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Thread: Detensioning - how much?
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12th May 2015, 12:46 PM #1
Detensioning - how much?
I just got my first bandsaw and am having fun with it. I did a fair bit of research, but one thing I couldn't find too much about was how much to detension the blade when closing for the day.
When I retension the blade next day, the tracking changes and I need to redo the guides. Is this what is supposed to happen? Or do you only release the tension a certain amount using the wheel and leave the detensioning lever alone?
Apart from that, everything seems to be going OK!
Thanks for your answers, I couldn't find anything out in my books about this except a hint in Duginske's book about "record the number of turns you detension", but he doesn't go into more detail.
Cheers
SwiftySwifty
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12th May 2015, 01:16 PM #2GOLD MEMBER
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I undo mine by 2 turns but not sure if that is the accepted number. I have put a marker on the knob so that it is turned exactly each time. I have a block of wood that then hangs on the saw to remind me to re-tension it. I hang it so that I must see it before using the saw again.
Tom
"It's good enough" is low aim
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12th May 2015, 02:55 PM #3
I use the detensioning lever, and haven't had any drama; spinning the wheels by hand restores tracking if necessary. But my bandsaw is on a mobile base. I always retension before moving it from storage to workplace. That seems to help.
Cheers,
JoeOf course truth is stranger than fiction.
Fiction has to make sense. - Mark Twain
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12th May 2015, 04:54 PM #4China
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I've been using bandsws both domesticly and industrialy for 40+ years and in my opinion it is a complete waste of time
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12th May 2015, 05:07 PM #5
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12th May 2015, 05:10 PM #6
Hi China,
You've never seen a blade so-called stretch? Not even if its idle for a long time (ie: weeks)?
I usually do wind off the tension. There have been times when I have forgotten, and can't say I've noticed any difference. Or is it supposed to relieve tension on other components such as wheels and bearings (and not blade stretching)?
Nathan.
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12th May 2015, 05:26 PM #7SENIOR MEMBER
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I use the lever and hang the keys on it.
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12th May 2015, 06:07 PM #8GOLD MEMBER
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12th May 2015, 06:26 PM #9
It is not about stretching the blade but compressing the rubber tyres and causing flat spots on them. I use the leaver and leave the tension knob alone. I have to admit that I have forgot to detension now and then and not suffered any bad result but would not like to leave it long periods under tension.
Regards
John
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12th May 2015, 06:35 PM #10
My Carbatec 4300 bandsaw has a de-tensioning lever at the back, when I finish using the bandsaw I flip it up, when I want to use it again I pull it down again.
No other adjustments needed.
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12th May 2015, 09:07 PM #11.
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I have a 19" CT BS with the detensioning handle - I use it when I remember - probably 1 in 3 times?
On the metal cutting bandsaw (metal wheels) I don't bother.
On the BS sawmill with the 2" wide blades the blade gets tensioned to over 2000 psi with a hydraulic jack like piston/ram - gets fully detensioned every time.
The tyres are loose fitting C size V belts. These are quite hard but I suppose they could still get a flat spot.
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12th May 2015, 09:47 PM #12Taking a break
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I'm also with China. Never heard of it, wasn't taught it at trade school (no surprises there) and no one at work ever mentioned it either.
I'll put money on the work bandsaws never being de-tensioned except to change the blade; even over the 5 week summer shut-down they're under full tension and there are no flat spots or stretching when we get back.
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12th May 2015, 11:36 PM #13.
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Here is what Timber Wolf Bandsaw blades say about detensioning
ALWAYS DETENSION YOUR BANDSWhen you are done cutting for the day, take the tension off your blade. Band saw blades, when warmed up from cutting, always stretch; and upon cooling shrink by tens of thousandths of an inch each cooling period. Therefore, blades, when left on the saw over tension themselves and leave the memory of the two wheels in the steel of the band, which will cause cracking in the gullet. When you leave the band on your saw under tension, not only do you distort the crown and flatten out the tires (which makes them very hard), but you also place undue stress on your bearings and shafts. Believe it or not; you can, and will damage your wheel geometry sooner or later and considerably shorten bearing life. You are also crushing your tires or V-belts.
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13th May 2015, 09:55 AM #14GOLD MEMBER
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13th May 2015, 10:22 AM #15.
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They're not BS makers - they are bandsaw blade manufacturers based in the US.
It's interesting to see that Lennox does not mention this on their website.
I think the detensioning concept comes from the use of large blades especially on saw mills where tons of pressure are used to tension blades.
On smaller blades with lower pressures is clearly not a big deal