Blade tensioner

woodNthings · November 18, 2013, 03:24:06 PM

Looking to the minds for some input... as usual. I have an LT28 with manual blade tensioner and no way to measure blade tension. Your big fancy hydraulic mills have a handy pressure gauge and I'm jealous! >:(
Could someone kindly post a picture of that WM setup? I don't know that I'll go through the trouble of attempting that mod, but maybe I can mount a simple cylinder with a gauge to be able to measure blade tension.
I suspect some of my wavy cuts and rising blade issues are a result of insufficient tension. Do any of you guys with manual mills have a scientific way of measuring it? ???
Here's a picture showing the manual cam style on my mill.
Thanks in advance

Just for fun, here's a big Dogwood I cut on Sunday

WoodenHead · November 18, 2013, 04:34:30 PM

The lack of a hydraulic tensioner is one of the reasons I upgraded to an LT40 from the LT28. I'll try to capture a picture for you of the LT40 setup (if someone else doesn't do so first), but you'll find it is very different.

Have you tried to increase the tension to see if your wavy cuts go away? Most of the time for me it was a dull blade or going through a wide cut too fast. At this time of the year, partially frozen logs might also be an issue depending on your climate.

Peter Drouin · November 18, 2013, 05:24:10 PM

Did you add the rollers on the loader arms ?
On one of my old WM I had a spring .I guess tighten all you can I don; t think you can oventighten. Call WM.

Cutting Edge · November 18, 2013, 05:34:52 PM

You can use a caliper to check for proper tension. It is surprisingly accurate...I checked.

Here is a link to a thread that sheds some light on the matter. At least you could check what is currently is and adjust accordingly if needed.

https://forestryforum.com/board/index.php/topic,42669.msg616308.html#msg616308

Ga Mtn Man · November 18, 2013, 05:41:24 PM

Is that really the BEST thread you could find on the subject. It really wasn't much help at all. :

Ga Mtn Man · November 18, 2013, 05:42:45 PM

;D

Cutting Edge · November 18, 2013, 05:58:05 PM

Sorry Paul, What was I thinking??? ;)

I guess it would help if you knew what the tension needed to be, right??

According to WM instructions included with their Strain Gauge, LT28 tension should be 18,000 - 20,000 psi of strain if running an .042"/.045", 1¼" blade.

Simmonds sells a digital caliper minus the "caliper" part and they list 0.0045" of stretch measured over 5"-6" of blade to equal approx. 20,000 psi of strain on the blade. That should get you in the ball park.

Hope this helps.

Ga Mtn Man · November 18, 2013, 06:00:32 PM

Now that's more like it!

_grin

Nomad · November 18, 2013, 06:23:12 PM

Quote from: rwthom279 on November 18, 2013, 05:58:05 PM

Simmonds sells a digital caliper minus the "caliper" part and they list 0.0045" of stretch in a blade to equal approx. 20,000 psi of strain on the blade. That should get you in the ball park.

Hope this helps.

I've never seen this device. How long a distance does it span? I.E 1", 6", etc. I don't need one; just curious.

Cutting Edge · November 18, 2013, 06:34:56 PM

Quote from: nomad on November 18, 2013, 06:23:12 PM
I've never seen this device. How long a distance does it span? I.E 1", 6", etc. I don't need one; just curious.

It has a 6"+ travel like an El'cheapo caliper but it has magnets in its frame to attach it to the blade instead of using clamps.

Ga Mtn Man · November 18, 2013, 06:39:29 PM

http://www.simondsinternational.com/publications/digital-tension-gauge.pdf

Ga Mtn Man · November 18, 2013, 06:44:52 PM

Cutting Edge · November 18, 2013, 06:48:18 PM

Here is a better thread that gives a few more details:

https://forestryforum.com/board/index.php/topic,10765.msg186442.html#msg186442

Larry was kind enough include pictures as well as a detailed narrative.

thecfarm · November 18, 2013, 07:43:03 PM

I just guess at mine. :

Well I do push down on the blade too. But I only saw mostly softwood too.

coastlogger · November 18, 2013, 08:44:51 PM

Dont need a special gauge. A 6 inch dial or digital caliper will do the job fine.
Open it up to 6 inches, clamp the jaws to the blade and apply tension. Read the difference in the measurement(compared to no tension) which is the desired "stretch"

Brucer · November 19, 2013, 12:14:43 AM

A little clarification about Wood-Mizer's hydraulic tensioner. It does not tell you the tension on the blade. It tells you how much pressure is being applied to a 1" diameter piston that is pushing the idle side bandwheel away from the drive side.

Knowing the pressure and the piston size, you can calculate the force being use to stretch the blade. Knowing the stretching force, the blade thickness, and the blade width (at the gullet) you can calculate the tension on the blade. Most of us don't do that ;D. Wood-Mizer tells us how much pressure we should have for a given size blade, and that's what we use.

The real advantage of the system is that it gives us a reference number to look at. We don't need to know exactly what the number means as long as we know where it should be.

The caliper system is a simple strain gauge and gives an accurate indication of the actual tension -- provided you know the blade thickness, width at the gullet, and the modulus of elasticity of the blade material ;D. It happens to be less convenient than a pressure gauge.

Pushing sideways on the blade (I'd suggest upward) is another way to get a relative measure of the blade tension. Devise something similar to a belt tension indicator. See how much force it takes to deflect the blade a certain distance sideways. Don't forget -- the blade guide rollers have to be exactly the same distance apart each time you check the measurement.