BAndsaw problems

[Benchwayze]

I fitted a new, 3 TPI skiptooth , 1/2" blade to my Startrite 351 today.

I wanted to re-saw some 6"x 2" cedar into 6 x 1's.

I finally managed it, but for some reason the blade keeps up an irregular 'thumping or jumping into the cut. I think this might be vibration.

I am advised on various websites to increase the tension, yet the manual for the saw tells me tension should be ' low to medium' for the blade I have fitted.

The tyres are clean and there are no heavy wear ridges in them.
Blade runs on the crown of the wheels, no trouble and the sandwich-guides (A bit primitive on this machine) are set as close to the recommended settings as I can get with feelers. There is no excessive heat or smell of burning, and no sparking from the rear guide.

I have owned this saw for 18 years and have kept it up to snuff. I never had this problem before. I know that blades will squeal a bit on deep-cuts, but it seems as if the saw blade is slipping around the wheel now and again, causing this thumping in the cut. I wondered if this irregular thudding and jumping is what is known as vibration. I suspect that increased tension will help, but I have the tension quite high at the moment. It doesn't get worse as I decrease tension.

Does anyone know what this might be caused by, as it's ruining some good timber on deep cuts.

I'd appreciate any pointers.

Thanks in anticipation.

John ccasion5:

 

[Gary M]

Hi John,
Is it a good quality blade ?
Have you checked the weld ?
Sounds like the weld is catching.
Gary.

 

[Harbo]

Sounds like the blade to me - have you got another one to try?

Rod

 

[Benchwayze]

Hi Fellas,

I thought it might be thus!
I have another new one to try.
I had them from Axminster. Never had problems before.
There was a 'half-tooth' in the gullet, at the weld. I filed it into shape, but it didn't make any difference. the weld seems flat and true as far as I can tell. I'll try another blade tomorrow..
Thanks again and I'll keep you posted.


Regards
John

 

[iajon69]

For deep cutting then the tension should be high and a 3tpi should cope with 6" material with no problem.
It does sound like a blade problem though and you'll probably find that it's a duff blade - just hope that it didn't come from a faulty batch and that all the blades will be the same!!

Ian

 

[Timmo]

For what its worth in my little experience I had a similar problem on my Record BS250 although I wasn't cutting the size of material that you are...I ended up changing the blade and it was fine but never worked out what was wrong with the blade...in my ignorance I had just thought that I might have blunted it somehow...

 

[devonwoody]

I suspect it will be the blade but you could try some sawing on another piece of waste timber to see if the same thing happens. This would eliminate the timber being the cause.

 

[Benchwayze]

Hi Folks,

Thanks for all the input and advice. It was operator error; ](*,)
That is, despite what the manual says, I needed more tension on the blade. I added a couple of turns and the problem disappeared.

I suspect that with too little tension, the blade was flexing just as a handsaw blade would when it jams in a cut. On the machine of course the motor just plods on and causes the blade to thump its way through the cut.

So much for 'Read The Flippin' Manual'.

It just means I have dulled a new blade. A £10.00 lesson I should have learned; maybe I did, but I forgot! #-o the main thing is, the saw is now cutting well.
I put a note on the top cover: "Check the Tension'!
Thanks again everyone. Much appreciated.

Regards
John

 

[Harbo]

I ignore what it says on the machine and always wind my 352 to high or above when in use.

Slacken off to low after use but must remember not to switch it on at that setting - blade comes off!!

Rod

 

[Benchwayze]

Agreed Rod.
That's why I am putting a "tension-sticker" on the access door to remind me! I am getting to that forgetful age now.

Thanks again for the input everyone.
regards
John

 

[George_N]

Before this thread fades away I'd like to ask a question about blade tension, if I may. I fairly recently acquired this bandsaw from fellow forum member P111dom. It is fairly old and cast iron everything but it has no indicator of blade tension. Is there a rule of thumb for setting the tension without a gauge? I know it will vary from blade to blade...I currently have a couple of blades from Dragon Saws, a 1/2" x 3 tpi and a 1/4" x 6 tpi. I am currently taking up the slack and then giving it another turn or two. I guess if it cuts without barreling it is tight enough but I'd like something a bit more scientific (without having to shell out for a tensiometer if possible).

 

[Tusses]

I have heard you can pluck it like a guitar string - but you have to be experienced I guess, to tell what noise it should make.

 

[devonwoody]

Everytime I swap over a blade I run a scrap piece of timber through my bandsaw and make the adjustments if needed.

(funny thing happened whilst typing this post I typed scrap and it typed crap )

 

[George_N]

I occasionally build bicycle wheels and I check for even spoke tension by plucking them and listening to the tone. I don't have a particularly good ear for music but I can spot one or two out of 32 that sound a bit flat compared to the rest. Unfortunately there are no comparators on the bandsaw and without the experience to know the tone of a well tensioned blade it doesn't help a lot. I'll have to do as DW suggests and run some test pieces and re-tension as needed.

 

[George_N]

I've just done a quick search and found this thread, which may answer my question. It states that a 25 thou stretch of the blade equals 15,000 psi tension (measured using a digital caliper clamped to the blade). I'm not an engineer or materials scientist so I have no idea if the stretch is the same regardless of blade width/thickness...any ideas?

edit; just read the full thread and the answers are in there...seems to be independant of blade size for blades of the same material (Young's Modulus?).

 

[Harbo]

Just read an article in The Woodworker about bandsaws.

The tried and tested method to check tension: A moderate push on the blade with forefinger (with guard lifted up) should give about 5mm deflection.

Rod

 

[Tusses]

surely that depends on the size of the saw and blade !

 

[Tusses]

surely that depends on the size of the saw and blade !

 

[devonwoody]

surely that depends on the size of the saw and blade !

Do you stutter as well? .

 

[Tusses]

n n n n not that I n notice ? w w why ?