The importance of staying aligned while sawing
By Trevor Shpeley
Feb. 13, 2017 - For as long as mill workers have been running wood through saws we have understood the importance of having every part of the machine positioned at exactly the right pre-determined location and angle to facilitate the smooth passage of the log and the straightest cut possible. A very small change in the inclination of a roll can mean the difference between a good day and a disaster. A slightly off angled saw will heat up and destroy itself in short order.
There are many different types of saw-centres out there, but lucky for us, you don’t need to know how to do every one as long as you understand the basic principle of alignment, which is to pick a level or vertical surface that is immobile as a base point (datum) and make everything else plumb, level and square to that. Most mills have fixed points in their sawlines for attaching tautly strung piano wire to serve that purpose; others use guide bars or optical lines for the same thing. It doesn’t really matter as long as it doesn’t move.
It is important to remember that not everything is to be level or square. Some parts are toed in or out, some rolls are canted forward or back but these exceptions are well known and mostly hold true from machine to machine.
The tools needed for a proper alignment can be costly or very cheap. The expensive tools give you the capability for improved accuracy, but you can absolutely do a very good alignment with a minimum investment in equipment. The most common methods of alignment used in mills today are the “wire method”, lasers and optical jig-transits.
The wire method involves stretching a length of piano wire from one end of the machine to the other, parallel to the wood flow, typically right down the centre of the profile, spline or sharp chain. The wire is made as tight as possible to minimize the possibility of movement. Other lines are strung at 90 degrees to the first wire where needed. This technique is tried and true. The downside is that the act of measuring against the wire sometimes changes the measurement and when 0.002 of an inch is a large number, it doesn’t take much of a push to get that much of an error.
Laser alignments are another popular method. A laser is directed through the machine and through mirrors and prisms to achieve the desired angles. Then a detector is used to measure the relationship between the equipment and the beam of light. Lasers are very accurate and many swear by them.
The other procedure gaining strength in recent years is to use an optical jig-transit, a device originally used for the very precise alignments required in the aerospace industry. The advantage of optical alignment is extreme accuracy. It allows you to take very precise measurements of every component in your line horizontally as well as vertically and it works over long distances. Difficult to measure objects such as the angle of spike rolls are easily determined and you can quickly check a press roll through its entire arc of travel. The disadvantages? It’s a pricey piece of gear and somewhat delicate. It requires a practiced skill level to setup and a non-running mill due to vibration interference. Is it worth the money given that? For me the answer is yes, but then, I don’t write the cheques.
Unfortunately for the sawmill industry, alignments have dropped out of favour somewhat. Everybody knows they are a good idea and yet they don’t get done nearly as often as they should. In some mills “rarely” is optimistic. There are many reasons for that. One is inter-trade rivalry in which one group claims mechanical control over a piece of equipment and won’t let the sawfilers “on their turf” to do the job. Another problem is that some management does not fully understand the importance of a properly aligned machine and work on the principle of “If it ain’t broke, don’t fix it”. The bottom line is, make everything straight and you will make better lumber and spend less time fixing broken equipment.
Trevor Shpeley is on the executive of the BC Sawfilers Association and works as a filer at Kalesnikoff Lumber in British Columbia.