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smaller blades for ripping FYI

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  • #16
    I do not think that a smaller blade is better for cutting but it is more affordable and regardless of what size or type of blade I use there is normal some time spent jointing/sanding etc.I do own a 10" Freud 60 tooth blade that I am very fond of.

    Irregardless of blade radius and blade mass the ts motor will maintain 3450 rpm? How?? I do not dispute that if the larger blade makes one rotation in the same period as a smaller blade than the larger blade is traveling faster at the blade tip. The statements that I made previous did not assume constant rpm or negligable mass. I theorized that a large heavier blade cannot be spun at the same rpm as a smaller, lighter blade utilizing the same motor. I find it difficult to grasp that regardless of size or mass of a blade that the rpm of the blade remains constant.
    In theory, a larger diameter blade, that has more mass requires more power to accelerate and maintain rotation at any given rpm then a smaller blades. Now, if the motor shaft maintains 3450 rpm then that doesn't mean that the blade will. Power will be lost in maintaining the rpm of the blade. Less power will be lost on a smaller diameter blade. This lose may or may not be significant. I do not know that answer (nor am I conducting a physics experiment on my TS). Disclaimer: If the motor maintains a constant rpm regardless of blade radius and mass then it's Miller Time. Now momentum is a different story.

    Steve

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    • #17
      Steve, the motors on table saws are at least 1 and a 1/2 HP. With a motor that size, it would have no trouble turning a 7, 10, or even 12" blade at a constant RPM. Remember, saw blades don't weigh all that much, so the keeping the mass moving at 3450 rpm isn't all that hard.

      At work, I have a few 3 and 5 horse motors that turn large exhaust fan cages that weigh in excess of 50 pounds without a problem. (of course they are 3 phase, and I'm just waiting for one to need "upgrading or bearing replacement." Problably never happen though as I take really good care of the stuff.)

      Dave A, maybe the army could use some of those blades?? Perhaps you could sell them for the same cost as a toilet seat??

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      • #18
        Disclaimer: If the motor maintains a constant rpm regardless of blade radius and mass then it's Miller Time.

        Remember, no shop time after beer.

        Not a chance in the world I could explain why a synchronous speed motor works the way it does. But, there are lots of things in that category, that work even though I can't explain them.

        <quote>
        Calculating Synchronous Speed:

        AC motors are considered constant speed motors. This is because the synchronous speed of an induction motor is based on the supply frequency and the number of poles in the motor winding. Motor are designed for 60 hz use have synchronous speeds of 3600, 1800, 1200, 900, 720, 600, 514, and 450 rpm.
        <end quote> citation: http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm

        If an inductive motor of this type is run at a lower speed, as by applying too large a load, it will burn out. If it is run with no load, it will run at synchronous speed (less bearing drag and other minutiae).

        So, there you go. Happily, we never touched on centrifugal force or centripetal acceleration, because I never did figure that dang stuff out.

        Dave

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        • #19
          Steve,

          I'll not get involved in the speed, mass circumference physics debate, I got lost on that halfway down the thread. But your comment on not using Teflon Coated blades since the main portion of the blade doesn't come into contact with the wood.
          It's my understanding that this coating, which also appears on a number of Router Bits, is an attempt to prevent the buildup of pitch and resin, and nothing to do with helping the blades/bits through the material.
          Is this not so?
          David

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          • #20
            Steve---let's put it another way---if you had a motor which DID significantly increase in rpms, with a smaller blade, you'd really notice it---a motor so reactive to a minor change in the mass and size of a saw blade, would barely cut butter, let alone wood.

            I'd say this---if someone gave you a box full of 7 1/4" blades for free---by all means knock yourself out---but on economics, buy the 10". A good carbide tipped 10" will outlast many 7 inchers.
            Dave

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            • #21
              Well this has been an excellent conversation. I must (finally) agree that the mass is negligable. I calculated the velocity of the blades at 3450 rpm for both blades and besides some rounding and significant fiqures came up with the same results as JPM. When changing rpm for the 10" to 3000, the blade still had a velocity of 89.6 mph.
              It was nice dusting off my ole physics books. Let's drink some beer. Thanks for all your input and patience. Now, where can you order those depleted uranium tipped blades again?????

              Steve

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              • #22
                Cutbuff,
                I feel it is more gimicky then practical. If pitch is accumulating on the face of your blades, then pitch is likely accumulating on your teeth too. Personally, I haven't seen much in the way of accumulation on the face of the blade. Most of the accumulation occurs on the teeth. I just make it a blanket policy to clean my blades after I complete a project or if a see a noticeable degradation of blade performance. I keep my 7-1/4" blades clean too. Now, what does everyone use to keep their blades clean?? Oven cleaner, baking soda/hot water, commerical cleaners??

                Steve

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                • #23
                  I know this topic has been beat to death, but, the suggestion that a heavier blade will require more power/energy to maintain a constant speed goes against a very basic physics law. An object in motion will stay in motion until acted upon by another force. The forces acting on a SPINNING blade should not be affected by size. Sure, there will be a little more weight on the bearing(negligible), and the larger blade will have slightly more surface area, so more air friction, (also negligible). As to weather more teeth would increase drag, I think that would need to be tested, but I'm sure the effects are small. What you might notice with a smaller blade is a reduction in start up time(acceleration). I'm done.
                  As for cleaning off pitch, Simple Green works great.

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                  • #24
                    Agree---Simple Green is fantastic---err, sorry, that's another product Works in a few minutes. Also, I use it to clean my cast iron tops, followed by good coat of paste wax.

                    Steve---yea, let's spill a little beer on the physics book
                    Dave

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                    • #25
                      Steve L. writes: I feel it is more gimicky then practical.

                      Steve, I'm not picking on you, I swear. But, your profile here says you are a Scientist. I am too, of sorts.

                      Would you agree with me that "feel" is not a particularly scientific word? Have you tested teflon coated blades to determine how well they work in comparision with plain steel ones?

                      I haven't either. But, a friend works for Freud, and they have. Oddly, a teflon coated blade experiences lower heat rise in testing than a plain steel one. Chrome plated did even better, if I recall correctly. Why? I don't know, because the way you "feel" makes sense to me too. But, the tests don't support it.

                      Dave

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                      • #26
                        Steve, I felt the same as you and posted the same thing about the same blades in my old Delta bench saw on another forum. The same result was thrust upon me and I also had to agree with them. The fact did remain though, that the result they spoke of was under NO LOAD....when you toss solid Maple into the discussion, the drag on the larger thicker blade slowed the tip speed down to UNDER that of the thin kerf 7.25" blade with the same feed rate. That's why the stock goes through easier and the cut bogs the motor down less.

                        While this was tested in real life and found to be true, the more powerful the motor, the less this would matter. On a 13 amp bench saw, the difference was stunning...on my 15 amp belt drive Ridgid, it was a little less prominant...on a cabinet saw with 3 hp? I'd say it wouldn't matter.

                        So under a load such as solid Maple or Oak, the tip speed of a thin kerf 7.25" blade can out perform that of a thick kerf 10". The drawback though...none of those thin kerfs are made for smooth edges....
                        Kelly C. Hanna<br /><a href=\"http://www.hannawoodworks.com\" target=\"_blank\">Hanna Woodworks</a>

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                        • #27
                          “on my 15 amp belt drive Ridgid, it was a little less prominant..”

                          Kelly, yours is a little more powerful than mine “Emerson 1.5 HP, 13/6 Amps, 120V-240V Induction/Capacitor Start & Run”. This thread has been very entertaining, thanks.

                          Woodslayer

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                          • #28
                            Don't sweat it Dave A. My mind is always open. I can guarantee you that my official reports that I produce do not contain the word feel or guess.
                            My question is this how does teflon help dissipate the heat? Does your friend know how or why the lower temperatures are created? Is the differences only measureable in a laboratory? How would this affect all of those non-stick cooking pans?? Teflon has a well established lubricative quality that reduces the friction between moving parts. Teflon is a man made polymer created by DuPont. Lower friction levels mean less heat. But, how much contact occurs between the teflon coated surfaces and the wood? Most carbide tipped saws cut a kerf that is wider than the metal blade. If that is so then there should be minimum contact with the side of the blade. Most of the heat should be generated at the teeth. Freud website states that, "Permanent red Teflon coating on some Freud blades guarantees less working friction and less resin adhesion while preventing the development of rust." I clean and oil my blades regularly. If you regularly clean the pitch out of the carbide teeth, how much extra effort would it take to clean the face of the blades? I have never had a blade rust. I also do not believe that the friction reduction they speak of is measureable by the average woodworker or is worth the extra expense. That is why I feel it is gimicky. If it worked so well, why isn't everyone doing it?
                            Steve [img]tongue.gif[/img]

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                            • #29
                              I guess the rate I'm going I will never get one of those neat little stars under my name.
                              Nice to hear from you Kelly. There are more variables at play but I think I fired Dave up enough this week.

                              Steve

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                              • #30
                                (Dave hangs himself at mention of the "if it's so great why doesn't everyone do it" argument ) My car is supercharged, it runs great and gets better gas mileage than it should for its size and the way I drive it. Why aren't all cars supercharged?

                                I will ask my friend for more details. I haven't a clue why it reduces running temperature, and he probably doesn't either. With luck, maybe he can find out.

                                Teflon is a man made polymer created by DuPont.
                                How does this snippet add to the conversation, please? Teflon is the registered trademark of the DuPont company for polytetrafluroethylene (assuming I spelled that anywhere close to right). IIRC, it was discovered serendipituously by a researcher trying, humorously, to develop a better adhesive. But that has nothing at all to do with its use as a sawblade coating, it is just additional background noise.

                                Dave

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