Harbor Freight Hydraulic Ram For Blade Tensioner?

[George B]

Hi there, 

I built a sawmill two years back and I'm doing some upgrades. I wanted to upgrade my blade tensioner. I have a simple bolt right now and thought about adding a spring after watching some YouTube videos on wavy cut fixes. But, the more I read, I like the hydraulic option. 

Two questions....

1. Is adding a spring to the blade tensioner design a way to keep tension in the system and deal with the blade cooling and heating characteristics. Or is it just a simple way to quickly eyeball your normal tension with noting where the spring compresses. 

2. Has anyone used the harbor freight hydraulic ram? If so, is there a way to add a gauge to that pump? 

4 ton Portable Hydraulic Equipment Kit

[KenMac]

Your plan sounds good but I'm not familiar with the HF ram. I do know a little about springs in the tensioner. On my Cook's mill the spring apparently handles any slight variation in blade length due to stretch or shrinkage since I've never had to adjust tension after installing and tensioning a fresh blade. I don't know the specs on the spring Cook's uses but I'm sure you can purchase one from them and be confident it will be sufficient for your needs. Cook's uses a hydraulic jack positioned horizontally for tensioning. Not all hydraulic jacks will work horizontally from what I've heard. Good luck with your project.

[charles mann]

Iv got the 10tn version ofvthe HF portapower. I use it for more than just tensioning my band. I too have thought of adding some springs to absorb debris impact between the band and band wheel or the heating/cooling affects on the band. 

[Crusarius]

this is what I used. It is pricey but works great!!!

Parts and Accessories - Linn Lumber Sawmills

Scroll down to:
HYDRAULIC BLADE TENSIONER

[barbender]

My Woodmizer LT40 uses a hydraulic tensioner. There is no spring on it, and I haven't felt the need. The long jack handle of a porta-power would be nice! 

 My tensioner uses a hydraulic pressure guage. Woodmizer has the suggested pressure marked. If you installed a gauge, once you knew the appropriate pressure  for the correct tension you could either mark it or memorize it.

[ladylake]

 A heavy spring with a 3/4   6tpi acme rod and nut is simple and cheap and has some give.  Plus you never have to babysit it once it's tensioned up.  Steve

[JoshNZ]

My setup is what you're describing, with no spring. I also have a valve at the end of the pump as the check valve can be leaky. And a gauge teed in after that. Never felt a need for a spring, I have V belt type wheels though.

I do like the simplicity of spring and bolt design but I like having the gauge there while sawing, real-time tension read out.

[ladylake]

 
With  a heavy  spring no need for a gauge. No babysitting the tension.  Steve

[Nebraska]

Both my mills used the spring tension system, it's simple and repeatable.

[barbender]

You're not babysitting the tension because of the gauge. The tension of the band changes from temperature, be it from operation or the ambient temp changing. Just because you don't know it, don't mean it isn't happening. 

[ladylake]

 
With a hyd tensioner with no give soon as the blade heats up for any reason it will lose tension.  A heavy spring it doesn't matter as it has a lot of give. I never have to adjust the tension once tensioned up. My mill came with a gauge which broke 19 years ago, no need for it.  Steve

[barbender]

What I'm getting at, is your tension is changing too. You have a set amount of preload on that spring, with a band that is varying in resistance based on temperature. The fact that there is no gauge letting you know in real time doesn't change that. 

[ladylake]

 
 If a heavy spring with quite a bit of compression moves a little bit it's not going to change the tension very much.  If a hyd tensioner moves a little bit going to lose tension fast and needs a gage to keep track of the tension. Steve

[Ed_K]

 With a hydraulic ram /gage and a heavy compression spring, wouldn't that be the way to go?

[barbender]

It might get us to stop arguing🤷‍♂️😂

[JoshNZ]

Lol I do agree with Steve it's simpler and more reliable, I only dislike that you can't visually see a tension level. If your spring deforms or another length in the mechanism changes for some odd reason, different band length, etc.

[charles mann]

Lol I do agree with Steve it's simpler and more reliable, I only dislike that you can't visually see a tension level. If your spring deforms or another length in the mechanism changes for some odd reason, different band length, etc.

Actually you could have a visual reference using just a spring and bolt method. Put a compression measuring load cell between the mechanical force and spring or the spring and the idle wheel tension apparatus. 
I had thought of getting one just to confirm the lbs of force (est 3400ish lbs) required to tension my band. But at $200 for a 1 time use, i see no reason for it. I was trying to find one the went from zero-20,000 lbs in 1 lb increments but could only find in 10 lb increments. 

[ladylake]

 
On my mill with the acme thread the spring get tensioned down to 1 7/8" which is 3 turns after getting it snug.  The length of the band doesn't matter, it could be off by a inch or so.  Steve

[customsawyer]

Just to throw another thought at y'all. I really like the air bag on the LT70s.

[DMcCoy]

I use a HF 4 T for my blade tensioner.  V belts in V pulleys for wheels. I usually tighten it up a little after the blade warms up.  No gauge. Release it when I am done sawing for the day.  Works fine imho. I did have to change the valve handle casting to a steel bolt head and I now use a wrench.  Having a sharp blade is a bigger concern in my experience.
I could see where having a spring would help.  Lots of equipment still use springs, like train cars.

[ladylake]

Just to throw another thought at y'all. I really like the air bag on the LT70s.

Yes a air bag would have lots of give.  Steve

[Tom King]

If you're thinking about incorporating a spring in it, the type of spring to look for is called a "die spring".

They come in Many sizes, and aren't that expensive.  I've bought them to use for various things over the years.

Online sellers, like springstore, have calculators so you can figure which one you need if you know travel and pressure needed.