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Dave's Bandsaw Mill

Started by northdesign, November 30, 2016, 11:42:33 PM

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AncientTom

Thanks, Pabene, for this. I will now consider incorporating a spring in the tensioning adjustment. when I purchase my blades, I will ask the manufacturer what they suggest for tension on their blades.

Kbeitz

You might want to look for one of these off E-bay...
You want around 12,000lbs to 15,000 of strain on an 1-1/2" band.



 
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Cutting Edge

Quote from: Kbeitz on January 13, 2018, 08:03:44 PM


You want around 12,000lbs to 15,000 of strain on an 1-1/2" band.




Where did you get this information from ?

"Winning an argument isn't everything, as long as you are heard and understood" - W.S.


Cutting Edge Saw Service, LLC -
- Sharpening Services
- Portable/Custom Milling and Slabbing
- On-Site Sawmill Maintenance/Repair Services

Factory Direct Kasco WoodMaxx Blades
Ph- (304) 878-3343

Kbeitz

Quote from: Cutting Edge on January 14, 2018, 07:38:50 AM
Quote from: Kbeitz on January 13, 2018, 08:03:44 PM


You want around 12,000lbs to 15,000 of strain on an 1-1/2" band.




Where did you get this information from ?

It's all over the WWW. Some places quote 25-30,000 .

One read up... I hope it's OK to post this link here.

http://www.sawmillcreek.org/showthread.php?251853-bandsaw-tension-guidelines
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Cutting Edge

12K-15K on an 1-1/2" wide would make for one SLOW cutting headrig.  The "specs" you posted would be lucky to keep a 1-1/4", .035" blade stable in the cut.

There are a couple hobby level band headrigs that are lucky to produce 16K of tension on a band just before the main frame/beam begins to succumb to deformation.  The lumber produced can/is a direct reflection of this.  Just because it resembled a board, doesn't mean that it is what most would consider a usable piece of lumber.

To proof is in the product and low blade tension, regardless of the brand of sawmill, IMO is a crutch to cover up for other shortcomings.  Most reputable blade brands can sustain near twice the tensions that you posted and have a reasonable expected life span with multiple sharpenings.

The weld quality is absolutely critical running at higher tensions.


But if it's  all over the WWW ("12K-16K tension"), it must be true  ???

"Winning an argument isn't everything, as long as you are heard and understood" - W.S.


Cutting Edge Saw Service, LLC -
- Sharpening Services
- Portable/Custom Milling and Slabbing
- On-Site Sawmill Maintenance/Repair Services

Factory Direct Kasco WoodMaxx Blades
Ph- (304) 878-3343

Kbeitz

Lenox recommends up to 30,000 PSI.
Wood Mizer says 12,500-15,000.
Woodland Mills says 20,000 -30,000
Norwood says 12,500-15,000 PSI.
Hudson says 12,500-15,000 PSI .
Lumber mate says 12,500-15,000 PSI.
TimberKing  says 12,500-15,000 PSI.


Gotta get the info some where...

But if it's  all over the WWW ("12K-16K tension"), it must be true  ???
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Cutting Edge

Kbeitz,

The majority of recommended tensions you gave, are for manufactured sawmills.  May or may not apply to certain models or even DIY/homemade machines.

I will address one correction, only because the image below is an excellent example.

W-M's recommendations are based on what the machine itself is able to produce and have durability/longevity over it's expected lifetime of components. 

Example:  An LT10 is not built heavy enough to sustain tensions that an LT40 is capable of.  Two completely different machines. 

This information is straight from W-M's instructions for their strain gauge, Part# WMBTG.  LT10, LT15 and LT35 are not listed, so this helps with an approximation of time period.  (Unknown date of actual publication)  Certain models now have more robust components and consistently run in excess of 22,000+ lbs of strain with no issue of a reduction in life of consumables nor blade life.




As you and others can see, there is an extremely broad range of recommended tension, which varies by machine and blade combination.

The reason for posting this is to helps others that are reading this information in the future.  The machine a person has, may not be able to reach those numbers due to the construction (might be a homemade sawmill) and self-destructs (12k-16K).  Or possibly a new owner of an LT70 running literally 1/2 what the machine NEEDs to have a properly tensioned blade (24k-30K).

Again, many blades can exceed what the machine is capable of producing.  Other blades are not, without causing issues with curvature, camber, etc.

Hope this helps.   ;)



"Winning an argument isn't everything, as long as you are heard and understood" - W.S.


Cutting Edge Saw Service, LLC -
- Sharpening Services
- Portable/Custom Milling and Slabbing
- On-Site Sawmill Maintenance/Repair Services

Factory Direct Kasco WoodMaxx Blades
Ph- (304) 878-3343

JB Griffin

Imo, 12-15k lbs of strain is inadequate for sawing at a decent feed speed.
I routinely run the pressure on my 40 at 2800psi up to 3000psi, thats around 23.5k of strain, thats where it will cut the best,  with no shortening of blade life. At work I have the blade tension at around 27k pounds of strain on the blade and have used as much as 35k lbs of strain. I would NEVER use only 12k of strain for several reasons.  1) lack of blade control,  with that little tension you will push the blade around like a wet noodle. 2) inability to use a decent feed speed, see #1. 3) loss of cut quality see #1. 4) loss of blade life see #2.
2000 LT40hyd remote 33hp Kubota with 6gpm hyd unit, 150 Prentice, WM bms250, Suffolk dual tooth setter

Over 3.5million bdft sawn with a Baker Dominator.

Kbeitz

I agree 100 percent... When I was building my mill I just googled
for information and thats what I found. After experimenting with
different settings I found what was best for my mill but I used what
I found to give me a starting base.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

JB Griffin

I just don't want to see inaccurate info touted as fact.
If someone was to read this and build a mill that can't handle the tension required to cut flat accurate lumber that would give us sawyers a bad rap and people would think we don't know what we are talking about.

There is a fb page for sawmills that is already FULL of misinformation and people don't know what is true and won't listen to the people who actually know because we don't post pictures and comment all the time, we're too busy sawing for that.
2000 LT40hyd remote 33hp Kubota with 6gpm hyd unit, 150 Prentice, WM bms250, Suffolk dual tooth setter

Over 3.5million bdft sawn with a Baker Dominator.

Kbeitz

I don't see it as inaccurate at all... You should build your mill to tolerate
the tension needed that the blade company's state. So for a 1/1/4"
blade that should be around 12,500-15,000 PSI . I'm thinking to get
the best cut you need this tension.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Pabene

The recommended tension for a blade is measured in one part. If you transform that tension to  the force you need to reach that tension, you then have to take that force times two, to see the real load on the wheel bearings. It is also that force as want to "bend" your saw frame. It is also just the static load. When the saw is running there are dynamic load as you have to add in your design.
I have a "tension meter" to check my blade tension in my mill. The blade prolongs about 1mm/1000mm for the tension the blade manufacturer recommends.
I like the possibility to read the real blade tension when I am sawing. If you have a "hydraulic jack" to pre load your tension spring, it is good to have a pressure gauge in the system. If the blade heats up more than normal it prolongs more and the tension drops.

Kbeitz

That's what I did. I took a hollow hydraulic cylinder and put a pressure gauge
on it.



 

Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

ladylake


Without any numbers all I know is if I tension my mill much more that what TK recommends it starts breaking bands fast. Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

AncientTom

Wow again on blade tension. With all these new posts on tensioning, I had to re-think what is going on here about blade tensioning being measured in PSI and how it relates to the actual stress that is applied to the blade. I looked at more posts on this subject and found a couple of excellent videos. Within the hour of watching them, I got quite an education.
Bandsaw tensioning:  https://www.youtube.com/watch?v=92nTjHkUFE0
Bandsaw setup:  https://www.youtube.com/watch?v=wGbZqWac0jU

I had decided that I would just use the way that Woodland Mills tensions their mill blade. They suggest using a torque wrench to a tension on their tensioning screw of 35 foot/lbs. That sounded like a nominally good pull on the blade, so that's what decided to go with. When I saw the 5 digit PSI specs on blade tension, It still blows me away as to how a thin saw blade could take that much stress and not break. But, If that is what it is, then that is what it is. It took me a long time to wrap my head around this but I then started looking at all the variables that had to be plugged into a formula to calculate the actual stress applied to the blade. After doing the math, I can see how Woodland Mills came up with a 35 lb/ft setting on their mill and that it could actually be applying 15,000 PSI to the blade.

After watching the excellent presentation by Carter Products on setting up a band saw, I now have another question to deal with before starting my build. How much offset should I apply to my drive wheel? (as mentioned in the video as all manufacturers do)

AncientTom

One more quick post to  see if I have the math correct.
A 1-1/4" x .035" blade that is about 1-1/16" to the bottom of the gullet would be; 1.0625×.035x15000 = 557.8125 lbs. linear pull in the blade for proper tensioning. Since it's a circular blade, the force on it has to be doubled (2 x 557.8125 lbs. = 1115.625) to be tensioned properly. That's over 1/2 ton of pull on my wheel. I think that my saw frame will have to be reinforced.

Also, looking for a source for a spring for shock absorption on my tensioning  design.

Kbeitz

Be careful using a torque wrench. One drop of oil on the threads
changes everything. You got dry torque and wet torque .
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

AncientTom

I'll be using a tension gauge at first.

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