BS blade tension article

[MilDoc]

In the new Woodworkers Journal, an article by Mark Duginske, tested BS blade tensioning. Conclusions:

1. the built in tension gauge on band saws were very accurate and reproducible.

2. the springs etc. that come with band saws are good and work well, so replacement springs are not needed

3. mechanical tension gauges they tested were neither accurate nor reproducible, and were not recommended

4. the carter electronic gauge was both accurate and reproducible and the only one they would recommend. However, since the built in gauge is accurate, carter is not really needed either.

[AlanWS]

That is interesting. Which bandsaws did he test and find accurate, and which blade tension gauges were inaccurate? I am more surprised that the gauges are inaccurate than that name brand bandsaws have relatively accurate tension indicators.

There was a test in Fine Woodworking in 2001 that found tension varying from 8000 psi to 15000 psi with the same setting for a 3/4" blade on different bandsaws.
http://www.taunton.com/finewoodworki...F.aspx?id=2766
I wonder if the tension settings have improved, or if Duginske used a narrower selection of saws. I'd consider it unlikely that White screwed up the measurements in that review.

I have used the John White tension measurement that requires two C clamps, a couple of blocks of wood, and a feeler gauge or dial indicator.
http://www.taunton.com/finewoodworki...F.aspx?id=2702
I have found the direct reading on my HF bandsaw to be quite reproducible, but not very accurate. I need to set it almost to the 3/4" setting to properly tension a 1/2" blade with a 0.022" band.

[MilDoc]

The article didn't name names of the saws tested. The mechanical gauges he considered inaccurate were from Iturra, Starrett, and Lenox. I didn't see the White article. How did he measure the tension?

[AlanWS]

In White's review (the top link I gave) he says he used a tension gauge, but doesn't say which one. I would think tension gauges should be accurate (repeated measurements cluster around the actual value) but they may not be very precise (not good at distinguishing 15000 psi from 14500 psi.) The springs on the bandsaws I would expect to be more precise, but less accurate.

The way any actual tension gauge works is to measure how much the blade stretches when you apply force. If you don't have a FWW online subscription, you can't download the article from the second link I gave above, but if you can see the thumbnail of the page there, you can see the general idea: two blocks of wood are clamped to the blade with clamps a set distance apart. You measure the spacing of the blocks very precisely, and again after applying tension to the blade. At 15000 psi, a 6" length of blade will stretch by 0.003". It takes more force to reach 15000 psi if the blade is wider or thicker: psi = lbs/sq inch of blade cross section. The relevant width of the blade is from the gullet to the back, so a blade with smaller teeth is wider than one of nominally the same width with larger teeth (deeper gullets.)

I've seen 1/2" blades from 0.022" thick to 0.032" thick (with 0.025" most common.) The thick blade would need almost 1.5 times as much force to properly tension as would the thin blade, even though both are 1/2" blades. That's why I thought a tension meter had an advantage over the markings on the saw.

But I didn't think it mattered all that much exactly what the tension was. Once you find a setting that works for a blade, the bandsaw spring position should let you return fairly precisely to that setting. My bandsaw has pencil marks showing where to tension the blades I tend to use. I will look for the Duginske article, as I learned most of my bandsaw knowledge from him, and respect his opinion.

[MilDoc]

Exactly, but Duginske says tension gauges he used were neither accurate nor reproducible (except for the Carter) and goes into detail why. So, if FWW used a mechanical gauge, that could account for the marked variation they saw.

I do wish Duginske stated what saws were tested, but the illustration of the built in gauge looks like any of the Chinese imports.

[SARGE..g-47]

Afternoon Paul...

Caught your post a little earlier as have been very busy in the shop. I glanced at the Woodworkers Journal at Lowe's when I had to go out for some naptha. I didn't see the article but would like to read it.

Did you just recieve the issus (subscriber) or did you puchase it.. and what month is on the cover? I may have just missed it and will go back latter after dinner if the current rack issue is it?

Thanks for the post as it sounds very interesting. I always wanted one of those tension guages, but the cost makes just testing with scrap till you hit "pay-dirt" is a more more cost effective and lucrative appoach! :>)

Regards...

[MilDoc]

It's the Feb 2007 issue of Woodworker's Journal, came in the mail yesterday.

And yeah, just can't justify hundreds for a Carter gauge, and the mechanical ones don't seem to be good.

[SARGE..g-47]

Thanks for the quick response Paul, it saved me another trip to Lowe's or Border's next door to that. The answer is that one has not hit the stand yet. I don't normally purchase all the mags as I used too, but again I would like to read the article by Mark as I hold him in high esteem with Band-saws.

BTW.. I have bought used pick-ups (well.. maybe not lately) for what that Carter cost! ha.. ha...

Regards...

[LCHIEN]

In White's review (the top link I gave) he says he used a tension gauge, but doesn't say which one. I would think tension gauges should be accurate (repeated measurements cluster around the actual value) but they may not be very precise (not good at distinguishing 15000 psi from 14500 psi.) The springs on the bandsaws I would expect to be more precise, but less accurate.

The way any actual tension gauge works is to measure how much the blade stretches when you apply force. If you don't have a FWW online subscription, you can't download the article from the second link I gave above, but if you can see the thumbnail of the page there, you can see the general idea: two blocks of wood are clamped to the blade with clamps a set distance apart. You measure the spacing of the blocks very precisely, and again after applying tension to the blade. At 15000 psi, a 6" length of blade will stretch by 0.003". It takes more force to reach 15000 psi if the blade is wider or thicker: psi = lbs/sq inch of blade cross section. The relevant width of the blade is from the gullet to the back, so a blade with smaller teeth is wider than one of nominally the same width with larger teeth (deeper gullets.)

I've seen 1/2" blades from 0.022" thick to 0.032" thick (with 0.025" most common.) The thick blade would need almost 1.5 times as much force to properly tension as would the thin blade, even though both are 1/2" blades. That's why I thought a tension meter had an advantage over the markings on the saw.

But I didn't think it mattered all that much exactly what the tension was. Once you find a setting that works for a blade, the bandsaw spring position should let you return fairly precisely to that setting. My bandsaw has pencil marks showing where to tension the blades I tend to use. I will look for the Duginske article, as I learned most of my bandsaw knowledge from him, and respect his opinion.

I think there was an article in one of the woodworking mags last year,
showed a simpler way of doing the stretch measurement.

It involves a 6" digital or dial caliper ($16 at HF) and a couple of clamps.
open the jaws to ~6". Use small clamps to clamp the jaws to the bandsaw blade 6" apart when the blade is untensioned. The clamps don't neeed to withstand 15,000 psi, just hold the caliper jaws to the blade, because the friction of the calipers sliding will be small. Zero the calipers. Now tension the blade and when the calipers read .003" then you have stretched the that (and all other) 6" sections of the blade by .003"
and therefore have achieved the 15,000 psi loading you reccommend.

The good is that the 15,000 psi is reached no matter whether it is a thin or thick blade and the depth of the blade is also irrelevant. Unlike the scale on the saw, it isn't affected by any extra length of blade.

The bad part is the resolution of the caliper is .0005" and as a percentage of reading is only 1 part in 6 which means the overall repeatability will only be about 16% or so, but that's not bad.

Unfortunately longer calipers are rare and most hobbiest bandsaws don't have more than 6" of straight and accessible free span anyway.

[MilDoc]

I'm aware of that measuring technique using calipers, but this is essentially what the mechanical tension meters do, and they proved inaccurate and nonreproducible, and would probably slip less than clamps / calipers would. Guess it would get you in the ballpark though. Actually, using 6" and a 0.003 reading gives a tension of 14,500 for steel blades.

But to me the main point of the article is that the built-in tension gauges on most bandsaws are accurate enough for use.

[calec]

Can the caliper span be scaled down?

I think there was an article in one of the woodworking mags last year,
showed a simpler way of doing the stretch measurement.

It involves a 6" digital or dial caliper ($16 at HF) and a couple of clamps.
open the jaws to ~6". Use small clamps to clamp the jaws to the bandsaw blade 6" apart when the blade is untensioned. The clamps don't neeed to withstand 15,000 psi, just hold the caliper jaws to the blade, because the friction of the calipers sliding will be small. Zero the calipers. Now tension the blade and when the calipers read .003" then you have stretched the that (and all other) 6" sections of the blade by .003"
and therefore have achieved the 15,000 psi loading you reccommend.

The good is that the 15,000 psi is reached no matter whether it is a thin or thick blade and the depth of the blade is also irrelevant. Unlike the scale on the saw, it isn't affected by any extra length of blade.

The bad part is the resolution of the caliper is .0005" and as a percentage of reading is only 1 part in 6 which means the overall repeatability will only be about 16% or so, but that's not bad.

Unfortunately longer calipers are rare and most hobbiest bandsaws don't have more than 6" of straight and accessible free span anyway.

If the caliper span is reduced to 4" 15,000lb = .002?