Despite the advances in technology, the circle sawmill blade will still experience the following problems at some point. These tips and tricks will help narrow and resolve hard to pinpoint saw problems while being a simple and straightforward guideline to follow.
Once a mill gets some age to it, and millions of board feet have run over it, it can be hard to pinpoint little blade problems. A lot of times sawyers point to the setworks whenever there are inconsistencies, but you need to check your saw and collar too.
The common areas you need to check for on older sawmill problems are the collar, plumbness of the saw, and of course lead of saw. Let’s dig into it.
Saw Collar Basics
The saw collar holds the saw on the mandrel, but more importantly, it also gives support to the saw blade. Most manufacturer’s like Montgomery use 8″ collars nowadays. The larger collar gives better support; thus, the more stable the saw will run.
Some manufacturers of sawmill equipment furnish mandrels with flat collars with one collar concave, usually the outside one, and one collar flat, the inside one. It’s recommended matching both collars with a slight concave about 0.020”-0.030”, or from the periphery to the edge of the recess), or (1.5 to 2 degrees off of parallel of the flat bearing surface.) see Figure 1.
When the collars are tightened against the saw blade, they should have their most significant bearing force on the outside edge, see Figure 2.
Collar trouble is a very common problem, and as mentioned, it can be hard to pinpoint. Issues with the collar can even go unnoticed, but here’s a quick way to test and check your mill. Remember to power down and lockout and tag out.
- Keeping the saw stationary, loosen the guide plugs.
- Loosen the mandrel nut on the arbor.
- Tighten the collar nut by hand so that the loose collar is snug to the saw.
- Re-set the guide plugs, so there is 1/16″ clearance on either side of the saw.
- Slowly rotate the saw to see if it leads in and out in comparison with the guide plugs.
- Without moving the saw, tighten the nut with a wrench your usual manner, being careful not to move the saw.
- Check the distance between guide plugs and saw, did they move?
- Try the rotate test again and see if it stays true.
Results from the Quick Check
If the saw is closer to one plug than the other (rubbing), the saw has become dished, due to a worn or damaged collar, which should be repaired or replaced.
Refacing the Collar
When refacing collars, you should start at the recess and work toward the periphery. If this method is used, any cutting tool wear experienced will result in the concavity. On the other hand, if the cutting tool is started from the outside and the tool dulls 0.003″ – 0.004″ it will result in the collar being flat or convex.
Temporary Collar Repair
It’s possible to rectify collar trouble with a paper washer temporarily. After determining which collar is bad, cut a paper washer about half the width of the collar lip (1/2″ – 3/4″ wide), from a medium weight paper. A manila envelope is usually perfect. The paper washer diameter should be as big or a little bigger than the diameter of the collar. You can cut the excess off after tightening the mandrel nut on the outer collar. Also, you can attach the paper washer to the collar with lightweight grease. see Figure 3.
If the saw is dishing toward the husk, the paper washer should be attached to the back collar. If the saw is dishing toward the log, then the paper washer should be attached to the loose or outside collar.
How to Check for a Plumb Saw
To cut good lumber, the carriage and carriage blocks should be level, square, and a plumb saw. If the carriage is good, but the saw is not plumb, the last cant or board can be wedged shaped from edge to edge. Do not try to correct this with the saw guide; it will cause the saw to heat and affect performance by weaving or snaking through the cut.
When the saw is not plumb and leans toward the carriage, the saw will tend to lead into the log. On the other hand, when the saw is leaning toward the husk, the saw will tend to lead out of the log. A simple check is to shut down and lock-out-tag-out power, then drop a plumb line and bob along the saw face while, missing the collar, and hooking the line over the top of the saw at the shoulder, see Figure 4. The line should not touch anything but the metal plate of the saw. Not the shanks, teeth, or collar. see Figure 5.
Figure 4 Figure 5
To make the saw plumb, just adjust the mandrel bearings with spacers and or wedges to level the mandrel. Leveling the entire husk may be more desirable. Regardless of which method is used, a plumb line should be used to check the saw.
A level isn’t a proper method for checking plumb of a saw because the saw blade is dished. The dish comes from the tensioning of the blade so the metal disk will stand straight while turning up to RPM. Using a string allows you to go the complete distance, unlike a level that may not be centered in the dishing. Another thing you can push on the saw while trying to hold the level to it and distort the dishing.
Improper Lead of a Saw in the Sawmill
Improper lead is a great cause of saw trouble. To overcome the tendency of the saw running out of the log while slabbing, and to give clearance on carriage return, the mandrel should be adjusted slightly so that the saw will lead into the log. Often times a saw will heat and dodge in the cut or behave like a saw in need of tensioning or hammering because of improper lead.
A simple method for checking lead are as follows
- Pick a tooth and mark it. Now measure the distance between the tooth corner and an end of a carriage block.
- Move the block to the opposite side of the blade and rotate the saw so that the marked tooth is at the same carriage block.
- Now, measure again. About 1/16” is the standard nowadays for the correct amount of lead (in a 56″ saw) on most sawmills, see Figure 6.
You may need to adjust it in or out to give optimum performance. Lead can be anywhere from a 1/32” to 3/32 and still be set up properly.
Adjusting the Lead
The lead is adjusted by moving the saw end of the mandrel left or right. This is called “sluing.” Never attempt to adjust the lead while the saw is running. A mandrel with three bearings will be easier by only adjusting the front and back bearings allowing the middle bearing to pivot.
If too much lead is in the saw, the boards will rub on the blade before the splitter. This can heat the rim of the saw, causing it to dodge, even when sawing small cants. A shiny rim on the saw can often times be a sign of this condition. Too little lead will create heat nearer the eye of the saw and cause the saw to lead in or out. A shiny area on the saw body can often indicate this condition.
When changing lead, it is essential to loosen all the mandrel bearing to prevent a distorted mandrel and premature bearing wear. Belt tension should be released to adjust lead as well.
All maintenance of sawmill equipment should be done with the power off and lock-out-tag-out devices used. Safety First!
Hopefully, we were able to give you some insight and enough information regarding how to troubleshoot old circle blade sawmill problems within the following areas of collars, plumbness, and proper lead.
If you read over this and you are still having problems you may need more info or a replacement part? Feel free to reach out to us with further questions or issues you may have.
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