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smaller blades for ripping FYI

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  • smaller blades for ripping FYI

    I'm not sure if I saw a post on this forum, or another, but the suggestion was made to cut/rip plywood with the smaller 7 1/4" saw blades. they're cheaper and pretty much disposable, as opposed to a $100 blade, or even a $20 sharpening.

    Thought I would mention that HD has Freud 7 1/4" 24 T blades for $9.99 and it comes with a free one. (only $5 each) The blades are pretty nice and have the same features as their higher end table saw blades. the kerf is also very thin, even for a 7 1/4" blade. [img]smile.gif[/img]

  • #2
    Think your first consideration is the number of teeth and if the results are good for plywood. However, when you switch from a 10" to smaller blade, the rim speed of the blade (number of inches of circumference/sec.) will drop, possibly making for more effort to cut the stock---and, of course, the smaller blade will dull faster for the same number of cuts--since each tooth has to cut more frequently.
    Dave

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    • #3
      What would the benefit be?

      Dave

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      • #4
        yes, you may have to cut slower, and the blade may wear faster, but... For $10 you get two disposable blades.

        The cost of a sharpening on a standard 10" blade is around $20 depending on where you go. Sooo, for the same cost of one sharpening on the 10" you get 4 disposable carbide tipped blades to use when you rip thinner stock (I believe thickness would be about 1" or less)

        I for one don't want to wear out a 10" blade when I can pop in a cheap smaller one for the job. Besides, I normally rip the wood close, then do finish cut with the smaller, more manageable pieces.

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        • #5
          It would seem to me that if i am building a project, like furniture or cabinet out of a good wood, that an extra $30.00 or so for a good 60 or 80 tooth blade wouldn't hurt my budget that much that i would sacrifice the quality of the project.
          Your quality is only as good as the tools you use.

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          • #6
            I have and do use 7-1/4" blades for ripping. Since the blade is smaller it will spin faster than a 10" (less rotating mass). The faster spinning blade should cut better than a similar larger one but it would also dull faster. Like Mike3206 stated, the price is right. So far, I cannot afford to spend $75++ for a blade. The Freud blades that I have used still required jointing/sanding. Stay away from teflon coated blades. The lubricative properties of teflon is never utilized because the teflon coating never touches the wood.
            Steve

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            • #7
              Since the blade is smaller it will spin faster than a 10" (less rotating mass).

              I would like to challenge this statement. Most tablesaws use synchronous induction motors that have a nearly fixed speed that derives from line frequency. As well, once a blade is spun up to speed, it's mass has nothing to do with the power required to sustain it.

              The cutting tip speed of a smaller blade will be lower than a larger one, because the circumference of the blade is smaller.

              Dave

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              • #8
                Simple physics my friend. If the motor shaft speed is held constant, as blade diameter increase the speed at the blade tips will decrease. Larger blades will have to travel through a greater distance - circumference.
                Mass also has a lot to do with cutting. Rotating mass provides the momentum that helps your saw cut through thick or dense wood. Smaller blades with less mass will stall quicker than a larger blade. If rotating mass was not important than no car with a manual transmission would have flywheels. I think you are confusing mass with torque.
                My knowledge of synchronous induction motors is very limited so I cannot discuss them.
                Steve

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                • #9
                  You have me entirely confused, as you are contradicting yourself, and stating things backward.

                  -----------------------------------------------
                  Regarding speed:
                  -----------------------------------------------
                  Quote one, Steve: Since the blade is smaller it will spin faster than a 10" (less rotating mass).

                  Quote two, Dave: The cutting tip speed of a smaller blade will be lower than a larger one, because the circumference of the blade is smaller.

                  Quote three, Steve: If the motor shaft speed is held constant, as blade diameter increase the speed at the blade tips will decrease. Larger blades will have to travel through a greater distance - circumference.

                  In quote three, your first sentence is stated backward. The second sentence is correct.

                  Let's use an extreme example to see the effect more easily. We have two disks, each revolving at one r.p.m. One of them is one inch in diameter, the other one is fifteen feet. A dot on the edge of each will pass a given point one time each minute. During that minute, the dot on the small disk will have traveled roughly 3.14 inches (circumference = diameter X pi). The dot on the large disk, in the same time, traveled over 565 inches, about 180 times faster. Since fifteen feet is 180 inches, this isn't surprising.

                  -----------------------------------------------
                  Regarding mass.
                  -----------------------------------------------
                  Smaller blades with less mass will stall quicker than a larger blade.

                  I agree. But, don't you think this is counterexample to your first post, where you imply the smaller blade is better?

                  Dave
                  Next, let's do centrifugal force vs. centripetal acceleration...

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                  • #10
                    Steve---sorry but I fully agree with Dave A.---it's that darned "Dave Thing" again The rim speed (where the teeth are) is the issue and Dave's example is correct.

                    As to flywheels, and Dave can correct me, but they are used to sustain speed under load, and if my memory on this is correct, that's another point if favor of a 10" blade.
                    Dave

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                    • #11
                      I did goof up a bit. I will follow up with a clearer explanation when I get off the company clock.
                      Steve

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                      • #12
                        Another simple way to think about blade speed(speed of teeth). [Speed(velocity)=distance/time]
                        With a constant rotation you have constant time. What is changing is distance. As Dave and others have established, a larger blade has a larger circumfrence. So increasing the distance in the equation will increase speed. With an RPM of 3450, a tooth on a 10 inch blade travels 102.6 MPH. With 7 1/4" blade the speed is only 74.4 MPH. I'd have to dig out my Dynamics book to enter into the centrifugal discussion!

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                        • #13
                          Wow, sorry about the can of worms.

                          Yes, the blade rim speed will be slower with the 7 1/4, and as I mentioned, you would have to feed slower. However, I have yet to see a quality 60 tooth blade for less than $40, and since I always cut a little larger when ripping, (so I have more control over final cut) I think it makes sense to get something cheap that will do the job.

                          I would have to disagree though with the point made about the mass of the 10" blade making it spin better or cut better than the smaller one. The difference of mass in a blade that narrow doesn't do that much. Now, if the blade was say... 2 pounds, then I would agree about spinning mass making a big difference.

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                          • #14
                            if the blade was say... 2 pounds

                            Hmm, maybe there is a market for blades with tips of depleted uranium?

                            Dave
                            Goofy toward the end of the day

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                            • #15
                              Heard they sell those blades in North Korea
                              Dave

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