The Bottom Line about Sawing Straight - Part 2

by Tim Cook

Tim Cook

In the last issue (Issue 3 2012) I gave you a little history as to how I came to realize many of the blade discoveries that garnered me some insight toward sawing straighter and faster.  These findings revealed some key foundational truths about blade characteristics that led me on to experimenting more with blade life.  The next area I decided to start testing was band wheels since you can have the best blade in the world but if your band wheels aren’t up to the task then even the best blade will not perform.

In the early years of portable sawmills there was really only one major manufacturer and they happen to use belted band wheels (and still do) on their sawmills.  Belted wheels worked relatively well and as these were the only machines on the market belted wheels became the norm as the industry grew.  We also used both belt inserts and urethane for quite some time.  The fact is that true wheels are best whether steel, rubber coated, or belted.

So which one is going to give you better blade life, straighter cuts, faster feed speeds…etc?  Well that was what we were set to find out back in the 90’s when we starting experimenting extensively with all sorts of setups.

The first thing I realized upon close examination is that there was not one v-belt sheave that ran true regardless of the manufacturer.  After talking with a few engineers from some of the sheave manufacturers it became evident that these sheaves didn’t have to be true for their intended purpose (which obviously is not sawmill band wheels).  They are manufactured within a tolerance good enough to drive a belt at a certain speed and being true is not pertinent to proper functionality.  That is why if you’ll notice drive belts on machines bounce up and down (some more than others) continually.

How does putting a v-belt sheave affect a band blade? Well that is where the belt insert comes in.  The belt plays a couple of roles, one being that it acts as a shock absorber for the blade and secondly it provides a crown (rounded back belts) to guide the blade.

What we observed was as the belt started to wear down the blade began to touch the band wheel (sheave) but since the sheaves are untrue the blade would only make contact with a small area of the sheave.  At the speeds needed to saw this caused the blade to ‘slap’ as it made contact with these areas of the sheave causing the blade to break pre-maturely. I realized this was what many people were experiencing and from this type of issue the term was coined ‘steel on steel breaks the band quickly’.  The fact is, as we discovered that this wwas far from the truth.

Not only did the problem lay in the fact that v-belt sheaves were not true, it was compounded in that the belts themselves were not true.  Again, they work great for their intended purpose and were not designed to be perfectly true on the outside.  This is especially evident often times where the belt is fused together at the ends.  This is clearly evident as you can observe a blade running on belted wheels often times looks as though it is 1/8” thick; this is a result of it bouncing up and down on the belt.

The other detriment to rubber belts or inserts is that their shape changes much faster in comparison to steel.  Steel is also not affected by diesel fuel, mineral spirits, or other fluids used to clean and lubricate the blade. Also with belted wheels when a blade breaks there is always the chance of it cutting into the rubber wheel or belt and if you’ve run a mill long enough with this setup then you have probably experienced this more than once; this is a non-issue with steel wheels.

As we continued to test it became clearly evident that crowned and true steel wheels were superior in every regard.  The blade life was increased by no less than 25% on any test that was done.  The sawmill itself acted as if it had more horsepower because it cut faster.  We were also able to enter the log at the same speed we would saw the log without deviation up or down upon entering. Plus the life of the crown on a steel wheel was an added bonus. It was a clear decision for us and before too long we had put production band wheel grinders in place and switched all of our manufactured sawmills over to steel wheels.

There are many people who use belted wheels and are content with them.  That is great. If it works for you then by all means keep doing what you’re doing.  However, whenever the question is asked and I give an answer there is always a few who beats there chest in defense of belted wheels because they’ve never had a problem and the company that made their sawmill could never be wrong.  I get it, but at the end of the day I ask the same question “How much time and money have you spent testing?” If I was a betting man I bet 99% of the naysayers have spent little to nothing outside of their normal day to day or occasional sawing. The only backing they have is that it is good enough for them or their favorite sawmill manufacturer does it and that’s good enough for them as well. I can make the same claim, so who’s right?

Well there is certainly much more that can be said regarding this ongoing debate, but in the end (at least for me) I’ve put both through extensive testing in a variety of environments and steel wheels, although more expensive, have always come out the clear winner.

Hopefully in the next issue well continue this discussion on sawing straighter when we’ll take a look at blade curvature and how it effects your sawing.