Blade tension - spring info needed

[flht01]

My mill uses an all-thread to push the idler side wheel and framework straight away from the driven side wheel to tension the blade. The idler wheel framework is square tubing and slides over a smaller square tubing welded to the main carriage, no pivot points involved. The all-thread runs thru a nut welded to the carriage and pushes against a plate welded to the idler wheel frame.

I'm trying to find a mill that uses a similiar system to tension the band blade, one that uses a spring between the tensioning bolt and idler wheel. I'd like to find a compression spring that would put around 25,000# tension on the band before bottoming out. I'm just not sure what size (rating) spring to buy short of the trial and error method.

I've been using a band blade tension meter to set the bands but my current set-up doesn't compensate for any stretch in the bands. I'm thinking a spring set-up would keep the tension a little more consistant. Opinions welcomed.

Thanks for your help

[Tom]

Baker Products uses a tensioned spring to stretch their band blades.  Click on their link, to the left to locate their contact number.

[KENROD]

 First, Welcome aboard!
What kind of mill do your have? My Timberking uses this setup for band tension.
25000# is wayyy too much tension(unless you ment 2500#). 2500# is still about twice the tesion I run on my mill, but the spring would not have a problem with that much tension. You could call Timberking and order a spring from them.

[flht01]

Baker Products uses a tensioned spring to stretch their band blades.  Click on their link, to the left to locate their contact number.

I called Baker and had a good talk with them, nice folks. They use shims to preload the spring depending on the mill their spring pack is going on. They were hesitant to recommend their assembly without knowing more about my application, completely understandable. I guessing here, but I suspect they are turning the adjusting bolt until it bottoms out and are using the shims in the spring pack to set the tension.

Thanks

[Tom]

You got it.    the adjusting bolt bottoms out on the shims.  Their length determines the pressure applied.

If you get a chance, look at one in real life.  It's a pretty simple and very effective design.

[flht01]

First, Welcome aboard!
What kind of mill do your have? My Timberking uses this setup for band tension.
25000# is wayyy too much tension(unless you ment 2500#). 2500# is still about twice the tesion I run on my mill, but the spring would not have a problem with that much tension. You could call Timberking and order a spring from them.

I'm running a Logmaster LM-1. The psi readings I'm talking about are from a Starrett strain gage. I'll give Timberking a call and see what they have to say.

Thanks for the welcome, I've spent a lot of hours reading the archives and current posts but haven't posted much. Just started running a bandmill recently so you'll start seeing more posts in the future.

[raycon]

Don't know if the following helps but what I think you are saying is  you want to tension the band to 25,000 PSI.  If the area of the band is .042 (thickness) * 1.00(height)  = .042in^2

Tension/Compression (stress, psi) =  Force/Area

Remember when you push/pull on the band wheel the force is split in two. If the force needed is 1000lbs you'll want 2000lbs from the spring since the band wraps around the wheel. 
McMasterCarr.com should have a spring. Skipping the spring and getting  a hydraulic tensioner would be ideal.

[Tom]

I think he is really talking about a band tension of 2,500 lbs.   I've experienced mechanical, spring and hydraulic tensioners and think, if I were to build one for myself it would be a hydraulic tensioner that compresses the spring.  The main reason is that temperature can change the amount of pressure that a small hydraulic cylinder applies because of the expanding oil.

It is pretty easy to put a pressure guage on a manual hydraulic pump/ram and the spring will absorb a lot of shock that could damage a band or saw parts but will return to its proper tension.

By using hydraulics instead of mechanical compression devices with shims, compensation could always be made for a weakening spring without any special operator concerns.

That's just a thought that's been in my head for a long time. It's actual function could be less than satisfactory.

[flht01]

I think he is really talking about a band tension of 2,500 lbs.   I've experienced mechanical, spring and hydraulic tensioners and think, if I were to build one for myself it would be a hydraulic tensioner that compresses the spring.  The main reason is that temperature can change the amount of pressure that a small hydraulic cylinder applies because of the expanding oil.

It is pretty easy to put a pressure guage on a manual hydraulic pump/ram and the spring will absorb a lot of shock that could damage a band or saw parts but will return to its proper tension.

By using hydraulics instead of mechanical compression devices with shims, compensation could always be made for a weakening spring without any special operator concerns.

That's just a thought that's been in my head for a long time. It's actual function could be less than satisfactory.

I'm not sure what method the mill mfg's are using to measure the blade tension on their tensioning scales, and since my mill doesn't have a scale I don't have any way to compare the Starrett's (682EMZ ) results with the method most mill use. I have talked to Suffolk and Diamond Saw and both recommended using #20,000 to #25,000 psi using the Starrett for their blades. FWIW, I did the flutter test with the Diamond blade and found a little under 20,000# started smoothing out. I'd sure like to understand the difference between the mill's tensioning measurements and the measurements on the Starrett.

I have talked to TimberKing earlier and, on their recommendation, ended up talking to Cook's. Their mill uses a tensioning spring rated at 850#, I'll just have to call back and make sure their mill's tensioning system doesn't rely on a pivot point to swing the wheel in place and whether it would make a difference on the spring tension. I should have paid more attention in school  :P

I also looked thru a McMaster Carr catalog and there are several choices for spring's under #1,000. May just have to start with tiral and error. ;D

[raycon]

flht01 first post made me think of the caliper c-clamped to the band posted by Gilman and others.

https://forestryforum.com/board/index.php?topic=10765.0

[flht01]

flht01 first post made me think of the caliper c-clamped to the band posted by Gilman and others.

https://forestryforum.com/board/index.php?topic=10765.0

I read it earlier today and will go back thru it again( it usually takes 5 or 6 time to soak in). I'll try to use the info in your post to calculate the spring tension needed for 1 1/4" .042 blades that are 14'-7" long. Oh BTW, I'm not opposed to all the help I can get  :D

[Larry]

You can tension with either a spring or hydraulics...no opinion on which is best because I have little experience with spring tension.

I do have one very strong opinion...whichever system you use must have some type of gauge on it.  You calibrate your gauge number to the actual tension on your blade as measured by your Starrett.  Depending on the blade manufacture they will recommend something in the range of 15,000 to 30,000 psi of tension on the band.  A little further to help explain the numbers...the numbers on any of the gauges are pretty much meaningless.  The only number that is real is the psi on the band...and it will be in the range of 15 to 30,000 psi.

The reason I like a gauge so much is it is another indicator of what the blade is doing.  Example...put on a blade and tension it to 25,000 psi.  Cut or two later its heated up and lost a little tension.  Tension back up to 25,000 and it will hold that setting...until it starts to heat again from being dull, lost set, or something else.

If I was trying to fabricate a tension device, think I would start with a small bottle jack and plumb in a gauge.

[flht01]

....
The reason I like a gauge so much is it is another indicator of what the blade is doing.  Example...put on a blade and tension it to 25,000 psi.  Cut or two later its heated up and lost a little tension.  Tension back up to 25,000 and it will hold that setting...until it starts to heat again from being dull, lost set, or something else.

If I was trying to fabricate a tension device, think I would start with a small bottle jack and plumb in a gauge.

The tension loss after the first few cuts was the reason I started thinking about using a spring, something to absorb the small changes without getting too complicated. Since resetting the blade tension only takes a minute or so using the guage, I'll test the next blade to see how much it changes (tension) before pulling it off the mill. I might be frettin over nuthin'

[Bro. Noble]

We had an old WM with spring tension,  now we have a WM with the hydraulic tensioner.  To me there is no comparison,  but if I were building a mill,  there is another option that hasn't been mentioned-----air.  Our resaw has an air can like is used on truck air brakes.  There is a regulator that is set to the proper setting to get the correct tension.  When we are ready to saw,  an air hose is plugged in with a quick connector and the blade is at the right tension.  This has required absolutely no adjustment or maintenance for the 6 or 8 years that we have owned it.  The blade keeps the same tension reguardless of temperature,  sap buildup,  make of blade, or sharpmess.  All of the components are sold at the local autoparts store.

[mike_van]

I use a die spring on my mill, i think thats what your after? It's been on there 15 years, still working. Travers Tool in NYC has them, mine is #79-201-036. It's 1 1/4" dia, 5/8" bore, when compressed 3/4" it's 1139 lbs.  Too light? I don't know, i've cut flat boards for a long time, and don't break bands [till they're shot]  You can see it in the pic, it's yellow.

[rewimmer]

Hello flh01,
When I picked up my TimberKing B-20, they said to tension the blade to 1200 lbs.  It has worked for me great. My old mill did not have a gauge and I just learned to tension it by feel.
Robert in Virginia

[flht01]

I use a die spring on my mill, i think thats what your after? It's been on there 15 years, still working. Travers Tool in NYC has them, mine is #79-201-036. It's 1 1/4" dia, 5/8" bore, when compressed 3/4" it's 1139 lbs.  Too light? I don't know, i've cut flat boards for a long time, and don't break bands [till they're shot]  You can see it in the pic, it's yellow.

Mike, I think that's what I'm after. Do you compress the spring the full 3/4" to tension a blade or is that the max range for that spring?

Robert in Virginia, I'd bet the 1200# on your B-20 would be refering to the hyd pressure on the tensioning system. That b-20's a nice mill, gotta love them hydraulics.

Using the air bellow system sounds like a good way to go, expecially if the mill is set up with 12 volts and an alternator system. It shouldn't take much cfm to keep the bellows at the set pressure. My mill is about as manual as they come, no hyd's or 12 volt accessories. On the up side, maintenance should be at a minimum.

Thanks for all the responses.

[mike_van]

It's probably compressed to where there's 1/8" between the spring coils.  It works well there.  I've found if i start getting a bad cut, the blades lost some set, it's dull, or both.  When i used to send blades out, i'd push 'em right to the bitter end, now it comes off  & gets touched up if i even think it needs it.   I read somewhere where a guy wrote "anything that cuts with an edge should be sharpened BEFORE it's dull" 

[tcsmpsi]

Hey, flht01, glad to see you on the board. 

I look forward to seeing what you come up with on the tension.  Since you've started that, I believe I'll let you go ahead and figure something out.   ;D

I just keep torque wrench handy and check it every now and again.  Since there was a bit of discrepency as to what the 'manual'  :D said and the guys in the shop said, I tweaked out my own nominal torque for blade tension (gives me something else to do with a little coffee). 

How do you like working the mill?  Had any more issues with it? 

[flht01]

It's probably compressed to where there's 1/8" between the spring coils.  It works well there.  I've found if i start getting a bad cut, the blades lost some set, it's dull, or both.  When i used to send blades out, i'd push 'em right to the bitter end, now it comes off  & gets touched up if i even think it needs it.   I read somewhere where a guy wrote "anything that cuts with an edge should be sharpened BEFORE it's dull" 

I was hoping there was still some room, lets the spring give a little in case something gets between the blade and the wheel. I found the Travers website and will post the results. Thanks to all for the help.

I promised myself I would send the blades out for resharpening but I've sure been spending too much time reading up on the different systems. I'm afraid that's one promise I'll probably break  :

[flht01]

Hey, flht01, glad to see you on the board. 

I look forward to seeing what you come up with on the tension.  Since you've started that, I believe I'll let you go ahead and figure something out.   ;D

I just keep torque wrench handy and check it every now and again.  Since there was a bit of discrepency as to what the 'manual'  :D said and the guys in the shop said, I tweaked out my own nominal torque for blade tension (gives me something else to do with a little coffee). 

How do you like working the mill?  Had any more issues with it? 

I ran one blade at their recommendations even though the mill was trying to tell me it didn't like it. On the second blade, I pulled out the gage and torqued the band to their recommendations so I called Diamond Saw and got their recommendations (#20,000 on a strain gage). I ended up spending all day doing a flutter test, setting the guides to 3/8" down pressure and leveling them, adjusting the cables on the head, etc... Much Much better but now I'm going to replace the tires, that one band at their settings started flattening them out. BTW, if you put a little neversieze on the jackbolt threads and set your torque wrench to about 30 ft/lbs you'll be in the ballpark, at least according to the strain gage (between #25,000 and #30,000). I was really amazed to see the difference in psi between bands using the same settings on the wrench. I think most of the variation is due to not having something between the bolt and plate (air bag, hydraulics, spring etc...) Doesn't take much to swing the pressure one way or the other.

Mill's running great, I've cut about 2,500 bf so far with good results. A few minor issues but no show stoppers, really starting to enjoy it. That little log loader/turner has turned out to be the biggest suprise, couldn't do without it. I guess the only thing (beside the tensioning set-up) I'm going to do is add a few log stops. Unless I'm just missing the big picture here, just how are you supposed to use the existing stops (when loading logs) when the log stop and log dog both raise and lower together?  :D

[tcsmpsi]

Are you working with Bob Comunale from Diamond?

You never did supply me with any pics of your loading system, buddy boy.   ;D

Definately, if you are going to use the 'log stops' for actually stopping logs, then adding some would be a good thing. 

Did you refer back to the mfr. over any of your issues?

What are you going to do for bandwheel tires? 

[flht01]

Are you working with Bob Comunale from Diamond?

I can't rember who I talked to at Diamond; it's been a couple of weeks and I've slept too many nights since to remember. The one thing that has really suprised me, especially from the list of sponsers, was how willing they were to try to help. Especially considering it wasn't related to one of their products.

You never did supply me with any pics of your loading system, buddy boy.   ;D

Sorry about that, see what I mean about remembering  :D

Definately, if you are going to use the 'log stops' for actually stopping logs, then adding some would be a good thing. 

I'm think about building another loading arm to help with loading a 16'+ log and using these for the log stops as well. I'm still pondering over this one, might change it up a little. The current loading arm works great until I try to use it to roll a 29" log, the winch handle hits the log. Still in all, wouldn't do without it.

Did you refer back to the mfr. over any of your issues?

When I bought the mill, I feel like I accepted their design even though I want to change a couple of things. I had a couple of welds break on the log dogs and the fender bracket welds broke as well. I called them and talked to Herman about this and their response was very positive, couldn't have ask for anything more. I'm about 2 hours from them and didn't want to make the drive again so they sent me everything I needed and didn't want the old parts back. The fenders and brackets had enough stiffeners on them this time that they'll be there for the long haul. As far as the design changes, if any of the changes I do really turn out to make a big difference I'll let them know in case they want to use them. On these small homeowner type mills it's hard to expect them to completely meet everybody's needs. For example, if I had a front end loader I probably wouldn't be concerned about the log stops or log turner.

What are you going to do for bandwheel tires? 

Since our lube tank is metal, I wanted to try the diesel/kerosene bar oil mix to help stop any potential for rust. With that in mind, I picked up a pair if the urethane (sp?) belts from Suffolk. Really looking forward to putting them on  :D

[tcsmpsi]

Slept?  What the heck you wanta go and do somehting like that for?

I noticed from the website there is a pic of a regular length trailered LM1, now. The brackets on the trailer fenders are not like mine.   Looks like they might have tried to 'lighten' that up some.  If yours are like those, that might have had something to do with it. 

Logstops are handy, even with a loader.  I take extra care not to cause any unnecessary shock to the squaring dogs to keep me from having to adjust any more than I just have to. 

I'm going to build a log rack to feed logs onto the mill from w/retractable arms to get to and from the deck.  But, not today.   :D

[flht01]

...
You never did supply me with any pics of your loading system, buddy boy.   ;D
...

I finally got around to snapping a couple of pictures of the loader. I'll get a picture or two of them being used next time I get to mill a little.


If I get around to building a second arm/winch, I'll set the winch at least the handle's length from the vertical upright. The upright would be 15" above the bed and would work as the log stop and the winch set back far enough to clear the log.

I'm going to build a log rack to feed logs onto the mill from w/retractable arms to get to and from the deck.

I built a couple of sawhorses to set under 2 of the loading arms that would have them level with the bed to make it easier to set a log on. Haven't used them yet so I can't say if it was worth the time or not.

I just keep torque wrench handy and check it every now and again.  Since there was a bit of discrepency as to what the 'manual'  Ya dats a good one! said and the guys in the shop said, I tweaked out my own nominal torque for blade tension (gives me something else to do with a little coffee).

What procedure did you end up using to tension your bands?

I'll try to get better pictures soon.