Blade tension differences on brands of mills

[redbeard]

Been curious about blade tension,
On the Timberking recommended blade tension is 1200 psi some run up too 1800 psi
Woodmizers run up too 3000 psi,
Are the mechanical application different that makes it read higher?
Just curious for thoughts

[John Bartley]

The blade stress is determined by the blade only and the manufacturer has a rating in pounds for the stress.  How that translates to the mill is determined by the size of the tensioning cylinder.  Different size cylinders will have higher or lower pressures in the tension cylinder to get to the correct force or stress on the band.  A larger cylinder will need less pressure than a smaller cylinder.

[tacks Y]

My LM3 (Logmaster) calls for 6k psi, looks to be a 5/8 or 3/4" ram.

[redbeard]

On my Hud-Son 60 there's no gauge or spring too keep track of tension I found where I like the blade and set my torque wrench so I know Iam in the area, and just tighten as needed til flutter goes away. I wouldn't think you need too keep tighten after that.
 

[Chaser357]

I've been wondering about this too.   Looks like to me 1800 psi tension on the blade would be 1800psi whether it was a big cylinder or little cylinder.   But I'm not very smart and am probably wrong.  Been running about 2000 psi on my timberking and the cuts are straighter when pushing the blade harder with a turbo 7.   

[Southside]

The recommendation when using Turbos is to keep the tension up quite high, so that makes sense.  Just to add to the confusion my Super 70 measures the air pressure in the air bladder (basically looks like a suspension air bag) which is compressed by the hydraulic tensioner and I run that at 100 PSI.  

The formula for measuring the output of a hydraulic cylinder takes into account the rod diameter and fluid PSI, increase the rod diameter while keeping the PSI the same and you get greater output (force), that makes me think that if one is using PSI as a means of measure and output is consistent (band tension), then rod size will impact the PSI reading, so it's consistent to the size of the rod, not the brand of the mill.      

[bandmiller2]

Bands will last longer with the minimum tension. Its sharp teeth and proper set that makes a band cut true, tension just keeps it straight. Experiment with less tension and see how your band life will increase. Frank C. 

[John Bartley]

Bands will last longer with the minimum tension. Its sharp teeth and proper set that makes a band cut true, tension just keeps it straight. Experiment with less tension and see how your band life will increase. Frank C.

This is correct, but I'd like to add one minor exception.  Under-tensioning too much will contribute to an uneven thickness across the width of the board.  So, yes, reducing tension definitely extends band life and as long as the bands are properly set and sharpened it won't affect cut quality, but there is a "minimum" to the amount of tension needed.

[GAB]

When considering band tension one needs to consider band width and thickness.  Tension is measured in PSI's or pounds per square inch.
When using a band if it heats up it will stretch and your tension will drop.  That is where the pressure gage comes in handy.
The more tension there is in the band the higher the load on the bearings and that does reduce the life of them.
One has to make a decision more bearing life or a bad reputation for sawing thick and thin.
Gerald

[John Bartley]

When considering band tension one needs to consider band width and thickness.

I think the most important factor is the "stress" rating that the "manufacturer" has for their bands.  The manufacturer is the one authority on what tension their bands should be at, and until we know our mills intimately, we should use their spec's and translate them (do the math) to calculate the pressure that our mills would use to achieve their stress rating.

[JB Griffin]

The formula for measuring the output of a hydraulic cylinder takes into account the rod diameter and fluid PSI

Thats only half right. In reality it is fluid pressure and piston diameter not rod diameter,  rod diameter is only a factor with the retract stroke where the rod is taking up some of the available piston real estate for the fluid to push against.

A hyd cylinder cannot pull as much as it can push.