The pivot bore is 8mm diameter, with a 'squaring' at one side of one shear. I imagine the idea of the squaring was to hold the pivot screw from rotating when the nut was installed and/or adjusted -- not an essential feature. I'll file[1] away the squaring so there'll be a clear 8mm bore all the way through.
An obvious way to repair this would be to install an M8 screw and nut to act as a pivot, but that's a poor practice. It makes for a pivot with very little bearing surface -- only the crests of the screw's threads. It would be prone to wear quickly, and the relatively large M8 screw head and nut would look awful. A much better pivot will obtain from an 8mm diameter rod bored through for an M4 screw.
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Here's the rod in the lathe having just been squared off and bored to sufficient depth.
(By the way, a 5/32" drill is as close to 4mm as 'damn' is to swearing; 5/32" = 3.97mm.)
It would be nice now if I could just part off the needed length of bored rod, but I haven't yet acquired a parting cutter for this lathe. I'll have to saw off a slightly overlong piece and trim it down to correct length; i.e. just a bit less than the total thickness of the shears' two halves at the pivot point.
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Here are all the components ready for assembly.
A ny-lock nut is ideal here; it will stay put once installed and adjusted. The screw was a standard 25mm long one that I ground down to exact length for this application. The flat washers are oversize No. 6. They just fit over the threaded portion of that M4 screw. I had to bore one out just a little for it to fit the unthreaded shank. The god of even numbers must have smiling on me while I was trimming the rod to length by trial-and-error; its finished length turned out to be exactly 10.0 mm.
And here are the shears sharpened, oiled and back together ready for use.
Quite a neat job, if I do say so myself.
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[1] The steel at the pivot point is quite hard, but not too hard to file with chainsaw files. I could have drilled it through on the drill press, but it would have been an awkward thing to secure for drilling safely, and would probably have dulled a drill badly.
Had I thought of them, I had just the little hand grinder stones I needed sitting in a drawer.
They're chainsaw sharpening stones. I should get all the sizes of them, and keep them where I can see them. I can see this style of stone being quite versatile.
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