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Using to bore holes in hackle berry tree stump. Used, old, spade bit paid 75 cents for one time use

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    Short answer: yes.
    – Graphus
    Feb 27, 2018 at 14:53
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    @Graphus how unlike you! :)
    – Ast Pace
    Mar 3, 2018 at 4:34

3 Answers 3

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Yes, you could use sandpaper to sharpen a spade bit. You'd need to attach it to a backer board sized to fit between the spurs and the lip (see the picture below identifying parts of a spade bit). The backer board could be wood or plywood or MDF -- anything with a flat surface sized to fit between the spur and lip. Then you'd set about sharpening, working your way through progressive grits, trying to maintain a consistent angle.

With a little bit of cleverness, you could probably build a jig for this to help maintain the consistent angle. Or you could just eyeball it. But as you can see, this is a lot of effort to go through to sharpen a bit for a single use.

And if you don't already have the materials on hand (sand paper, scraps of wood, some means to fasten sandpaper to the wood -- glue or tape? -- etc.), it's probably cheaper just to buy a new spade bit.

Alternatively, you might try to pick up a set of needle files, and use those to sharpen the bit. You can find a cheap set for $4-$12 USD at various places online. But again, I'm not confident these cheap needle files will last any longer than a single sharpening. And even if they do, a new spade bit is going to be cheaper. The needle files only make sense if you plan on sharpening it over and over (and in that case, you'd probably want a nicer set of files anyway).

Parts of a spade bit Picture credit: Wonkee Donkey Tools

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  • I'd say you don't necessarily need to attach the sandpaper to anything, if you can hold a sheet on a flat surface (bench top would be fine but ideally something metal or glass) and run the bit over it by hand. A file is going to be better but in a pinch sandpaper can work just fine, especially if it doesn't need to be razor sharp.
    – WhatEvil
    Feb 28, 2018 at 10:33
  • Mostly I was trying to make sure the spurs on the bit don't get in the way. I haven't looked closely at my own spade bits to see if that is a common feature or not. Feb 28, 2018 at 14:55
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I'd use a file rather than sandpaper. You won't be able to wrap the sandpaper round a block, and free-form sandpaper will just mould to the contours of the surface (rather than giving nice planar surfaces).

If you are desperate, you could wrap the sandpaper round some sort of former, and use it as a make-shift file.

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You can sharpen just fine with sandpaper wrapped around or on just about anything flat and firm. Drilling implements are quite forgiving if you don't care much for the cleanliness of the bore. There is a fair range of sharpness and form that will still effectively poke a hole in wood.

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