Thread: Tensioning jig for bandsaw

Yep, got one. Do I use it? Not really. I think the tension that is right for the job at hand varies a bit. Having said that they do provide a starting point from which you can adjust tension.

Some of the blades I've ordered of the same width have differing lengths even coming from the same manufacturer on the same order so I have to re-tension every time. I'm also a gadget aholic and this one got my curiosity. If it just provides a good starting point then I'm happy with that but the big question, what's a good ending point?

I was hoping to get started on making one, but got sidetracked as me shed is upside down for the time being.
Here's a thread which may be of interest, with some measurements taken of the Lennox gauge.

Bandsaw tension meter build questions | Page 2 | UKworkshop.co.uk

Tom

I tension by sound.

Pluck it on the the non-guide block side.

D3 is about right for me... D3 Piano Note - YouTube

If you are not getting a musical note at all it is not tight enough!

Neil, my aging ears aren't good enough to use that method. I just watched 2 conflicting youtube videos. Using the blade section near the upper wheel, one said push the blade and make sure you don't get more than 1/4" (6mm) and the other said tap the same section not push it. It seems every one has their own pet way of doing this and I guess if it works and gives you acceptable cuts then that's fine but as a newish bandsaw owner (Rikon 10-326 for about a year and a half) these conflicting methods are confusing.

Originally Posted by barri

Neil, my aging ears aren't good enough to use that method.

Right oh!

Only comment on the EZtension, as I understand it they are set to read 15,000 psi. That is OK if you are doing some deep re-sawing, but IME you don't need as much as that for most work. But having said that, many BSs are set with far less tension than ideal.

If going as high as 15,000 psi I wouldn't leave mine set at that after a workshop session, but there are different thoughts about that.

The tension indicators that come on most bandsaws are too inaccurate to be useful in setting the tension, but once you have set the tension by another means I find them consistent enough for returning to that tension with your own temporary markings against their scales, particularly if you release the tension between workshop sessions. The bands do stretch with use and periodic re-calibrations may be required.

I tensioned my 1/2" blade to where I felt it was right and adjusted the pointer to point to 1/2". It was pointing close to 3/4", so yes the tension indicator was way off as most are. After that adjustment my 3/16" and 1/4" blades were almost bang on so I now have a great starting point but I know that not all blades are the same length and consequently adjustments have to be made. I'm super curious to see if the EZtension jig points to roughly the same spot. Still impatiently waiting on delivery. The other annoying thing is that they make 2 jigs. One from 1/4" upward and one from 3/16" downward. I swap between a 1/2" blade for resawing and 3/16" for bandsaw boxes and tight curves all the time. I bet I'm not the only one who makes that swap.

I don't understand why you are referring to the length of the blade in relation to tension. Whenever you put a different blade on you have to adjust the tensioning knob to adjust for any length variation and then set the tension from there. Am I missing something?

I ordered 3 by 3/16" blades from the same manufacturer at the same time expecting them to be at the same tension but they weren't so they were obviously of different lengths assuming they were of the same material. Of course you have to adjust each blade individually because no two blades even from the same manufacturer using the same material and same width will have exactly the same length. Maybe I could have phrased that better but given my earlier post I thought that was obvious.

Originally Posted by Treecycle

I don't understand why you are referring to the length of the blade in relation to tension. Whenever you put a different blade on you have to adjust the tensioning knob to adjust for any length variation and then set the tension from there. Am I missing something?

No, you are not missing something with your technique. However, the crude tension 'indicators' installed on most bandsaw machines use a principle that does rely upon the length of the blade and the extension of the tensioning thread to "indicate' tension - very poorly I might suggest!

Originally Posted by Treecycle

I don't understand why you are referring to the length of the blade in relation to tension. Whenever you put a different blade on you have to adjust the tensioning knob to adjust for any length variation and then set the tension from there. Am I missing something?

Yes, with a new blade, the first bit of turning the tension mechanism is just taking up any slack. Any variation in blade length is inconsequential in terms of getting the final tension set right. There should also be minimal variation in the tension required between blades from the same supplier of the same material type, width and thickness, regardless of any variation in length.

The tension required is calculated on the cross section of the blade (not its length). Bands of the same material and cross section should be set within the same tension range. Typically the bands used in bi-metal blades require more tension. The greater the cross section of blade the greater the tension required.

The required tension range for a blade is calculated using Young's Modulus for each band material, but manufacturers will have worked that out for us and there are also tables that set out the typical tension range for each cross section of blade. The following table is for standard spring steel blades...

Bandsaw blade tensions
Blade Width	Mini/Max psi tension
1/8"	7,000/10,000
3/16"	7,500/10,500
1/4"	8,000/11,000
3/8"	9,000/12,000
3/8" x .032	11,000/14,000
1/2"	10,000/13,000
1/2" x .032	12,000/15,000
3/4" x .025	11,000/14,000
3/4"	13,000/16,000
1"	14,000/17,000

Note: the table shows blade widths, which is measured from tooth tip to back of blade. The tension calculations will have been made using the 'band' width, which is measured from the gullet to the back of the blade, times the thickness of the blade to give the cross section of the band material.

Tension gauges that can precisely measure those band tensions (eg LENOX) are hideously expensive and not an option or sensible for most of us. If you are wanting to check how accurate the reading is on the inbuilt gauge on your bandsaws without going to that expense there are two DIY approaches that involve some calculations:

Method 1. Remove the blade and possibly also the table, if tilt is insufficient, and attach a hoist scale (something like this) between the top and bottom of the saw (not to the wheels, but somewhere on the shafts or moving part of the tensioning mechanism) and use the formula:
PSI Tension = Force (in lbs) on scale/(Cross-Sectional Area of Blade in Sq inches to be used x 2)


The reading on the hoist scale is divided by two in the formula because there will be two sections of the blade connecting the top and bottom wheels and sharing the force when in use.

Re-calibrate the scale for that size blade on your BS. Repeat for any other size blade that you use.

Method 2. This method uses equipment that you may already have, but involves more calculation. With the blade on the saw measure the distance between two points then apply tension by the amount indicated on the inbuilt scale on the BS. Then measure the stretch in inches in the blade from applying that force using either verniers or a dial indicator.

Then use the following formula:
Relative stretch = Increase in length under tension measured in inches devided by Starting span without tension measured in inches

Then multiply the relative stretch figure by Young's modules for steel, which is 29,000,000 PSI and that then gives the PSI being applied for that blade. It is likely to be under the recommended PSI by the blade manufacturer, so increase the tension until the recommended minimum PSI is achieved for that size blade and mark that on the inbuilt scale. Repeat for any other size blade that you use.

Increase the tension up to the max PSI for re-sawing and in deep green wood and release tension when BS is not in use.

See some suggested ways of mounting the verniers or dial indicator to take the above stretch readings...

Bandsaw tensioning

Bandsaw Blade Tension Meter - JTenEyck - Woodworker

https://www.ukworkshop.co.uk/threads...2/#post-220123

https://www.garagewoodworks.com/BS_Tension.php

Once you get the tension right you will start to recognise that it is right without having to go back to re-measure that...

Back now to plucking away my blades...

EZ tension arrived today after a slow 4 week delivery and I must say I'm actually impressed. I tried it with a 1/4" and 1/2" blade and the tension indicator on the bandsaw was actually pointing to where I roughly have it for these 2 blades just using just a deflection technique. The photos are with a 1/2" blade and I adjusted the pointer to roughly 1/2" when I installed and adjusted this blade a week ago so the jig returned me to the same place. So I will definitely keep using this as a good starting, maybe finishing point sometimes.

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