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  1. #1
    Join Date
    Jun 2010
    Location
    Canberra
    Posts
    1,322

    Default Hedge Trimmer Mod

    I've just taken delivery of this hedge trimmer:
    IMG_0151.jpg

    In this video (at this time point) https://youtu.be/MTmvxEMS6Dk?t=620 the guy points out a particularly poor aspect of a similar hedger's design.
    IMG_0152.jpg

    Specifically, there's no kind of bearing for the drive fork pivot, meaning the hole, bolt or both are likely to get flogged out pretty quickly:
    IMG_0153.jpg

    Given there isn't a heap of material to work with, my first thought is maybe a bronze sleeve pressed into an enlarged hole the driven part with a grease nipple added to the side, and then some kind of sleeve for the bolt? Any suggestions welcomed.

  2. #2
    Join Date
    Mar 2011
    Location
    Southern Flinders Ranges
    Posts
    1,536

    Default

    If I were doing it, I’d torque the fastener to yield with a lock nut and run it. That joint is designed as a clamp not a point of articulation. If you have movement yes it will flog out, correct torque on the fastener means the joint is clamped as it should be with no movement. That’s why it’s designed without a bush. If I was looking at reengineering it I’d be looking to add more clamping surface to both parts of the joint so a second bolt could be fitted.

  3. #3
    Join Date
    Jun 2010
    Location
    Canberra
    Posts
    1,322

    Default

    Quote Originally Posted by racingtadpole View Post
    If I were doing it, I’d torque the fastener to yield with a lock nut and run it. That joint is designed as a clamp not a point of articulation.
    If you imagine the drive rod's movement as the eccentric rotates, you'll see that it changes angle, so the fork rocks back and forth.

  4. #4
    Join Date
    Jul 2016
    Location
    Melbourne
    Age
    35
    Posts
    1,522

    Default

    Id consider straight up reengineering it, I dont really think there's anything you can do with such small surfaces to get it to really last? Some kind of hard pin and bronze bush will do for a while but not forever.

    Sent from my SM-G973F using Tapatalk

  5. #5
    Join Date
    Mar 2011
    Location
    Southern Flinders Ranges
    Posts
    1,536

    Default

    Quote Originally Posted by RustyArc View Post
    If you imagine the drive rod's movement as the eccentric rotates, you'll see that it changes angle, so the fork rocks back and forth.
    If the spring loaded greased joint above it isn’t there to take the rotary motion out of it like I was imagining then I’d remake the plate on the blade with a spherical bearing in it.

  6. #6
    Join Date
    Jun 2010
    Location
    Canberra
    Posts
    1,322

    Default

    Quote Originally Posted by racingtadpole View Post
    If the spring loaded greased joint above it isn’t there to take the rotary motion out of it like I was imagining then I’d remake the plate on the blade with a spherical bearing in it.
    While I haven't fired it up yet, I'm assuming it'll behave like this:
    https://youtu.be/MTmvxEMS6Dk?t=131

    As you suggest, a larger block to take a decent sized bearing may be the go.

  7. #7
    Join Date
    Mar 2014
    Location
    South of Adelaide
    Posts
    1,225

    Default

    Id just replace the set screw with a shoulder bolt (https://www.boltandnut.com.au/12mm-x...gaAivlEALw_wcB) and run it until its a problem.

    Then remake the bracket to suit a self aligning bearing. I wouldn't mind betting it will last a long time before it needs fixing.

  8. #8
    Join Date
    Jul 2007
    Location
    Perth
    Posts
    332

    Default

    My 2 cents worth, as snapatap says a shoulder bolt, but I would put a grease nipple and drill / bore the connecting path to get lube to where it does the most use in the block, similar to earthmoving equipment, then 1/2 spherical washers between the conrod and yolk to account for whatever movement remains. If you were feeling like doing a full job, then bore out the drive block and bush it for the shoulder bolt, but doubt this would be necessary if greased. Alan.

  9. #9
    Join Date
    Jun 2010
    Location
    Canberra
    Posts
    1,322

    Default

    We're pretty desperate for the machine to get going, as there's a heap of hedging to be done, so I've added a grease nipple, and hunted high a low for a high tensile M12 bolt with an unthreaded section that would span the drive block, but couldn't find anything, and left it too late for the fastener shop, so the original fully-threaded bolt has gone back in. Not sure if the grease will do anything, particularly as there's nothing retaining it - the spherical washer suggestion should address that.

    I hope to have it mounted on the tractor tomorrow and I'll see how it holds up.

  10. #10
    Join Date
    Feb 2020
    Location
    Melbourne
    Posts
    55

    Default Plain Pin

    If it's supported on both sides of that brazed-on block (ie; the 'piston strap' engages on both sides of the block on the moving part of the scissor, then a plain, hard pin with a couple of washers and split-pins (or R-clips) would be cheap and way better than a set-screw.
    It could also come out easily for the frequent application of heavy grease or a suitable tough lubricant.
    When it starts to get sloppy, you could ream-out all three holes in-line, press in three plain bearings and use another, slightly-smaller perhaps, plain pin.

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