band saw tension

Re: band saw tension

Dick Coers

No, a 14" Rockwell will not tension a 3/4" blade correctly. You'll likely bend the top adjustment casting that carries the top axle shaft. Personally, a 3/4" blade is major overkill. That saw doesn't have the horsepower to utilize that blade. Proper feed speed on a 1/2" blade will produce very good results.

While I agree with Dick,

Keith Newton

If you already have the blade, I'd try it anyway, adjusted to the 1/2" setting. If it has fewer teeth and deeper gullet than offered on a 1/2" blade, that would be a good thing.

Re: While I agree with Dick,

mike mcnerney

I've got a 2 tpi. So you are saying if I start over tightening, the band won't break but the casting may bend? Years ago I think I rigged up a support to the right of the blade & down to the floor (2 pieces) to prevent that. And I still had room to resaw. My last blade was a 1/2" 3 tpi & I couldn't get it to track very well. Maybe my saw isn't big or strong enough but do you agree that the highest tension you can get will be more accurate, iow less deflection.

thanks for your thoughts

Re: While I agree with Dick,

Keith Newton

Yes, higher tension is better for less deflection. Think of it as if it were just a wire like a guitar string. Low tension would bend backward with the slightest pressure. When the blade bends backward in the middle, this tightens the back, while loosening the front of the blade. This will then cause it to wander from side to side.

As for doing damage to your saw by over-tightening , it isn't just the main casting supporting the top wheel, it's more likely the little parts that make the adjustments for supporting it inside could fail. Check them out next time you have the cover open.

If I were you, I would just tighten it as if it was 1/2" and see what you get.

Re: band saw tension

Bill Tindall, E.Tn.

If I recall what the tech rep from Lenox said you can't tighten a 14" saw as much as it needs to be for optimum on a 3/4" blade with 0.032" thickness.

Bottom line, if it is cutting ok carry on.

Re: band saw tension

Don Stephan

I've been a Suffolk band saw blade customer for years. The suggestion I was given once was to set the tension per the saw marks, then slowly back off until the blade starts to flutter. Tighten just enough so the flutter goes away. Presumably this recommendation is for all of their blade widths, but most of my band saw use these days is to rough out green bowl blanks with their 1/2" AS 3 tooth blade.

Re: band saw tension

Yonak

Don, does this mean fluttrer with the guides on or off ?

Re: While I agree with Dick,  *LINK*

Dick Coers

Wasn't it Jim Cummins, an editor for Fine Woodworking that told readers to apply higher tension to their 14" bandsaws. Viewers then starting breaking parts on the upper end of their saws. Delta was not happy, and I think it was not good for Jim. Here's a link to the assembly that fails. Either the casting bends or breaks, or the nut and tensioning bolt strips. That hinge assembly has been the weak point of those saws for decades!


https://www.amazon.com/band-saw-shaft-hinge-assembly/dp/B000HESRSG

Supply and demand says it all...

John in NM

- That they are selling on Amazon is evidence enough of the weak point!

Looks like a lot of cast zinc in that part, no wonder it fails when over tensioned. OP has a Rockwell though, they might have had a bit more iron parts before Delta bought them. It would be worth a look.

My experience

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

- quit using 3/4" blades

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.

HOW TO MAKE AN ACCURATE TENSION GAUGE for free or cheap

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

Re: band saw tension

John C Lucas

I use the flutter method. What i do is raise the guide all the way up. I dont loosen the blade guides. I loosen the blade until it flutters and then tighten until the flutter stops. That has worked well for me. Finewoodworking had an artiicle.years ago where you clamp 2 brass pins to the blade. Measure this gap. Then you tension the blade which stretches this gap and measure again until.you reach the gap given in a chart.. you use feeler gauges to measure. Doing that is how i determined that the flutter test worked.

Re: While I agree with Dick, 

Doug Wolf

Mike,

You said "My last blade was a 1/2" 3 tpi & I couldn't get it to track very well. "



You might want to inspect your upper wheel support carefully. This is what mine looked like when I couldn't get the blades to track.

Re: band saw tension

TM Stock

A 3/4" blade will likely be at least 0.032" thick, and the usual recommendation is 15,000 minimum and closer to 25,000 PSI for adequate resaw tensioning, That's 400 lbs of tension on a 1/2" wide band (3/4" - 1/4" depth gullets), which is why lightly built 14" cast iron saws will be running with their tension springs bottomed out and a lot of frame distortion. You'll get better results with a 1/2" wide blade, an aftermarket tension spring, and careful set-up each time before resaw.

If you want to do resaw work on a routine basis, consider going to a welded sheet metal framed saw large enough to tension a 1" wide blade and with wheels of large enough diameter that fatigue of the band is a secondary consideration in blade life. If footprint seems like a big issue, keep in mind that a 17" class bandsaw takes up just over 7 square feet (32" x 32" foot print), while the classic Rockwell 14" saw takes up just under 5 sf (26" x 27") in motor-under configuration...very little real difference for a 17" at 6" deeper and 5" wider. Even the 19" saws don't add much to the footprint, with 8 sf (36" x 32").

Disclaimer: I love huge old cast iron saws and the material is awesome if you can move a 1500 lb saw into and out of your shop. Nothing damps vibes like cast iron, but a 14" saw has so little of it that the vibe reduction is not noticeable versus a 14" welded frame saw.

Re: band saw tension

del schisler

i don't belive a 3/4" resaw blade is recommend for the 14" Rockwell i have that same saw and i use a 1/2" and look at the tension guide and take it to that mark , and never have a problem i am sure you will get lot's of response's here

I've never liked welded steel frames...

John in NM

I've only used a few, and they were probably not well set up and tuned, but in my experience they are way too flexible for consistent results.

I prefer a full frame cast iron saw for a small shop - basically a 14" saw that does everything well and requires no tuning. Unfortunately, no one makes these saws anymore as the more lightly built, much cheaper to manufacture models displaced the better design. The General 590/690 was the last, as far as I know. Powermatic 141's are readily available used and are excellent saws for a small shop.

Re: band saw tension

TomD

The best resawing I even did 14" knock off was with 3/8" bands, and it did a better job than the Laguna I got to replace it with Carter Guides. Sliced thin parts 12" wide, no problems. I got Jim's video, and applied some of his thinking, but I think the art of sawing on inadequate saws was more complicated than that. More about finding a sweet spot where everything came together.

Re: My experience

mike mcnerney

John, Thanks to you. it really sounds like you have done your research & learned from experience. Even though I've got the experience I haven't always learned. I'm going to have to go back & look over my BS tune up I did a few years ago after I discovered Itura. I did buy the lenox carbide but have broke it twice so I need some sensitivity training.

Thanks to all other responses too I need to start over.