Troubleshooting Wobble in a 48-Inch Sawmill Blade
Detailed discussion of the factors that can make a circular sawmill blade deform enough to start wobbling. August 30, 2007
Question
I'm new to the sawing business, having rebuilt an old Frick. I've had the old blade tensioned, but after sawing for a couple dozen hours, it's developed a distinct wobble. Is this normal, or do I need to take it back in to get it re-hammered?
Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
This is not normal. Did you accidentally heat the blade, maybe with a piece of wood wedged along side? If not, then did the person that hammered the blade ask you for the RPMs? Are you running at that RPM? Blades are hammered for a specific RPM and it is unusual to see them lose tension so quickly unless they were not at the correct RPM initially or if heat were applied. (If it has inserted teeth, did you change the location of any shanks? When changing bits, change one at a time.)
From the original questioner:
Actually, I did discover a piece of cedar board trapped under the saw shortly after I noticed the wobble. The sawdust had built up around the base because the chain had quit and I had not noticed. Could something that small cause the blade to heat to the point of losing tension?
Come to think of it, the blade did start cutting poorly around then; I then adjusted the blade guide a little tighter and replaced all the teeth, and it seemed better. I'm paying $100 to tension the blade...This is going to be expensive. Could you give me some pointers on how I can keep this from happening again?
From Professor Gene Wengert, forum technical advisor:
Did you replace all the teeth but do it one at a time, making sure the shank went back into the same location it was before? The tight guide could also generate heat. It is hard to believe that you generated enough heat with the one piece of cedar, but the original hammering could have been poorly done. What about RPMs? It is tough to run such a large saw, as I mentioned before.
From the original questioner:
I have a RPM gauge and had it hammered to the correct speed. The guides are not adjusted too tight, but with the wobble are probably making a little contact with the saw. I did replace all the teeth, and was as careful as possible with the shanks. It does seem odd that just a small piece of wood could heat it up enough to take the tension out, but prior to all this, the blade was standing up perfectly... After that stuff jammed at the bottom, it wobbles. By the way, the wobble is a deflection of maybe 1/8 of an inch.
From Professor Gene Wengert, forum technical advisor:
What is the blade rpm? Around 600 to 650? Can you perhaps slow the blade down by 25 rpm?
From the original questioner:
RPM is 550. Well, perhaps I should put the gauge on it again... It's a '48 Minneapolis Moline power unit, and the governor could have let it rise up. Your point being that it will wobble if not operating at the correct RPM. Good.
Also, on another subject, since I seem to have a circle saw expert's ear... Why would the boards that come off be slightly thicker, maybe 1/8th, in the middle (from day one of rebuilding the mill)? I get a headache thinking of all the variables that might cause that. Carriage or track, perhaps?
From contributor G:
First, a very small piece of wood in the wrong place can heat up the blade. On the 1/8", if you have a two head block mill, you need to turn the log every two cuts 1/4 or 1/2 turns. This will keep the stress equal. I sawed on a M-14 for 5 years and unless I turned after two cuts, I had the same trouble. Next, test your rpm's under load. Most of the time they drop, but I have seen it go up on some power units. The $100 for hammering the blade again is just the cost to go to school as you learn how to saw with your mill.
From Professor Gene Wengert, forum technical advisor:
The thick center can be caused by improper lead. Do you know what this is? There is a great circular saw book by Lunstrum that covers these details. See link below.
Cicular Sawmills and Their Efficient Operation
From contributor R:
Wobble can be caused by a lot of different reasons. Heat is the usual culprit, but heat can come from a variety of areas. That little piece of wood or bark that lays against a running saw will do it. Sometimes you'll find a piece of bark between the saw and your deck behind saw. Dull teeth will cause heat, as will an improper angle on your teeth. Improper swaging or damaged teeth can also cause heat.
Saw guides out of adjustment will allow your saw to open up and allow the log to rub the eye. Saw guides should be adjusted on a running saw. Ultimate care should be taken during this process.
Saw not running at the right RPM or feeding too fast can cause a wobble. Feeding too fast will cause your RPMs to drop and your saw will lay over. This will cause the log to rub at the eye.
A sprung arbor can also cause wobble. If you have 3 bearings on your arbor, make sure they line up. It's very easy to push the middle one over too far.
As to your last problem of thick and thin lumber. Several areas can cause it. Tracks must be straight. If there is a bow in the guide track, you can have a problem. Another area to check is your trucks. If they are loose, then your carriage can move off line.
A big problem is feeding your saw. If you hit the log too fast, then your saw may want to dodge out. You may also bog down the saw, which changes your RPM. The sound of the saw shouldn't change from the beginning of the cut to the end. If it does, then you're not feeding it correctly. Another area to check is your belt tightness. If your belts are slipping, your RPMs will drop.
