Hydraulic Tensioner

[jrokusek]

Still slowly working on my homemade bandmill.  I was going to tension the blade with a threaded rod.  I think I read here or somewhere else that may not be the best option since the blade heats up and stretches and you can loose some of your tension that way.

Someone mentioned to me that using a hydraulic tensioner may be the way to go.  Specifically, using a cylinder from a hydraulic jack may work.  I'm not sure if that would be any better or not.  I'm guessing that hydraulic tensioners on bandmills work differently than a simple hydraulic cylinder.  Now before I grab my grinder and cut out the hydraulic cylinder from my floor jack.....can someone enlighten me?

Jim

[flip]

I am using a "mini" ram from Northern Hydraulics ($20)?  and a master cylinder from Napa (single line rebuilt $25) I can make up to 3500psi on my blade if needed.  Kinda like you, I'm still in the building phase of my mill but this tensioner works like a charm ;)  I wish I knew how to post pics :'( >:(

[Buzz-sawyer]

flip

Go to the home button then click on Behind the Forum.look for a post Dang started I put pics in there to show ya how....look for how to post pics

[jrokusek]

I am using a "mini" ram from Northern Hydraulics ($20)?  and a master cylinder from Napa (single line rebuilt $25) I can make up to 3500psi on my blade if needed.  Kinda like you, I'm still in the building phase of my mill but this tensioner works like a charm ;)  I wish I knew how to post pics :'( >:(

Do you use the master cylinder to pump up the hydraulic ram or is is just for holding the fluid?  I guess I'm asking if you use a Hydraulic Ram Pump or just the master cylinder alone.   Do you have a guage?  Is it obvious I don't know a great deal about hydraulics?

Jim

[slowzuki]

I suspect he uses the master cyl to pressurize the other cylinder.   I think that is a great idea as opposed to my big honking lever pump.  I could just have a threaded handle push on the master cylinder to pressurize my little tensioner :P.

[flip]

Bingo!  I have a threaded rod that pumps up the cylinder and keeps tension on the ram.  You have to be careful not to use oil because it will damage the MC seals and no brake fluid because it will take out the seals in the ram--Silicone at NAPA.  I have a guage to tell me pressure, but I will have to move stuff around now that I have guards on, dang! >:(

[slowzuki]

Ya know once I had a little incident out in da woods with a loss of brake fluid and ended up using ATF to get back home... I wonder what the seals look like now?

Bingo!  I have a threaded rod that pumps up the cylinder and keeps tension on the ram.  You have to be careful not to use oil because it will damage the MC seals and no brake fluid because it will take out the seals in the ram--Silicone at NAPA.  I have a guage to tell me pressure, but I will have to move stuff around now that I have guards on, dang! >:(

[flip]

Here goes...

OK well I give up.  If you want a couple of pics. of how my hydro. system is set up send me your email address, too much trouble to post a pic here, sorry.

flip

[jrokusek]

Ya know once I had a little incident out in da woods with a loss of brake fluid and ended up using ATF to get back home... I wonder what the seals look like now?

In my youth I accidentally put power steering fluid in the master cylinder.  BAD DEAL!  All the rubber seals swelled and all needed to be replaced and the system flushed.  Had to rebuild each wheel cylinder (slave cylinder) also.

Jim

[mike_van]

On my mill, I use a large die spring I bought from Mcmaster-Carr. I can't remember off hand the tension, but a 5/8" bolt goes through it, it's about an 1 1/4 in dia.  When it compresses x amount, it gives x amount of force.  Of course, always back it off when through sawing. Been on there 10 years anyway.

[flip]

OK I have the pictures in my gallery now what?  It says I can't post them because they are in JPEG form.

[Furby]

Real close!
Go to your gallery and click on the pick you want.
After it opens in a new window, look for the line: Click to copy photo insertion code
Just click on the words in that line and then go to your post and hit "paste".
It will copy the code, hit "preview" to see the pic.

[Tom]

clicking on your picture will give you this image.
clicking on the words "click to copy photo insertion code" will put the highlighted line (URL) on your notepad.

go to your update window and "paste" where you want the picture.  You can also use Cntrl V to paste.

When you do a preview or post the message, the picture will appear in the post.

[flip]

DOES DAT WORK?

[D._Frederick]

Don't forget to measure the diameter of your hydraulic cylinder so you can figure the force you are applying to the saw blade.

[jrokusek]

OK.  I now understand the basic concept. Does a hydraulic cylinder really have an advantage over a threaded rod?  It would seem that both share the same limitations - can't adjust for band stretch.  I guess you could glance down at the pressure guage on a hydraulic system and see what's happening.

I think I'm still going to use the screw tension method and adjust it by using a caliper like on this thread:  https://forestryforum.com/board/index.php?topic=7923.0       Probably not a perfect system but I'm kind of considering this a "prototype" sawmill anyway.   

Thanks for all the help!
Jim

[D._Frederick]

J-,

If you plan on doing much sawing and need to change a lot of blades, the hydrualic tensioning will save a lot of time. Unless your blades are all the same exact length, you will need to dig out your calibers everytime you change blades.

[mike_van]

photo [I hope] of the blade tension spring I use. It may be too small to see well, if anyone is really interested, email me & i'll send a full size one. 

[mike_van]

My error on the source for the spring [funny how the memory fades]  It came from Travers Tool Co.  in Flushing N.Y.  # 79-201-036   it's 1 1/4" dia with a 5/8" bore.  load in pounds is 1190 & the deflection is shown as 1.57 in.  When I first made this mill up, I had a solid bolt to tighten.  I did  break quite a few blades.  Much better with the spring.   My Travers catalog is so old, there is no web site listed on it!!!!!!So, i've been sawing pre dotcom. :D

[dail_h]

   The abvantage of spring,and or hydraulic,is that as your blade heats and streches,they both tend to maintain a more uniform tension. Also if a chunk of bark or somthing goes  'round the wheel,there's some give.Y'all already knew that,I'm sure. My Norwood mill uses a spring,wit a tension mark on the frame-ok,but I don't know how much pressure I'm putting on the band. Ahydraulic cylinder and guage would give you a way to keep optim tension all the time. You'de just have to do the math

[Rockn H]

One reason I would have to go with a hydraulic gauge, or some type of gauge that would show your band tension constantly. Maybe a manual tension gauge that you could attach you tensioning bolt to.  I know Grainger had some .  That way you can monitor the temp of your blade while you cut.  If the pressure drops you know your blade is getting hot so you can make corrections to your sawing right then.  Heat will dull a blade quick.

[countrysaw]

just a thougt,  has anyone ever thought of getting an accumulator to hold hyd. pressure, so that when the blade gets hot and "stretches" you would hold a constant pressure on the blade?  we have had good luck with accumulators in varying load conditions, where the force applied has to stay the same.  Pretty simple to use too, to tune the pressure, just fill with fluid, attach a valve to the line, and screw a gauge into the end of it, and figure out what pressure the cyl needs for the blade, and take it to a shop and have it filled with dry nitrogen, and open the valve and have them fill until it is at the pressure you need, this should avoid all of the extra pumping and fine tuning.  i looked around and found a small one too
http://www.surpluscenter.com/item.asp?UID=2005061104364921&item=9-6127&catname=hydraulic
you will still need a pump and gauges, and i would reccomend the valve on the tank so you can releive pressure and stop leakdown after done sawing

zach

[sprucebunny]

Here's a picture of one part of the hydraulic tensioner on a Champion sawmill. I don't know how the other end works....yet ;D

[Buzz-sawyer]

Hey Spruce
Do tell some more about that hydraulic jack/tensioner........ is the gauge mounted in the lift? Did they drill and tap a seperate output, does the jack still go up?
Buzz

[sprucebunny]

Buzz    I don't think anything goes up...it looks like they tapped the top of an ordinary bottle jack. You can see the T fitting and the hose to the adjuster coming out.
I know that pictures help me think about things and I thought a picture might help someone else ;D