours on it is more like 3 hours. I assume you mean clock hours. I plan on switching after 2 hours on the clock. This week I am doing the annual machine maintenance so I will start cutting next week.
From contributor D:
I run my blades about two clock hours but like the others, I can tell by the way my mill cuts and sounds if the blade is getting dull. Your blade should run about 5500 surface feet per minute in soft wood. However I slow mine down by 20% when cutting hard wood and have at times slowed it down in real knotty pine. I have posted on this forum before at length on speeds and feeds but have forgotten where.
From the original questioner:
Your post is under the title: HP for band mills. It is not that I can't tell the blade is becoming dull, but I can hear how hard the mill is working and like most folks I can slow down the feed to reduce the amount of power put into the blade. After 2 hours I will have approximately 300 board feet of wood cut. If I doubled the feed speed to produce at a higher rate I think the blade would last 30 minutes. I guess what I am hearing is the blade should last 2 hours. Does that mean they never break? Or can you tell me how many blades make it through all sharpening without breaking? With a box of ten new blades, how many make it through 5-6 sharpenings?
From contributor E:
What blades are you running now? It sounds like you're saying that you're getting 150 board feet per hour? That being said, what is your average feed rate? How much of that hour is the saw in the wood? Is this a manual or automatic mill? If you're running an automatic, with a slow feed, I'd say speed up. If you're running a manual, and spending time turning and clamping, I'd say to run the saw longer and don't worry about the 2 hour timer.
To answer you questions in the previous post, a blade should last 2 hours without breaking. But remember - it only takes one saw line to dull a blade. It's so much a function of the lumber - the feed rate, the saw tension, the cleanliness of the logs. Once in a while you may pop one, but if a machine regularly breaks blades, you are doing something wrong.
I run a Baker, with 1.5" x .042 or .047 saws, and normally run about 375-400 board feet / hour of 4/4 oak. I run saws 1.5 to 2 hours at most. I pay attention to engine rpms and cut quality, but the indicator that I primarily use to determine when to change saws is feed pressure. I have a hydraulic gauge that is a clear and real time indicator of resistance to feed at a given rate.
One of the biggest factors in keeping blade life up in my opinion is maintaining proper tracking and keeping the guides set right. Saws cut more accurate, faster, and last longer when those two things are given proper attention. I sharpen my own saws, and usually get 4 to 5 grinds, before they won't hold a point (I'm through the hardened tip).
From the original questioner:
It is Mighty Mite Mark IV which is a hydraulic band mill. I am using a 1.5 x .045 blade 7/8" pitch. Yes, I would say I am using most of the time to saw wood. According to my sharpening service the Mighty Mite has a reputation of being easy on blades compared to the other brands he sharpens.
The mill does not have a debarker so I would have four cuts on every log through the bark. My typical logs size set my rate at three logs in two hours (300 bf). On the average I would be ready to change blades after the third log. I set the feed rate based on sound or engine loading, and by the third log it appears to be slower than the first log, but I do not have a machine measurement to relate to, or my feed speed dial is too small for me to read. I guess I could use a marker to keep track of the setting.
I did download the Baker owner's manual so I could see what you are doing and what you meant about the guide adjustment. It looked good to me. I believe that if I speed up the machine the blade will not last two hours. From what I have heard here some folks say they don't care about the cut rate, and other are saying the mill should cut 200 board feet per hour. Please keep in mind I am talking about Dfir, high pitch, sometimes older logs, that always seems hard.
From contributor B:
On the LT70 we change about every 2 hours (when we take a break) and will have sawn between 800 and 1,200 board feet. On the LT40 we change when it gets dull or the cut rate starts to fall. I send my blades back to Re-Sharp and it is about $9.00 round trip. If I am sawing on the LT40 and getting 200 board feet an hour and the blade gets dull or cut rate starts to drop I change the blade. I saw for a living and if I drop production by just 25 board feet an hour I will have lost more in 2 hours than if I had stopped and changed the blade. You need to figure your blade cost per board foot and at what point that slowing down costs more than changing the blade. When you have hired help and the blade is getting dull and it is 30 minutes to break, then keep sawing. But if it is 30 minutes past break and you get some dirt and dull the blade then change and keep making money rather than losing it trying to save it. On the LT70 I have $40 an hour of hired help standing around so we change at break to keep production up and just count it in with blade cost. So changing when dull may not be the most cost effective and sawing while dull is not making you money. Having said this, if you are just sawing to be sawing then run that little darling as long as you are having fun.
From the original questioner:
To contributor B: Could you answer a couple of questions? You have double the product with the LT70, compared to the LT40 - what are the differences to achieve this - blades, power, logs, feed rate? It is very helpful to hear that a common approach is to change the blade every 2 hours. You make it sound like I could up my feed rate and obtain the same results. Have you cut Douglas Fir? Does it work the same way? Are you running a debarker?
From contributor E:
I just looked at the Mighty Mite website - nice looking machine. Have you tried other blades on your mill? You said if you sped up that you didn't think the blades would last but have you tried it? If so, what were the results? With your blades, and the size of your machine, you should be able to saw faster than the 300 board feet in two hours. I'm on the east coast, and have never sawn DFir, but I think it would be fairly similar sawing to old growth SYP that I saw all the time. I'd speed up to a sawing rate of at least 35-40 fpm and see what happens. With your small logs, that mill should have no problem at that rate.
From contributor B:
Yes, I have debarkers on both mills. I would not own a mill with out one. The LT40HDG25 is a 25hp gas, hydraulic mill with 1-1/4" blades. Good production is 250 board feet an hour but most of the time around 200. I have one man tailing and a loader bringing logs and taking lumber and slabs away.
The LT70E25 is a 25hp 480V hydraulic mill and you save most of your time in the coming back and powerful hydraulics where you can run two at a time. It has a computer that helps in cutting and dropping and the darn thing is just plain fast. It has a chain turner that goes both ways and board return. There are 3 men behind me with a loader bringing logs and taking lumber and slabs away. Most logs are over 12" DIB and 8' to 16' long. It is a mix of oak, walnut and SYP. Both mills have Twin Blade edgers behind them. We do not have DFir in the Ozarks so I have not sawn any. It can not be any worse than heart pine or white oak. Lube on the blade, such as PineSol and water help a lot. I use WM 10 degree blades most of the time.
From the original questioner:
I haven't tried that speed with a fresh blade on a fresh cant. I would agree that the mill is plenty big enough and I have the optional diesel engine too. I am suspicious of our island bark. We have wind conditions that tend to affect the trees. If I saw in the evenings I can often see sparks on what appears to be perfectly clean logs (most of my logs have been carried, not moved by skidding). I will try the speedup. I can use one blade to make the cant then another to cut the boards and see what fpm will work.
I have tried different blades. My blade service is in Forks, WA. They are known for their rain and softwood production and the service has been very helpful. I even ran a 2" blade for awhile but have moved back to the current 1-5/8" German blade. Its claim to fame is a deeper heat treatment which helps the tooth keep it set longer, and it also tends not to drift in knotty wood. It definitely works compared to the Timberwolf blades I ran previously (don't get me wrong, I do like the Timberwolf blade). I won't be surprised if this comes down to a problem with the bark. I wonder is there is an after market debarker?
I spent the afternoon looking for an add-on debarking saw. I did not find one. I certainly saw plenty of machines, but nothing setup to add onto a sawmill. I may try to add a circular saw to my mill and use it to cut a debark kerf. The purpose would be to measure the improved saw blade performance and to determine the saw size and power requirements for the added circular saw.
From contributor F:
Couldn't you put a dado blade set on an arbor with a spring loaded tension bracket? Or just buy the unit from Woodmizer? I run a Lucas and we don't skid logs or we have to power wash them. The bark and the sparks issues - I have seen sand blown into the bark, or flood silt, etc. stuck in the bark. But the carbide tips of the swing blade seem to handle it ok.
From contributor E:
It sounds like the bark is your problem. I doubt you'll find an add-on debarker, but you can probably buy the assembly from another mill manufacturer and modify it to go on your machine. In the meantime you can lay out a couple hours of logs, and hit them with a powerwasher. It takes a few extra minutes, but can be very effective.
From contributor D:
My mill came with a debarker for $1500.00 and was not worth $15. I pulled it off and I am also going to make one from a skill saw. However, the point I wanted to make was that mine has three saw blades on it sandwiched together and the center one is reversed to keep it from cutting too deep and bogging down. This blade concept is the only good thing about my debarker.
From the original questioner:
Here are the results thus far: I had a phone conversation with a member and determined that I should rotate my logs in the opposite direction so that I only cut through the bark one time (instead of four times). As you can imagine, this greatly increased the sharpness of my blade.
Before I started cutting I went through the saw alignment procedure and added to that the delivery of three loads of logs, so I only had time to cut one log. I set the feed rate to 30 feet per minute and worked on a 21 inch log. I found my clutch slipped. I tightened the clutch and the diesel had no troubles cutting at that rate. I pulled the blade off and checked it, and it was still sharp.
On my next log I will attempt to determine the maximum feed rate. There is an earlier post suggesting I should use a 30-45 fpm. What rates do you use?
From contributor E:
Sound like you are making progress! Did you time yourself on that 21" log at the new feed rate? Like I said before, I run a Baker with 38hp diesel. The machine is set up to turn logs as you mentioned, minimizing the number of cuts through bark, which I think does make a huge difference. I don't think I push the saw rate as high as I could. That being said, I vary the saw rate, primarily based on width of cut, rather than species, with a few exceptions. For 12-16" wide cuts I run about 40-45 fpm.
From the original questioner:
Here's another update. I cut an 18 foot long 16" white fir today at 60 fpm. This is the second log on this blade. It was cutting easily, with no waviness. The blade was still sharp when I finished. The diesel wasn't loading down and didn't seem to be working very hard. I have a two day portable job next week, and then a four day maple job. These should be enough to finalize my cutting speed, and blade run time.
I finished the blade off by cutting a third log. The blade was becoming dull and it was not exiting the log straight. Logs number 2 and 3 were cut through the bark due to the requirement of the buyer. I could tell the bark was dulling the blade faster. The two logs I used for this customer were from the top of the tree where the bark was quite thin but it still had a rapid effect on the blade sharpness. I would guess that even two passes through the heavy bark of the base of a Dfir tree would result in a dull blade.
On the next job, portable location was poor due to little room, hence cut rate was affected by this location. I was cutting Hemlock. The Mighty Mite and I were able to produce 1200 board feet in 3 hours. That is 400 board feet per hour with one blade change and the second blade is still sharp. I would estimate I spent at least 30 minutes of that moving material around.
Job totals for the hemlock job were 2700 board feet. Using four blades - removed after 2 hours of cutting, and all seemed sharp to the touch. Cut rate was 400 board feet per hour. I found that my old method of cutting through the bark four times was making the blades dull (dull even before the first board was cut). This caused me to reduce the saws feed rate. By rotating the logs so that the saw cut through the bark only one time the saw blades remain sharp and I could run the feed rate at 30-60 fpm. These results are for hemlock. I hope Dfir will do as well.
From contributor D:
I have been following your success and glad you are getting good output. I have a TK B-20 and had to pull the debarker off shortly after purchasing it because it is a $1500.00 piece of crap. I am making and have made modifications to the mill and one is I am redesigning my debarker. How are you accurately orientating your log 90 Deg. on your second cut? I would like to try your method until my debarker is finished which may be a couple months away. I know the Timber Harvester mills cut in the opposite direction and the log stops are on the side of the blade cutting direction. Of course in this method you are cutting into the bark only once like you are doing.
From the original questioner:
I'm sorry to say I do not have a fancy way to set the 90 degree angle. I just sight down the log and use my two hydraulic log rollers to set the final position. There is a good view of the side of the log and the table. I didn't observe any problems with this. My sharpening service says he has a hand square that he uses. The Mighty Mite has a full length fence that is used to set the angle for rolling the log the wrong direction. It is really great for cutting cants - you set the fence just under the saw cut and continue to drop it as you saw the cant. It is very fast and there is no need to set any clamps.
From contributor G:
I've been cutting DFir as well and I have noticed the same thing you have - cutting through the bark dulls the blades. I noticed the dust spark thing too. I wonder if it would be worth it to buy a carbide tip saw just for the first two or three cuts - get the L cant made then change to regular blades for making lumber. That way, you're always in new wood, the bark is on the exit side and you're not dragging whatever is in the bark thru the cut. My mill is homebuilt and it's a 2 minute change out on the blade so although it may not be advantageous for you to swap blades, for me it might be.
