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6th Nov 2023, 07:48 PM #1Diamond Member
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Hafco EB-320 bandsaw - eating blades
Have an unusual problem with the big bandsaw.
The last blade I bought only lasted a few weeks
Today, was cutting some 90mm box section (6mm wall),
and the blade started its tell-tale bounce, indicating a tear.
I nursed it along for a few cuts, at the lowest speed,
and notices there were actually 3 major tears.
Then it broke, and I took a good look at the band:
IMG_4711.jpg IMG_4712.jpg IMG_4713.jpg
not good photos, but there are small tears about every 30 or 40mm,
from the base of the deepest gullets, where the variable pitch is coarsest.
It seems to be the whole length of the blade !
I usually use Hare and Forbes blades, which are Starret.
This was the first time I have used an Excelsior (German made?) blade.
'twas 10/6tpi, used carefully, mostly with coolant, slow blade descent rate.
No stainless, only mild steel and Alum'm. The teeth still feel sharp.
The only thing I could think of was some problem with the saw,
so I cleaned out the blade guides. This model has carbide bumps to locate the blade,
and I did notice the top of the left side has broken off:
IMG_4714.jpg IMG_4715.jpg
on both the front and back guide.
Which might cause some strange wear on the top (non-cutting) edge of the blade,
but I can't imagine it causing fractures between many of the teeth?
Any suggestions?Nigel, from a cave FULL of unfinished projects and lost tools.
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6th Nov 2023, 08:37 PM #2Philomath in training
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In the first instance, I'd be going back to the seller (or manufacturer) and putting that question to them. To my eye, it looks like a blade manufacturing error rather than something wrong with the bandsaw.
Either the tool that forms the gullet is putting a stress raiser in or the heat treatment has not been well enough done and it is too brittle. I would guess if you did some microscopic inspection or die-pen on the blade, most of the gullets would show signs of cracking.
Michael
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6th Nov 2023, 10:26 PM #3Most Valued Member
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I agree with Michael - certainly looks like a blade issue to me.
I use Arntz brand bi-metal blades that I get from Specialty Saws. I’ve ripped teeth off due to operator error but never had one break. From memory the last ones I bought were around $50 each delivered.
What width and thickness blades does the saw use?
Steve
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7th Nov 2023, 03:55 AM #4Senior Member
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I have a much smaller, crapper Hafco saw. All my blades end up cracked like that but that is after years of service. I once looked up some troubleshooting and cracking is associated with overtension which makes sense but not much incentive to do anything about it in my case because I'm getting a good service life (and generally missing a load of teeth by then anyway).
Two weeks seems awfully short though. For context what is your normal blade life?
Also agree with the others that it could be a manufacturing issue but I'll also throw tension into the mix, and it might not be tensioner related but some other misalignment that is bending the blade across its width. i.e. opening up the toothed side to promote cracking in the gullet.
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7th Nov 2023, 11:09 AM #5Senior Member
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Excessive tension on the blade guides can cause blade failure. If the guides squeeze the blade too tight, they can deform it. The teeth/ gullets should not be in the guides and so you get differential deformation
https://www.sawblade.com/common-caus...saw-blades.cfm
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7th Nov 2023, 01:21 PM #6Intermediate Member
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Unless the tension spring is bottomed out( completely compressed) it is very very difficult to put too much tension on most bandsaws. I suspect this is not the cause which is actually a manufacturing fault
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7th Nov 2023, 06:29 PM #7Diamond Member
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7th Nov 2023, 08:27 PM #8Most Valued Member
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8th Nov 2023, 07:53 PM #9Diamond Member
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8th Nov 2023, 08:01 PM #10Diamond Member
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I'm still digesting all that, but they do mention "One of the main problems that causes saw blade back cracks is when you have your machine?s guide arms spread to far apart, so be sure to keep them properly spread"
This blade did several cuts across wide 10mm or 12mm plate. 200mm wide and 300mm wide plate.
300mm is close to max, which means the front guide is very far back, and the blade has a tight twist between the wheel and the guide block/rollers.Nigel, from a cave FULL of unfinished projects and lost tools.
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8th Nov 2023, 08:12 PM #11Diamond Member
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Tension is an interesting one. This machine has a gauge:
IMG_4720.jpg
with a helpful green zone. Easy to check for each cut. It stays in the green.
However, the blade tag mentions a tension spec:
IMG_4719.jpg
of 300N/mm2, which by my calculations is 300MPa or 30.581kg/mm2.
The green zone on the gauge is 1000-1500kg/cm2, or 10-15kg/mm2, or 98-147MPa?
So, if the gauge is to be believed, green zone is half the required tension?Nigel, from a cave FULL of unfinished projects and lost tools.
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8th Nov 2023, 08:25 PM #12
Hi Nigel,
This blade did several cuts across wide 10mm or 12mm plate. 200mm wide and 300mm wide plate.
300mm is close to max, which means the front guide is very far back, and the blade has a tight twist between the wheel and the guide block/rollers.Best Regards:
Baron J.
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8th Nov 2023, 09:03 PM #13Diamond Member
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Probably fractured in the past from dropping the blade on a work piece?
(descent hydraulics set with too little damping/braking)
The carbide is ground with a little hook/step on the top:
4BM0102--BLADE-GUIDE-SQUARE-no.102.jpg
https://www.machineryhouse.com.au/4bm0102
(upside down object photograph. Thanks Hare & Forbes!)
That step makes it a fragile shape.
But at $78 each, I'm not keen to replace the pair just to see if there is any improvementNigel, from a cave FULL of unfinished projects and lost tools.
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9th Nov 2023, 02:26 AM #14
Hi Nigel,
At that price I wouldn't like it either !
Can you source some from China ? It certainly would be more cost effective.Best Regards:
Baron J.
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11th Nov 2023, 10:26 AM #15Most Valued Member
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While it may not directly fix your problem, I've had quite an association with an EB 320 running 6/10 Exelsior blades in a production workshop as part of an alternative education program. That poor saw digested everything from 75X10 flats, cut 5 lengths at a time, to 25X25X1.6 Duragal SHS cut in blocks of 25 lengths, or as single lengths, down to Y12 deformed bar cut in groups of 6 lengths (this one was particularly hard on blades if you didn't set it up properly). Most of this work was performed by 14-16 year old students, which means of course that there were the occasional accidental over feeds and dropping of the blade onto the workpiece as well as starting the saw with the blade already in contact with the work - the latter two known blade killing sins. Blade tension was set in the green zone of the gauge.
In having said all that, I cannot fault the performance of the Exelsior blades, and over a 5 year period, I would estimate that I would have been lucky to have snapped maybe half a dozen blades, as the usual mode of failure was either just wearing out and losing teeth when cutting the Y12 bar.
Based upon my experience, I'd be surprised if the cause of your issues was the Exelsior blades, although I guess a manufacturing defect cannot be ruled out. The broken blade guides are a definite clue in my view, as those carbide guides work pretty darn hard when you think of it. Does the blade seem to run nicely without bumps or jumps when you put it on and power it up?
Overall, it's a bit of a puzzle as cutting 90X90X6 should be an absolute walk in the park for that saw and blade and a real contrast to what our EB 320 endured without complaint.
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