$100 chinese 4" vise deflection + DIY force gauge

[Glenn_ca]

Re: $100 chinese 4" vise deflection data

not really..

say your piston is 1 square inch

and you put 1 lb on it

your gauge will read 1 pound per square inch (convenient)

now say the piston is 10 square inches

and you put 1 lb on it

now the gauge reads 0.1 psi (do some multiplication)

now just replace "you put x lb on it" with "the vice exerts x lbs clamp force on it"

the area within the jaws is irrelevant because it translates into the same force on the piston, regardless of how much of the piston is inside the jaws. If the entire piston isnt within the jaws thats not good for this simple design, because the piston will tilt to the side and probably not work right, but for discussions sake, it doesnt matter, because whatever force you are exerting on the piston does not depend on how much of the piston you put it on.

Kind of like how your bathroom scale doesnt care how big your feet are, or if you decided to balance yourself on a soda can on top of the bathroom scale..youd get the same weight (plus the soda can).

are you sure we're talking about the same thing?

If you read your own response through I think you will find that you have proved my point especially the second to last line. Take the top off your bathroom scale and replace it with one of a smaller or larger size of the same weight the reading on the scale will not change.

 

[Andre]

Re: $100 chinese 4" vise deflection data

You might want to use a 1.1283791670955125738961589031215 reamer, it's a bit closer to 1 in[SUP]2[/SUP]

For a piston to cover an area of one square inch, remember the area of a circle is radius squared times pi. .5641895835477563 squared is .31830988618. Multiply that my PI equals 1. So to create a piston/bore that will displace one psi with one pound on it I need a bore that measures .5641895835477563. Please correct me if my math is wrong.

 

[Glenn_ca]

Re: $100 chinese 4" vise deflection data

For a piston to cover an area of one square inch, remember the area of a circle is radius squared times pi. .5641895835477563 squared is .31830988618. Multiply that my PI equals 1. So to create a piston/bore that will displace one psi with one pound on it I need a bore that measures .5641895835477563. Please correct me if my math is wrong.

You need to calculate the diameter not the radius.

 

[JimDawson]

Re: $100 chinese 4" vise deflection data

For a piston to cover an area of one square inch, remember the area of a circle is radius squared times pi. .5641895835477563 squared is .31830988618. Multiply that my PI equals 1. So to create a piston/bore that will displace one psi with one pound on it I need a bore that measures .5641895835477563. Please correct me if my math is wrong.

You are correct, if you are using a .5641895835477563 RADIUS reamer. Reamers are normally measured in diameter thus 1.12837.... DIAMETER :whistle:

 

[spaceman_spiff]

Re: $100 chinese 4" vise deflection data

If you read your own response through I think you will find that you have proved my point especially the second to last line. Take the top off your bathroom scale and replace it with one of a smaller or larger size of the same weight the reading on the scale will not change.

Yeah but the bathroom scale reads in lbs force not lbs force per square inch like the gauge.

So just to be clear, you are saying that a given force on a piston does not pressurize the fluid behind the piston differently as piston diameter changes? That would basically mean all hydraulic circuits which generate mechanical advantage through different piston sizes wouldn't work.

 

[Andre]

Re: $100 chinese 4" vise deflection data

If you read your own response through I think you will find that you have proved my point especially the second to last line. Take the top off your bathroom scale and replace it with one of a smaller or larger size of the same weight the reading on the scale will not change.

Were not talking about weight, were talking about pressure.

Piston size DOES matter. Imagine a hydraulic cylinder, with a piston face that measures one square inch. Pump 100 psi of hydraulic fluid into it, it can lift 100 pounds. Try that same 100 psi into a cylinder with a piston face of 10 square inches, and it can lift 1000 pounds.

 

[Andre]

Re: $100 chinese 4" vise deflection data

You are correct, if you are using a .5641895835477563 RADIUS reamer. Reamers are normally measured in diameter thus 1.12837.... DIAMETER :whistle:

Oh, I feel stupid now.

Thank you for pointing that out! My bad.

 

[Glenn_ca]

Re: $100 chinese 4" vise deflection data

Were not talking about weight, were talking about pressure.

Piston size DOES matter. Imagine a hydraulic cylinder, with a piston face that measures one square inch. Pump 100 psi of hydraulic fluid into it, it can lift 100 pounds. Try that same 100 psi into a cylinder with a piston face of 10 square inches, and it can lift 1000 pounds.

Certainly piston size in that instance is of importance when we are talking about work capacity but what we are talking about here is gauge pressure. Apply the same force to a 4" piston as a 1" piston and the hydraulic pressure within the cylinders will be the same. The work they can do is different but the pressure within the cylinder is the same and that is what we are looking at with this force gauge.

 

[JimDawson]

Re: $100 chinese 4" vise deflection data

The pressure can be calculated with the formula p = F/A. where:


p = pressure (psi)
F = force (pound)
A = area (square inch)

 

[spaceman_spiff]

Re: $100 chinese 4" vise deflection data

Apply the same force to a 4" piston as a 1" piston and the hydraulic pressure within the cylinders will be the same.

This is incorrect.

Think about the term PSI. Pounds PER square inch. Pounds per SURFACE AREA. Think about it. A 4" circle has alot more surface area than a 1" circle. How could the PSI of the fluid behind it be the same? Pressure is not measured in lbs, its measured in lbs per surface area.

Think about the brake circuit in your car. A small master cylinder at the pedal pressurizes the fluid to say 1000 psi. At the caliper, the piston is much larger, magnifying the force 100 times (for instance).

The tradeoff is distance. Just like a mechanical lever. The larger cylinder will move much less than the smaller cylinder, so the power stays the same.

Or a bottle jack. You pump it up with a teeny cylinder and have to move the lever up and down a dozen times just to get the big piston to move 1 inch. Where does the mechanical advantage come from? It comes from you moving a little cylinder a very long distance (through a valve), pressurizing the fluid to maybe 50psi. But the jack output piston is MUCH larger, but moves much less, magnifying the force 100 times or more, just like a mechanical lever would.