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General Category => General Scroll Saw Talk => Topic started by: spiderman on July 17, 2013, 03:08:13 pm

Title: blade tension disorder
Post by: spiderman on July 17, 2013, 03:08:13 pm

I read somewhere that the smaller the blade the less the tension and the bigger the blade is the more tension is need. is this ture?

Title: Re: blade tension disorder
Post by: UHMNL on July 17, 2013, 03:24:27 pm

The tension should be about the same for small and bigger blades.
The blade should not move sideways more than 1/8" and that is almost too much.
Have good speed and low feed rate. Let the blade do the cutting, they say.
FD Mike

Title: Re: blade tension disorder
Post by: EIEIO on July 17, 2013, 03:33:59 pm

Yes. The bigger blade used in thicker wood needs more tension to keep it straight, and the smaller blade with less cross-sectional area cannot take the tension (in lbs, not PSI) that the bigger blade can take. The EX-21 tension lever will put the same spring tension (lbs) on a blade as long as the blade does not slip in the clamps or stretch in length.

Steel has a modulus of elasticity of 29e6 psi.

A 2/0 blade is 0.010"x0.022" or 0.00022 sq in cross section. Putting a 10# pull on the blade results in stress = 10/.00022 =  45,454 psi and it  stretches PL/AE = 10*5/(.00022*29e6) =  0.0078".

A #9 blade is 0.018x0.053 = 0.000954 sq in. The same 10# spring force applies a stress of 10/.000954 = 10,482 psi, and a stretch = 10*5/(0.000954*29e6)=0.0018".

So the #9 can tolerate 4 times the spring tension (lbs) of a 2/0 blade.

Title: Re: blade tension disorder
Post by: Shogun on July 18, 2013, 09:55:58 am

I have to agree here that both statements are correct however I believe that even though a thicker blade can take more tension it is not necessarily needed. In general the same amount of tension will work for thicker or thinner blades. As long as I get that "ping" when I test my tension I very rarely change it, no matter what size blade I'm using.

Title: Re: blade tension disorder
Post by: crupiea on July 18, 2013, 09:59:02 am

I use super thin blades. 2/0 and 3/0 and they will break just putting the tension on them if I am not careful. They work best with less tension and last much longer.  Of course I go on the slowest speed and only use 1/8" baltic birch as well.

Title: Re: blade tension disorder
Post by: Dan26 on July 18, 2013, 08:00:00 pm

 :D When I read the title of this post, I was expecting a question about some medical condition.  :D :D :D

Title: Re: blade tension disorder
Post by: spiderman on July 24, 2013, 01:23:03 pm

Quote from: Dan26 on July 18, 2013, 08:00:00 pm

:D When I read the title of this post, I was expecting a question about some medical condition.  :D :D :D

lol