Bandsaw blade tension gauge build questions

**Tom trees** · 22nd July 2022, 05:53 AM

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 for those
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" John Teneyck's one for example
or what I guess is a fractionally smaller size, i.e 1/3 or 1/4 the size.
like 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.

SAM_6328.jpg SAM_6333.jpg
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?
SAM_6339.jpg
Thanks folks
Tom

**bjmh46** · 22nd July 2022, 08:24 PM

tensiongage.dxf tension-gage-frt.JPG tension-gage-side.JPG

Here's what I did FWIW. The dxf contains all the dimensions. It's worked very well for over 20 years, although I did originally build it with a .001" indicator, I later changed it out for a .0001" unit. Your approach is different, but I thought I'd share what I had!

Regards
Bob

**Tom trees** · 23rd July 2022, 09:15 AM

Thanks Bob for your reply.
I've posted this on the ukworkshop forum on a thread titled....bandsaw tension meter build questions,
and gotten replies there too!
That is a great looking jig and along the lines of what I was thinking.
Very informative to note that a thou difference makes 3000 PSI change!

I was trying to get my head around whether the likes of the Lennox gauge, and many others have
set distances in some sort of mechanical fashion, and was informed that this is referred to as a 3 : 1 mechanical multiplier
and to know more look up law of the lever, or "archimedes law of the lever"

I haven't gotten around to looking this up yet, but I'm guessing it will explain everything, should I be able to understand is another matter.
Along with this advise, I got a sketch of the important bits of the Lennox meter, so will likely copy this,
should I get some advice not to for some reason or another.

I get the impression that your device measures more than the 100mm distance between the blade clamping points?, in which the Lennox device has...
If so, Is this to make a round number i.e 3000 PSI to mate with the indicator markings?

Another thing which I've been pondering about some, and it seems yours displays this better,
It appears that there looks to be locking screws on the back side,
Do both of these permanent positioned bolts also have blunt points made into them, or does the points meet flats?

Thanks for your help.
I've got a few days before I can get at making this, so might have some more questions, which might be a bit better informed.
Will keep ye posted
Cheers

Tom

**bjmh46** · 23rd July 2022, 08:56 PM

tensiongage.png

Hi Tom
It occurred to me that you and others my not be able to open the dxf file that I provided--so the above image file is exported from my cad software. Interesting that Lenox uses 4.0" gaging length and a 3:1 lever ratio. Both of these effect both accuracy and resolution. I chose my numbers based on my judgement, i.e.: a SWAG. (scientific wild a$$ guess)! As I said, I later changed out the indicator for a tenth reading unit which makes a huge difference. I wasn't particularly copying any of the commercial gages, although I'd seen them. The biggest headache in developing my version was repeatability, and that came down to the blade attaching screws. I tried several screw/anvil designs, but finally settled on a fixed, flat, center relieved anvil (modified 10-24 set screw), and thumbscrew made from a 10-24 SHCS modified by very carefully fitting and grinding a carbide point on the screw. This gave me excellent repeatability!

Just use your judgement, but follow the basics: change in length=(Stress x gaging length)/Modulus of elasticity
Modulus is nominally 28-30 x 10⁶ depending on the text you reference.

Best Regards,
Bob

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