Amtech F0770 3 Piece flat wood bit extension bar set

I used it to extend my flat wood bits to drill out the old broken fence posts. Makes replacing the old fence posts easy without removing the concrete.

Brilliant as long as you use it with a standard hex shaft bit, e.g. a typical spade bit. The grub screws tighten against an edge of the hex shaft and keep things central. If you want to use it with a round shaft bit you’ll need to ensure that the shaft is the right diameter to keep everything central, otherwise it will not be straight and will wobble around and produce potentially damaging results.

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I bought these to hollow out large turned wooden forms. They work... ok.The holes that hold the bits aren't quite parallel to the main axis of the extension bars, which introduces considerable runout to the bits. This puts more stress on the extension bars and the bits and means holes are drilled oversize. If you just need to make a big hole, that might not be a problem, but don't expect precision.

There is nothing to not like about it , I’ve got two different depths I can drill now 👍👍

Works

This extension bar is very poor. The Allen key fixings do not hold a hexanagal wood bit shaft firmly. The screws come loose after just a few seconds of use. I had to constantly relighting the grub screws. The supplied Allen key is quite soft so the end rounded off after a few retightens. I resorted to my bahco keys as these are much better. The internal of the bit holder is round. It would have made sense for this to be hexagonal the same as the standard wood bit. I was drilling 1 hole in a wall joists. It should have taken less than a minute to complete but it took me over 30mins. And I ended up swapping out the grub scews for small bolts.

Excellent addition to my drill bit tools