Why does thicker metal take longer to cut?

Cutting metal requires pressure to make the cut. This is very obvious when drilling or turning. Without pressure a drill won't cut which is why drilling manually ytakes longer than on a drill press. When turning, we see deflection of the part due to the cutting pressure. The deeper the cut, the greater the pressure and the deflection.
For a saw blade the applied force is divided between all the teeth in contact. If you increase the number of teeth, the pressure per tooth drops and it takes a smaller cut. If you increased the pressure per tooth to equal what the thinner stock sees by increasing the force, it would cut just a quickly, assuming you have the horsepower to move the blade.
 
Regardless of which way the stock is turned, the thicker piece requires the removal of a greater number of cubic inches of material. Assuming a constant rate of stock removal, the thicker piece will always take longer to cut. A piece 4x thicker will take 4x longer (all other factors being equal).
 
Regardless of which way the stock is turned, the thicker piece requires the removal of a greater number of cubic inches of material.
Not exactly true. If the stock material is set on edge so that the 1/2" or 1/4" side is parallel to the blade so that it cuts into that presented 1/2" or 1/4" wide edge length wise the blade will have the same number of teeth in contact with the material for both pieces. Although I dont know why someone would choose to do this however In a case such as this, the blade should cut both pieces at the exact same rate because it is cutting through the exact same amount of material....assuming the blade kerf falls completely within the span and all other measurements remain identical. The only other factor i can maybe see having an effect is heat dispersion being much different between the 2 pieces regardless of which way its cut.
 
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Not sure of the thinking here. Thicker will always equate to longer times. Looking at your theory, it should take the same amount of time to cut a 5" wide piece regardless of thickness. Unless I am missing something, or this is some of that 'new' math....... Also how can it be said that whether 1/4 or 1/2 thickness you will have the same number of teeth in the cut when set on edge. Unless you have like 2 teeth per inch. Again, wider material can only mean more teeth in the cut. Am I really missing something here?
 
Not exactly true. If the stock material is set on edge so that the 1/2" or 1/4" side is parallel to the blade so that it cuts into that presented 1/2" or 1/4" wide edge length wise the blade will have the same number of teeth in contact with the material for both pieces. Although I dont know why someone would choose to do this however In a case such as this, the blade should cut both pieces at the exact same rate

Yes, it will cut "at the exact same rate". The "rate" being measured in cubic inches per minute, the thicker piece will take twice as long. It will cut thru the first 1/4 inch of the 1/2 inch plate in the same amount of time as it cuts thru the first 1/4 inch of the 1/4 inch plate. Let's assume a .035 kerf width and 5 inch width. The amount of stock removed for the 1/4 inch plate =.035 x 5 x .25 = .04375 cubic inches. For the 1/2 inch plate = .035 x 5 x .5 = .0875 cubic inches, which is, of course, twice as much stock. ALL OTHER FACTORS BEING EQUAL, it will take twice as long to cut the 1/2 inch plate.
 
Work equals force times displacement. If you're displacing chips, you are doing more work when the thickness increases. Power is work over time. If you are doing more work, either you need more power or it takes more time. It takes either more power or more time to displace those chips.
 
Cutting speed is not proportional to cutting pressure. I cut a 3/8" x 3" piece of aluminum in 57 seconds by cutting the 3/8" side but it took 135 seconds to cut it cutting the 3" side.
 
Cutting speed is not proportional to cutting pressure. I cut a 3/8" x 3" piece of aluminum in 57 seconds by cutting the 3/8" side but it took 135 seconds to cut it cutting the 3" side.

Thanks for doing the test, that is exactly where this question led my brain, which way cuts faster, thin side or wide side.

I suspected what you found, although I am surprised that the difference is so significant a little more than 50% longer to cut through.
 
...if you cut along the 5" width...

You would never cut across the widest dimension--always the narrowest. You want to minimize the number of teeth contacting the material at the same time, maximizing the pressure on each tooth.
 
Work equals force times displacement. If you're displacing chips, you are doing more work when the thickness increases. Power is work over time. If you are doing more work, either you need more power or it takes more time. It takes either more power or more time to displace those chips.

Physics, the laws you can't disobey ;)
 
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