Wood Business

Maximum levelling

Aug. 20, 2007 - Getting the most from your bandsaw leveler requires doing a few basic things correctly, and ensuring that the machine is properly aligned.  Some key things don’t seem logical at first glance, but do indeed make sense when we look a little deeper. Let’s look at both daily operational tactics, and some common set-up problems to look at when things don’t seem to be working.

Daily Operation
Three things are important in the everyday operation of a bandsaw leveler: Where you get your reference “zero”; how you get your reference “zero”; and how you move across the saw.  It’s not surprising that establishing “zero” accounts for two of the three points. Without a proper “zero”, all bets are off.  Let’s look at these one at a time:

• Get “zero” over the saw support rails (figure 1):  Your leveler is intended to put the saw flat, meaning on a plane. The only plane available is the one established by the top surface of the carbide rails, so the only place you can get zero is directly over those rails.  It’s okay to work on the saw out past the rails, but if you establish your zero reference someplace besides the rails you will likely be telling the machine to move the saw to a plane that the rails make it impossible to reach, unless the saw is perfectly flat to begin with! This will cause ridges over and adjacent to the rails.  

• Get “zero” on the fly:  Equally important in establishing zero is having the saw moving.  This will prevent accidentally setting zero on a bump, which will again have the machine trying to move the saw up to the plane of that bump, a place the saw cannot possibly reach.  When getting your zero this way you should look for your indicator (or sensor) to work from zero UP only, because a bump DOWN cannot move past the rail.  On the machines that use indicators (the pretty red machines!) this means the indicator will work from “0” to the right only, and will not move left of “0” unless you run over a thin spot like a weld.

• Take big steps: One of the important counter-intuitive things we have learned is that it’s vital to take big steps across the saw. If you take small steps, the machine will routinely start seeing bends before it reaches the worst part of the bend. It will then start trying to fix the bend too soon, and overwork the saw.  This will cause a saw in rough condition to end up with hard ridges the machine has actually pushed into the saw – these are hard to get out again, and will waste time.  

The worse shape a saw is in, the bigger the steps you need to take moving across it. For instance, if a saw is dished, set your machine to make a couple of passes at 1" or 1-1/4" spacing to get the dish out, then dial it back to 1/2" and let it have another couple of passes to find the little stuff. You’ll save lots of time and get superior results.  Don’t get caught in the “I really want a flat saw, so I’ll set it for 1/8" advance” trap!  Never set your machine for less than 3/8" or 1/2" advance, and if it’s in tough shape open that up to 1" or more and you will get better saws in less time!

Common Set-Up Problems
If after the above you are not getting the results you need, take a look at some of the basic set-up points on your machine.  A good place to start is checking that you are set to fire at the same tolerance on both sides of zero. We set our machines up to fire the first stage reaction at ± .03mm each side of zero. This is three marks on the face of the dial indicators that we use, and is equal to .0012" (one point two thousandths of an inch!).  This is quite a small tolerance – a piece of notebook paper is about 2-1/2 times this dimension. Setting the tolerance closer will not improve leveling, and may cause the machine to simply shove the saw back and forth.  

The second stage on our indicators is usually set at ± .12mm, which is about .005" and is the point where the machine will add pressure for a bump that is worse than this. It is not terribly critical that this 12 mark second stage is exactly the same both sides of zero. Within a couple marks is fine, but the 3 mark (.03mm) first stage needs to be the same both sides (within 1/2 mark).

Now check that you are leveling as close to the gullets and edge of the saw as possible. Set your limit switches so that you move the large diameter flat on the outside of the female roll over the bottom of the gullet, or the sliver tooth or back edge of the saw. This will get you out close to the edges without damaging the indicator.

Another key is getting the height of the bottom leveling rolls correct in relation to the bed line of the machine (established by the plane of the saw support rails and the drive).  The bottom leveling rolls must be at or just barely below this line (no more than .010" lower).  If the rolls are too high, they’ll lift the saw as they move across during processing, changing the measurements. If the bottom rolls are too low when the top rolls fire, they will drive the saw down, breaking the saw over the leading edge of the saw support rails and causing the tension to pop up (figure 2). If you have to adjust these bottom rolls be sure that you turn them the correct direction to keep their eccentrics mated with their top rolls.  On the left hand roll turn it clockwise to raise it (counter-clockwise to lower it), but on the right hand roll do the opposite – turn counter-clockwise to raise it, and clockwise to lower it.

Worn drive rolls can also cause tight ridges that coincide with the edges of the rolls.  This will start to show up after the machine has many hours of service, but these ridges can be very difficult to get out.  It’s a result of the change in diameter of the drive parts from normal wear, which causes them to become miss-aligned.  When they wear enough for their centre-lines to shift apart a bit, they will start to work like a panning roll, but always bending exactly the same place in the saw, creating small hard ridges.  If these parts wear – replace them. If your machine has a steel top drive, replace it with the newer polyurethane replacement, which will last virtually forever.  

If you have checked all of the maintenance and operating items thus far and still are not satisfied with the results, it’s time to look at how the saw support rails are aligned with each other, and how the head moves in relation to these rails.

The two carbide-faced saw support rails must be flat and they must be set up with their top surfaces parallel to each other. Check for flatness by pivoting the hold down rolls out of the way and laying a good straightedge on the full length of the rail.  If wear is evident, get the rails surfaced or replaced. Now use a depth micrometer to measure from the top of each rail down to the plate that supports them on both the leading edge and the trailing edge (as close to the head as possible and as far from it as possible) and adjust the rails until they are parallel.  These four measurements should all be within .001" – .002" of each other.

Once you are certain that these rails are parallel, you need to establish that the workhead is moving parallel to the plane of these rails.  An easy and very accurate way to do this is by mounting a magnetic base dial indicator on the workhead of the machine, resting the point of the indicator on a straightedge laid across the rails, then running the head in and out to verify that the indicator reads the same on both rails and between them (figure 3).  If you find that the indicator is off more than .005" over the working width of the saw, shim the entire support mechanism that holds the rails in place until you get that movement down to within that five thou.

One important note – don’t let bent teeth confuse you when it comes to what the leveler is doing.  The levelers are indispensable tools, but they cannot level the teeth themselves.  If you see problems in the front quarter of your saws after they come off the leveler, make sure it’s not a result of bent teeth.  Move your saw so that the whole tooth is off the anvil. Does that make the problem vanish?  If so, the teeth are bent down! Move your straightedge back so that it is not resting on the tooth at all. Does that make the problem vanish? If so, your teeth are bent up! You can verify this using your leveler. With the mach­ine stopped, move the indicator right out onto several teeth in the suspect area, one at a time. The indicator will tell you very quickly if the teeth are bent in either direction. You can’t level out that far, but with the saw stationary you can use the leveler to measure.

There are lots of other ways that the operation of a leveler can be impacted by worn parts or bad set up, but the ones outlined above are a solid beginning based on our experience with these machines.  If you go through these steps and still need help, contact the firm that supplied your machine, and they will be eager to help get you running right.

Russell Barratt is a sawfiling specialist with Simonds International, based out of wherever saws are being doctored. He has been involved in filing and sawmill gear for 27 years. This is the third in a series he has written exclusively for Canadian Wood Products Magazine.

April 28, 2017
By Russell Barratt

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