Doweling Jigs

Dowel joinery lives or dies on hole alignment, and hole alignment by eye does not work. A doweling jig fixes the bit's position relative to the workpiece so that the holes in both halves land in the same place.

Self-centring is the feature worth paying for

The better jigs centre themselves. Clamp the body onto the edge of a board and the mechanism moves both faces inward equally, so the bushing ends up on the centreline regardless of whether the stock is 18mm or 32mm thick. You never measure, and thickness variation between boards stops mattering.

That is a genuinely different tool from a simple drill guide block, which holds the bit square but leaves the positioning to you.

Not to be confused with a dowel maker, which is a plate that cuts dowels out of scrap. The names are close; the tools do opposite halves of the same joint.

What to look for

• Hardened steel bushings, and a range of them. 6, 8 and 10mm cover most furniture; 20mm exists for heavy stock.
• A bushing that matches your dowels exactly. 8mm dowels through an 8.5mm bushing is 0.5mm of slop at each end and a joint that will not close square.
• Enough clamping force to stay put. A jig that shifts mid-hole is worse than no jig, because you now trust a hole that moved.
• Depth control. Most rely on a stop collar on the bit. Set it so the two holes together are slightly deeper than the dowel is long -- a dowel bottoming out holds the joint open.

The honest limitation

Dowels are a fine joint and a fussy one. Two holes that are each half a degree off will fight each other, and unlike a mortise and tenon there is no slop anywhere in the system to absorb the error. Glue-up is unforgiving: dowels grab quickly, so a joint that is not square when it goes together is not going to be talked into it.

If you find yourself fighting dowels repeatedly, that is not a sign you need a better jig. It is usually a sign the job wants dominos, pocket holes, or a joint with some assembly tolerance in it.