Blade Tension

[Stuart]

1. Does anyone use an actual tension gauge when tensioning up their blade?
2. Is it worth considering? (getting 15000 psi + by guesswork doesn't thrill me)
3. Are they incredibly expensive?
4. Is it worth it?

Please answer any of the above, 'cause the answer to one will cover the rest as well!!!

Just want to use my tools as well as I should, and bandsaw blade tension keeps cropping up as being very important for optimum performance, and tends to be difficult to really work out just how tense a blade should be (yeah, I know, high C and all that)

On that point, as any guitarist will tell you musical pitch of a wire under tension gives an exact measure of that string's tension. Is there any way of utilising this fact for bandsaw blades?

[ptc]

Give Henry Bro's a call.( It does depend on the blade.)

[Sprog]

Check this out, might be of interest

http://www.homemetalshopclub.org/news/jun02/jun02.html

[Stuart]

Thanks Sprog.
What a bunch of frea...... ;)

I tried ringing Henry's, but it was too late in the day on a Friday. Bugger is, I only rang them 2 days ago when I was ordering some new blades. (Couple of 1/8" 14 TPI, and a 1/2" bimetal 3 TPI blade).

[bsrlee]

If you have Taunton "New Best of" series book on shop machinery, there is an article by Mario Rodriquez on making your own tension guage, measuring the stretch with feeler gauges. Based on that, I have a 'get round to it' project to convert one of the plastic digital verniers into a tension gauge.

I was looking at the commercial ones, but all they are is a standard dial guage with a new face pasted on in a basic frame with a couple of bolts to clamp to the saw blade. There is a new one out that uses some sort of pressure sensing pad, but it will only work on some bandsaws as it goes between the frame & the spring.

[Stuart]

Good point - hard part would be calibrating it. On that though - given a dial gauge is around $80, shouldn't a bandsaw tension gauge be about the same price?

Like the idea of a homemade variety......now where did I put my copy of Google....?

[China]

You don't need a gauge, 80% of bandsaws don't have them there is a message in that

[scooter]

Stu, checkout Taunton's site, I think I read an article there about measuring stretch in the blade & relating it to tension.

I've heard of using cheapo digital verniers clamped to the blade, open jaws to an arbitrary figure, clamp top & bottom jaws to blade, then tension 'til desired stretch is achieved.


Cheers.............Sean

[Termite]

I use a combination of a thumbnail and a calibrated ear.;)

[Toymaker Len]

Maybe a guitar tuner and a plectrum... Try B#

[Skew ChiDAMN!!]

Wouldn't the "desired" note vary with width, length & thickness of the blade?

I'm another who plays the BS by ear. I simply back off the guides and tension until I get a nice note (any note!) instead of a dull twang/thud/rattle.

Had no problems with stretch or bow-cut veneers yet. [fingers Xed. ;)]

[TTIT]

Is tension really that important? In a Fine Woodworking article by Michael Fortune (December 2004), he suggests undertensioning enough that the blade deflects about 1/4" without the fingertips going white (blade stationary of course or fingers go red!:eek::eek::eek:. I've been using this technique with no problems so far other than adding a little more tension to stop the blade slapping against the back of the frame on one blade.

[Greg Q]

I think that it depends on the saw. I bought a gauge from Louis Iturra in Florida when I first got my 24" saw and was having difficulties. I have used it twice to calibrate myself WRT tension. It turns out that the 1" Lenox blade that I installed last year is staying on the saw, and the tension stays on too, so the gauge may not see much use. Frankly, the quality of the cut and the blade tracking should be your guide to tension*

*unless, like me, you are of the 'more is better' school. A big saw can easily over-tension a 1/2" blade. Blade failure and weld rupture is an experience not soon forgotten.

Greg

[CameronPotter]

Is tension really that important? In a Fine Woodworking article by Michael Fortune (December 2004), he suggests undertensioning enough that the blade deflects about 1/4" without the fingertips going white (blade stationary of course or fingers go red!:eek::eek::eek:. I've been using this technique with no problems so far other than adding a little more tension to stop the blade slapping against the back of the frame on one blade.

Surely that would depend on how much blade is exposed between the guides though...

Cam

[TTIT]

Surely that would depend on how much blade is exposed between the guides though...

Cam

Cam- He's referring to a 14" saw so I suppose he means with the guides in the uppermost position. When I got my saw (16" Hafco), I was told you had to wind up the tension until all the spring was fully compressed then another couple of turns for good measure. I found this was twisting everything and I couldn't 'tune' the drift out of it or keep anything constant. Since slackening off a bit, drift adjustments have been much easier to make and hold.

[Greg Q]

Cam- He's referring to a 14" saw so I suppose he means with the guides in the uppermost position. When I got my saw (16" Hafco), I was told you had to wind up the tension until all the spring was fully compressed then another couple of turns for good measure. I found this was twisting everything and I couldn't 'tune' the drift out of it or keep anything constant. Since slackening off a bit, drift adjustments have been much easier to make and hold.

that's the goofiest advice I have ever heard. The spring provides some shock resistance for the blade. If the coils are touching you are going to get rapid blade failure, and winding more tension past that point is pointless.

I'm glad that you sussed that out, and are now getting good results. there are also after-market springs which will allow more tensioning without compressing the spring too much, if you ever have problems in the future.

Many of the lighter weight saws can't cope with tensioning a blade to the proper valves without suffering some frame distortion. This of course makes tracking the blade a hit-and-miss affair.

Greg

[CameronPotter]

Yeah, I use mine and I haven't had any problems - yet, but there is certainly no science to my madness...

I would quite like to use a blade tensioner (if only once) to see what I SHOULD be doing. :cool:

[Skew ChiDAMN!!]

TTiT's method stirred the ol' grey matter...

We had a bloke give a talk at our turning club some time ago about the care'n'maintenance of bandsaws. He demo'd the use of a tensioner but also added that as far as the home-user is concerned it's not worth the expense, then showed a method similar to TTiT's: adjusting the tension so it deflects a certain amount on the return side of the blade without white-knuckle effort. I do remember his saying all BS's should deflect by about the same amount when correctly tensioned, regardless of size of blade or wheels.

I don't remember how much it should be 'cos I wasn't paying attention. :o On my BS the return side is enclosed in a C channel and the method can't be used...

Perhaps a few of us who can access theirs can post how far it deflects so we can compare?

[Stuart]

So long as the guides are backed off, shouldn't the return side and the 'normal' side deflect the same amount? After all, on a 2 wheel BS, the distance is identical!!

The whole reason I thought of asking that started this thread was either an article I read or a video I watched that showed just how accurate a finely tuned (including tensioned) BS can be. BS blade tension gives the blade beam strength. This ?article? talked on how often Bandsaws are used well below the optimum tension for the blade, degrading their performance.

[RichardL]

that's the goofiest advice I have ever heard. The spring provides some shock resistance for the blade. If the coils are touching you are going to get rapid blade failure, and winding more tension past that point is pointless.

I'm glad that you sussed that out, and are now getting good results. there are also after-market springs which will allow more tensioning without compressing the spring too much, if you ever have problems in the future.

Many of the lighter weight saws can't cope with tensioning a blade to the proper valves without suffering some frame distortion. This of course makes tracking the blade a hit-and-miss affair.

Greg

Hmmm, I posted a question a few weeks ago about a BAS350 I recently bought. As far as I can make out, these BSs don't have a tension spring at all, you just hand tighten the screw on the top which pulls the top wheel up. I guess the flex in the components act as a sort of spring but as has been said - rather hit and miss. I have been advised that you can't really over tighten the blade by hand using the smallish knob provided.

Tightening the blade to different degrees certainly alters the tracking on the wheels though - which I suppose indicates things are distorting.

[Stuart]

Ow - sounds painful. Sure you can't fit your own spring?

[Tiger]

Stuart,

I have a Boss guitar tuner which operates off a 9v battery, have used it with some success when tensioning blades. Easy to use, and I paid around $80 some time ago.

John White from Taunton's has a shop-made tension gauge and I have the article somewhere. Let me know if you want to look at it. It was in a Fine Woodworking issue a few years ago.

The device you mentioned in your first post is exorbitant. Only people I know who have it are people who repair Bandsaws. Not worth it, in my opinion.

[Stuart]

Thanks Tiger - I have a guitar tuner - was wondering about that, but each blade would have it's own pitch wouldn't it? Same way guitar strings have different pitch, and different diameters.

I'd be very keen to see the Taunton's article if you can find it.

Now my mind is buzzing with old engineering formulae etc. Strain gauges attached to rods as we broke them and looked at failure mechanisms. Always enjoyed the practical side - hated trying to work out the formulae - bloody Mechanics of Solids I & II! Who would have thought that stuff would actually be useful one day.

[Tiger]

Stuart, as I remember the pitches were pretty close regardless of blades. I wouldn't say that this is an extremely accurate way of gauging tension, but it's quick. If you send me a pm, I will dig that old article up and send it to you.

[CameronPotter]

Me too please Tiger... :cool:

[Tiger]

No problems Cam, just need an address to send to.

[Auld Bassoon]

Cam - if one tightens the tension coil to full compression, then there's no further possible shock-absorber capacity left, and any further tightening (using a pipe wrench?) would only distort the frame.

[CameronPotter]

Auld Bassoon, that certainly wasn't my advice!! :eek:

My EB spring would cause the blade to snap before I got it that tight...

I simply tighten until it feels about right.

Cam

[Auld Bassoon]

Yep Cam, I wasn't implying that it was your advice, but it surely is wrong!

[TTIT]

Yep Cam, I wasn't implying that it was your advice, but it surely is wrong!

Auld - that advice was given to me by the vendor:eek: - needless to say, I haven't asked for any more help from them!:mad:

[CameronPotter]

Yep Cam, I wasn't implying that it was your advice, but it surely is wrong!

No problems.

Actually, I get scared WAY before my spring compresses even much. Maybe I am being a chicken, but I would prefer to be a living chicken. ;) Actually, the thing is that no matter what I throw at the saw, it cuts its with very little barreling (so little that I haven't noticed any).

Thus, I am happy.

Cam

[Skew ChiDAMN!!]

So long as the guides are backed off, shouldn't the return side and the 'normal' side deflect the same amount? After all, on a 2 wheel BS, the distance is identical!!

Yup... but on some BS's the setting of the guides is a major operation in itself. I know I spend more time tweaking 'em than I do with everything else involved in a blade change added together. (Including recoiling the old blade. ;) )

If it's easier to access the return of the blade to check tension, so be it.

I have to agree with your comment about running under-tension... mine's a cheapy CT model and I didn't expect it to do much more than rough-cut bowl blanks. Once I overcame my fear of overtensioning and could get it right, I was very pleasantly surprised at how well it handles cutting 1.5mm(ish) veneers from 6" redgum.

Correct tension makes a BIG difference, no two ways about that!

[Stuart]

:D So does a decent blade. Even on a cheap bandsaw (which is what - 2 wheels and a motor), if the actual cutting edge is high quality, things can't help but work better. (Put a razor sharp blade in a cheap plane - you still may have issues, but it will still work substantially better than it did out-of-the box.

Just talked with Henry Bros - my new bimetal blade should be in my letterbox today :D Now all I have to do is work out when it is properly tensioned..........

[Tiger]

Stuart, from memory the note was around the "E" but it's been a while since I've taken the time to check the tension. I overtension a little these days and when the blade breaks, I join it back together by brazing.

I have sent you and the others who requested the shop made tension gauge. You should get it in a day or two.

[Stuart]

Do you have some sort of jig for brazing blades? Had a look in Carbatec recently, but the only one they had looked very cheap & nasty.

[Harry72]

You wont regret the bi-metal blade Stuart, just watch the fingers!

[Tiger]

Stuart,

My jig is very crude, 2 bits of angle iron with holes tapped into them to take a bolt to hold down both sides of the blade. Stick it into the vice and away you go. There was a post on a very good home made jig on this forum, can't remember whether it was in the Metalwork or Bandsaw forum.