Thread: Bandsaw ID & tensioning

I've been pondering this too, my BS(bas470)has a tension indicator thingo but I dont think it is any good. Come up with two ideas(yes Im a blonde... err lateral thinker!)
1. I have this old anolog guitar tuner(very sensitive) that I never use, was thinking of doing test cuts to find the ideal tension and then measure the frequency of the blade when plucked, then repeat for every blade that I have.
2. Use one of those hand held fish weighing scales, find ideal tension(as above)then measure/pull the blade with scales to the point of deflection of the blade take note of weight/force used.

The February 2001 issue of FWW had an article on a home-made tension gauge.

Made from two bits of hardwood 10 x 19, the top one 115 long, the bottom one 19mm, with a long pin which worked as a slide to locate both bits, and a shorter one which fixes into the top piece but not the bottom.

Clamp to the blade with the pin butting against the timber, tension as desired and measure the distance off the face with feeler gauges.

Works every time apparently, but I'd like someone to report back!

Go on! It'd only take ten minutes to build!

Cheers,

P

Originally Posted by bitingmidge

Clamp to the blade with the pin butting against the timber, tension as desired and measure the distance off the face with feeler gauges.

Works every time apparently, but I'd like someone to report back!

Go on! It'd only take ten minutes to build!

So, how well does it work? Surely you've tried it; it only takes 10min to build!

Surely you'd need a "proper" gauge in the first place so that you could determine what the gap should be for the blade at correct tension? :confused: And you'd have to find the correct gap for each individual blade as the "stretch" would change depending on size, steel quality, etc?

Still, once you have those figures I think it'd be fairly reliable for retensioning after swapping out blades...

I like Harry72's second idea; I dunno if fish scales'll be in the right range but I'm sure I can find something that'll do. Thx fellas!

The best proper guage is a correctly set up bandsaw in the first place. You can have the tension spot on, which varies for each different width blade, but if the rest of the saw is not set up properly it will cut up to **1*.


Read Duginske's ( ? ) bandsaw book and also do a search on here for valuable information.

Originally Posted by Skew ChiDAMN!!

So, how well does it work? Surely you've tried it; it only takes 10min to build!

Sadly that's about 90 seconds more than my attention span. I've got a few of them lying around somewhere, almost finished, but in the meantime I worked out how to tension the blade well enough to get by.

Surely you'd need a "proper" gauge in the first place so that you could determine what the gap should be for the blade at correct tension? :confused: And you'd have to find the correct gap for each individual blade as the "stretch" would change depending on size, steel quality, etc?

I will have to re-read the article, but I think the gist is that once you've got one blade set up (see Joe's note above) the correct blade tension for any blade will give the same gap. Don't forget that bigger blades need more tension, but more tension will move them the same amount.

I like Harry72's second idea; I dunno if fish scales'll be in the right range but I'm sure I can find something that'll do. Thx fellas!

I think you'd need to do some maths as well??? Scales measure weight (force), doesn't the square root of the hypotoneuse or the sum of the sqares of the opposite sides come into a tension calculation?

Cheers,

P

Just my 2 bob's worth - I've never heard of a bandsaw being over tensioned, though I suppose a very thin blade, say 1/8", could be. I always just crak it up as tight as I can - seems to work fine. What Joe (GatieP) said about setting up the rest of the saw is spot on.

BTW those tension meters on the Cinese bandsaws are a joke. Firstly they depend on the exact length of the blade for their deflection, so if the blade is a few millimeters longer or shorter than the specified length the setting will be way out. Secondly as I've said before, the tension is difirent for different size blades. If you tension a 6 mm hobby thickness ( note thickness not width )blade to the same tension as is necessary for an industry thickness blade you'll hear a distinct BANG during the adjustment. Thirdly, who decided that the tension at the indicated mark is the optimum........someone who has never cut hardwood with the saw???? There are far too many variables for those indicators to be of any value!

I have never been able to over tension my bandsaw blades and I really crank them up. There has always been a reason other than tension for the broken blades on my bandsaws. Sometimes it can even be the lack of tension that caused it to break.

You can over tension, its when the shock absorbing tension spring is compressed till it cant compress any further, then the blade has no choice but snaping or streching if its on excentric wheels or jumps/snags while cutting.(from the Duginske book, my wording tho)

Originally Posted by midgey

I think you'd need to do some maths as well??? Scales measure weight (force), doesn't the square root of the hypotoneuse or the sum of the sqares of the opposite sides come into a tension calculation?

Not realy IMHO as youd find the ideal tension for each blade, then measure by pulling the blade sideways with the scales and take note how much force it takes to deflect the blade say 5mm(top guides would need to be set at the same height each time while measuring).

This discussion is making me all tense.

Well you should ask Mrs Grunt(very nicely)to adjust your tensioning lever!

Come on guys...Force is not weight...lol.

I think the spring balance idea might work....I have some V-belts which are 4000mm between centers. And i use the spring balance method to check tension.
Basically, i go to the mid span of the belt pull the spring balance at 90 degs to the lay of the belt untill i get 50mm deflection in the belt then read the weight on the spring balance then do the sums to see if i have over tensioned the shafts at either end of the belt. This method should work ok on a bandsaw as well. I think last time i checked average blade tension was around 18,000 psi. So as someone said doing the maths you can work out if at the mid span between your wheels. you pulled the blade...x amount. Read the spring weight you applied for a given deflection. You can then work out the stress in the blade. Ie...so many pound/kilo's or what ever you are applying.
But i agree mostly with what was said ealier, when i did my apprenticeship bandsaws were consderably heavier built than today consumer models. And you can't do the blades up nearly as tight without fear of tistorting the machine. So common sense needs to come into it. But if the blade is done up to a nice ping....and the blade is wondering then...1 you are pushing to hard for these lightly built machines. 2. The blade is cactus. 3. Your guides are not set up correctly.
Anyway i think everyone is already smart enough to know all this stuff anyway.
Sinjin.

1 you are pushing to hard for these lightly built machines. 2. The blade is cactus. 3. Your guides are not set up correctly.

Thanks for the feed-back fellas, I've finally determined the culprit.

I'd tried swapping my blades out for new ones, resetting the guides & tension each time. Thought I'd swap out the rollers for the ceramic guides to see if my fine blades also wandered and while removing the RH assembly the roller & half the assy came adrift in my hand, leaving the other half still bolted in place. :eek:

Metal fatigue! I'd never have guessed it... Oh well, time to place an order for replacements and thank god that no worse damage was done to either machine or me...


BTW, any chance of getting that anim Grunt? After some 20 odd years of playing with 'putas that just about sums it all up.