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  • Bandsaw damper, revised

    I gave some thought to the design of the hydraulic jack damper, if you can call it a design, and came up with a much better and just as simple solution. It's mechanically correct with proper linkage geometry.

    The bolt in the support plate is spaced by the washers so the assembly clears the side of the bandsaw. The washer stack is chosen so the nut is able to just bottom on the bolt shank, leaving the bolt free to rotate in the plate. I used a 7/16" bolt to avoid any deflection problems.

    A short piece of tubing is welded to the top of the jack ram adjuster.




    Damper in place. The 3/8" bolt is simply clinched to the upper frame with a nut on each side.




    Click the link to see an animated GIF showing the motion. The motion timing is not to scale.

    http://vts.bc.ca/pics2/damperani.gif

    Next I will experiment with the needle valve. When I have a solution I will post it.
    Last edited by Evan; 08-30-2007, 07:01 PM.
    Free software for calculating bolt circles and similar: Click Here

  • #2
    I like the MKII better....
    Paul in NE Ohio

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    • #3
      Thats really a good idea Evan, Somewhere I have a old cylinder off a wells bandsaw I need to find it and see if-n I can use it on HF saw....

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      • #4
        Can you explain the purpose of this modification to your bandsaw? I don't understand the benefit. I've seen hydralic springs added to larger bandsaws, but I thought those were use to assist in lift up the unit because they are very heavy.

        Do have the valve fully open when operating?

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        • #5
          Evan,
          Would this modification to the valve screw work?

          Using some sort of extra fine thread in the new plunger screw
          would allow much smaller adjustment to be made.
          A disk could be attached to the outer end and marked
          in some fashion like a clock to serve as a reference.
          Mike Green
          Mike Green

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          • #6
            Horizontal bandsaws require some method of controlling the cutting force applied to the blade. Too much and a number of bad things happen such as excess blade wear, chatter, stalling and even blade breakage. The small bandsaws control the force by using an adjustable counterbalance spring. Adjusting it changes the effective weight of the saw and therefor the cutting force. This works quite well but not in all circumstances. In particular, the spring has no direct control at all over feed rate. The saw can free fall if it isn't in contact with the work. Feed rate will vary depending on the cross sectional area to be cut.

            What needs to be controlled is not just the cutting pressure but the maximum feed rate. That is what limits maximum tooth chip load. When cutting a piece of material that present very different sections such as thin wall square tubing there is no correct setting of a spring counterbalance. It will either be too light for the horizontal walls or too heavy for the vertical walls.

            A hydraulic damper controls the maximum feed rate while allowing maximum feed pressure. If the feed pressure would result in too much chip load because of a change in cross section the damper prevents that by retarding the feed rate. Both the counterbalance spring and the hydraulic damper have a place and can work together with the spring controlling the maximum feed force and the damper controlling the maximum rate.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              This is what the stock needle looks like in my jack. I expect most are similar.
              The truncated end results in a loss of control as soon as it clears the tapered seat.



              I added a piece of bronze from some 1/8" brazing rod and tapered it. This has improved the control somewhat but not as much as I expected. I need to actually examine the seat to see what size the orifice is, not easy to do.

              Free software for calculating bolt circles and similar: Click Here

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              • #8
                Evan

                I was sorry to see that this interesting thread had petered out. I've had my trusty bandsaw for upwards of thirty years but have only recently started using the more costly bi-metallic blades. With a view to protecting these against the problems you mention in your reply to rotate I went out and bought a similar jack and am in the process of fitting this (thanks for the idea and the excellent photos!).

                I can see from some preliminary working of the ram that the control of the rate of descent is likely to be a key point and wondered whether you solved the problem of adjusting the valve to your satisfaction. Incidentally, it seems that my jack has a ball on a seat rather than a needle valve.

                ega

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                • #9
                  A simple double acting hydraulic ram can be used. Just plumb a line to complete the loop with a needle valve in the plumbing to control flow. It is essentially what the stock ones are on the bigger machines.

                  Andy

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                  • #10
                    Or you can make your own cylinder, see:
                    http://mikesworkshop.weebly.com/band...-cylinder.html
                    Mike

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                    • #11
                      Andy and Mike

                      Thanks for your posts which I have read on breaking for tea, having just got to the probable proof of concept stage in the workshop. I agree that the ideal solution for many would be a suitably-sized cylinder as fitted to the larger saws; others seem to have gone for alternatives on cost/availability grounds or because they like making things for themselves. I will have another look at the larger machines in my local stockist and will also make another attempt to join the yahoo group so that I can fully appreciate Mike's solution.

                      In the meantime, although this is the "revised" thread there is a good deal of useful comment in Evan's first thread including suggestions as to the stroke and bore of a cylinder suitable for the 4x6 saw.

                      ega

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                      • #12
                        At $125 to #$200 for an eBay replacement cut off saw feed control cylinder I ccan undestand why one would seek a more ecnomical approach.

                        A bottle jack is OK but I would think the seal friction high compared to the forces your application imposes. Seems to me that stick/slip may pose a problem.

                        I suggest instead of a 2 ton hydraulic jack you use a cylinder like this

                        http://www.ebay.com/itm/BIMBA-6-STRO...#ht_1616wt_867

                        where seal stick-tion is measured in ounces instead of tens of pounds.

                        Also you need a needle/check valve like this

                        http://www.ebay.com/itm/BIMBA-6-STRO...#ht_1616wt_867

                        which is expensive in this 2000 PSI model but much less from a pneumatic line. Of you can incorporate a check valve in the piston (if you can get the cylinder apart and back together) and use a plain needle valve to throttle descent. This eliminates a separate surge tank equal to the swept volume of the cylinder because the surge oil can be on the rod side of the piston.

                        The Bimba cyl and valve will allow a tidy and compact arrangement and you can mount the valve anywhere you can run tubing.

                        This assumes you have a little money to throw at the project. If your object is to use materials on hand then the bottle jack is an excellent expedient if you can accept seal friction.
                        Last edited by Forrest Addy; 01-21-2014, 08:48 PM.

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                        • #13
                          Forrest Addy:

                          Based on my experience so far I think your point about stiction will be valid in my case. One used to be able to buy a 1.5 tonne bottle jack which might have been better in this respect.

                          The BIMBA cylinder looks very nice but for this approach to be economic I would need to find one here in UK - ironic that the eBay vendor is in Rochester NY and I am in Rochester, Kent! If the jack doesn't work for me I'll certainly consider a cylinder-based solution.

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                          • #14
                            Since the pressures encountered in this application are way lower than hydraulic jacks or pneumatic cylinders are designed for, a simple cylinder could be easily fabricated from common copper water pipe, or even PVC. The piston needs nothing more than an O-ring for a seal or a leather cups, which can also be shop made.

                            The rest of the plumbing is simple enough to shop fabricate or adapt readily available components.
                            Jim H.

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                            • #15
                              Would a repurposed bicycle pump serve as an inexpensive starting point ?

                              .

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