I remember having a friendly conversation with a gentleman about sawguides and he said a few things that really bothered me. The first was that the people working in a sawmill couldn’t tell the difference between an accurate sawguide and one that’s less accurate. The second was that the accuracy they were giving their customers was good enough.
I may have seen some truth to this, fifty years ago, but not today. Fifty years ago we had plenty of old growth forest to harvest. The wood was large in diameter and readily accessible to the mill. The word recovery (or wasting less fibre) wasn’t even used. Back then, lumber was cut much thicker and a planer took care of the rest.
Today, fibre waste and recover are vitally important in high-speed edger lines. The industry is dealing with new growth forests, translating to smaller diameter logs. So nowadays, the accuracy of the sawguide IS the difference between a usable or unusable piece of lumber coming off the edger line.
Let’s start with the fact there’s only 0.0015” between a saw blade and Babbitt pad. If you have a sawguide that varies by +/- 0.0005” then you would have a variation of 0.001”. This variation equals 2/3 of your clearance. That’s a lot.
If this variation makes your clearance too large then the saw blade would wobble between the Babbitt pads and you’ll get more within board size deviation. This means the thickness of the board would vary, and the recovery from each log would be reduced.
If this variation makes your clearance too small, then the wobbling saw blades would hit the Babbitt pads more often, causing increased friction. This friction would cause the saw blade to heat up, lose tension and fold over. When this happens saw mill costs rise due to increased downtime and premature replacement of saw blades.
Ironically, I’ve seen many saw blade manufacturers blamed for bad saw blades when the actual problem is sawguide accuracy. I‘ve also seen sawmills compensate for inaccurate sawguides by increasing the clearance between the Babbit pad and the saw blade. But, as mentioned before, when you increase the clearance you end up with more within board variation. To compensate for this variation the mill would then need to increase the target size of the lumber (the thickness of the lumber coming out of the sawing edger) so the planer (which brings the lumber to its final size after drying) can ensure the lumber is at the proper finished dimension.
Therefore accurate sawguides ensure:
- Less downtime
- Less wasted lumber (greater recovery)
So to answer the question, how important is the accuracy of your saw guide? I would fathom to say, if you want to save your mill both time and money, accurate saw guides are very important.
How important are the accuracy of saw guides in your mill?
Author: Udo Jahn
