Blade tensioner, on a budget

[ladylake]

 
 The trouble with a hyd jack is not bleed off, it's when the blade gets warm you lose tension as it has no give.  You need a heavy spring in the tensioner.  A  6 tpi 3/4 acme rod and nut  might cost $30 or less and is real easy to build.   Steve

[JoshNZ]

That's just not the case for the two floor jacks I tried. I'd have to retension every 45 seconds, once it got bad. I put a mark on the sleeve, it was definitely leaking back.

The proper ram I bought to replace them holds the correct pressure all day long.

[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.

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.

No i was saying look at the way a toggle clamp is made.  One could easily flame cut their own toggle decive or mod a snap binder to incorporate a fine thread adjustment to jack into a coil spring or even pull a portion of leaf spring for an "emergency brake lever" sort of tensioner without any hydraulic grief.  Would need to be sure the lever swung in a way that a cheater pipe could clear the frame if needed. 

[ladylake]

 

 With a 6 tpi acme tread and heavy spring it takes 3 turns to tension up , why complicate things.  Steve

[mike_belben]

theres as many ways to make a sawmill as there is to make an ice cream cone.  just tossing fudgetracks at the wall here. he can decide what flavor he likes.  americans love complication. 

[Iwawoodwork]

Why can't a spring be mounted at the end of the jack ram if a person feels they need a cushion spring.   I agree that an upright bottle jack does not work well laying on the side with handle up, but have used then laying on the side with the handle/pump to the side and work fine, have not tried with handle/pump pointing down but might also work. the trick is getting fluid into the pump rather than air.  Also on a band mill a person will not need the full extended length of the bottle jack ram, should only need a couple inches of ram, so not as much fluid needed.  

[vasiliy]

I totally agree with most comments, and specifically, last 3.
Starting this thread I was thinking that the choice is either hydraulic or spring.
Thank you to you guys I have realized that I can not do it right without spring. So yes, simplest and most budget friendly way is to just use spring.
Adding jack with gauge to setup seems to be a good idea for later (if it holds pressure). It seems to be a convenience thing. Gauge seems to be a good way to measure / set tension. and not too expensive.

BTW. Called Cook's Saw. Those guys are helpful. Their spring is $30, so price is good. The only concern I have is that it has only 1400 lb max load. There is a fulcrum somewhere there in their tensioner. Not sure what is the geometry there. If they just double it or even more.
I do not have any fulcrum in my design yet. So looking into stronger springs in "die spring" category. I was checking some springs in "farm equipment" category, like for chisel plows. They look beefy, but after searching for hours I could not find any specs for them. 

Another thought I had, is that longer spring will hold tension better. (and if there is a leaky jack in sequence with the spring, system with longer spring will loose tension slower). It seems production saw use die spring too, about 4" long? Right?
I am looking for longest spring I can find. Will keep you posted.

[vasiliy]

Ended up ordering this spring:
https://www.asraymond.com/extra-heavy-duty-iso-d-die-spring/306928D
about $50. It has plenty of strength and rate about 2200 lb, so 6 turns of 3/4" acme screw to get to my target tension, about 2000 lb