Hydraulic pressure unit

[Fla._Deadheader]

I guess I'm not smart enough to use the search on this forum.  
  Seems that a while back, someone posted about a way to construct a blade tension unit that would show pressure on a gauge as the blade was tightened.
  I use a long 1/2" hard bolt for blade tension. It pushes the wheel away from the frame and tightens the blade.
   If I could design something to go between the end of the bolt and the frame it tightens against, that would show the amount of pressure exerted on the system.
   I have 2 "pancake" cylinders that could be extended and then a gauge fastened. When the bolt shoves against the piston, wouldn't that show pressure on the gauge??
  The cylinder is about 2" dia. and 1 1/4" thick.  Any ideas???

[D._Frederick]

Fla._,
This arangement is a load cell and will give you a reading that you can calculate force from. F= pressure  x cylinder area , your cylinder has an area of 3.1416 inches square. Your gauge should read lbs/ inch square.  Make yourself a chart of gauge pressure vs. force. Remember that the blade tension is half the Force. This will make your life easier for blade changes. For 1 1/4 x 0.042 carbon flex back, you should have a blade tension of  1000-1200 lbs. Good Luck.

[Fla._Deadheader]

Thanks, "D"

[Danny_S]

Hey Fla...

  I believe I will be using an air piston for tension (or to be technical, an pneumatic piston). It will be a bit of an trial and error session to find the right pressure to run at but it should work ok. I am sure someone else in here has used this or factory mills have this?  As long as there is no leaks, should be able to just use an air pig to supply the piston.  

  Oh, um D. Frederick, the formula you stated would only be true as long as the piston was pushing vertically strait against the spindle right?  like, if the spindle was mounted on a hindged like mount, this would give it leverage and change the force...  am I right?? I can draw an example if you don't understand what I am saying.. ;)

[ADfields]

What I plan to use is a air brake can off a truck.   It would just replace the bolt you have Harold.   They come in 2 types, one is called a spring maxie with a huge spring to stop the truck if it has no air and the other is a simple pancake and piston and no spring.   The simple kind is around $35 I think new from a truck parts place and comes in 5" and 7" if I remember right.   Take a look at this link so you know what I'm talking about.
 http://www.sandstruck.com/catalog2000/airsystems/servicebrakechambers.htm  
 
Use a small old propane tank as a pig and it should hold the same force to your band as it stretches and shrinks from hot and cool.   They are around $3 for a new diaphragm inside if it ever leaks and the rest of it is steel and can't leak.   This is what I will do when I ever get time to get back at my mill aneyhoo. :
Andy

[D._Frederick]

Buck,
You are correct, the cylinder must be in the same force plane as the wheel spindle to give a correct reading. The load cell can be used with the "hinge", but you would have to figure the mechanical advantage from the hinge to the spindle and from the spindle to the load cell. Since the hinge follows a circle, your movement would have to be limited to give a corrrect reading.
ADfields,
The air bladder will do everything you say, but you would need a way to calibrate the force the blade see.  Is the 5" & 7" the inside diameter of the bladder?

[Danny_S]

ok thanks, I kinda figured as much, I dont know much about the law of levers, other than, " if you cant lifter'  leave er'!!  :D
I will have to make a point of mounting my piston at the same plane as the spindle.  

[ADfields]

Ya -D- thats the diameter of the bladder and the push rods are 7/8's fine thread it's hole 12" length so they are ez to cut to size and work with.   At 26psi of air on the 7" brake can you get 1001lbs of pushing force, or about 38.5 lbs of force per 1 psi.   Also it has 2-7/8" live stroke, I think it would be the best way to go.   When I build mine I will use a hinge point like on the LT-70's and use the brake can in place of that Kenworth 4 bag type air spring that W/M used, that air spring is around $140 to the brake cans $35 and would do the same job, the can is also a lot tougher setup with the steel case covering all the rubber.
Andy