Electrical resistance and bandsaw blade tension

Wow, another guy really into bandsaws. Ok, I'll admit I now have three -- but the lil one is just Ryobi's lil 9" guy -- surprising how useful he is. I didn't mention this before, but I always release tension on my blades when I'm done with a cut. I also have an older Delta 14" -- I have the one they equipped with a gearbox for dual use in metal cutting.

Do you also find that you have blades that you keep for straight cuts, and others for curves?

I use very few blades really, Thom. My choice for re-saw (after trying a number over the years) is a 3/4" Lennox 3 tpi bi-metal in there Classic series. It gets the call for both re-saw and straight line ripping on stock over 4". My TS will handle 4" stock.

On my smaller BS I use for curves.. a 1/4" 6 tpi stays on the saw as it has proven to be the best all around performer for me making a lot of 1/2" MDF templates. I cut to 1 mm of the drawn line and clean up with a spindle sander.. files and rasp to the line as MDF is easy to work. Once the template is done I transfer the line to the actual stock then cut it to 1 mm of the line. Attach the template with screws (if that side will be hidden) or double carpet tape if both sides showing and take to the router table to be finished with an over-head bearing pattern bit.

But.. I do have both a 3/16" special "wet-wood" blade for the larger saw to use cutting green or wet blow-downs from my yard or I salvage after storms. And I have a standard carbon 3/16" to use when I need a bit tighter radius than the 1/4" can yield. For very tight radius cuts... I just do them on my DW scroll saw.

So.. two main blades (I do keep a spare of each as I am in the shop daily) do 95% of what I do making one-off carcass work. The other two are simply special situation blades but when you need them.. they are more appropriate than my two main go-to's...

Regards...

[tkarlmann]

Good point Ed. I am fortunate to have both a large BS for re-saw and a smaller one for curves. The same blade stays on both. I have a tension release on the larger which makes life simple. On the smaller I release tension after use and retension by hand before using it again. But.. a 1/4" 6 tpi stays on that saw and I just crank it up to around just under the 3/8" mark which is the proper tension for that saw and blade on my given brand regardless of what the dial indicates.

But.. I have demonstrated BS's for two machine manufacturers at WW'ing Shows and you have to switch blades relatively often during the course of a show. I used to have to do it also before adding the dedicated larger saw for re-saw. It doesn't really but a couple of minutes IMO and if you are using the same blades swithching around... you can simply put a tick mark with the tip of a black marker on the sweet spot on the tension dial.

Regards...

Wow, another guy really into bandsaws. Ok, I'll admit I now have three -- but the lil one is just Ryobi's lil 9" guy -- surprising how useful he is. I didn't mention this before, but I always release tension on my blades when I'm done with a cut. I also have an older Delta 14" -- I have the one they equipped with a gearbox for dual use in metal cutting.

Do you also find that you have blades that you keep for straight cuts, and others for curves?

I think what people are looking for is a way to set the tension on the first try, meaning that if they are re-sawing, they won't have to tension it 4 or 5 times to make a good cut. I haven't tried Phil's method, but it sounds very repeatable.

But Sarge makes it simple. If it has 2 pounds or 2 tons of tension, and the blade cuts properly, who cares?

Ed

Good point Ed. I am fortunate to have both a large BS for re-saw and a smaller one for curves. The same blade stays on both. I have a tension release on the larger which makes life simple. On the smaller I release tension after use and retension by hand before using it again. But.. a 1/4" 6 tpi stays on that saw and I just crank it up to around just under the 3/8" mark which is the proper tension for that saw and blade on my given brand regardless of what the dial indicates.

But.. I have demonstrated BS's for two machine manufacturers at WW'ing Shows and you have to switch blades relatively often during the course of a show. I used to have to do it also before adding the dedicated larger saw for re-saw. It doesn't really but a couple of minutes IMO and if you are using the same blades swithching around... you can simply put a tick mark with the tip of a black marker on the sweet spot on the tension dial.

Regards...

Did I err? Karl......

No!

An aside on Video-making woodworkers: I also think John White is one of the real thinkers and innovators for aligning shop tools... Karl

Couldn't agree more! JW is indeed a fine mind regarding machine maintenance and that is even more apparent since he left the FWW shop manager position to strike out on his own. I think he is a bit more public with his own views now without having to get prior approval from the editors at FWW magazine.

I really enjoyed Mark Duginski's earlier books and videos, but when I met him at a WW show a few years back he was selling some fixture or other that was the very thing his 'paper shims' ideas stated you should not buy!... Karl

Yep... amazing how views change when money becomes the bottom line!

Kelly Mehler, on the other hand, is exactly the same in-person as he appears in his videos.... Karl

I don't do videos but... I have seen Kelly Mehler twice in Seminar at Highland Hardware and I have great respect for his in-sight and techniques.

How you align your own bandsaw is up to YOU -- because everyone is responsible for their own cuts to their own acceptance... Karl

Yep... in WW there is more than one direction to take to reach the finish line. Some will choose the long way around before finding what they conclude is the shortest route. But.. in the end reaching the finish line is the main goal regardless of how long it took.

Regards...

[Ed62]

I think what people are looking for is a way to set the tension on the first try, meaning that if they are re-sawing, they won't have to tension it 4 or 5 times to make a good cut. I haven't tried Phil's method, but it sounds very repeatable.

But Sarge makes it simple. If it has 2 pounds or 2 tons of tension, and the blade cuts properly, who cares?

Ed

[tkarlmann]

Just to sum up...

I just thought that someone might benefit from John White's excellent work over at FWW regarding the bandsaw tensioning system I described earlier. (?)

Personally, I am not concerned with which stars everyone looks to when they turn their tension screws. I just thought that these forums were for sharing information. Did I err?

An aside on Video-making woodworkers: I also think John White is one of the real thinkers and innovators for aligning shop tools. I really enjoyed Mark Duginski's earlier books and videos, but when I met him at a WW show a few years back he was selling some fixture or other that was the very thing his 'paper shims' ideas stated you should not buy! Kelly Mehler, on the other hand, is exactly the same in-person as he appears in his videos.

How you align your own bandsaw is up to YOU -- because everyone is responsible for their own cuts to their own acceptance.

I took the time to read this thread and in the end came to a conclussion since guru "X" said this and guru "Y" said that which is just the opposite.... I am glad I am not an entry level to WW and Bandsaws. I might be a bit confused as to "what is" the "secret formula" that will allow me to tension a given BS blade so it won't wander in a cut?

Consequently... if I purchased a BS would it be a waste of money as I might not ever find the correct tension and not be able to re-saw a board or make a curve cut on my BS? That seems a bit risky to drop that many bucks on so....

But I was fortunate enough to have gotten into WW'ing before it was tauted you needed precise.. high tech solutions before you could suceed! Having owned various band-saw's since 1973.. using them frequently until two years ago when I began to use them daily... strangely, things have gone quite smoothly without any promlems tensioning a blade.

I am not a BS guru nor need the advise of one that has been tauted as one to find tension on a given blade. I do not need to know what the manufacturers recommendation of proper tension is nor do I need a high tech tool to reach the "promised land" of sucessful cuts without the blade wandering in the cut.

The secret (which is no secret) after the other factors (guides.. etc.) on the band-saw are properly set is I set the tension to just under the blade width on the band-saw's tension wheel indicator. With a scrap piece of wood I test it. If it wanders I raise or lower the tension gradually until it doesn't. Once I reach that point I am ready to use the saw. I cannot recall it ever taking more than two minutes to find the proper tension.

So.. what is the proper tension for that blade? I don't need to know either the true measured tension or what the blade or machines manufacturer reccomends. In reality.. it is ir-relevant as once the blade doesn't wander your ready to cut so why question the results? Life is simple and I have no personal intention of finding ways to complicate simple!

[tseavoy]

I have been avoiding replying to this post since I don't know much about tensioning bandsaw blades. As far as the resistance check, the only effect I can think of is that as the blade is stretched it becomes smaller in area (the same blade over a longer distance), but this would require a very accurate low resistance ohmmeter to measure, and then one would have to know the resistance vs strain relation of the steel in question. This is the principal of strain gauges. My favorite method is to wiggle the blade. If it is very hard to wiggle, as measured by my brain wiggle meter, it is too tight.

Tom on Marrowstone

[Mr__Bill]

I was taught that one adjusted the tension until the saw stopped wondering about with the cut. If the blade broke then the set was gone and you needed a new blade anyway. I believe that this is the proper way to tension Occam's Razor too.


Bill, over here adding some spice to the pot and giving it a stir.

[LCHIEN]

Won't the amount of stretch differ with different metals at the same psi?

yes, but virtually all ww band saw blades are HSS steel, which does not change Elasticity much for various HSS alloys.

so all blades of similar materials are strained similarly - and the strain stays constant in inches per inch per PSI regardless of blade thickness and width and even length. That is the stretch over a given distance stay constant for any blade geometry.

The tension in pounds goes proportionately higher by the inverse of blade thickness and width as that reduces the cross section area carrying the strain.

[just started]

i can't imagine how you might easily use a ohm-meter to measure bandsaw tension.
I liked the idea referenced above by Thom or the even simpler one of opening the jaws of a 6" digitl caliper to about 5 inches and clamping them to a untensioned BS blade on the saw 5" apart. Then increase the tension - each .001" of stretch over the 5" = 6000 psi of blade strain, about 2.7 mils is needed for a nominal recomended 15,000 psi. Makes sense to me.

But then I read the threads linked to sawmill creek and associated threads including responses by Mark Duginske and I'm totally confused. Mark for instance didn't seem to think much of that methodology.

I think I'll mosey on out to my shop and see what stretch reading my normal setting gives...

Won't the amount of stretch differ with different metals at the same psi?

[tkarlmann]

I think Duginske's problem w/ the gauges was that the results were not repeatable.

I still think my method of determining the frequency of a plucked blade has merit. One of these days I need to actually compare it to a saw w/ a DRO.

Actually, Jim Cummins also described this method in his tape for those of us unwilling to spend $300 for the gauge -- I guess he was also into music.

[cgallery]

using the manufacturer's scale and pointer on the back is what guru Duginske recommends but esteemed late bandsaw guru Cummins condemned many years ago. Cummins said the gauges he bought all said the scale on the back of commercial saws was way off.

Now Duginske claims the commercial gauges were all wrong and the scales are right.

The Duginske tests were actually performed by a degreed engineer (I think w/ a masters, I think he is a materials engineer). He was comparing results to the Carter DRO system.

The way it seemed to boil down was that the clamp-on gauges were not repeatable. The built-in gauges were at least repeatable.

[cgallery]

I think Duginske's problem w/ the gauges was that the results were not repeatable.

I still think my method of determining the frequency of a plucked blade has merit. One of these days I need to actually compare it to a saw w/ a DRO.

[LCHIEN]

I do something very similar to what tkarlmann does. I put the blade on the wheels and tighten it until the little metal gauge on the back looks about inline with the blade thickness I am using.

using the manufacturer's scale and pointer on the back is what guru Duginske recommends but esteemed late bandsaw guru Cummins condemned many years ago. Cummins said the gauges he bought all said the scale on the back of commercial saws was way off.

Now Duginske claims the commercial gauges were all wrong and the scales are right and cummins (who can't defend himself) is all wrong, and you can't believe everything you read on the internet.