Wm spring blade tensioner conversion

Magicman · May 22, 2017, 08:34:09 AM

When Arnold and his wife visited us December 21st, he was excited that he had just sawed his first portable job. He died ~two weeks later.

His sawmill is/was for sale.

Pabene · May 22, 2017, 12:02:18 PM

About blade tension.

I have noticed that the blade manufactures recommends a tension for their blades as are close to 10% of the load when it breaks.
To fulfill that recomendation means the blades will be prolonged by the tension force, the same amount, regardless of the blade dimensions. (If the steel quality is of the same sort in the blades body.)
It is important to see that the tension force needed, is different for different blade dimensions.
A tension-meter shows how much the blades are stretched out (prolongs).
To check the tension in the blade works with a caliper as are described here.
To get a higher accuracy in the check you can clamp the end of a longer rod on the free part of the blade. At some distance from the other end of the rod you can clamp a piece of steel, like a nut. Measure the distance from the other end to the nut before and after you have tensioned the blade.
At the recommended tension you will see that the blade is stretched very close to 1mm/1000mm.
To reach such tension in the blade, you need a stiff and stable saw frame. (My log band saw is to week to run the best blades at correct tension.)
In a report from a university here in Sweden, it was stated that a system with a spring was the best to create the tension for the blade. In my opinion hydraulic, weight or screw systems are good, but the best is to have a spring (or an "air pillow" like Wood Mizer) in the end, close to the idle wheel slide.
So, what I want to say here are: I think many saws shows a blade tension as are good for the saw, maybe not the best for the blade. After you have calibrated the gauge in your saw with a blade tension meter you can trust your saw gauge.
If you are going to a thicker and wider blade, be careful to increase the tension to much, so you don't overload your saw.

Kbeitz · May 22, 2017, 06:55:20 PM

So I wonder why builders don't use a hydraulic spring (accumulator) ?

Crossroads · May 23, 2017, 08:40:06 AM

The jury is in! After running the mill for 10 hours yesterday, there were only a couple of dips dives or waves and they were caused by either a dull blade or the blade guide hitting the edge of the log. Thank you all for the tips, I haven't really had time to study the mill to see how I can adapt Arnold's hyd tensioner, but will be looking at that.

Pabene · May 23, 2017, 02:50:31 PM

Screw- Hydraulic- and Weight-system, without any spring, as the last link to the wheel, are stiff and ridgid. There are no forgiving function in such design. When you are going on in a cut and a fragment of bark goes in between the blade and the wheel, it can cause extremly load to the blade in that moment. The saw frame can be deformed or the blade can break. If there is a spring or air-pillow as a transfer part to the wheel slide, the saw will take that like a car passing an obstacle on the road. It is also reccomended to have a "scraper" just in front of the fixt guide-roller to reduce the risk for fragment to go in under the roller and wheel tire.

Crossroads · June 03, 2017, 12:19:39 AM

Installed a new tension spring today and it didn't make any remarkable difference. I still have to bottom it out to get .005" of stretch. I can get .004" without bottoming out so, Sunday I'm going to do some sawing and see how it does there. Next step will be to find a small bottle jack and start modifying.

Kbeitz · June 03, 2017, 06:32:24 AM

I got thinking about making one for my mill.
I want to use a Hydraulic jack pump off a truck cab lift.

Crossroads · June 03, 2017, 08:36:35 AM

Quote from: Kbeitz on June 03, 2017, 06:32:24 AM
I got thinking about making one for my mill.
I want to use a Hydraulic jack pump off a truck cab lift.

Keep us posted! What s the pressure rating on that pump?

Magicman · June 03, 2017, 08:52:57 AM

You may have to position a bottle jack correctly for it to pump horizontally.

pineywoods · June 03, 2017, 10:40:30 AM

Bottle jack may not function reliably in a horizontal position..The main problem with them tho is physical size and shape. I greatly appreciate outside the box design, the wm tensioner is just that. 2 aluminum blocks with a one inch hole, 2 short piecs of 1 inch rod, 2 o ring seals and a big bolt..I'd bet Kbeitz could make one from scratch in a few hours. Someone mentioned such a system being rigid and unforgiving..In theory yes, but in actual practice there will always be an air bubble, think the wm designer even thought of that, there is no practical way to get the pump/cylinder completely full of oil..Pure genius..

ladylake · June 03, 2017, 04:47:58 PM

I'd put a accumulator rated for the pressure or a spring rated for the pressure on my mill.. I've heard enough of the pressure dropping off when the band gets warm to shy away from just a hydraulic tensioner. Mine is getting converted to the heavy spring(already has the heavy spring) with acme treads soon like the new TK mills, then it should take 4 half turns to tension up. Steve

Kbeitz · June 03, 2017, 06:30:08 PM

Quote from: Crossroads on June 03, 2017, 08:36:35 AM
Quote from: Kbeitz on June 03, 2017, 06:32:24 AM
I got thinking about making one for my mill.
I want to use a Hydraulic jack pump off a truck cab lift.

Keep us posted! What s the pressure rating on that pump?

I don't know the pressure rating yet. If it's low I will just use a larger dia. cly.

Crossroads · June 03, 2017, 07:18:42 PM

I haven't tried it yet, it would assume a bottle jack would work as long as the handle/pump was on the bottom and operates horizontal?? The spring wood Mizer sent me is green, is there one rated at a higher tension?

Kbeitz · June 03, 2017, 07:50:52 PM

What I was hoping to find and I'm still looking for is a screw in
hydraulic pump...

pineywoods · June 03, 2017, 09:45:50 PM

K, that is exactly what the wm tensioner is, a screw in hydraulic pump and a displacement type cylinder all in one piece. I have parts explosion in my manual, but it's copyrited, not nice to post it. Find yourself a nearby wmlt40 owner and borrow his manual...The design is pure genius, you could probably build one in a few hours, the seals are off=the shelf stuff and the rods are short pieces of hydraulic cylinder rod..

Kbeitz · June 04, 2017, 08:14:47 AM

Quote from: pineywoods on June 03, 2017, 09:45:50 PM
K, that is exactly what the wm tensioner is, a screw in hydraulic pump and a displacement type cylinder all in one piece. I have parts explosion in my manual, but it's copyrited, not nice to post it. Find yourself a nearby wmlt40 owner and borrow his manual...The design is pure genius, you could probably build one in a few hours, the seals are off=the shelf stuff and the rods are short pieces of hydraulic cylinder rod..

Thanks... I have seen them before on other machines.
I just don't know what they are called or where to buy one.

Kbeitz · June 04, 2017, 08:33:52 AM

I found this when googling "hydraulic tensioner"

https://forestryforum.com/board/index.php?topic=12610.20

Larry · June 04, 2017, 10:41:17 AM

Here ya go.

https://forestryforum.com/board/index.php?topic=70576.msg1058962#msg1058962

Building the assembly looks to be easy. Designing the "O" ring groove would be the hardest and slowest part for me. The groove has to be just right dimension and shape so the "O" ring will have the proper squish to work properly.

Fortunately Parker has put all their technical design documents online. They even have engineers that might assist if you can catch one in the right mood.

Parker O Ring Handbook

I've been making a few pneumatic assemblies and one low pressure hydraulic assembly with excellent results using their guidelines.

Larry, who much prefers the spring tensioner.

Ben Cut-wright · June 04, 2017, 11:14:15 AM

Quote from: Kbeitz on May 22, 2017, 06:55:20 PM
So I wonder why builders don't use a hydraulic spring (accumulator) ?

Hydraulic systems can be, some already are, provided with "surge absorbers/suppressors", similar to water hammer suppressor valves, somewhat similar to bladder in water tanks. This device provides X amount of 'give' in an otherwise rigid fluid system. This "give" does not come free, there will be a sharp rise in hydraulic pressure when the valve is forced to operate. Like the spring, imo, better than forcing the rigid components to flex.

Pabene · June 06, 2017, 03:11:49 PM

As stated in the report I wrote about, It is the quick forgiving action you are looking for. If you have to transfer the wheel slide movment, (to "swallow" a bark passage between the wheel and the blade) by an oil flow through a pipe in to the bladder, you are lost. It is a to stiff and slow system. A spring or air filled rubber pillow, close to the slide is the right way. I think also the homebuild saws with wheel from cars or motorcycles, as have air filled tires, take care of this kind of problem already in the wheel tire.
The force you need to create the blade tensioning can be convinient to do by a hydraulic system but if the saw has ridgid wheels you need a spring to save your blades.

Crossroads · June 07, 2017, 07:33:32 AM

Quote from: Pabene on June 06, 2017, 03:11:49 PM
As stated in the report I wrote about, It is the quick forgiving action you are looking for. If you have to transfer the wheel slide movment, (to "swallow" a bark passage between the wheel and the blade) by an oil flow through a pipe in to the bladder, you are lost. It is a to stiff and slow system. A spring or air filled rubber pillow, close to the slide is the right way. I think also the homebuild saws with wheel from cars or motorcycles, as have air filled tires, take care of this kind of problem already in the wheel tire.
The force you need to create the blade tensioning can be convinient to do by a hydraulic system but if the saw has ridgid wheels you need a spring to save your blades.

I believe I have proven your theory correct, although on a 1985 machine, then blade may no be the weakest link. I mentioned earlier about running the spring bottomed out. I did that for a day, but started hearing a hearing getting rough so, I started bottoming it out , then backing off one revolution. I started a job on Monday and by 2:30 the pillow block bearing on the wheel side of the idle wheel sounded so bad, I shut down and bought 2 new 1 7/16" bearings based on the parts list in my manual. Took the assembly home and removed the bad old bearings, cleaned up the shaft and discovered that on the early lt30, the shaft and bearings are 1 1/4". No problems, I was at the hearing shop early Tuesday morning and traded the wrong ones for the right ones and put everything back together on the job site. Made about 6 cuts and everything was sounding good, them boom the blade came off about 7' into an 8' cut. After 3 attempts to put the blade back on and line it up failed, I went looking for another problem. Low and behold the drive side bearings had failed. I believe the damage was done on the short time I ran it bottomed out. The drive side is kind of a pain to change out and the next 2 bearings had to be ordered and won't be here until Thursday.

Ben Cut-wright · June 07, 2017, 09:45:02 AM

"I believe the damage was done on the short time I ran it bottomed out. "

Testing with the spring completely coil-bound, rigid, seemed to provide enough tension to resolve your cut complaint. Perhaps these bearings were near the end of their lives and the extra strain exceeded their last limits?

There must be some cause/fault if the new spring had to be bottomed out to attain proper tension. Bad bearings alone would necessitate so great a dimensional change, (distance between axle centers), that this fault would be impossible to overlook, imo.

Kbeitz · June 07, 2017, 11:57:54 AM

You can buy pillow block bearings with a wide inner ring.
It's a much stronger bearing if you have the room for it.

https://www.thebigbearingstore.com/m2000-series-1/

Crossroads · June 07, 2017, 12:16:45 PM

Ben, it's very possible the bearings were at the end of their life cycle, I believe they are original. Until the major failure, the wear would have only been a few thousands and wouldn't make any substantial enter to center differences. I could be wrong, but there is plenty of adjustment to compress the spring and as long as the spring is compressed, the tension should be there regardless of the center to center distance.

K, I've already got the new bearings on order. I have access to a machine shop and will probably make new 1 7/16" shafts for next time. I may make the shafts stepped in order to use the larger bearings, yet not have to replace the sheaves and brake. I will check into the heavy duty 1 1/4" bearings too when I'm not on a timeline trying to finish a job.

Ben Cut-wright · June 07, 2017, 02:10:06 PM

You are correct about center to center differences. I did not do a very good job expressing myself regarding that matter. Should have constructed my paragraphs more sensibly. I actually thought you were giving the bad bearings some blame for having to compress the spring past its useful range. Thanks for your reply and I hope our dialectic will help resolve your problem-s.

Those bad bearings could be a huge contributor to your poor cut quality. But....that still does not answer why the spring has to be compressed so drastically. Replaced my tension spring maybe 6 times over several years. Never once because a spring had bottomed out. Only one broke, the rest were simply maintenance items, replaced because 'springs fatigue and do not provide exact performance'.

Not being critical of your skills in any way, is there any chance the (recently learned measuring procedure--converting stretch to tension) might have any errors? I use this same method to determine tension so I know there are potentials for errors. Properly set up, it is not too difficult to expect fairly exact repeatable results. You didn't say this but if all or most of your tension shows up at the bottom of the spring compression, the spring does not behave as a spring anymore. When the new spring behaved pretty much the same as the old spring, it was apparent there was more to this.