Bandsaw tension meter build questions

[Ttrees]

Hello there, hoping some of you clever folks can steer me the right direction on this, as I have been pondering about it for a few days.

I likely have suitable materials for the job,
Plenty of aluminium for making clamps, might get something a small bit lighter instead,
a good excuse to use some of this plate I have @11 3/8" long, would be the most suitable stuff for the body of the tool,
and lastly this metric thickness indicator tool should make up the guts of something fairly decent.

Not having delved into every post on the net about it yet,
but seemingly all I've seen are either 12" or what I guess is a fractionally smaller size
i.e Lennox or similar, as in keeping with less head scratching for working out the Young's modulus figures, which are seemingly easier when measured with imperial measurements.

As I have this cheap indicator and kinda want to have a use for it
(having purchased a green coloured middle isle special micrometer, it actually seems alright for a tenner, and will likely do a better job at measuring sawplate and whatnot.)
I'd like to know what ye think about utilizing this tool,
and should that mean altering the common sizes of these for less head scratching.

Another question I have is, are there set measurements for the dial indicator type,
as the bottom clamp is on a pivoting arm, from what I can make out...
Perhaps there are a pair of these, so the arm has linear motion?

Might get some more aluminium from the folks yet, just a taste of some possibly suitable materials.

Thanks
Tom

 

[Ttrees]

Just doing some mocking up, as I have more of this plate at the folks,
(without holes cut into them)
and can get about 13 1/2" with enough to bolt on/affix the clamps, say about 1 1/4" wide thereabouts, could be made a bit wider if needed.
although I would prefer something a bit more compact in length, if it can be as reliable,
i.e guessing at 12 inches between points being more accurate/forgiving, without needing Lennox indicator tolerances?

Tom

 

[Sandyn]

I had to google Lennox tension gauge to see what you are trying to achieve. I have never seen one before, but an interesting gauge to try to make. Am I right in thinking the Lennox is calibrated. How will you convert the linear movement to tension? by calculation? It seems for wood, about 15000psi. Rather than making the gauge longer, you could put some gain in the bottom pivot by selecting the pivot point, perhaps 2:1 or 3:1. My gut feeling is that it will be difficult to get repeatable results, the performance of the pivot will be critical. I would look at trying to use a bearing from a hard disk. Perhaps you could use more of the hard disk pivot mechanism?? Will be really interested to see how you get on.

 

[Ttrees]

I had to google Lennox tension gauge to see what you are trying to achieve. I have never seen one before, but an interesting gauge to try to make. Am I right in thinking the Lennox is calibrated. How will you convert the linear movement to tension? by calculation? It seems for wood, about 15000psi. Rather than making the gauge longer, you could put some gain in the bottom pivot by selecting the pivot point, perhaps 2:1 or 3:1. My gut feeling is that it will be difficult to get repeatable results, the performance of the pivot will be critical. I would look at trying to use a bearing from a hard disk. Perhaps you could use more of the hard disk pivot mechanism?? Will be really interested to see how you get on.

Yes, having a bit of issues with beam tension, which may hopefully be simply down to tensioning the blade more...
but I ain't sure, and not going to destroy a blade going to what I guess might be in the realms of at least 15000 PSI.

I'm not going to pretend I know what I'm doing so holding out for someone to suggest
what might be the best course of action.
Here's an interesting article about it, and possibly the simplest, hence throwing out some possibilities of what's possible, i.e material and required throat depth to copy.
This is about as much as I've delved into it, a brief skim cuz I don't understand,
and even if I did, I would probably still make mistakes.
I was waiting until someone posted a video of various tensions with a somewhat hefty blade, i.e say 3/4" without obstruction to hear the note clearly, but haven't found something I'd be happy with, (in my head) to aim for.
https://sites.google.com/site/jteneyckwoodworker/current-projects/bandsaw-blade-tension-meter
Could be done with clamps, I've thought about just making some really simple brackets, but I don't want to use my fancy cailpers.
It's definitely plan B if you like, as I'm not going to plough on until I know better.
Would likely simplify the math, using a cheapo digital calipers changing to imperial, should I be able to figure out what I'm doing.

https://www.ukworkshop.co.uk/threads/shop-made-bandsaw-tension-meter.19772/

 

[Sideways]

The lenox has a 3:1 mechanical multiplier on the bottom end.
It's just a simple lever on a snug fitting pin. No bearings involved or needed because it isn't used that much and wear will be minimal.
I'm pretty sure when I measured it that the blade clamps were 100mm apart, so the 3:1 lever just makes for a more compact device.
You could make it longer or use a higher resolution clock to achieve the same accuracy.
Deema and I got to play with one during our adventures with the SCM minimax S45 bandsaw some months back. The Lenox is a nice tool, though way to expensive for anything but regular professional use.
Value wise, if you have the tools and skills, spend say £100 to £150 on a high quality digital dial gauge (a Mahr or a Mitutoyo) and fabricate the frame. You would have a better tool at under half the price of the Lenox.
It did prove very useful for diagnosing bandsaw tension. Scales that measure based on tension spring compression may be far from accurate. They may not be calibrated properly. Springs can be be overcompressed so the scale is no longer accurate and spring rates may not even be known, never mind being what they are supposed to be.

 

[Ttrees]

I'm afraid I won't be spending anything more than time on making this,
but since you said it about the fancy dial gauge,
I suppose I will have to double check my findings with my fancy Mitutoyo calipers...
Maybe just a better idea not to bother, and make some clamps up instead?

I wasn't really expecting this job to be such a high tolerance gig for the indicator
and small errors only making a fraction of difference regarding PSI,
say a tolerence of under 1000 PSI would be alright and likely get me where I'd want to go without the mucking about and potential damage to the tool/blade.
From what you say, and other comments I've read, it sounds even difficult to get
an accurate reading with even the Lennox one you documented?

I don't know what a 3 : 1 mechanical multiplier means, never heard the reference before, whether its referring to size being a compact version of John's jig,
(pot shot guessing so)
but if it perhaps means the levers point of contact is referenced to the pin
in some three to one pivoting fashion, then I guess I would need dimensions to even stand half a chance at making it.

It would seem to me no working out would be involved with something
more akin to the calipers, but guessing that doesn't work for whatever reason,
otherwise I don't understand how the length of the arm would be caliberated with the indicator, I'm guessing all versions of these match, even Bahco make'em these days.

Hence my eagerness to chance making it work with my cheapo indicator which I have no use for otherwise.

Thanks for the reference Sideways, I will google that.
Tom

 

[Sideways]

Don't be concerned about the dial indicator. All I was getting at is the Lenox sells for £300 to £400 I think. It has a decent enough looking dial gauge with a colour coded scale (hardly important) but nothing special and the frame is an alloy casting for light weight. Simple to make something equivalent. If I were making one, I could spend a lot less than the Lenox and still upgrade the clock.
Good clocks are a real nice to have if you do any sort of engineering. Tools like the Lenox bandsaw gauge and the Oneway jig that is super useful for setting up tablesaws and planer thicknessers use relatively cheap clocks and would be so much nicer to use if these were better.

I don't remember the Lenox being hard to use. It's very straightforward, repeatable and usable as it is.

3:1 multiplier
I was just trying to describe what's effectively a see saw. A simple lever with the pivot 1/4 of the way from one end. Short end has a screw clamp that pinches on the blade, long arm presses on the dial gauge plunger. Changes in the length of that 100mm section of blade are multiplied 3 fold so you get a bigger movement on the gauge and it's easier to read. The total lever length in the Lenox is only about an inch (?). In their version the gauge has a custom scale so that it reads directly in psi. This means that the lever has to be made accurately because if the ratio is off, it won't shown the correct tension.

On a DIY version, you are just dealing with stress / strain in the linear region so you measure stetch per 100mm or whatever length, do the math and make a lookup table to turn strain into stress (psi or metric).

 

[Inspector]

Interesting what you can find with a search.
https://www.eztension.com/buy-one-now/eztension-bandsaw-tension-gaugehttps://canadianwoodworking.com/tools/eztension-bandsaw-blade-tension-gauge/
Maybe not perfect for all situations but food for thought.

Pete

 

[Ttrees]

Trying to make sense of this 3 to 1 mechanical multiplier Sideways,
no hits on google as of yet.
Started looking at the Lennox one again, and bear with me,
but getting the impression that I maybe overthinking things.
Just for an attempt at some clarification since I'm not that bright,
but might it be the case that the lever might travel the same amount when
triangulated (when attached to blade)
i.e moving the same amount regardless of arm length, making that possibly a non issue, as I only need to know how much distance the blade needs to stretch.

I would have expected the pin to be on centre, but looking closer it looks to be about a third or a quarter closer to blade point.

Had a look at these on video already, trying to make out whether there is a divot/hole on the blade clamps,
I've think it's these ones which the points are ground to a blunt point to grab the blade or make more precise/both, but couldn't make what's on the anvil side if its just a flat profile or otherwise.
Seems I might have to inspect these some more, plenty around it seems
Some nice machinists ones out there also, but no WIP's what I can find.

Tom

 

[Si465]

In case it helps I made one following this as a guide.
https://woodgears.ca/bandsaw/tension.htmlNo idea on accuracy but I scaled it up to use most of the resaw height of my bandsaw and redid the calcs. Results seemed repeatable.
I haven't used it since, so maybe don't spend too much time on it!

 

[pgrbff]

I printed this one.

 

[Richard_C]

If you are still looking for the 3:1 explanation search for "law of the lever" or even "archimedes law of the lever".

The post 2 above says "not used it much". Hmmm. I can see that a tension gauge might be useful with big machines in a professional environment but I will continue with my SHF* method.

* Standard Human Finger.

 

[deema]

I would say that a blade tension meter is essential for two reasons. The first is that it will enable you to work out the spring constant and determine what size blade your machine can actually tension up properly (not what marketing says it can!). Springs can only be compressed by an absolute maximum of 25% of their length, and preferably around 15 to 18%. If you exceed the 25% rule you will destroy the spring and need new ones.
Secondly, to allow your blade to cut correctly and not heat up due to it rubbing against the blade guides. Blade guides MUST not touch the blade in use. They are only a safety device to stop too much blade deflection causing the blade to snap. So fancy blade guides are just a waste of money, it’s just marketing.
A cooler blade will cut better and last longer, so having the tight tension is probably the most important thing you need to do.
Sideways started a thread on renovation a S45 which he has referenced. I would highly recommend looking it up for insights into blade tension calculations and spring theory.
I wrote a thread about blade guides highlighting what they do and what they don’t do.

@Ttrees When Sideways and I had the kind loan of the Lenux from Ian at Tuffsaws I measured the key dimensions (metric). Here is my highly technical drawing

 

[Ttrees]

Thank you everyone for your replies, and especially very much thanks to Deema, exactly what I was looking for
I must have a proper look at this when I get time,
and might be back with a question or two.
Having posted this on the Auzzie bandsaw forum also,
I see I have gotten replies there too.
Seems I'll be good to go and get making this once I get some other house jobs done for the next few days.

Will keep ye posted
Cheers folks

Tom

 

[--Tom--]

I have the Starrett gauge through some fortunate ebaying. If any pics or measurements would be helpful let me know.

 

[cmoops2]

I use the 'blade wobble' method that I picked up from a Fine Woodworking video clip and it really works very well. Firstly disconnect the machine from the power supply and then open up the throat to max, loosen off the side bearing / cool block and then manually turn the wheels to ensure the blade is tracking on the crown of the wheels. Next tension the blade by whatever 'rule of thumb' method you normally use to get in the the ballpark and, when all is well, close the doors. Before you reconnect the power, get really focussed on the following words: MAJOR HEALTH WARNING - THERE'S A LOT OF BLADE EXPOSED HERE so do the next bit carefully ! Stand in front of the machine fire it up. Visually observe the blade - in virtually all cases you'll see some side-to-side 'wobble' going on. Being VERY cautious of the moving blade, increase the blade tension incrementally until the 'wobble' stops. Stop the machine, close the throat right down, re-adjust the side bearings / cool blocks and carry on ...

 

[Sideways]

We found through experimenting with the blade flutter method, plucking the blade and trying to determine the frequency with an app, etc is that these are all approximate measures. They are cheap and they may help you but they are not an engineering quality method. I have micron resolution clocks and micrometers because when I measure something (not woodwork !) I want to know what's actually going on.

A well made lenox type tension gauge is acceptably and usefully accurate. We were able to check it by clamping another gauge to the blade and taking an independent measure of the stretch, then calculating strain >> blade tension.

Once we had a trustworthy way of measuring blade tension, we realised that the bandsaw we were working on at the time - which was a substantial saw, far better than a typical DIY machine - was not even capable of tensioning it's largest blades fully. As a side effect of that, its spring had been overcompressed in an attempt to get it to cut properly and its scale no longer read correctly.

After modification to properly tension the blade (thicker, stiffer springs and 3 of them in parallel instead of one !) , the saw's cutting performance became excellent.
It's an engineering thing. You need high tension to resist sideways deflection of a beam. Proper tension is what makes a saw cut well, not an expensive set of blade guides.

Without an accurate means of measurement you can't diagnose this stuff and will never really know if your saw is setup as well as it can be.

The upside is that vernier calipers, dial gauges etc are relatively cheap these days and something like the lenox can be made for a lot less money than they cost to buy. If it matters to you to get a saw working really well, it might be worth it.

 

[Ttrees]

Thanks again folks, seems I'll be the guts of a week until I can get back to this.
I think 've got the necessary info to keep me going before I get near a hacksaw.

Sideways hit on a lot of points which are various reasons why I want this jig,
as this "light industrial" 600mm machine is being a bit troublesome, in regards to
beam tension, and the blade is acting like something half the width and giving in,
in regards to excessive use/wear of the thrust guide, and not returning quickly.
No fluttering on my machine as I done a good job of dressing the tires,
but so have some fore and aft and I need to do some more experiments with my machine to see if I can solve that.

Basically saying the beam tension in a 3/4" blade tensioned, say to 20 or 25.000 PSI if need be,
shouldn't require much involvement in regards to the thrust guide, or side rollers for that matter, in general day to day stuff, say making some skirting up etc.

Not the results I've experienced in the past, could be a few issues going on which I've yet to figure out, but after watching Trevanion's posts on some issues to look for concerning damaged blades, I must say it may have cured any remnants of use in anger, well not really, but you might get the gist of AvE's motto...
"tighten her up till you hear the crack, then back her off a quarter of a turn"

Not that I was hearing any cracks or anything like that, just saying I may have been a slight bit braver concerning tensioning than now, and not keen on damaging a blade
to find out, well not without at least learning something which may be more than speculation.

Have a look at the results in which a machine in this capability can achieve,
even if I got around half those results, I think I'd be happy.

Yes it's likely a Woodmaster CT @ 1.3TPI or Resaw king or similar carbide blade,
and likely a larger motor, but the stock isn't massive, and I would expect up to half that speed with similar blade...
The 3 TPI blade on it now suggests that aint gonna happen,
even though they have been proven to run well not so long ago.

 

[ivan]

Here's a simple tension "meter":
Shopmade Tension Gauge - FineWoodworking. No need to be a subscriber for this one.

Also posts here have shown a digital caliper (£10 Lidl) jigged up to do the same job. It's held to the blade with tiny 25mm G clamps. It's what I use. Search posts for bandsaw tension.

"Tension" is actually measured as pounds per sq. inch of blade cross section. The article above explains it well. You will be measuring blade stretch over a few inches (USA article) from 1 to maybe 6 thousandths of an inch, and a simple multiplication gives the tension is psi. We set for about 15,000 psi on a 1" blade for deep resawing, and maybe half that for more everyday sawing with 3/4" blades or less.

 

[hlvd]

I wonder if a spoke tension meter could be adapted to measure bandsaw blades

Spokes are probably a higher tension but both spokes and bandsaw blades are in tension between two points


https://www.sjscycles.co.uk/tools/ztto-professional-spoke-tension-meter/