Advanced BS blade discussion

[Perry Holbrook]

I know there are a lot of BS blade questions here, but I just ran into something that I have not seen discussed.

Background. I do a lot of band sawing and have recently upgraded from an 18" Jet saw to a Grizzly G698 17" saw. I use bi metal blades. For a good bit of my work I use a 3/16 wide blade. I discovered that instead of using the standard kerf .025" blades that if I use an M42 blade with a .035" kerf that I can cut smaller radius turns. This is preferred over a thinner width blades because I cut 2" maple with the table tilted at 25 deg making small radius turns. Making those cuts you tend to pull against the blade and the smaller/thinner blades deflect too much.

I ordered a standard kerf and an M42 from my local saw shop when I bought the saw. The standard blade has had no problems. However the M42 has now broken twice. Both times it lasted less than 2 hrs. I took it to the shop this morning and discussed this with the owner. He said that the blade may be too thick for a 17" wheel. He said that as the weld is flexed around the wheel, the thicker blade doesn't bend as well as the standard, creating stress that breaks the blade. He said he has seen it several times on bench top saws and thought it could be true for me too.

I few things to consider. The M42 always ran well on the 18" saw. Tension should not be an issue, the blade is tensioned correctly and as a matter of fact, the thicker kerf blade should withstand more tension due to it's increaded cross surface area. The 17" saw has almost a 50% higher blade speed, 3000 vs 4500 so the blade does flex a lot more often.

The saw shop is going to re-weld again, this time with a little more heat and more annealing. Due to my schedule it will be a couple of weeks before I can try it out again.

So, anybody have any thoughts or past experiences.

Thanks, Perry

[bob hertle]

Perry,

When you say .025 kerf, and .035 kerf, are you referrring to the body thickness? I doubt that you are seeing .025 or even .035 kerf. Tightness of turn capability of a blade is based on the relationship between body width, set, and to a lesser extent body thickness. Most .025 body blades cut a kerf between .039 and .053 inches, with the vast majority at .043-.044 inches. I don't use thick (.035) body blades smaller than 3/4, but most of the 3/4 blades cut a kerf in the neighborhood of .058-.060.

The .035 blade if properly welded and annealed, should live a long life on a 17 inch wheel. I don't think the wheel is your problem. Check the actual kerf of both the .025, and the .035. Could be that you are pushing the .035 blade a little too hard when it comes to tight turns. I've learned from experience to use a blade one size narrower than the radius charts tell me, although some blades with heavier set will perform to the charts. Could it be that your newest .035 blade has less set than your original .035 blade for the 18 inch saw?

Regards,
Bob

[Van Huskey]

First, the wheel size should not be an issue with that width of bi-metal blade, a wide carbide blade yes, but not this one.

Second, you say it is tensioned correctly. How did you determine this, the bi-metal blade needs more tension than a carbon or silicon steel blade and the thicker blade you have now as you noted will need more tension than the previous blade to get the same beam strength. If you are using the saws scale you almost definately need to move up maybe half a blade width on the scale to get the correct beam strength. The scale probably gives you about 15,000 psi on a "standard" thinkness carbon blade of a given size, you need to be at about 25,000 psi for a bi-metal or carbide tipped blade.

Third, get a Carter blade stabilizer it will do more for the accuracy and ease of curve cutting than almost anything else!