On the level
By Trevor Shpeley
Aug. 16, 2016 - On the surface, levelling a saw sounds pretty simple. You just put a straight edge against the saw with a light behind it and look for a dark spot. Then you hit it with a hammer until it is gone. In reality, levelling a saw is very difficult to learn and perform properly.
One of the reasons levelling is so important is that everything else is dependent upon the saw being perfectly flat. That means no twist, no cupping or bowing, no ridges and especially, no bumps. Any bump bigger than .001 of an inch needs to be removed before any tensioning, sharpening or tipping can take place.
So why is levelling so hard to learn? Let’s go back to the basic mechanics of the task. You take a piece of steel that you have ground perfectly straight on a specialized grinder and you place it on the saw between yourself and a light. Bumps will show up as a black spot along the bottom of your straightedge, so will tension. In fact, tension can look exactly like a bump. If the tension is too heavy or unevenly distributed, the saw will want to cup or bow making levelling the saw almost impossible.
To complicate matters, a saw has two faces and bumps will appear on both. The saw filer will use levers and other homemade devices to push a dent out from the bottom of the saw or they will climb down into “the pit” to level the inside of a saw directly. The round saw filer will just flip the saw from side to side until everything is smooth. It would be nice if you could just flatten all the bumps you could find in one area and then go on to the next but when that is attempted you will bow or dish the saw by over-levelling. The trick is to hit the worst bumps all around the saw and keep going over and over until the saw is flat.
If you fail to get the saw perfectly level before performing the rest of the benching procedure, you will never get the saws to run right. A small bump can hold up the tension so that it looks like you need to add more. After you do that and put the saw in the run, typically the bump will “pop” and suddenly your saw will be all over the place due to the massive amount of tension you put in when you thought there wasn’t enough. It is also common to put bumps into the underside of the saw by hitting them too hard while trying to remove the ones on your side. A trained hand and a delicate touch is required to level a saw without creating new problems.
The most common levelling method is to use a hammer to pound out the bumps. Hammers come in different weights and styles of head shape for different sizes of saws and types of defects. The levelling is done on a soft anvil so that the squishing of the saw between the anvil and the hammer is minimized in order to avoid adding more tension to the saw during the levelling process. Hammers work well and a skilled saw filer can do wonders with a good one but many benchmen eventually graduate to doing most of their band saw levelling with stretcher rolls.
Rolls have the advantage over hammers in that you can do a lot of heavy levelling without adding any tension or causing any bumps on the reverse side of the saw. It is also much easier to remove twist and ridges with the use of rolls and you don’t get that “peened” look you get from heavy hammer work. There are still areas where hammers are definitely the best tool for the job but most band saw levelling can be done more effectively with the use of rolls. In round saws, rolls are the best for removing ridges or fixing a dished saw but hammers still play a very large part in the circular world.
Several manufacturers now produce very fine auto-levelling machines. Some are more complicated than others but most have one thing in common: they do the job of levelling a saw very well – these are not your grandfather’s auto-levellers! The newer generation machines do the job with no drama and minimal tinkering between saws. Choosing which leveller to buy can be tricky as they have different scanners and methods for removing defects and the price can vary widely. But if you do your homework, you can be sure of getting a decent tool that can take the grunt-work out of levelling saws.
In the end, it doesn’t matter what you use to level your saws as long as they are level. No matter how good you are at every other aspect of the job, if you can’t get your saws perfectly flat then you are just spinning your wheels. When you get it right though, everything else gets a whole lot easier!
Trevor Shpeley is the head filer for Tolko’s Kelowna division and is currently the financial secretary for the BC Saw Filers Association.