Band Saw Blade Tension Measurement

[GarageWoodworks]

I was looking for ideas for a DIY band saw blade tensioner today and came across this one:

think I am going to try and make it. It looks like the lower part of the device pivots on a bar and the movement is measured by the dial indicator. It looks like the bar would have to be exactly in the center to be accurate.?. According to a FWW article I read, 5" of blade will stretch

0.001" for every 6,000 lbs of tension (over a 5" length of blade). For those with a FWW account here is the article: I don't like the one detailed in the article (I prefer a dial indicator over feeler gauges).

Has anyone tried to make one of these before? Or have you made a better one??

Thanks...

[Swingman]

"GarageWoodworks" wrote\

Fortunate enough to fall heir to an Iturra .. but I highly recommend beg, borrowing, stealing, or making one just to calibrate your tension spring at least once. Amazing how far off those factory marks can be for each width of blade.

[GarageWoodworks]

Yeah, those look nice. I just can't justify that street price at the moment.

Steal one...now that's an idea. Hey, where in Texas are you? :^)

[Swingman]

"GarageWoodworks" wrote

LOL ... probably a better opportunity than you realize. At the moment I'm sitting on a balcony (thanks to broadband wireless) overlooking what's left of this morning's snow/sleet on Lake Hamilton, in Hot Springs, AR. (Can't believe that the famed "Vapors" night club, where Ol' Blue Eyes used to perform for the Mafia big guns, has a huge sign out front proclaiming "Jesus is Lord")

... oh well!

But the old Arlington Hotel is alive and well ... the ginger bread house therein was as impressive as ever yesterday.

[Mike in Arkansas]

Swingman, glad the snow stayed south of use here in Fort Smith. I've stayed at the Arlington on a couple of occasions as well as their sister hotel down the street. One memorable occasion about 20 years ago had use eating in the fancy restaurant (can't think of it's name) down in the basement. The had a violinist who played requests at each table and the claim was he knew every song. I tried to throw him a curve by requesting "Orange Blossom Special". He played it, whistles, chugs and all. A real hoedown. The whole room was toe tapping and later someone else had him play it again. I was at school in Arkadelphia when Rockefeller 'cleaned up' Hot Springs in the 60's. Wasn't much reason to go there after that. I purchased my drill press from a gentleman down on Lake Hamilton that was moving out of state a couple of years ago. Nice place to live. Mike

[David]

I made the FWW one but added a dial indicator. (If you are interested I could try to post some pictures on abpw.) Seems to work well (ie repeatable readings), but I have no way of testing the accuracy. I increased the length to about 10" to double the sensitivity. You could also build the one in the pix and move the indicator farther from the pivot point on the lower bar to do the same thing, although a little math may be required! Given the FWW numbers, it doesn't take much blade "stretch" to represent a big tension change. I also found that starting with a little tension on the blade (just enough that it wasn't slack) increased the repeatability considerably, as did making sure the device wasn't resting on the bandsaw table.

I also spoke to Louis Iturra about a year ago, and he said he was working on a much less expensive device. I never called back to check.

David

GarageWoodworks wrote:

[Gerald Ross]

Bought a very nice turned vase there around 1994. Signed Barksdale. That was before I knew how difficult it must have been to make. (In Hot Springs, that is, not the Arlington)

[GarageWoodworks]

Yes! Please post pictures. Thank you.

Given how cheap it appears to make one, I am not sure why they can't make a less expensive model...

[Swingman]

"Mike in Arkansas" wrote

It wasn't bad ... actually, there was more snow in Houston at Christmas a few years back. :)

Had dinner _from_ there on Christmas eve ( SWMBO brought "take out" to me, as I was relieving her from bedside duties with her Dad, who's in stage 4 cancer and the reason we're here for Christmas) .

SWMBO's from an old Hot Springs family, was born here, her grandfather was sheriff back in the 50's, before it was "cleaned up", and she still has a lot of family in the area. Although I can't imagine the sheriff not being involved in what made Hot Springs 'hot' as a resort town in those days, she actually worked for Rockefeller's campaign out of high school ... go figure.

Our youngest, who simply can't get back to Texas quick enough, is a senior at HSU in Arkadelphia this year.

Looking out the balcony door at said lake, about 50' away, as this is being typed ... the place would need a BIG woodshop and be a bit warmer to entice me ... and while I'm not sure a coonass can ever get used to fishing in water clear enough for the fish to be looking back at him, I might give the idea some consideration.

(still trying to figure out how he got amongst all these folks who don't appreciate seasoning in their food)

[alexy]

I think you hit the nail on the head there. I made the kind that uses feeler gauges. Used it calibrate the spring indicator. Will probably check every year or so in case spring is getting fatigued.

Re: feeler gauges versus dial indicator: How precise do you think is important? It is nice to know if you have about 10,000 psi or about

15k psi. But you really aren't going to measure 13,527 psi! Seriously, does +/- 10% make any difference? The factory indicator is probably reliable to +/- 60%!

[J. Clarke]

I think the big benefit of the dial indicator is convenience, not precision. Just watch it and crank until it hits the number you want, no crank a little feel a little crank a little feel a little. Grizzly has one that goes to .0005 for ten bucks that should be plenty accurate enough for this kind of thing.

[Bonehenge (B A R R Y)]

Ditto that!

A useful technique all over the shop.

Like jointer knives... Install 'em low, semi-tighten the jibs, and crank them into place as you watch the indicator. A five minute three knife change.

It's all much faster than slipping go/no-go gauges in and out.

[eclipsme]

I have neither feeler gauges nor dial gauge. I think I got my technique from Ittura, but possibly not.

Mount the blade, adjust the tracking. Leave the guide blocks well clear of the blade. Rough adjust the tension.

Start the saw and watch the blade at the guides. It will flutter.

Adjust the tension to minimize the flutter.

Stop the saw and adjust the guides.

This seems to work well for me, but I am willing to learn...

Harvey

[Gerald Ross]

I got and use the same method from the TimberWolf blade folks.

It seems like the dial indicator method is measuring blade stretch, not tension. It seems like blade stretch on a 1/8 inch blade would be much more than that on a 1/2" blade so I would still have to know the end point (actual tension) to know what the dial indicator meant.

Maybe I just don't understand the whole thing.

[Bonehenge (B A R R Y)]

That's exactly what I do. I was only commenting on the overall usefulness of a cheap dial indicator.

[Tom Veatch]

The blade stretch (strain) on any size blade will be the same if the blade stress is the same and the blade material is the same.

If the blades are tensioned correctly, the stress (pounds per square inch) in each blade will be the same. Therefore, the strain (inches elongation per inch of blade length) will be the same in each blade. The total force will be about 4 times greater on the 1/2" blade than on the 1/8" blade

This method measures the strain, not the total force. What does the dial indicator mean? The dial indicator measures the total elongation of the blade between the two clamps. Divide the dial indicator reading by the distance between the clamps and you have the strain on the blade.

In case anyone's interested, multiply the strain be Young's Modulus for the material (about 30,000,000 for steel in the English measurement system) and you have the stress (PSI). Multiply the stress by the cross sectional area of the blade (width x thickness) and you have the tension (Pounds) in the blade.

Tom Veatch Wichita, KS USA