CNC band saw blade life

Have had this machine now for a little over 3 years and been a great saw and it runs 8 hours almost every day. I was never really pleased with the blade life cutting 6061 rod, most 4-1/4" to 6" using Lennox classic pro 3-4 pitch blades. We use Lennox online blade speed calculator to set the speeds and feeds based on their recommendations but we still only get 100-120 hrs before the blade breaks at the weld. We have tried several different vendors but the results are pretty consistent. We did get one that went 400hrs once

I maintain the machines myself and keep the blade brush replaced as needed. 6 months ago I replaced all the blade guide bearings but not the carbide guides as they showed very little wear.

So my thought now is maybe coolant. We use the drained coolant for all the hoppers to keep the band saw full and add a little mix to keep it ~10%. Do you guys run your coolant at a higher mix?

I have never had great luck with Lennox blades lasting very long. I have a Behringer that we run about 4 hours a day and it came with about 50 Lennox blades still boxed up, and like you would get about a month out of them (if they did not break in the first hour). Switched over to Haberle blade stock welded up by a localish supplier and we get 3 to 4 months out of them. I hate changing blades so we use the same ones on everything from stainless to aluminum and because the saw does constant feed we don't knock the teeth off with little stock (I just leave 2-3 pitch blades in it). As far as speeds and feeds go, I crank it all the way up for aluminum and plastic, and slow it down to about 70 for steel. I set the feed by how the chips look and try not to outthink it.

You shouldn't be breaking blades at the welds, no matter how old they are. We have an Amada that has been running a steady diet of 347 lately, and we certainly wear out the business end before the backing. Many years and a couple of saws ago, we had a smaller saw that would break the blades from fatigue. At first I thought the blades would break at the weld, but after looking closely, the entire backing would be fractured every ~4"-6" and it was still quite sharp and cutting well. Point is, the blades would never break at a weld - I haven't had a blade break at a weld in almost 20 years. We have a local blade shop make them for us, and since switching to them I have not had any issues other than operator induced. I think you need to find a new blade supplier.

Steve

Check the band wheels with the blade fully tensioned to make sure they're both parallel and in the same plane. Hopefully you can check across both wheels with a straightedge (piece of CF steel flat bar will suffice) with the cover open as that makes it pretty simple.

I bought a used automatic saw that was in excellent condition but it would break blades at the weld. I eventually found the idler wheel was out of parallel with the drive wheel. Once I adjusted it to parallel, it was out of plane. Apparently, someone had replaced a bearing or something in the past and got the idler out of plane. Then, when the blade didn't run fully on the wheel as it should, they canted it to make the blade move onto the wheel properly. The problem with a canted wheel is that the blade is then running on a section of a cone, so the tension isn't distributed evenly across the width of the blade. Spent 2-3 hours getting it back to the proper geometry and haven't had any problem with blade breakage since.

One other potential cause I ran across while reading online trying to solve my problem is related to the guides. Some saws have ball bearing guides on the sides of the blades that are offset from one another. If adjusted too tight, they don't squeeze the blade but rather force it to do a jog motion as it passes thru the guides. This will cause breakage, typically at the weld since even a good weld leaves something of a discontinuity in the blade as compared to the rest of the undisturbed blade stock.

Another guide related problem that can occur on saws whose blade guides are adjustable laterally is that they can be adjusted such that the saw cuts straight but the guides are forcing the blade out of line as opposed to just twisting it to a vertical position. As with the guide problem above, this causes the blade to go thru lateral deflection which eventually fatigues the blade and causes it to break.

Re the coolant, 10% concentration should be fine. If you're cutting 6" round with a 12 ft blade, for example, any given tooth is only in the cut a max of 1/24 of the time, or about 4%, and that's only happening when you're cutting across the full 6" dia. Hardly a heavy duty cutting operation, particularly in aluminum. The main function of the coolant in this case is to flush chips and prevent a chip jamming and breaking a tooth (or 20). Plain water would likely work fine were it not so unfriendly to the saw itself.

You shouldn't ever be breaking blades.
If its gets to that point, your cut must be 1/2" off square...

SOmething else must be wrong.

ManualEd said:

You shouldn't ever be breaking blades.
If its gets to that point, your cut must be 1/2" off square...

SOmething else must be wrong.

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That's the point the dam thing cuts perfect. On a 6" rod using a presion square you might be able to get a .005" feeler gage under the square from top to bottom, left to right is dead nuts.

Since it was mentioned about the drive and idler wheels checking for alignment or canting got me to thinking about where the blade starts to break first. Generally when you hear the blade start making noise you only have maybe 30 seconds or less to get over there and see what happening. The few times I have been nearby I did notice the blade was always breaking in the weld from the top down.

I'll see if I can get access to the wheel to check squareness without tearing too deep into the sheet metal otherwise it will have to wait till next weekend.

Thanks for all the advise on this!

I am with the group that says if you break blades something is wrong with the saw. I have an old as dirt Kysor-Johnson that uses 11 1/2 foot long x 1" blades that I cut everything with using what I would call a multi purpose blade as I hate changing them. In 20 years of use I have never broken a blade. I use the same coolant I use in the CNC lathes and make sure the chip brush is doing it's job. I use Morse brand blades. The only saw I have ever snapped a blade on is an HF piece of crap that uses 1/2" blades I use for cutting one of something small. It always snaps them before the teeth are dulled all the way, but it is a piece of junk saw, and I use it so little I never bother to figure out what is wrong with it and it is used dry.

Dualkit said:

I am with the group that says if you break blades something is wrong with the saw. I have an old as dirt Kysor-Johnson that uses 11 1/2 foot long x 1" blades that I cut everything with using what I would call a multi purpose blade as I hate changing them. In 20 years of use I have never broken a blade. I use the same coolant I use in the CNC lathes and make sure the chip brush is doing it's job. I use Morse brand blades. The only saw I have ever snapped a blade on is an HF piece of crap that uses 1/2" blades I use for cutting one of something small. It always snaps them before the teeth are dulled all the way, but it is a piece of junk saw, and I use it so little I never bother to figure out what is wrong with it and it is used dry.

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Our Johnson saw is old as dirt as well. Damn thing just keeps cutting. I had the lennox tech in one day and he walked into a job setup on the saw that was...."improvised" shall we say. He asked to take a picture of it because he'd never seen someone do what we were doing with a Johnson saw. He requested that if we ever sell it...to give him first dibs.

I agree, breaking at the welds is strange. We beat the crap out of our 1 inch blades and they are dull as shit or damaged before they break. Operator error causes most of the issue. Saws aren't hard to use correctly, but some guys make it look like brain surgery.

I have a HydMech on the way. The Johnson might get retired...easily one of the best pieces of equipment we've owned.

Could you be getting chip build up between the wheels and blade? The added tension would snap a blade pretty easily.

I have to take the blade off the saw and scrape the chips off the drive and idler wheels that have gotten imbedded, probably every 10 hours of cutting.

It gets even worse when we're bucking up brass and aluminum. The stuff gets everywhere and sticks like shit to a blanket.

Dualkit said:

I am with the group that says if you break blades something is wrong with the saw. I have an old as dirt Kysor-Johnson that uses 11 1/2 foot long x 1" blades that I cut everything with using what I would call a multi purpose blade as I hate changing them. In 20 years of use I have never broken a blade. I use the same coolant I use in the CNC lathes and make sure the chip brush is doing it's job. I use Morse brand blades. The only saw I have ever snapped a blade on is an HF piece of crap that uses 1/2" blades I use for cutting one of something small. It always snaps them before the teeth are dulled all the way, but it is a piece of junk saw, and I use it so little I never bother to figure out what is wrong with it and it is used dry.

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XD341 said:

Our Johnson saw is old as dirt as well. Damn thing just keeps cutting. I had the lennox tech in one day and he walked into a job setup on the saw that was...."improvised" shall we say. He asked to take a picture of it because he'd never seen someone do what we were doing with a Johnson saw. He requested that if we ever sell it...to give him first dibs.

I agree, breaking at the welds is strange. We beat the crap out of our 1 inch blades and they are dull as shit or damaged before they break. Operator error causes most of the issue. Saws aren't hard to use correctly, but some guys make it look like brain surgery.

I have a HydMech on the way. The Johnson might get retired...easily one of the best pieces of equipment we've owned.

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Ha,ha, I bet mine is uglier than yours. I tried to date mine and I think it is an early 70's model that looked used hard when I bought it 20 years ago for $300, it had been stored outside uncovered and the motor went up in smoke when I hooked it up and the counter weight was missing. I made a counter weight, replaced the motor, sanded the corroded contactor contacts and she has been reliable as ever for two decades.

ManualEd said:

Could you be getting chip build up between the wheels and blade? The added tension would snap a blade pretty easily.

I have to take the blade off the saw and scrape the chips off the drive and idler wheels that have gotten imbedded, probably every 10 hours of cutting.

It gets even worse when we're bucking up brass and aluminum. The stuff gets everywhere and sticks like shit to a blanket.

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That never happens to me, is something wrong with your coolant flow direction or the chip brush?

Dualkit said:

That never happens to me, is something wrong with your coolant flow direction or the chip brush?

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Its just a poorly designed saw. 10 hours cut time on saw is about a month for us.
The chip brush does an okay job, but 1 or 2 chips every 10 revolutions adds up.

I do open the covers every morning and flush out the chips that do make it inside and around the band wheels with coolant and keep the brush wheel adjusted or replaced as needed. I would think that with a Hydro tension system a little chip build up on the wheels wouldn't be that big of an issue but could be wrong.

Captdave said:

I do open the covers every morning and flush out the chips that do make it inside and around the band wheels with coolant and keep the brush wheel adjusted or replaced as needed. I would think that with a Hydro tension system a little chip build up on the wheels wouldn't be that big of an issue but could be wrong.

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I wonder if that's the problem. The HEM saws I was looking at have a giant die spring to maintain tension. If you got chips between the blade and the wheel the spring would give a little to maintain the pressure. A hydro won't ( I wouldn't think) and would make one hell of a stress concentration.

What do the wheels look like? Any dings or damage?

We have an old Kysor/Johnson, sounds the same as the one DualKit is using,. Same blade anyway. Thing was reclaimed from being out in a FIELD years before I came here, and that was 13 years ago. That thing just cuts. Got it mounted on big casters so we can move it outta te way if we need to. Use it for just about whatever we decide to cut. Mostly 1144 or Stressproof. Plus whatever I need to cut for fixtures and such. It's just bulletproof. Very seldom it breaks a blade unless some dip fails to get the vise tight and lets the work kick around. I won't say it's all that good a saw, but it's damn sure durable.

IME im with metlmuncher, the guides must just twist the saw straight, if the horizontal - thrust pads are pushing down on the blade or the works bowing it up that will cause your problem as your then trying to bow the blade the hard way and the stress numbers go through the roof.

Does the crack always start at the teeth or at the back of the blade? If its always the same side, its a clear indicator thats the ouside - most stretched direction and should help you narrow your options down a bit.

FYI i disagree with the above posters, blades do have a fatigue life especially on smaller saws which have smaller wheels. if your truly encountering the blades fatigue life you want to run em faster and feed a little harder so you blunt em first :-) Takes a exceptional weld for a blade to fail from fatigue else were though, generally on most the saws i have been around, you have to reweld the blades at least once to get em to the point that the cracks form else were.

Spent some time last night messing with this and the first thing I found was the top of the carbide guides had some slack in them, maybe .030" on left side and a little less on the right side. Spoke with a tech and he said to adjust the tilt on the idler wheel till the blade was running .010-.020" from the top first. Did that and it brought the blade up to just lightly touching the top carbide guides on both sides.

What do the wheels look like? Any dings or damage?

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Found a small chuck of metal caught in the ribs of the drive wheel a dug it out with a pick.

So I have to agree with the guys that caught that the blade saw breaking in the weld from the top and mentioned the possibility of the blade bowing under the pressure of the cut seems spot on. The current blade has 30 hrs on it I'll let you know when it pops!
Thanks for all your insight!

ManualEd said:

sticks like shit to a blanket.

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Ok, now THAT'S funny!
I've never heard that saying before.

Personally I don't like Lennox...have had too many fail at the welds. Yes, they take them back and replace with new...but I hate changing blades. Then your out of the ones you need and start using the wrong blade for wrong job. Have to ship out...follow up.

Starret..not a fan either.


I'll tell you the least expensive and the Blades I'd pay the most for...SawBlade.com, 601 Bi-Metal Blades. Unless we make an Oops they just run constantly for weeks and weeks.

I throw mine in the oven at 500F for an hour.