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Which way should the blade face?

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  • #16
    Cutting into the fixed jaw is right, but as far as the blade itself, "push" and "pull" don't really mean anything. It is relevant to a hand-held hack saw where it describes what your _arm_ is doing but that understanding shouldn't be applied to a power hacksaw. A hacksaw blade itself is too flexible to be pushed - it is always pulled. On a power hacksaw, it is in a frame that goes back & forth, but that frame is rigid enough that its being pushed or pulled is only a matter of which end the driving force is attached to. Imagine a power hacksaw where the frame is being driven at it's mid point - it would work the same but "push" & "pull" can't even be defined. On every stoke, 1/2 the frame is being pulled & the other 1/2 pushed.

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    • #17
      I've never seen one made with the frame driven at the midpoint. While technically correct, that idea seems more academic than practical.
      Kansas City area

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      • #18
        Bob, I understand what you're saying. And yes, the blade doesn't care because it's tensioned in the frame.

        But the frame is typically being driven by the connecting rod off a crankshaft. And that connecting rod is pushing and pulling the frame with every cycle. So there's our directions for this discussion.

        And from there and looking at a few YT videos showing some manner of return lifting feature or pressure reducing feature now we have a reason to pay attention to the blade orientation.
        Chilliwack BC, Canada

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        • #19
          Originally posted by Bob Engelhardt View Post
          ...It is relevant to a hand-held hack saw where it describes what your _arm_ is doing but that understanding shouldn't be applied to a power hacksaw. A hacksaw blade itself is too flexible to be pushed - it is always pulled...
          I must be missing something here because hand hacksaws are typically set to cut on the push stroke

          Location: Northern WI

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          • #20
            Originally posted by Toolguy View Post
            I've never seen one made with the frame driven at the midpoint. While technically correct, that idea seems more academic than practical.
            Of course, that's why I said "Imagine [a saw] driven at it's mid point ..."

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            • #21
              Hi,

              Just how many angels can dance on the head of a pin?

              From a more practical view if your saw doesn't a lifted return stroke, try the blade in both directions. If one direction provides a better and more accurate cut, mount your blade in that direction. If it's a tie, either pick one and stick to it, or don't sweat the details so much.

              My one power hacksaw cut far better on the pull stroke. (The blade frame was driven from the motor/solid jaw end pulling the work down and into the frame and solid jaw with the teeth set in that direction. Can one call that a pull cut?). The return was push. There was no frame lift on the return stroke. But the teeth biting in could provide some bit of extra downwards pressure on the cut as it was pulled I suppose. Not that it would maybe matter that much.

              Nor are hand hacksaw and power hacksaw blades the same. Power hacksaw blades are far taller and thicker with coarser tooth counts and therefore much more rigid and aggressive than the flimsy hand operated versions. Put a hand hacksaw blade in to try if you can find one that fits. And be amazed at the poor quality cut pushed or pulled. I've tried it a pinch a couple times. I was never that pinched again.

              And even if your blade is meant to cut pushing into the movable jaw according to the manufacturer, unless your work holding vice is that flimsy, I suspect it don't mean bupkis in a big ship which direction the blade runs as far as rigidity goes. And if it does, fix your vise.
              If you think you understand what is going on, you haven't been paying attention.

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              • #22
                Originally posted by Galaxie View Post
                I must be missing something here because hand hacksaws are typically set to cut on the push stroke
                My point was that handsaws are where the whole idea of push or pull making a difference came from. You could have a hand saw that cut on pull & your use of it would be different than when using a cut-on-push. Because it's your arm doing the push or pull. A power hack saw's "arm" doesn't care which way it's loaded - push or pull, it's all the same to it. The blade doesn't know either. It's just in our minds that push is different than pull, because it is with handsaws.

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                • #23
                  Cutting on the pull stoke if possible. This lets you pull on all the excess clearance in the worn out pivot points and linkages on those older more "experienced" machines. Pushing on too sloppy a machine could introduce binding, bending, and other undesirable outcomes.

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                  • #24
                    Originally posted by BCRider View Post
                    ...
                    But the frame is typically being driven by the connecting rod off a crankshaft. And that connecting rod is pushing and pulling the frame with every cycle. So there's our directions for this discussion.
                    ...
                    True, but it doesn't matter to the blade & how it cuts.

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                    • #25
                      Here's a link to a short video of a Racine power hacksaw in action. This particular brand uses a hydraulic cylinder and valve arrangement to apply pressure on the pull stroke and raise the blade on the push stroke.

                      Racine 14" power hacksaw - YouTube

                      The down pressure is adjustable using the numbered dial just inside the tall shut off knob with the black handle.

                      Here's a link to a Racine sales brochure with a brief explanation as to how the hydraulic system works.

                      Image (59) (vintagemachinery.org)

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                      • #26
                        Thankyou all for your interesting and useful comments.
                        My machine never had a relieving device,
                        I repaired the pivot point and theres hardly a thous freedom at the outer end of the main arm
                        The vice is man enough to hold the sizes of work I usually need cutting without worrying about which jaw is better to resist the thrust. While I wait for delivery of some new blades I continue to use the ancient well worn one which was in it when I got it, set so it cuts on the pull stroke.
                        Cuts in thicker material are a little off square, but till I get new blades I cannot be sure where the fault lies, or if it is the blade itself.
                        Regards David Powell.

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                        • #27
                          David, I'd still run the saw while holding the beam up just above the work. The angle the connecting rod is at during the push and pull portions of each cycle can cause some lift or push down which you should be able to feel through the guide beam. And that will suggest the optimum way to face the teeth.
                          Chilliwack BC, Canada

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