Checked my blade tension

[D6c]

Found a blade tension gauge and checked what my old LT40 ('87) is doing.
Measured out at about 11,000 psi.
I gather that's low for today's machines, which I hear are more like 17-18,000.
Is it worth my trouble to see if I can get it up to nearer that tension?

[Ben Cut-wright]

I take it your mill uses the machine spring to tension the blade?  What marks are you using to determine the adjustment at this time?  Did you attempt to bring the tension up to specs after measuring with the tool? If the spring will not provide proper tension it should be replaced.

[kelLOGg]

When I was under-tensioned I experienced bands that would rise or fall in the cut. I re-tensioned using the caliper method to 20,000 psi and got marked improvement in cutting. Do a search for it in FF.

[dgdrls]

Call WM and ask for the spec
Are you having issues with your cuts?

D

[ladylake]

 

If your having trouble cutting straight try giving more tension and see if it helps.  I tried that and it didn't seem to help. other issues like not enough set , dull blade or out of alignment.  Steve

[Southside]

You need to know the specs from WM for your machine. Too much tension and you will take out the bearings on the band wheels. 

Give them a call and they will tell you. 

[D6c]

I do have some trouble with wavy cuts through hard spots unless absolutely sharp.
It is a spring tension type.  To pull it up near the 17-18k tension I think the spring would be stacked tight.
I was wondering about the bearings on the idler wheel.  Not concerned about the drive wheel since it's much heavier.

[Ben Cut-wright]

I do have some trouble with wavy cuts through hard spots unless absolutely sharp.
It is a spring tension type.  To pull it up near the 17-18k tension I think the spring would be stacked tight.
I was wondering about the bearings on the idler wheel.  Not concerned about the drive wheel since it's much heavier.

Wavy cuts can have several causes, as you know.  Getting the blade tension *correct might alleviate most of the cause.


The reason I inquired as to what "marks" you use to determine when the spring is properly compressed was in hopes of determining the condition of the spring.  IF it will not achieve manufacturers recommended strain on the blade it should be replaced.


There is an upgrade for the idler bearing. Can't recall if it requires an upgrade wheel to accommodate the heavier bearing. The original will handle the strain if it's sound.

[Magicman]

I do have some trouble with wavy cuts through hard spots unless absolutely sharp

You should only be using absolutely sharp blades anyway.  

I sorta classify sharpness in three categories: Sharp, not sharp, and dull.

[Old Greenhorn]

.....
I sorta classify sharpness in three categories: Sharp, not sharp, and dull.

Lynn, I love it when you get all technical sounding and use those fancy professional descriptions!

[Magicman]

 :  I know but there is a distinct difference between the three. 

[Percy]

I sorta classify sharpness in three categories: Sharp, not sharp, and dull.

:D :D :D
I have/use a similar system for blade life, three categories as well: New, not broken, and broken.

[D6c]

I do have some trouble with wavy cuts through hard spots unless absolutely sharp.
It is a spring tension type.  To pull it up near the 17-18k tension I think the spring would be stacked tight.
I was wondering about the bearings on the idler wheel.  Not concerned about the drive wheel since it's much heavier.

Wavy cuts can have several causes, as you know.  Getting the blade tension *correct might alleviate most of the cause.


The reason I inquired as to what "marks" you use to determine when the spring is properly compressed was in hopes of determining the condition of the spring.  IF it will not achieve manufacturers recommended strain on the blade it should be replaced.


There is an upgrade for the idler bearing. Can't recall if it requires an upgrade wheel to accommodate the heavier bearing. The original will handle the strain if it's sound.

On this mill you tighten the spring down unit the washer at the end of the spring is flush with the tube that contains the spring.
I'll have to ask WM what the tension it was designed to and if they think I can get away with raising it some.

[D6c]

Spoke to WM.  Apparently there was an upgrade available at one time to increase the size of the spring to 2" dia. so it must have been an issue.
That's no longer available but you can upgrade to a hydraulic tensioner for $340.

My other option would be to modify it to accept a 2" spring, which wouldn't be too big of a job.  With my tension gauge I should be able to be pretty consistent.  

He told me the newer mills are running 21-24,000 psi tension.  Does that sound about right?  I was watching a Cooks sawmill video the other day and they're recommending 17-18,000.

[GAB]

I had a W-M employee at a show tell me the blade tension should be 25,000 psi +/- 1000.
On the LT40 I run at 3000 psi +/- a little.  Saws well.
GAB

[kelLOGg]

I want to make sure we are all on the same page when we talk about tension. I have a spring tensioner so tension to me is the psi on the actual band - there is no gauge reading. In GAB's last post he says he runs 3000 psi which sounds like a hydraulic gauge reading and not tension on the band.

[Crossroads]

When I had the 85 lt30, I went through this and found that it wasn't getting enough tension ( measured the stretch). I replaced the spring and it didn't improve. I ended up ignoring the marks and would bottom the spring out, then back it off1 full turn. The stretch was still a bit short, but it was close. 

[GAB]

I want to make sure we are all on the same page when we talk about tension. I have a spring tensioner so tension to me is the psi on the actual band - there is no gauge reading. In GAB's last post he says he runs 3000 psi which sounds like a hydraulic gauge reading and not tension on the band.

kelLOGg:
You are correct. In my case the 3000 psi is the LT40 pressure gage reading.
Sorry if there was any confusion.
GAB

[Ben Cut-wright]

The dedicated 'strain gauge' performs a *stretch measurement on the blade, as the caliper method does.  Whatever device is utilized to adjust the tension to achieve proper strain should have (some marks or a pressure gauge reading. etc.) in order to quickly return the setting to the same point when installing blades.  IOW, accurately repeating the tension adjustments should result in similar strain on the blade.

[Ben Cut-wright]

Spoke to WM.  Apparently there was an upgrade available at one time to increase the size of the spring to 2" dia. so it must have been an issue.
That's no longer available but you can upgrade to a hydraulic tensioner for $340.

My other option would be to modify it to accept a 2" spring, which wouldn't be too big of a job.  With my tension gauge I should be able to be pretty consistent.  

He told me the newer mills are running 21-24,000 psi tension.  Does that sound about right?  I was watching a Cooks sawmill video the other day and they're recommending 17-18,000.

Mills with the original spring dimensions in good condition are able to achieve the specified strain. Is your spring correct, could it be fatigued? Perhaps the larger 2" diameter spring provides *longer useful life? Adjusting the spring to the point the washer is aligned with the spring tube does NOT bottom out the spring,  there is more adjustment left.  Did you attempt to adjust further or stop at the normal point?  You are correct the 2" spring would not be hard to adapt, if it is necessary or desired. 


It might be wise to double check the tension meter gauge you have by measuring the specified stretch with calipers.

[Ljohnsaw]

I tend to over think things.  When using a hydraulic tensioner, you have an absolute measurement on the pressure gauge.  When using the spring tensioner, you have a mark that you compress the spring to.  But, what if the blades are slightly different lengths?  Not much but what if a blade is 1/10" longer or shorter and you adjust the tension to the mark, how significant of a change would that represent in the tension?  Maybe that is why one blade cuts differently than the last?  Why you sometimes need to increase just a bit more?

Maybe I'm over thinking it...

[RAYAR]

I tend to over think things.  When using a hydraulic tensioner, you have an absolute measurement on the pressure gauge.  When using the spring tensioner, you have a mark that you compress the spring to.  But, what if the blades are slightly different lengths?  Not much but what if a blade is 1/10" longer or shorter and you adjust the tension to the mark, how significant of a change would that represent in the tension?  Maybe that is why one blade cuts differently than the last?  Why you sometimes need to increase just a bit more?

Maybe I'm over thinking it...

On mine with a Cook's style of spring tensioner, a slight difference in blade length doesn't make any difference as the spring tension is the the amount of tension being applied to the band wheel.

The nice thing about this set-up is if a piece of wood, bark or something happens to pass between the band and the band wheel, the spring usually has enough give to compensate for this and doesn't tend to spike up the blade tension when this happens.

[D6c]

The original spring is a 1½" dia x 3".  It still measures 3" long do I don't think it's fatigued.  Usually they'll get shorter if they're getting weak.  A 2" die spring has considerably more force than an 1½ of the same grade. 

The tension gauge I have is a Starrett but I could check it against a caliper if I knew the stretch specs.

Today I was messing with the tension to see what I'd get if I cranked it down till the spring stacked.  Was still a little under tension but as soon as the spring bottomed the bronze nut on the tension screw split in two.  Oops.  A little lightly built.

Talked to WM again and got some good info.  There's a complete upgrade kit to go to the hyd tensioner but it also includes a new idler band wheel and support with heavier bearings.  They also recommend upgrading the drive side bearings  but probably wouldn't do it unless they fail.  A little over $700 for the kit.
Hyd tensioner by itself is about $350.

I could upgrade the band wheel, put in a 2" spring, and beef up the tension screw, but if it doesn't work I'll end up spending more than the kit price to change to hydraulic later.

I'll fix the broken nut for now and decide what to do.

[Southside]

The hydraulic system gives you a visual key of how your band is performing too.  If the band is heating up then the gauge pressure will drop, I doubt you will be able to see that on the spring, I know I can't see that on my 35 as is has a similar compression set up.  On my 70 it's an air gauge, because it's a hydraulic over air system, but the gauge does the same thing for me, if I notice it dropping then I know something isn't right or the band is getting dull, etc.  

Personally I think the complete upgrade will be money well spent.  It won't take many diving bands wrecking lumber, that should have been avoided, to pay for itself.  

[ladylake]

I'll take the spring setup any day, tension it up and forget it.  I know when my blade is dull.  Steve