MDJ - Marvel Dowel Jig

This jig has the following features:

• 3 dowel diameters - 6, 8, 10 mm
• works for the boards up to 50 mm
• quickly centers on the edge of the board
• helps to quickly make the matching blind holes for dowels
• the fence can be easily removed
• easy to print without supports

The hardware you need:

• Metal pipe for 6 mm dowels: OD 8 mm, ID 6 mm, length 30 mm
• Metal pipe for 8 mm dowels: OD 10 mm, ID 8 mm, length 30 mm
• Metal pipe for 10 mm dowels: OD 12 mm, ID 10 mm, length 30 mm
• M5*50 mm (without the head thickness) screw with hex head (8 mm spanner size); the screw can be up to 70mm long
• M5 nut (8 mm spanner size)

The pipes can be found in hardware stores and cut to size with any available method

Printing

• use 0.2mm layer height
• use 5 or more perimeters and 50 % infill
• orient the parts on the buildplate to maximize the strength

Post-processing

Remove all the membranes from the handle screw hole and the fence

Assembling

• press-fit the pipes to the corresponding holes
• press-fit the nut inside the hut knob (screw itself can be used for this)
• insert the handle into the body part
• insert  the screw and thread in the knob, but not fully
• attach the fence by waiving the screw head through the corresponding hex hole in the fence, then slide the fence and tighten the knob (use reverse order of steps to remove the fence)

Using

• determine which connecting board can accept the longer holes and start from it
• to center the dowel jig, place it onto the edge of the board and rotate it until there is a secure contact between the jig's pins and the board sides
• while holding the jig rotated and applying the pressure towards the edge,  drill the hole (drilling depth should be marked in advance or use drill stops)
• repeat the two previous steps as many times as you need (but usually two or three dowels is enough)
• insert the dowels to the holes in the board
• when connecting edge to edge (like corner of the box), insert the jig to one of the dowels using the hole with the corresponding diameter. The insert should result in the situation when the fence is on the outer side of the corner (the board side facing outwards)
• slide the fence so it fully touches the board surface and tighten the knob, then remove the jig from the dowel
• place the board with dowels onto the second connecting board, the concat should be between inner boards' surfaces, the second board should be below the first one
• slide the top board away from the edge of the bottom one to have a place to drill the holes and have a place for the jig
• use the jig to verify that there's enough space. For this, place the jig with the fence side to the top side of the bottom board and slide till the fence contacts the bottom board's edge. The jig will push the top board further away from the edge. To be totally sure, push the top board a bit further
• align left and right edges of two boards and clamp them together
• check if there is still enough room for the jig. If not, unclamp the boards and slide the top one
• make sure that the boards are securely clamped
• place the jig so that the corresponding groove slides onto the dowel and the fence is pressed to the edge of the bottom board
• mark the drill depth to prevent the accidental drilling completely through the bottom board
• drill the hole
• repeat the previous three steps for the remaining dowels
• join the boards

This video shows the example of the jig usage.

Enjoy the jig and have a good luck in your woodworking projects!