One of the reasons the Crucible Iron Holdfast works so well is there is a close fit between its untapered shaft and its hole in the workbench top. To get this tight fit, we think you need to drill each hole in your workbench and then gently ream it out a bit to get a nice, close fit.
It takes about two minutes per hole. But the results are worth it.
To bore and ream the hole, we recommend the WoodOwl 1”/25mm auger bit. These are the best auger bits we have encountered, and they work well in electric drills and braces.
The WoodOwl bit is metric, so it is slightly undersized compared to the shaft of the holdfast, which is approximately .970” +/-. So the holdfast will not fit in a freshly bored hole until you ream it out a bit.
You ream the hole by spinning the bit (we use a corded drill), while plunging the bit in and out of the hole while providing sideways pressure. After your first hole you will become an expert.
Drill and Ream Holdfast Holes from Christopher Schwarz on Vimeo.
The above video shows the process from start to finish using a WoodOwl bit and a simple jig that keeps your bit plumb. You can download plans for the jig and full instructions for the holdfast here:
— Christopher Schwarz