Setting Bandsaw tension

[Mike-W]

I have had a Startrite bandsaw for a fair while and have always set the correct tension using a built in indicator where you set it against the blade width. Its always worked well for me although the screw thread on the adjuster can get 'gummed' up with sawdust making it hard to turn the adjuster wheel, i generally sort this by removing the bandsaw and giving the mechanism a 'bit of a shake' and lubricate the thread with PTFE spray. I did this the other day and found i had then lost the ability to set the tension on the scale (it was reading off the top of the scale and obviously not tensioned up correctly).
I had to disconnect the cable from the scale and reset it so i have lost the factory set tension setting on the scale.

In the absence of an acurate tension setting scale what method do you guys use for getting the correct tension setting on your bandsaw?



Mike

 

[Duncan A]

First of all, the built-in tension adjuster is not accurate. Even if the indicator itself is accurate (unlikely), there is no way that it can know the thickness of the blade or the material from which the blade is made. Both of these vary, and both affect tensioning, so the width of the blade is only a very general guide to tensioning.
Blade tension in my view is not terribly important as long as it prevents the blade slipping on the tyre and holds it sufficiently taut not to flutter.
Two common methods to adjust tension, both with the blade guides pulled back away from the blade:
1. Tension it enough to keep it on the tyres. Run the bandsaw - almost certainly, the blade will flutter. Slowly and carefully tighten the blade until the fluttering stops. Lock down the adjuster and re-check before setting the guides.
2. Unplug the bandsaw from the power supply. With the blade undertensioned, on the longest unsupported run of blade, often at the back of the saw, twang the blade. It will make a dull "boing" sound - or something like that! Slowly and carefully tighten the blade, give it a full turn by hand and twang it again, repeating until you have a nice "tuneful" sound. Lock down the adjuster, run the bandsaw then re-check before setting the guides.
Loads of info on-line, and from our very own Steve Maskery.
Good luck,
Duncan

 

[Steve Maskery]

Hi Mike
Tension scales are a very rough guide anyway, so you are not losing much in the way of facility. Two blades of the same size can require different tensions. A thin-kerf blade will need less than a thick one, because there is less steel to stretch, even if it is the same width and length.

I tension mine by sound. I pluck the blade and if it sounds right it is right. Yes, I know, how do you know when it sounds right? Well you do very quickly get to know what it should sound like. If it is dull and heavy, tighten it up. If it sounds strained, back it off a bit.

Duncan has beaten me to it.

 

[Mike-W]

Thanks both,
I have come across the flutter test and was thinking of going down that route, the 'sound test' i had not come across and may well be my way forward as long as its low pitch as my hearing is useless with high pitch noise.
I have a new blade due today so as soon as i can get into the workshop I'll give setting up the tension a go.

Best wishes

Mike

 

[MusicMan]

I use sound also. And note that the pitch of the note that you hear on the twang is the same for all types and widths of blades as long as they are all steel (which they are), for a given bandsaw. It will only change when the length of the blade between the wheels changes, i.e. a different saw will have a different note.

The maths does verify this but I am sure nobody is interested! There is a thread on this somewhere.

Keith

 

[Mike-W]

I did see a post on this forum on using a tuning fork to set the blade tension, but i wasn't buying into that one!

Mike

 

[Random Orbital Bob]

when you can play duelling banjo's on it it's about right

 

[Mike-W]

I was never good at music at school,
pity you can't upload a recording onto this forum!

Mike

 

[MusicMan]

I did see a post on this forum on using a tuning fork to set the blade tension, but i wasn't buying into that one!

Mike

It works perfectly well, but you have to be not tone deaf! You can always use a cheap guitar tuner.

As any harpist will tell you, a harp string of a given length breaks at the same pitch whatever its thickness, as long as it is made of the same material. The tension (force) is of course higher in the thicker strings (blades), but the stress (force per unit area) is the same at breakage.

Twang away.

Keith

 

[Paddy Roxburgh]

Other than potentially damaging the bandsaw frame (unlikely in my case with an 8 foot tall wadkin) is there any disadvantage in over tensioning a blade?

 

[Alexam]

If you havent seen video's, this may help
CHECKING BLADE TENSION - Flutter test Video's -
https://www.youtube.com/watch?v=chyo9chuwJs and https://www.youtube.com/watch?v=z8zZuDosSy0


Also, the new Alex Snodgrass video shows another way.https://www.youtube.com/watch?v=bxVyKsbuwZQ

 

[RogerM]

The factory demonstrator at the Yandles Show explained how to tension a blade on a Startrite 352E. It was based on blade deflection. It's no use trying it at the "business end" as the deflection effort will depend on how close the upper blade guards have been set to the table. Instead, open the upper door and deflect the blade with your index finger level with the bottom of the upper wheel. About 1/4 inch using your index finger before coming against excessive resistance seems to work well, regardless of blade width and thickness.