Bandsaw tensioning redux

[Erik Loza]

My experiences with Italian bandsaws:

-Never used or felt the need for a tension gauge, either on-machine or handheld.
-The #1 cause cause of unsatisfactory cut quality or performance was caused by inadequate blade tension. Every new owner seemed afraid to hurt their machine by cranking on it. There is literally nothing you can do to hurt a Centauro. The blade will snap long before anything happens to the machine, so keep cranking.
-#2 cause of poor performance was owners setting the guides too close on the wider blades. That actually could create a wandering cut in addition to torching the thrust bearings.
-I always used the flutter test "plus a little more" on 1" carbides. The blade will go long before the actual machine has issues.
-IMO, you don't really need max tension unless you're cutting something really tall, like veneers, milling, etc. Again, I never used a tension gauge but can probably say that for the average 8/4, 12/4, etc resaw job, I was probably using a lot less then 25K psi or whatever. Sure, you need really specific tire pressure for a race car but it doesn't matter if you're just to the corner store for some milk. My rule of thumb always was to try to use the minimum amount of tension needed for whatever the cut was. You just get to a point where you can feel the machine cutting smoothly, no weird sounds from the guides, etc.

Just what worked for me.

Erik

[John TenEyck]

Careful, theres a good chance youre right at the limit of the spring and stacking it if you went from 24k to 42k in a half turn. This is the perfect example of why measuring tension accurately is so important as we approach the limits of our machines.

It wasn't even close, John. When I had 42 ksi on the 1" blade the spring still had a lot of air between the coils. Grizzly claims the G0636X can tension a 1-3/8" blade. Extrapolating my measurements on the 1" x 0.035" blade shows it indeed should be able to reach at least 25 ksi on a 1-3/8" x 0.042" blade. It is a very robust saw.

You are absolutely correct that we need to be able measure tension accurately. This might be even more important on lower stiffness saws than ones with high stiffness. My 14" Delta will not tolerate more than about 12 ksi on a 1/2" blade, even though the owner's manual says you can use blades up to 3/4". Many an upper yoke have been broken on those saws when folks have tried to run high tension on those wider blades. At 15 ksi on a 1/2" x 0.025" blade the upper guides on my saw will deflect at least a blade width to the right. The Iturra spring I have on it is actually not of all that much value because the frame can't handle the forces involved. So while my G0636X is happy running a 1" blade the 14" Delta is best suited to a 1/4" blade.

John

[John Lanciani]

It wasn't even close, John. When I had 42 ksi on the 1" blade the spring still had a lot of air between the coils. Grizzly claims the G0636X can tension a 1-3/8" blade. Extrapolating my measurements on the 1" x 0.035" blade shows it indeed should be able to reach at least 25 ksi on a 1-3/8" x 0.042" blade. It is a very robust saw.


John

That's good to know John. The MM20 that I recently parted with could only achieve 18ksi on a 1" trimaster with the stock spring fully compressed. Once I replaced the spring (with a properly sized off-the-shelf die spring from McMaster) and could accurately and repeatably tension up to 30k it was routine to cut 12"-16" wide veneer 1/16" thick that was ready for the vacuum press right off of the blade.

And yes, for those of you wondering; a trimaster cuts significantly better as the tension is increased.

[Tom Trees]

Nice one Eric, I wasn't aware that Andy had any content regarding the subject.
Strange that the algorithm didn't suggest that for me.
Gonna luck him up to see if I can learn anything.
Thanks
Tom

[John TenEyck]

Eric, Lennox rates their blades for tensions up to 30 ksi, at least the carbide one I use. My friend has the same G0636X as I with the same 1" Woodmaster CT blade on it with 25 ksi on it. He never releases the tension. It's been on his saw for at least 2 years now and still cuts really well.

This article in FWW may be helpful, too: https://www.finewoodworking.com/2012...-blade-tension

John

[John TenEyck]

That's good to know John. The MM20 that I recently parted with could only achieve 18ksi on a 1" trimaster with the stock spring fully compressed. Once I replaced the spring (with a properly sized off-the-shelf die spring from McMaster) and could accurately and repeatably tension up to 30k it was routine to cut 12"-16" wide veneer 1/16" thick that was ready for the vacuum press right off of the blade.

And yes, for those of you wondering; a trimaster cuts significantly better as the tension is increased.

Several of the vaunted Euro machines struggle to put 25 ksi on blades the manufacturer says they can handle. Do they cut OK at 18 or even 15 ksi? Sure, but as you said, not nearly as well as they will at higher tension. As some folks here have pointed out in other threads, when the tension is high enough guides are almost irrelevant to cutting straight. And that makes deep resawing and especially slicing veneer of consistent thickness much, much easier.

John

[John TenEyck]

From Lenox:

https://support.lenoxtools.com/hc/en...-blade-handle-

John

[Erik Loza]

I do think that main tension springs fatigue if you keep a really stiff blade like a carbide tensioned for long periods of time. That is not a machine issue, it's a spring issue. Let's not confuse this with a FRAME STRENGTH issue, which is the primary limitation when trying to put 1" carbides on less robust machines. Also, I found the Woodmaster CT to be more forgiving as far as tension requirements than the Tri-Master, which was the "original" carbide blade and not really designed for wood cutting in the first place.

Erik

[John TenEyck]

I do think that main tension springs fatigue if you keep a really stiff blade like a carbide tensioned for long periods of time. That is not a machine issue, it's a spring issue. Let's not confuse this with a FRAME STRENGTH issue, which is the primary limitation when trying to put 1" carbides on less robust machines. Also, I found the Woodmaster CT to be more forgiving as far as tension requirements than the Tri-Master, which was the "original" carbide blade and not really designed for wood cutting in the first place.

Erik

I wasn't suggesting the machines were at fault Eric, but the springs they put on it were. John L. proved that by changing the spring on his MM20; 18ksi with the factory spring, 30 ksi with an aftermarket one, the saw happy with either. There was another thread on here a year or two ago with another (brand new) Euro saw that couldn't put 25 ksi on a 1" blade, yet it was rated for 1" blades. Again, it was the spring that wasn't up to the task. But we as consumers buy a machine with a spring. If the manufacturer claims it can handle a blade of X width we expect that it will be able to do so w/o compromise. What that point of compromise is is open to interpretation, but it's clear that blades perform better at higher tension. Anyone who has done anything more than casual evaluation will know that to be true. Lenox buries the info. deep on their website, but it's there; their blades are rated for up to 30 ksi. To me that means that machines rated for a blade of X width should be able to apply something close to 30 ksi on that blade.

Cheap springs or ones that must be over compressed to tension a blade definitely will fatigue. Quality springs that operate within their rated range do not over any practical period of time. Look at overhead cam springs in automotive engines. They do their job for years w/o complaint.

John

When I put 24 ksi on the 1" Woodmaster CT on my G0636X the on board tension meter is within a pointer tip of 1". I can't remember if it's above or below but it's really close. And that, to me, means that Grizzly thinks that reasonably high tension gives better performance and designed that saw to deliver it without compromise. Better still, it's a pleasure to use.

John

[Eric Arnsdorff]

Nice one Eric, I wasn't aware that Andy had any content regarding the subject.
Strange that the algorithm didn't suggest that for me.
Gonna luck him up to see if I can learn anything.
Thanks
Tom

Tom I'm not sure if there are different versions out there but on my iPhone app the parameters have a setting for if it is carbide tipped or not. I've attached a screenshot.
Inkleind Tension Params.png

[Eric Arnsdorff]

From Lenox:

https://support.lenoxtools.com/hc/en...-blade-handle-

John

I'm not sure how to take this spec. Are they saying not to exceed 30 ksi? If this is the case then I wouldn't want to tension it at 30 ksi (which will have uncertainty associated with it) then startup and other stresses from cutting could easily exceed this limit and then stretch or break the blade. Maybe they are saying tension to 30 ksi isn't an issue and the elastic limit is much higher.

This was the response I received from Lenox.

Lenox Reply.png

It does sound like others are using tension above 20 ksi and some are indicating above 40 ksi. Since the 30 ksi value corresponds to the typical low strength carbon steel elastic limit along with these indications, I'm going to stick with 20 ksi as an upper limit.

I'm not a power bandsaw user but in my hobby shop I've never broke a blade. I have made some bad cuts (most due to lack of user skills and some due to blade condition). A little added tension and/or a sharper blade has always seemed to make things work for me. Others commenting here have much more bandsaw experience than I do.

The FWW article John posted indicates the 15-20 ksi value I've seen. But it does indicate going up to 25-30 ksi for carbide tipped blades. I don't know why this is. I expected they simply welded the tips onto the same metal but maybe they use a different alloy because of the this added welding process.

I share the concern for blade tension because I only use my saw on occasion as a hobbyist and I change blades. I want a good cut first try and I don't want to break my blades (or the machine but most of my machine damage concern has been eliminated with my new to me 24" bandsaw). I'm sure others here who use bandsaws much more than myself have become comfortable with how to tension the blade by "feel".