Bandsaw Tension Gauge

[Sshire]

Harbor Freight Bandsaw Blade Tension Gauge

Had a few things to pick up at the market and on my way out…"Oh look! Harbor Freight"
I had a coupon (that's like saying the Atlantic Ocean is wet). Even people who have no need for anything at HF and have never gone inside, have a coupon.

I had forgotten where I saw it, but there was an interesting technique for measuring the tension of bandsaw blades. It seems you open a pair of calipers to a fixed distance (makes no difference what distance as long as you know what it is. We can call it Jaw Opening), loosen the tension on the bandsaw, clamp the calipers to the blade, zero the calipers and then re-tension the blade until you get a specific reading.

It all has to do with Young's Modulus of Elasticity. (basically, how much tension stretches stuff.)
Young's Modulus for steel is 29,000,000.

Dividing that into the desired blade tension will give the amount of stretch per inch. Multiply that times the Jaw opening in inches and you know what movement you need to achieve a desired tension.

I did a quick spreadsheet.

 

[Tin Falcon]

Interesting look here


http://www.simondsinternational.com/publications/digital-tension-gauge.pdf
you could probably glue a couple magnets on to hold yours in place.


Tin

 

[Tin Falcon]

I have a shop made dial type . a buddy was making and selling these . the production model was engraved with his logo. I helped him with the development and sales he gave me this one.
it is 5 inches clamp to clamp.

I could add one of these http://www.grizzly.com/products/Dial-Indicator-0-05-Range-x-0-0001-/G9806
only $31

Tin

 

[Lakc]

Silly me, I always just plucked the blade like a one string harp until it was "just about right". ;D

 

[Tin Falcon]

if you have perfect pitch and know what note you need why not. I have been told I am tone deaf. I could compare the results of the gage to the electronic tuner and see if that works.
Tin

 

[Lew Hartswick]

Silly me, I always just plucked the blade like a one string harp until it was "just about right". ;D

TSAR (that sounds about right). Just like the soaring instructor taught me landing
patterns TLAR (that looks about right).
...lew...

 

[DanP]

OK, I understand the concept here but wouldn't these numbers change depending on the thickness of the blade? Also what is the correct tension? It must vary between bandsaws. If you have a very small bandsaw I would think the tension should be less than say a very large bandsaw. My saw was built in the late 1920's, it has wood wheels and a wood frame, all the other parts, the top guide and tension mechanism are metal, the bottom guide is iron wood. It uses a 96" blade and will take up to a 3/4" wide blade. I tension it by feel then turn it on and off, if it doesn't cost about 6" of blade travel it's too tight and too loose if it travels more.

 

[Tin Falcon]

OK, I understand the concept here but wouldn't these numbers change depending on the thickness of the blade? Also what is the correct tension? It must vary between bandsaws

the tension will vary depending on the blade.

for example my old blade for my grizzly is .312 x.025 in cross section .or .0078 square inches multiply this by 20,000 psi and you come up with 156lbs of force applied. take a blade that is 3/4" with a .050 tooth and .035 thick
you get .700 x.035 x 20,000 psi and you are applying 490 lbs of force .

so you can see the applied force is proportional to the size of the blade.

the correct tension for a carbon steel blade is 20,000psi. bi metal can be as high as 35,000 psi.

look here Lennox blade guide for mor information on getting the most from your saw and blades.
As far as band saws a lighter blade requires less force and will put less strain on the wheels. IIRC cheaper saws usually specify thinner blades.

Tin

 

[Forestgnome]

I just go on the notion that on a home shop bandsaw you can't apply too much tension using the hand tensioner. I just tighten it until I can't tighten any further.

 

[gus]

With my Makita Bandsaw,I have the O------full tension at lever dead end. So far so good. Am glad I bought the bandsaw and Gus no longer procrastinate when it comes to hacksawing bar stocks and leave me wheezing away.
Gus just cannot manual hacksaw straight on the marked line.
When the bandsaw keeps wandering of the path,its time to replace same. Just found out weeks ago.

 

[jgedde]

Harbor Freight Bandsaw Blade Tension Gauge

Had a few things to pick up at the market and on my way out…"Oh look! Harbor Freight"
I had a coupon (that's like saying the Atlantic Ocean is wet). Even people who have no need for anything at HF and have never gone inside, have a coupon.

I had forgotten where I saw it, but there was an interesting technique for measuring the tension of bandsaw blades. It seems you open a pair of calipers to a fixed distance (makes no difference what distance as long as you know what it is. We can call it Jaw Opening), loosen the tension on the bandsaw, clamp the calipers to the blade, zero the calipers and then re-tension the blade until you get a specific reading.

It all has to do with Young's Modulus of Elasticity. (basically, how much tension stretches stuff.)
Young's Modulus for steel is 29,000,000.

Dividing that into the desired blade tension will give the amount of stretch per inch. Multiply that times the Jaw opening in inches and you know what movement you need to achieve a desired tension.

I did a quick spreadsheet.

Very clever! I love simple yet powerful ideas. I tension my blade until it sounds right when I pluck it. Like a musical instrument! Not very scientific of course.

Now the obvious question is what is the recommended tension for a blade in psi?

Does the table hold true for different size blades? In other words, does the cross sectional area of the blade affect anything? My initial thoughts indicate that it doesn't matter since your table is in psi for a given elongation... So, the cross sectional area is already accounted for.

John

 

[jgedde]

After posting my last response I started thinking... Being one of those "sounds about right" guys, I started reasoning that one could compute the frequency of the sounds from plucking the blade for a given tension. Turns out someone already did this...

http://www.jpthien.com/tg.htm

Now that we have a method of computing the sound frequency and we have a method of actually measuring blade tension, I've got a hankering for some experimentation...

Maybe a band (no pun intended) that plays tools as instruments...

John

 

[gus]

Makita Bimetal Bandsaw Blade to cut steel.

Will pickup above today. Just been told ,will cost me-----US$ 50. Then normal cost US$45 for a box of three but cutting life is very short when cutting too much steel bars.