## Messages

Subject:
My experience *PIC*
Response To:

John K Jordan
I used to run 3/4" blades in my 14" Delta with riser block and tensioned the best I could to make them work. I even tried 1" blades (ha!). The Delta part Dick Coers shows in the Amazon picture is exactly what bent on my saw. From my reading at the time this is a common problem. You might have the feeling or hope that your bandsaw can handle what the Delta cannot. Good luck! If you measure the tension then you will know.

I did three four things to vastly improve my bandsawing with that little saw.
- Replaced the casting with a stronger one from Iturra Design
- Replaced the tension spring with a stronger one from Iturra Design
- tuned up my saw by following Duginske's book
- began tensioning with a Starrett tension gauge

The resawing got better. Cutting up thick green wood for turning blanks got better. Life got better.

I recommend the tension gauge that has over other methods like plucking or fluttering. It is an eye-opener how much tension is required for a large blade - I don't think the 14" Delta could even tension it high enough according to the numbers. Other 14" saws are probably the same.

You don't have to buy a Starrett gauge. Iturra Design sells an inexpensive one. You can make one for zero cost. You might even be able to borrow one, set the tension properly one time for a given blade or two, then repeat that setting every time.

Needed: digital caliper, small clamps, math

By John TenEyck

(Measuring tension with digital calipers)
...the blade guides are removed or at least backed away from the blade. Clamp the vernier with about a 5" gage length so that each jaw is on the flat of the blade, between two teeth. On really narrow blades it's best to face the vernier towards the back of the saw in order to avoid the teeth altogether.

The basic calculation is Young's Modulus = Stress/Strain, where:

1) The Young's Modulus of steel is about 30 x 10^6 psi.
2) Stress, the value you are after - the tension in the blade in psi.
3) Strain = Deflection / gage length. The vernier measures deflection, and the gage length is the starting distance between the jaws under zero load.

So, you rewrite the equation as Stress = Young's Modulus x Strain = 30 X 10^6 x deflection/gage length

The gage length I started with was 4.768", so when I measured a deflection of 0.003" that was equal to a blade tension of 30 X 10^ x 0.003/4.768 = 18,876 psi.

My little Delta was more than maxed out with the 1/2" blade I was using. The Iturra spring was nearly fully compressed, the frame was distorted by nearly 0.010" and that pulled the upper guide completely out of alignment. The data showed that I can't really run more than about 12K psi on a 1/2" blade. But with a 1/4" blade I can run at nearly 25K psi w/o over stressing the saw. The 1/2" blade will still cut OK at 12K psi, but I have to run more slowly than I would if I could apply higher tension to avoid blade deflection.

John TenEyck's photo:

JKJ