Sawing frozen logs

      Solutions for problems encountered when sawing frozen logs. February 7, 2001

Question
I am re-sawing frozen white pine logs and having trouble. Sawdust sticks to the sides and when we pass the cant back through the linebar resaw, the resulting board is off in thickness top to bottom. The sawdust is very fine, and when I tried slowing the feed down, the problem intensified. We are using a small frost pick filed into gullet when sharpening. Our machine is a McDonough 60" band that was working just fine until it got so cold (-20 degrees C).

Forum Responses
Remove every other tooth! The teeth need to take a bigger bite. (I know that this is hard to do, but it does work.)

Gene Wengert, forum technical advisor



Sounds like you have a frost chair in the face of your tooth. Bring the swage down on your tooth (drop your kerf). If you have fine dust, you may be feeding too slow. I assume you are running a wide band with swaged and shaped teeth, not a narrow band set toothed saw.

The idea in frost is to keep the sawdust from spilling out of the gullet of the tooth and making the saw run. The frost chair will catch a wad of dust and tends to wipe the cut clean.

You can not feed as hard in frozen wood, because your saw will run and you will break teeth. But when you feed slower, your sawdust will be finer. So do not swage your tooth as wide as you normally would, to make for less clearance between the saw and the cut, to keep the finer dust from spilling out of the gullet.

Expect some problems no matter what in the fall and spring when your wood is not frozen all the way through. The running in the cut is not all a result of sawdust spilling out of the gullet of the tooth. Frozen wood cuts harder, loads the saw more and eventually pulls the tension out of the saw. I have used the above system on a 5 foot Horz. slatt bed resaw and a 54" McDonough line bar with good results.



From the original questioner:
I dropped the kerf by one gauge after sharpening and swaging, and I am going to try dropping one more size. The next thing I am going to try is slowing down the speed of the blade by changing the pulley on the drive motor.


I would look at changing the feed rate rather than the speed of the saw. Your saw speed should be between 7,000 - 10,000 surface feet per minute. As a starting point, the tooth bite for a saw with 1 3/4" tooth spacing and a 5/8" gullet depth (.625 square inch gullet area) with an average depth of cut of 11.5" would be .043" per tooth.

You can figure out how many teeth per minute for a given tooth space, wheel diameter and wheel RPM and figure feed rate in feet per minute.

Normal tooth bite may be .043" to .052", depending on depth of cut, gage of saw plate and width of saw. That is for unfrozen wood.

A book named "Sawmill Feeds and Speeds" Published by Armstrong Mfg. Co., Copyright 1964, gives this formula for tooth bite: "Tooth bite equals saw thickness, less 4% for each inch less than 10" of saw width, or plus 4% for each inch over 10" of saw width. On a saw 10" wide tooth bite equals saw thickness." Quelch, in the "Armstrong Saw Filers Handbook" recommends the following average speeds in lineal feet per minute:

Softwood 8,500 to 10,000
Hardwood 7,500 to 8,500
Frozen Timber 6,500 to 7,500

RPM of a 4 1/2 ft. wheel for a given saw speed in feet per minute is:
354 rpm = 5,000 sfpm
425 rpm = 6,000 sfpm
495 rpm = 7,000 sfpm
566 rpm = 8,000 sfpm
637 rpm = 9,000 sfpm
707 rpm =10,000 sfpm
778 rpm =11,000 sfpm

I would drop the kerf a bit more and make sure you are not under feeding and you are not short on HP.



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

Comment from contributor A:
I also had some problems cutting frozen white and red pine, so I ground a frostnotch into my 12 inch .078 doublecuts. Ever since I got it in I haven't had a problem. I now have a frostnotch in all my 6 running resaws and 2 doublecut headrigs year round.



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