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4 x 6 bandsaw problem

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  • 4 x 6 bandsaw problem

    Small Jet saw I've had for years was working fine until I installed a hydraulic down feed unit.
    Now the blade binds in the cut and jumps off the wheels.
    I'm running at 200 sfpm with a 14 tpi blade.
    Yesterday was cutting 1.5" round bar 6061 with a very slow feed
    thinking 14 tpi is too fine to clear the dust.
    It repeatedly got into the kerf about .375" and that was it.
    I turned the material in the vise, set the blade back down and it finished the cut no problem.
    I don't have enough material around to conduct a lot of experiments so has anyone had this happen?

    Again, no problem before installing the down feed unit.


    Len

  • #2
    I suspect it was not able to clear the swarf for that wide a cut and with the gullets jammed it pushed the blade to one side and stuck. When you turned the work it was no longer as wide and was able to clear the swarf fast enough. I'll bet it was still a pretty near thing as it passed the mid point and the widest portion of the cut though.

    The issue with the hydraulic gizmos is that if the cut is slowed by the type of material the cylinder still continues to leak down on the low cost ones. This is unlike the helper spring originally on the machine that sets the load on the blade and holds it at that figure regardless of how fast or slow the cut might proceed. So for these machines I'm thinking the spring is a better match since they are rather prone to throwing the blade at the slightest increase in the load from cutting or binding.
    Last edited by BCRider; 08-09-2022, 12:30 PM.
    Chilliwack BC, Canada

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    • #3
      I have a 8/12 tpi blade coming, think that will help?
      My way of saying I probably tossed the helper spring.
      Len

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      • #4
        Before I upgraded from my 4x6 I frequently cut material much larger than that, and probably with about the same tooth count you used. However, my saw only had the spring. With my new larger saw I have a much coarser tooth count and hydraulic feed, but am still able to easily cut thin material with the coarser blade as long a I set the down feed rate carefully. This was also true on the smaller saw - I could cut thin material with a coarse blade if I manually restrained the down feed. I'm now finding that 6-8 TPI is as fine as I need even for thin material. Presumably your hydraulic feed has a control valve that can be set?
        "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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        • #5
          Yes, a little needle valve, very sensitive.
          Len

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          • #6
            I’m not familiar with how the little 4x6 saws are setup but isn’t both the spring and hydraulic feed ideal for horizontal bandsaws? The hydraulic controls the feed rate while the spring control how much down pressure there is.

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            • #7
              I place a block of wax in front of the work when cutting aluminum. Teeth have a little fresh wax every time they enter the cut.

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              • #8
                Originally posted by QSIMDO View Post
                Yes, a little needle valve, very sensitive.
                That's the problem, the ones I've seen tend to be TOO sensitive.

                I wonder if it would be possible to make a new needle valve with a two stage taper. One taper with a very shallow angle for setting the down rate using pretty generous movements of the needle then a steeper secondary taper for faster dropping when you just want to lower the ram fairly fast. And perhaps a micrometer style barrel for a handle so you have an easier time returning to the setting? This would mean setting it up so the needle sits horizontal so you can read the side of the inner barrel much like a micrometer thimble. But that way you could have something like 5 turns AND the thimble settings for partial turns and still not have a touchy to set needle.

                Or perhaps one of the simple mechanical counters? One that runs both directions? Use that for the number of turns then just the index line and collar numbers?
                Chilliwack BC, Canada

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                • #9
                  Flood coolant is your friend, saw cutting aluminum dry is madness.

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                  • #10
                    Originally posted by oxford View Post
                    I’m not familiar with how the little 4x6 saws are setup but isn’t both the spring and hydraulic feed ideal for horizontal bandsaws? The hydraulic controls the feed rate while the spring control how much down pressure there is.
                    Yes. They would kinda be working against each other, in a good way. The spring gives plenty of down force and the ram limits it feed rate. I had to hang a 5lb weight on the handle side of my saw's arm to increase the down force. JR

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                    • #11
                      Maybe you could mount a small wire wheel or a small wire brush at the out feed of the cut to clean the swarf from the blade
                      I have a old famco unit with both the spring and hyd. Feed with a 3/4 x14 tpi blade and use kerosene to lube the blade

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                      • #12
                        Originally posted by JRouche View Post

                        Yes. They would kinda be working against each other, in a good way. The spring gives plenty of down force and the ram limits it feed rate. I had to hang a 5lb weight on the handle side of my saw's arm to increase the down force. JR
                        The little saws must be back heavy if I’m understanding correctly.

                        All the bigger saws I’ve used needed the spring to take weight off of the “handle” side.

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                        • #13
                          The 4X6, as made by a number of OEMs and sold by even more retailers, does not come with any kind of feed rate control. Just the spring which does not actually pull the blade down. Instead, gravity pulls the whole arm down and the spring partially compensates for that force. So the tighter the spring is adjusted, the lighter the pressure on the blade is and vice-versa.

                          Since he tossed the spring away, he now has the full weight of the arm on the blade. If he adjusts that "very sensitive" needle valve a bit too fast then the only thing holding the entire arm up will be the upwards force on the blade, which is probably too much. In other words, the saw blade is not cutting fast enough for the feed rate he has set then the downward force on the saw increases to a maximum. Then the saw blade can buckle and cut crooked. And the tension on the blade will increase: that is probably what makes it jump off the wheels. And the desired feed rate, which the needle valve makes difficult to adjust, will be different for different alloys and/or materials.

                          The spring is a simple and easy way around this problem by maintaining a constant force instead of a constant feed rate. He should have kept it! I suggest getting another one along with whatever other parts of the spring adjustment mechanism that he also tossed away and reinstall it.

                          Another possibility would be to install a new and SHARPER blade which would cut faster, perhaps fast enough to keep up with the feed rate.

                          I have had a 4x6 for over 15 years and the bloody thing is almost a textbook example of the KISS principle. A simple design that works very well. I really don't see any need for any kind of feed rate device. But if you do install one, it should have a much better adjustment than just a "very sensitive" needle valve. I learned to curse those things when I made and flew model aircraft.



                          Originally posted by oxford View Post
                          I’m not familiar with how the little 4x6 saws are setup but isn’t both the spring and hydraulic feed ideal for horizontal bandsaws? The hydraulic controls the feed rate while the spring control how much down pressure there is.
                          Paul A.
                          SE Texas

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

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                          • #14
                            There is one thing about the 4x6 that a feed rate limiter device would improve and that is it's tendency to let the blade drop rapidly on a piece of stock. The shock of hitting the stock can bend the blade and/or strip teeth off of it. When I first used one of these saws, I fell into that trap and had to replace a couple of blades. But this can also be addressed with just a more gentle hand while lowering the saw when starting a cut. And not letting it fall rapidly if the cut passes through a hole in the stock.

                            I learned both of these lessons through damaged blades. The "hole in the stock" incident happened while I was cutting some of the angle stock with pre-punched hole patterns. So I learned to gently lower the blade on the stock and if there are holes in the stock, I stand by with my finger ready to add upward force on the arm as the blade enters that hole.

                            So, yes, a hydraulic feed system may help those problems. But so can an attentive operator.
                            Paul A.
                            SE Texas

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

                            Comment


                            • #15
                              Originally posted by BCRider View Post

                              That's the problem, the ones I've seen tend to be TOO sensitive.

                              I wonder if it would be possible to make a new needle valve with a two stage taper. One taper with a very shallow angle for setting the down rate using pretty generous movements of the needle then a steeper secondary taper for faster dropping when you just want to lower the ram fairly fast.
                              I've been looking for a push-button valve to bypass the needle for rapid down. That way I don't lose the down-feed setting.

                              My hydraulics are a bit of a frankenstein, built exclusively with parts on hand.

                              Click image for larger version

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                              It's all mind over matter.
                              If you don't mind, it don't matter.

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