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Modifying the 4 1/2" x 6" band saw

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  • Modifying the 4 1/2" x 6" band saw

    One of my toys, is an older model, 4 1/2" x 6" Harbor freight band saw (the green one). I reinforced it's flimsy stand several years ago, and added a swarf collection pan to it. The saw has worked well, and suited my needs until about a month or so ago, when the original motor overheated and burned out. Now, while waiting for a new and better quality motor to arrive, I'm toying with the idea of modifying the overarm lowering mechanism. I'm thinking that replacing the tension spring, with an air or hydraulic lowering mechanism would be a nice improvement. Since my inventory of "May be of use some day" parts includes a suitable air cylinder, I'm leaning towards going pneumatic. One port would be open to the atmosphere, to allow air in when raising the overarm. An adjustable bleed off valve would be attached to the other port to regulate the drop/feed rate. I have yet to work out the mechanics of attaching the cylinder between the saw's bed, and the overarm. At this point the project exists only in my feeble mind, and may not be practicable in the real world. Any comments, ideas, or criticisms are welcome, and will be appreciated.
    “I know lots of people who are educated far beyond their intelligence”

    Lewis Grizzard

  • #2
    One problem to overcome is that the downward force increases as the saw tilts coming down. The spring compensates for this rather well. I wonder if the attachment point and angle variation of the thrust line can help.

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    • #3
      This subject has been discussed for months in the Yahoo group 4x6bandsaw. Join up, relax and read all about it.....

      Dan
      Salem, Oregon

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      • #4
        Originally posted by Baz View Post
        One problem to overcome is that the downward force increases as the saw tilts coming down. The spring compensates for this rather well. I wonder if the attachment point and angle variation of the thrust line can help.
        You are absolutely right, and you have opened up a whole new can of worms for me. The spring tension increases as the saw tilts downward. So how do the hydraulic systems work on industrial saws? From what I remember of my days in that environment, they were pretty much as I had described in my op. I'll admit that I never gave them much thought, or paid attention to their workings. Just made force adjustments with a knob when required.
        “I know lots of people who are educated far beyond their intelligence”

        Lewis Grizzard

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        • #5
          Originally posted by Danl View Post
          This subject has been discussed for months in the Yahoo group 4x6bandsaw. Join up, relax and read all about it.....

          Dan
          Tried that several times but get: Sorry, an error occurred while loading the content. The page says it is a restricted group. Are no new members allowed?
          “I know lots of people who are educated far beyond their intelligence”

          Lewis Grizzard

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          • #6
            Originally posted by Dave C View Post
            Tried that several times but get: Sorry, an error occurred while loading the content. The page says it is a restricted group. Are no new members allowed?
            You should be able to submit a join request there somewhere. Sometimes it takes a day or so....

            Dan
            Salem, Oregon

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            • #7
              The hydraulic cylinders on horizontal saws don't control force, they control the feed rate into the cut. The spring controls the force not the speed which is why it does a poor job. So a needle valve sets the speed of fall and you can in fact add weight to the head and still get a controlled feed rate if your needle valve is up to the task. The valve needs to have a reverse check valve so the saw can be raised without needing to change the valve adjustment. Also you want a metering valve with a long needle that changes the flow over several rotations of the knob not just a fraction of a turn. This makes a big difference on how well it works. You also need to bleed every bit of the air from the cylinder and piping otherwise you get bouncing which makes a lousy cut and short blade life.

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              • #8
                Thanks Gary, this is just the sort of information I am looking for.
                “I know lots of people who are educated far beyond their intelligence”

                Lewis Grizzard

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                • #9
                  Someone posted plans for a hydraulic cylinder that you could easily make. That same person also had plans for a tilting table. I made both and love em. The hydraulic cylinder works just like garylucus described above. Both sets of plans are on the internet somewhere and the were made in millimeters, thus you may need to convert to English.

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                  • #10
                    I think my air cylinder will work for low pressure hydraulics.
                    “I know lots of people who are educated far beyond their intelligence”

                    Lewis Grizzard

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                    • #11
                      Dave, Mike Cox has some good bandsaw mods on his site one of which is a homemade hydraulic cylinder.

                      Paul

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                      • #12
                        That's it!!! Thanks. _Paul_

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                        • #13
                          A needle valve will provide a constant rate of flow? Just where does this idea come from? I would expect that as the downward force changes, the amount of flow through any orifice, needle valve or otherwise, would also change. And that downward force will change as the angle of the saw changes as it progresses through the cut.

                          I grant you that the amount of force that a spring exerts will change with the amount of extension (spring scales) and with the angle of the arm it it attached to. Perhaps it will change more than a cylinder with a needle valve, but to say that a needle valve is some kind of flow regulator where the rate will not change sounds erroneous.



                          Originally posted by garyhlucas View Post
                          The hydraulic cylinders on horizontal saws don't control force, they control the feed rate into the cut. The spring controls the force not the speed which is why it does a poor job. So a needle valve sets the speed of fall and you can in fact add weight to the head and still get a controlled feed rate if your needle valve is up to the task. The valve needs to have a reverse check valve so the saw can be raised without needing to change the valve adjustment. Also you want a metering valve with a long needle that changes the flow over several rotations of the knob not just a fraction of a turn. This makes a big difference on how well it works. You also need to bleed every bit of the air from the cylinder and piping otherwise you get bouncing which makes a lousy cut and short blade life.
                          Paul A.
                          SE Texas

                          And if you look REAL close at an analog signal,
                          You will find that it has discrete steps.

                          Comment


                          • #14
                            It won't provide a constant rate of flow, although the flow will only be proportional to the square root of the load. What it does do is control the flow/ down speed rather than just some of the load. So the blade gets fed into the cut at a controllable rate without being able to bounce and flutter.

                            Based on my recent experience, the best thing to do with a 6"x4" bandsaw, even after replacing the motor, belt, NVR switch, stand, many blades, etc. is to retire it and get a 12x7" saw. The little one did a lot of work, but the bigger one is much nicer, doesn't take up that much more room, has an hydraulic cylinder and has a coolant pump.
                            Last edited by Mark Rand; 06-17-2015, 09:51 AM.
                            Location- Rugby, Warwickshire. UK

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                            • #15
                              Get something like this: https://www.surpluscenter.com/Hydrau...L-9-7960-4.axd. It restricts flow in one direction and not in the other so you can tilt the saw back up without fiddling with the valve.

                              I used a double acting 1" cylinder and ATF for mine. It is impossible get it perfectly bled because of the difference in volume between the shaft side and the other so there is a spongy zone at the beginning of the travel. I am sure that I could have done a better job to mitigate it but I have since gotten a new old saw to replace it.

                              bob

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