Troubleshooting Wavy Cuts in Large Logs

      A newcomer to sawmilling gets help tuning his bandsaw mill up to cut straight in big hardwood logs. September 17, 2008

Question
I run a Mister Sawmill model 30 with a 24hp Honda engine. Right now I'm running Wood-Mizer bands that are for "extreme hardwood". My basic question is whether it's realistic for a bandsaw mill to saw logs near the upper capacity limit and still cut straight lumber.

Mine cuts logs up to 20" perfectly but above that things get wavy. Recently I was cutting a 24" poplar and when I was squaring the log into a cant the unedged boards coming off were very wavy - even with a new band. After I got the cant down to 15" and brought the blade guides closer together then things straightened back out. Is there anything I can do to improve the situation (I have lots of large timber - most of it harder than poplar) or is this just something that a bandsaw mill shouldn’t be expected to do?

Forum Responses
(Sawing and Drying Forum)
From contributor S:
What feed rate do you use for the saw's cut width? It certainly needs to be reduced for the wider cut. What blade tension do you use? At some point you would need a certain amount of horse power to cut wider, I don't know if you have reached that point but if the blade is tensioned and feed rate matches what others are using then it should work.



From Gene Wengert, forum technical advisor:
The larger logs have more sawdust per tooth and there is a risk that the gullet will fill and then the sawdust will spill out of the tooth. This creates rubbing on the blade and wood, which causes a wavy blade and cut. A bigger gullet would help. You can also try to cool the blade - do you use a lube?


From contributor S:
What width blades are you running? The 1.5" have a little more stability than the 1.25". Also, is your 24 hp motor slowing down when you are cutting the big logs? If you can't maintain blade speed you are feeding too fast. I used to have a 35 hp Wisconsin gas motor on mill and felt it was underpowered.

Woodmizer's blades are pretty good so I don't think that's the problem, but maybe you should call Suffolk Machine and talk your problem over with them. They might have a Timberwolf blade that would help. In the end there is a limit of what you can expect from a mill with a 24 hp motor.



From the original questioner:
Thanks for all the responses. I'm relatively new to milling so I'll try to answer questions without too many questions. For the feed rate - I slow down for the larger logs. I'm not crawling through them but I'm also not going nearly as fast as with smaller stuff. Should I be talking about this in feet per second? Inches per second? Basically, how slow is slow? I'm nearly as clueless with blade tension and the answer is again subjective. I was told to look at how much the blade "flutters" on the bottom. Is there a way of measuring this concretely so we can discuss it better?

I have not been using any lube. I was told that on smaller logs it's unnecessary but I once tried chainsaw bar oil. The result was oil stained wood. So what does everybody use as far as lube goes? I've heard diesel and water, diesel and blade lube, and just water? Are any (or none) or these right?

The one question I can accurate answer is that my blades are 1.25 inch. As far as the gullet - is that the space between teeth? I'm used to talking about sawdust being pulled out by rakers (like on a chainsaw) and don’t know how it works on these bands. The motor on my saw doesn't seem to have a problem with the wood but we’ve already proven I'm new to this. It will grunt when entering the cut but then will come back up to speed. Thanks again for all the help



From contributor R:
Assuming you have a real plumed and squared mill that has been done properly. I would look at the surface feet per minute that your blade is running. It should be running about 5500 SFM and I have found that even in some soft woods and always in hard woods, I slow my speed down by about 20%.

I have worked on a lot of mills and most of the time the mill has gotten out of plum. Most manuals are worthless in going far enough to realign a mill properly. Throw the torpedo level away and go to the orange store and buy a 24" blue level and you will have a level that is accurate enough to plum a mill properly. Your mill should saw good lumber from a 24" log.



From contributor W:
If you’re using sharp blades I’d say your feed rate is too fast. So slow down until it cuts straight. That’s what I do on larger logs - remember it’s not a circle mill.


From contributor A:
I would look at getting a lube system hooked up for your mill. It can be a jug with a valve that allows water to drip off of a 1/4 plastic tube by the guide before the blade enters the log. This will help keep the blade cool as much as anything else. I think in the wider cuts you blade is heating up and losing tension and that may be your problem. I run water with a shot of Dawn and Pinesol in it.

Also check to make sure your blade is level with the bed when the guide is all the way in and all the way out. If it tilts it will cause the problem you have. I cut most everything with WM 10 degree blades so you might want to try them.



From contributor P:
There seems to be many reasons for wavy cuts off the band mill. Most of the time I change the blade, slow down a little, and tighten everything and press on. As for feed rate I have timed many cuts and find I get the following:
8" pine clear or nearly clear - 12 sec in a 12' log + 60 fpm
10"-12" 20-24 sec 33-30 fpm use 30
16"-18" 40 sec + 18 fps
I’ve never timed a 24 " cut.


From contributor J:
I recently ran into the same trouble that you're having and here's what my experience was. I was using 1-1/4" - 0.042" - 7/8 pitch blades that were set at 0.021". I cut a bunch of frozen 12"-16" elm with no trouble. Then I tackled a 30" frozen white pine and had waves that you could surf on. I tried everything that you've tried and have been told about. Nothing worked for me but that's not saying that the suggestions won't work for you though.

Finally I tried increasing the set until I got to 0.025" and that's when the waves went away. I have an all manual mill with a 25hp Kohler. With hook at 10 degrees and set at 0.025", I can now cut 200+ bdft per hour in frozen white pine logs that are up to 30" diameter and 9'-14' long.



From contributor O:
I agree with Contributor J as well, increase your set a little, and see what happens. I've had this exact problem with poplar, and the set was the cure for me. You can order from Suffolk Machinery with a specific set, and they'll walk you through the different applications.


From Gene Wengert, forum technical advisor:
Indeed, a larger set allows the sawdust to escape the gullet and not rub on the blade as easily, create heat, and wobble.



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