Blade tensioner, on a budget

[vasiliy]

I am building my 1st bandsaw sawmill. using 3" square tubing as backbone and pulleys mounted to 3.5 square tubing sliding on a the backbone. I did not build any tensioning mechanism yet, but everything else is somewhat together.

I was thinking to put blade on and see if it is tracking before I go any further. And I have tried that and realized that I can not do that without some real tension. Tried some sticks and shoestrings. Did not work. So I am making tensioning mechanism next.

I searched this forum and others. And here is my understanding.
There are 2 mechanisms to consider (for me at least):
1. Hydraulic, chap bottle jack with gauge
2. Compression spring with threaded rod (ACME preferred)

There are some questions I could not find clear answer to:
1. With hydraulic option, there were some statements out there that after you set your tension, you need to "lock" it somehow. Is that right? What would that locking mechanism look like?
2. If I go spring route, is there a budget spring to use? My uneducated calculations tell me I need at least 2100 lb force to max out some random online blade. Someone suggested engine valve springs. I have checked some autozone valve springs, they are in a 200 lb range. Any suggestion for a spring?
3. Comparing hydraulic and spring options, does spring hold tension better? Like if blade elongates a little due to temperature, it seems that hydraulic tensioner will drop pressure much more rapidly then spring would. Again uneducated guess.

Thank you for you time guys.

[mike_belben]

Look up "toggle clamp" and "destaco"


You could drill the piston in a cheap bottle jack to tap it for a pressure gauge as long as the retract doesnt interfere with the guage.  I have also machined new pistons for bottle jack based contraptions.  My diesel injector pop testor is just a customized scrap bottle jack. 

[farmfromkansas]

My MP 32 Cooks mill has spring tension.  If you need a spring, you could just call Cooks, they will sell you one.  Other parts as well.  Their phone number is on the left.

[Iwawoodwork]

My 1985 Mighty Mite mill uses a double spring, one on each side of tensioning screw, could mount 4 springs around the screws if the springs were light. My 2 springs look to be similar in height to automotive valve springs but thicker coils.  

[vasiliy]

Look up "toggle clamp" and "destaco"


You could drill the piston in a cheap bottle jack to tap it for a pressure gauge as long as the retract doesnt interfere with the guage.  I have also machined new pistons for bottle jack based contraptions.  My diesel injector pop testor is just a customized scrap bottle jack.

I am assuming that you confirming that tension after been set needs to locked. Not sure how toggle clamp can be used there. Is it strong enough to prevent things sliding under 2000-3000 lb of force?
Interesting idea drilling piston for a gauge. I was considering drilling the bottom of the jack.

[Den-Den]

I am using converted jack hydraulic system and a threaded rod.  I set the tension by pressure gauge and then lock that setting with the threaded rod.  I am using tires for band wheels,they have enough give, I feel a spring is not needed.  For steel wheels, a spring makes sense to me.

[kelLOGg]

I run 1.25" Kasco bands that are 0.045" thick and about 1" wide (excluding the tooth height) and Kasco recommends 20,000 psi tension on the band. With a cross sectional area of 0.045 sq in that's 900 pounds of force on the band which takes a pretty hefty spring.

[KenMac]

My MP 32 Cooks mill has spring tension.  If you need a spring, you could just call Cooks, they will sell you one.  Other parts as well.  Their phone number is on the left.

I was going to suggest checking out Cook's tensioning system on their AC 36 mill. It may be similar or totally different than the MP 32- not sure. It consists of a bottle jack mounted sideways pumping against a spring to a predetermined point marked by a wire. Simple and effective. The tension is locked by the hydraulic jack and the spring keeps tension consistent and allows some give if needed.

[ladylake]

 
 What ever you use too apply presure get a heavy sping in there.  Just hydraulic  loses tensions as soon as the blade heats up a little.  Steve

[GAB]

I run 1.25" Kasco bands that are 0.045" thick and about 1" wide (excluding the tooth height) and Kasco recommends 20,000 psi tension on the band. With a cross sectional area of 0.045 sq in that's 900 pounds of force on the band which takes a pretty hefty spring.

I was told by a former W-M employee that the blade tension should be 25,000 psi +/- 1000.
GAB

[JoshNZ]

I went with the hydraulic mechanism on my mill and tried two bottle jacks before swapping out for a proper ram. Bottle jacks just won't hold the load long, they're designed to hoist a load then let it down on chocks and their job is done. They'll leak down with vibration and you'll lose tension while sawing.

I have a porta pump, then hydraulic valve (because the porta pumps check valve ball bearing isn't super reliable), then gauge, then small ram that I modified to fit.

I run it up to tension then close valve, might tweak it once more after 30 seconds, I dont know if blade heats up or things settle in but anyway. Gets left there on 1900-2100 psi for the rest of the sawing session, that number I got from a blade tension metre. If the jack were pushing on the rim of the pulley right under the bands track the math would be simple enough but because it's a lever with frictions involved it makes it quite complex to calculate, so you're better off using verniers or whatever to measure then read off gauge.

I didn't read much of the thread but I'm sure it's already been mention that your tracking needs to be adjustable. A bottle jack would work for setting up/figuring things out during build but you'll have to swap it out before going to work. Good luck!

[trapper]

My lt30 uses a screw and spring  I bought a new spring just because it was recommended by woodmiser tech when he was here 

[vasiliy]

I run 1.25" Kasco bands that are 0.045" thick and about 1" wide (excluding the tooth height) and Kasco recommends 20,000 psi tension on the band. With a cross sectional area of 0.045 sq in that's 900 pounds of force on the band which takes a pretty hefty spring.

Just want to check my formula. Should it be 1800 pounds, on a spring? since you have 2 length of band pullling?

[vasiliy]

I was going to suggest checking out Cook's tensioning system on their AC 36 mill. It may be similar or totally different than the MP 32- not sure. It consists of a bottle jack mounted sideways pumping against a spring to a predetermined point marked by a wire. Simple and effective.

Have not thought about using both bottle jack and spring. I do not have access to AC 36 to check. But if it is simply running jack and spring in sequence, it makes total sense.
Thank you to JoshNZ for pointing out potential problem with bottle jacks, loosing pressure. Based on all replies, it feels that I would need some spring regardless. Will call cook and check some other options. Will add bottle jack with gauge in sequence with the spring as an upgrade. If jack will start loosing pressure, then simply locking treaded rod after pressure is set on a string should remedy that. 
Thank you all again.

[ladylake]

  There is nothing wrong with using 6 tooth per inch 3/4 " acme thread with a heavy spring/ it's simple and works great.  Never loses pressure.  Steve

[KenMac]

I was going to suggest checking out Cook's tensioning system on their AC 36 mill. It may be similar or totally different than the MP 32- not sure. It consists of a bottle jack mounted sideways pumping against a spring to a predetermined point marked by a wire. Simple and effective.

Have not thought about using both bottle jack and spring. I do not have access to AC 36 to check. But if it is simply running jack and spring in sequence, it makes total sense.
Thank you to JoshNZ for pointing out potential problem with bottle jacks, loosing pressure. Based on all replies, it feels that I would need some spring regardless. Will call cook and check some other options. Will add bottle jack with gauge in sequence with the spring as an upgrade. If jack will start loosing pressure, then simply locking treaded rod after pressure is set on a string should remedy that.
Thank you all again.

Google will help you get a real close idea of the Cook's system. They have detailed YouTube videos showing their mills. I have had no problem with the bottle jack losing pressure and , therefore, tension. The spring gives a certain amount of leeway in adjustment.

[kelLOGg]

I run 1.25" Kasco bands that are 0.045" thick and about 1" wide (excluding the tooth height) and Kasco recommends 20,000 psi tension on the band. With a cross sectional area of 0.045 sq in that's 900 pounds of force on the band which takes a pretty hefty spring.

I was told by a former W-M employee that the blade tension should be 25,000 psi +/- 1000.
GAB

I assume required blade tensions can vary based on band thickness and alloy.

[kelLOGg]

I run 1.25" Kasco bands that are 0.045" thick and about 1" wide (excluding the tooth height) and Kasco recommends 20,000 psi tension on the band. With a cross sectional area of 0.045 sq in that's 900 pounds of force on the band which takes a pretty hefty spring.

Just want to check my formula. Should it be 1800 pounds, on a spring? since you have 2 length of band pullling?

I think you're right. I use calipers on the band to set tension and that is on one length. There would be another 900 lbs on the other length. If you're setting tension via the screw crank I suppose it should be 1800. I'd like others to weigh in here.  

[GAB]

I run 1.25" Kasco bands that are 0.045" thick and about 1" wide (excluding the tooth height) and Kasco recommends 20,000 psi tension on the band. With a cross sectional area of 0.045 sq in that's 900 pounds of force on the band which takes a pretty hefty spring.

I was told by a former W-M employee that the blade tension should be 25,000 psi +/- 1000.
GAB

I assume required blade tensions can vary based on band thickness and alloy.

Since the blade tension is in psi blade thickness has nothing to do with it.  However the force needed for the thicker bands will be more.
GAB

[bobnic]

I run 1.25" Kasco bands that are 0.045" thick and about 1" wide (excluding the tooth height) and Kasco recommends 20,000 psi tension on the band. With a cross sectional area of 0.045 sq in that's 900 pounds of force on the band which takes a pretty hefty spring.

I was told by a former W-M employee that the blade tension should be 25,000 psi +/- 1000.
GAB

I assume required blade tensions can vary based on band thickness and alloy.

Since the blade tension is in psi blade thickness has nothing to do with it.  However the force needed for the thicker bands will be more.
GAB

The blade thickness has everything to do with it.  The the applied tensioning force in pounds is divided by the blade cross section area (thickness x minimum width) resulting in the blade tensile stress in psi.  Also, don't confuse pressure (psi) in a hydraulic tensioner with the desired tensile stress (psi) of the blade.

[Iwawoodwork]

First have to disagree with hydraulic jacks bleeding off, Had two setting under a 745 Allis loader (about 40m lbs) for about 5 months and no bleed off / If a jack is bleeding down then something is wrong with it, Over the 25 years of this forum there have been a number of home-built bandsaws using bottle jacks to tension the blade and have not read about any tension loss, I am considering using a bottle jack and gauge to replace my tension screw to have a more positive  way to tell when tension is about correct .

[pineywoods]

Bottle jack don't work too well in horizontal position. Guts out of a cheap floor jack. you get pump, cylinder and a check valve. Drill and tap a hole in the base of the cylinder to thread a pressure gauge. Leak down not much of a problem, watch the gauge. the blade will stretch when it heats up, again, watch the gauge.

[CaseyK]

Very interested in this. I'm building a 4 head resaw with each head consisting of 2 slides on a section of  3x3 tubing. The 1st slide will be used to tighten the drive belts and the idler slide will be used for tensioning the blade. The acme rod and spring sounds interesting. 

[Ljohnsaw]

1. With hydraulic option, there were some statements out there that after you set your tension, you need to "lock" it somehow. Is that right? What would that locking mechanism look like?

I (now) use a porta power with a little puck ram and a piece of ¾" bolt as a 'lock'.

 I'm using 2"x2"x¼" tube sliding in 2½"x2½"x¼".  The ½" plate that bolt is passing through is welded to the end of the idle side wheel support.  The bolt is pressing on the head frame.  A porta power puck is stuck in between the two just to the left of the bolt.  Once I get the tension I want, I spin the nut snug up against the ½" plate and remove the puck.  I'm using steel (pulley) wheels with V-belts in them.  I do not have a spring and it seems to work fine.  I did pick up a pretty stiff "die" spring that I'll be testing to see if it is stiff enough.  It will fit over the lock bolt with another nut to adjust its tension.

What you see here is the drive side mount.  The frame with the notch is actually pallet rack rails.  The 2x4 blocks with the 2 vertical bolts at each end clamp the mount where I want it.  The horizontal threaded rods are used to adjust the tracking and keep the mount from moving under the tremendous tension load.

These rods are on both sides as you need to adjust the tracking of both wheels.

[JoshNZ]

First have to disagree with hydraulic jacks bleeding off, Had two setting under a 745 Allis loader (about 40m lbs) for about 5 months and no bleed off / If a jack is bleeding down then something is wrong with it, Over the 25 years of this forum there have been a number of home-built bandsaws using bottle jacks to tension the blade and have not read about any tension loss, I am considering using a bottle jack and gauge to replace my tension screw to have a more positive  way to tell when tension is about correct .

I'd say it is something to do with it being on its side. Whether an air bubble is trapped at upper arc of seal maybe I don't know. I tried two, and they sure did leak, couldn't make it one cut by the time I gave up. No oil dripping so it was obviously piston seals leaking back to reservoir