Thread: Band saw tension spring ??

My bandsaw was hard to tension and drove me batty for a while. Eventually I measured the spring and some other people measured theirs. Mine was 15mm shorter, on a new saw! The company sent me another for free. I could tension small blades but could not even hope to tension a 1" blade.

Originally Posted by Groggy

My bandsaw was hard to tension and drove me batty for a while. Eventually I measured the spring and some other people measured theirs. Mine was 15mm shorter, on a new saw! The company sent me another for free. I could tension small blades but could not even hope to tension a 1" blade.

First, I have to correct the brand of the saw, although I think you Woodies would guess it is a Hafco.

Now, the spring does not to appear to have any influence on the tensioning part.

If you look at the set up you will see that there is some device on which the wheel is attached which, in my case, has a threaded rod with 2 size threads on it to the tensioning knob on top of the saw.

The up and down winding of that threaded rod is what controls the tension. The spring gets tighter as you turn the knob as you would in tightening the wheel, so, in fact, the spring is working against the tension process. Conversely, it pushes the wheel down when loosening the wheel to remove a blade, but this pushing is not required as the total push is controlled by the thread on the lift/lower rod thread.

AS I mentioned, an engineer looked at my set up and he was the one that brought to my attention the seemingly unnecessary need for the spring other than for a noise damper. The fitting of a less tense spring controls that adn the tension on the thread or the threaded rod is reduced, which is good for the thread, as we proved.

Thank you for your reply
BB

Originally Posted by Black Bear

If you look at the set up you will see that t here is some device on which the wheel is attached which, in my case, has a threaded rod with 2 size threads on it to the tensioning know on top of the saw.

A pic or a link would help us in this case.

Originally Posted by Groggy

A pic or a link would help us in this case.

Without pulling the saw apart again, I could not get a suitable photo. The spring is enclosed, and out of sight.

I have sent an email to Hafco....Will be interesting if they can answer.

Hafco's reply:

Hi Peter
No we have no idea why the spring may be hard or soft
As I can see it is only holds the top wheel pushing up when the tension is released.
Maybe there was a model with a whick blade release lever and the heavier spring was incorporated in its locking?

We have not had these machines for 8 years and we did not have any problems with the springs being over engineered...

Thanks


Rob


BB

My BS "knowledge" may all be BS . But is the spring not there to actually tension the blade, yet provide a shock absorber? So yes it make tensioning tougher with a hard spring, but without it you will have slop and really have to tighten down on the spring and squash it to get tension.

Originally Posted by REALOldNick

My BS "knowledge" may all be BS . But is the spring not there to actually tension the blade, yet provide a shock absorber? So yes it make tensioning tougher with a hard spring, but without it you will have slop and really have to tighten down on the spring and squash it to get tension.

It doesn't work like that. You cannot tighten or loosen the tension past the thread. Teh spring does not supply the tension, the thread does.

One has to wind the tensioning thread up or down and the spring only puts tension on the thread, which we believe was the cause of the thread threading on my machine.

Everything works fine with a lesser tension on the thread. The strong spring was replaced with a less tense spring.

I still have no idea why such a heavy tension spring is needed, even after asking the supplier.

Thanks
BB

The bloke said to the doctor: :Sometimes, Doctor, I feel like a Tepee and others like a Wigwam".

The doc replied "I know your problem, you are too tense" (tents)

BB,

You are right. The spring applies tension to the thread so it acts like a locking nut/washer. This stops the tensioning thread undoing due any vibration within the saw.

Got no idea why they used such a stiff sping but if you use a softer sping be aware that tension on the blade maybe reduced as the thread may undo due to vibration when the saw is in use.

I stand corrected. It has been a long time since I used my old saw, and I have not set up my new one yet.

I have to admit I assumed it was for shock absorption and never gave it further thought.

But there seem to be a lot of people who believe what I do (did?).

Originally Posted by REALOldNick

I stand corrected. It has been a long time since I used my old saw, and I have not set up my new one yet.

I have to admit I assumed it was for shock absorption and never gave it further thought.

But there seem to be a lot of people who believe what I do (did?).

We must learn one new thing every day!!!!!

Sorry, seriously. I am not doing this because I am vindictive. I was genuinely puzzled so I kept looking.

I assume we are talking about the spring that is in the screw feed of the tensioner at the top of the saw. If I am right, my fear is that with the weaker spring, on bigger blades you may need to squash the spring until its coils touch and you have you have no shock takeup.

Mark Duginske clearly states that the spring is there to absorb shocks or at least allow for out of round wheels.

Attachment 168417

Band saw handbook - Google Books

[IMG]file:///C:/Users/Nick/AppData/Local/Temp/moz-screenshot.png[/IMG]

Originally Posted by REALOldNick

Sorry, seriously. I am not doing this because I am vindictive. I was genuinely puzzled so I kept looking.

I assume we are talking about the spring that is in the screw feed of the tensioner at the top of the saw. If I am right, my fear is that with the weaker spring, on bigger blades you may need to squash the spring until its coils touch and you have you have no shock takeup.

Mark Duginske clearly states that the spring is there to absorb shocks or at least allow for out of round wheels.

Attachment 168417

Band saw handbook - Google Books

[IMG]file:///C:/Users/Nick/AppData/Local/Temp/moz-screenshot.png[/IMG]

I had no thought that you were being vindictive, and I am most happy for your further investigation, however I am a odds with he spring having anything to do with the tension on the blade.

Imagine: An ordinary nut and bolt with a spring on the bolt. Now one has to tighten the nut to exert pressure on the spring, so in this scenario, what is the spring doing.

The tensioning bolt in the band saw will not move up or down without turning the handle that turns the threaded bolt that causes a lifting or lowering bracket to move up or down, the spring cannot do this by itself, nor does it appear to assist in this action as the work of up and down is done by the threaded tension bolt.

Thus: The question begs an answer: How can the spring stop up and down movement of the thread of the tension bolt.

Re: Tightening the spring so that the coils are compressed together would not come into the tension on larger blades as the distance that one gets out of the threaded bolt is what supplies the tension on the blade not the compression in the spring.

If out of shape caused bounce in the tension, the bolt would have to jump across the threads to cause this action.

I don't know, it just seems to be working as it is,

Originally Posted by Black Bear

I had no thought that you were being vindictive, and I am most happy for your further investigation,

..nothing personal, but one has to be careful on the web. ...no.... I really did feel as if I was prodding a bit. I thought long and hard with my mouse hovering over the submit button, but felt that it needed follow up and sorting out one way or t'other.

Originally Posted by Black Bear

however I am a odds with he spring having anything to do with the tension on the blade.

Imagine: An ordinary nut and bolt with a spring on the bolt. Now one has to tighten the nut to exert pressure on the spring, so in this scenario, what is the spring doing.

The tensioning bolt in the band saw will not move up or down without turning the handle that turns the threaded bolt that causes a lifting or lowering bracket to move up or down, the spring cannot do this by itself, nor does it appear to assist in this action as the work of up and down is done by the threaded tension bolt.

Thus: The question begs an answer: How can the spring stop up and down movement of the thread of the tension bolt.

Re: Tightening the spring so that the coils are compressed together would not come into the tension on larger blades as the distance that one gets out of the threaded bolt is what supplies the tension on the blade not the compression in the spring.

If out of shape caused bounce in the tension, the bolt would have to jump across the threads to cause this action.

don't know, it just seems to be working as it is,

OK. I have the bit between my teeth and I am going to look into this more. I was going to get the BS to the shed last weekend, but I need my wife's help and I made the tactical error of disagreeing with her last Saturday.

Originally Posted by REALOldNick

..nothing personal, but one has to be careful on the web. ...no.... I really did feel as if I was prodding a bit. I thought long and hard with my mouse hovering over the submit button, but felt that it needed follow up and sorting out one way or t'other.



OK. I have the bit between my teeth and I am going to look into this more. I was going to get the BS to the shed last weekend, but I need my wife's help and I made the tactical error of disagreeing with her last Saturday.

Oh! Oh! not the old wife thingo....I can disagree with my wife all I want, I haven't seen her for 14 years.

The Engineer that suggested the need for the lesser spring is going to "Get all technical" for us, so that will be interesting.

Tom is a fully qualified 'pigs ear' and taught at TAFE for almost 30 years, which for one thing means that he had to keep up to speed with engineering stuff.

I must make a correction in my posts, and this was pointed out to me by Tom. I used the term that the tensioning bolt was "Threaded", when in actual fact I should have said stripped, or the thread was stripped. Tom, correctly so, informs me that if it was threaded it meant that it had a thread.

So that puts things into a better aspect as I mentioned that the strong spring contributed to the stripping of the threaded tensioning bolt.

The spring, as Tom points out cannot control any wheel distortion as it is controlled by the thread and whatever slack is in the thread. I will go back to the concept that the spring might be some form of lock nut, as this threw Tom into a frenzy of thought today.

It is getting interesting, hey?

OK. The basic idea.

The threaded tension rod has a nut on it. The nutt cannot turn as it is helod in a square (or whatever) tube that prevents it. Therefore turning the rod moves the nut up and down the rod, which in my case remains vertically still, seated on the saw frame. The axle housing floats in a channel in the body. The threaded rod passes through it but has no effect on its position: the housing is a loose fit on the rod. Just for alignment.

As the nut moves up and down the rod, it decreases or increases the distance between the nut and the axle housing of the upper wheel. That is where the spring sits. So as you decrease the distance between the nut and the wheel axle, you compress the spring, which pushes against the axle and therefore the _spring_ is pushing the axle upwards and provides the tension and shock absorption.

There may be other variations, but the idea is that the spring gets compressed and released and presses against the axle housing. IMO if the saw is not set up like that there is something wrong.

So using a weaker spring _could_ result in having to wind it up until it provides no shock relief. The correct spring (if the saw had the original) will probably be needed if you are to use the largest blade width that the saw is rated for. It will also mean that if you simply use the tensioning gauge on the saw, you will have insufficient tension on your blades. You are compressing a weaker spring the same distance, and therefore not producing enough force on the axle.

I reckon that the thread being damaged was due to the gunk in the mechanism, or something faulty, or misuse. _Maybe_ somebody replaced the spring and used too strong a one, but I reckon that if kept clean and properly rated, actually winding the mechanism _without using extra leverage on the winding handle_ should not damage the thread, no matter how strong the spring. Long usage could wear it, I guess, until slop was enough to allow play and failure. But that would seem like a LOT of work with that saw under proper conditions.

Possibly the spring was wound until it was not providing relief and _that_ damaged the thread. Unlikely but another thought.