Why does thicker metal take longer to cut?

MontanaLon

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What I mean is if you are cutting it on the short edge. Clearly if you are cutting through a thicker piece through the thickness it will take longer but say you have 2 pieces of metal 5 inches wide. One is 1/4" thick and the other is 1/2" thick. But if you cut along the 5" width it should take the same amount of time to cut and it doesn't. The thicker piece will take longer. This is all given using the same tool to do the cut.

It just doesn't equate for me. Equal length strokes should remove equal amounts of material. But it appears to not be the case. Anyone have an explanation for my challenged mind?
 
Your description is unclear to me so maybe I'm seeing it wrong but if you mean that you are cutting two 5" long pieces of material, one 1/4" thick and one 1/2" thick, and you are cutting through the first one and half way through the second one with an end mill then yes, the thicker material takes longer. The reason is that you are cutting the thicker piece with both side and end, while the thinner piece is cutting only with the side; much smaller contact patch with the through cut, plus the chips clear easily so not much re-cutting is happening.
 
Assuming you're cutting with a saw of some sort, it depends on the tooth and gullet size. If you use a fine-tooth saw with thick stock, the gullets will fill up with chips before they get to the other side. If you use a coarse tooth saw with thin stock, you strip the teeth right off.

I have three different blades for my metal cutting bandsaw, each of different TPI, and they get swapped depending on what I'm cutting. Thin angle iron or tubing gets the high TPI blades; large-diameter bar stock gets the low TPI blades.

Ideally you should have at least three teeth in contact with the work at all time. Not sure about an upper bound, I think my coarsest blade is 6-10 TPI, and that does a decent job cutting 3 inch round bar.

Sent from my Pixel XL using Tapatalk
 
Under ideal conditions for a given horsepower you can remove some maximum volume of material per minute. If I understand your question correctly, then the volume of material removed in the 1/2 piece is twice that of the 1/4 inch piece. Given that the conditions are probably not ideal, then the cut time may not be directly linear.
 
Perhaps a better description of the cut or a picture would help.
 
Your description is unclear to me so maybe I'm seeing it wrong but if you mean that you are cutting two 5" long pieces of material, one 1/4" thick and one 1/2" thick, and you are cutting through the first one and half way through the second one with an end mill then yes, the thicker material takes longer. The reason is that you are cutting the thicker piece with both side and end, while the thinner piece is cutting only with the side; much smaller contact patch with the through cut, plus the chips clear easily so not much re-cutting is happening.
I was thinking more along the lines of a saw. If a piece of stock is 1/8" thick and 5" wide and the other is 1/2" thick and 5" wide and you lay them both on edge so you are cutting across the width (making the cut 5" long) then both pieces should cut through in the same amount of time. 5" cut is a 5" cut.

If you were cutting across the wide edge then you would be making a cut through 1/8" and 1/2" which is 4 times as thick so it should take 4 times as long.

Conversely if both pieces are the same thickness at 1/8" but different widths, say 3 and 5" if you cut through the thickness so each cut is 1/8" so should take the same amount of time all other things being equal.

It would bee like if you where drilling a hole through 2 pieces of stock of the same thickness but different widths. It would take the same amount of time to drill the same size hole as the width has nothing to do with the thickness.

It was just something that occured to me while cutting a piece of 1/2" plate with a hack saw. Too much time to think.
 
Are you talking about "rip cutting" the piece along the 5" edge length wise through the thickness so that for example if I cut the 1/2" thick by 5" long (missing the width measurements) piece in half as you are trying to describe i would end up with 2 pieces that are 5" long by 1/4" thick minus the blade kerf by however wide your piece started out as will remain the same length. Is this what you are asking?
 
I was thinking more along the lines of a saw. If a piece of stock is 1/8" thick and 5" wide and the other is 1/2" thick and 5" wide and you lay them both on edge so you are cutting across the width (making the cut 5" long) then both pieces should cut through in the same amount of time. 5" cut is a 5" cut.
The saws downward force would be across 4 time the area when cutting the 1/2" section so he pressure per tooth would only be a quarter - hence less metal removal per tooth pass.
 
A saw blade removes a volume of material, just like any other cutting tool. The volume in the first case is 5 x 1/8 x the saw kerf width, the second is 5 x 1/2 x the saw kerf width, ie 4 times more, so I'd expect the second to take at least 4 x longer, provided the saw gullets don't fill up as @pstemari said.
 
I need pictures...my head is spinning!
 
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