How to Make a 3D Printed Drill Jig for Dowel Joints

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Introduction: How to Make a 3D Printed Drill Jig for Dowel Joints

About: Crafting Ideas into Reality - Cleveland Maker with an Engineering Twist.

Dowel joints are a great alternative to biscuits or dominos for creating strong joints in woodworking. They also help keep larger glue-ups aligned and surfaces flush. While there are many drill jigs available to buy, I designed and 3D printed a simple jig with interchangeable inserts to drill perfectly centered holes. Read on, and I'll show you how.

You can watch the video to see how I designed the parts, or read on. All the parts were designed in Fusion360 and printed on the Monoprice Select Mini 3D printer in PLA.

STL Files are Posted here

Step 1: Begin With a Sketch

The first step in Fusion360 is to create a single sketch for the entire profile of the jig. I like using one sketch because it helps me to visualize the overall form of the object.

Start with the hexagon, using the polygon tool and set the distance between flats at 0.77". This is slightly oversized, and if the jig works well, I'll come back and make some aluminum inserts using 3/4" hex stock. I added a center hole 0.645" oversized to accept a 5/8" shank on the inserts.

The cylinders on either end are 0.40" in diameter and spaced 1.25" from the center. These dimensions are setup for the jig to accommodate stock up to 2 inches thick.

Once you're happy with the overall shape, exit the sketch and move on to creating the solid body.

Step 2: Create the Solid Body

To create the solid body, we'll extrude the sketch in three steps. Once you extrude the first profile, the sketch flips to invisible. To turn it back on, expand out the tree on the left side of Fusion360 and click the lightbulb to make the sketch visible again.


The steps I used are:

  1. Start by exturing the outer pins to 0.80" tall.
  2. Extrude the diamond shape at 0.40"
  3. Extrude the hexagon insert at 0.19" leaving a pocket that is 0.21" deep.

Step 3 will give a small clearance for the hexagon shaped inserts, which are 0.20" tall. Make sure you don't pull the circular hole along, too - we'll need a hole all the way through the jig to accept the inserts.

Step 3: Remove Excess Material

For the main part of the jig, we need the thickness to provide an adequate guide for the drill bit, but it uses a lot of material. The benefit of 3D printing, is it's really easy to cut out material we don't need for a functional part.

Create another sketch on the top surface of the jig, between the pins. Use the offset tool to bring the outside profile inside by 0.1". Repeat the same process to offset the hexagon outwards by 0.1". Finally, I added a rib across the center, partially because it looks good and mainly to keep enough surface area to provide a stable base when drilling.

Extrude all the pockets by 0.2", or halfway, through the solid to reduce the amount of filament needed.

Step 4: Finish the Edges

With the final shape created I like to come back around and dress up all the corners with fillets and chamfers. First I add fillets around any corners that are perpendicular to the build surface. These are the corners that the extruder will trace during the print. Then I add chamfers on all the corners that are parallel to the build surface. I find I get better looking results with chamfers than with fillets, but that's just an opinion.

Step 5: Add a Hole for a Set Screw

The final feature to add to the jig is a hole for a set screw. This is 0.11" in diameter and centered in on of the hex faces. After printing, I'll tap the hole to accept a #6-32 machine screw. This step is completely optional, but adds stability to the jig, and keeps the insert from falling out.

Step 6: Create the Inserts

Repeat the same process to create the inserts. I made 5 separate inserts for 1/8", 3/16", 1/4", 5/16" and 3/8" drill bits. The center holes are oversized by 0.02" to make for a smooth guide for the drill bit.

Critical dimensions for the inserts are:

  1. Hexagon Distance Across Flats: 0.75"
  2. Hexagon Extrusion Height: 0.20"
  3. Cylinder Diameter: 0.625"
  4. Cylinder Extrusion Height: 0.40"
  5. Center Holes: 0.145", 0.2075", 0.27", 0.3325", 0.395"

Step 7: Print It!

Export the models out to Cura, or the slicing software of your choice and adjust the parameters to suit the parts. I wanted this to be a very durable print, so increased the shell thicknesses and infill percentage higher than I usually use.
Slicing Parameters:
  • Layer Height: 0.21875mm
  • Shell Thickness: 2mm
  • Top and Bottom Thickness: 2mm
  • Infill: 50%

Step 8: Cut the Threads

With the print finished, use a standard metal tap to cut the threads for the set screw. I used a 6-32 socket head to secure the inserts in the jig. This is entirely optional. The inserts snap in to the pocket in the jig.

Step 9: Drill the Holes

To use the jig, set the hexagon side of the jig onto the surface you want to join. Twist the jig so that the pins make contact on both sides of the board, this is how the self-centering feature works. The hole in the insert will be perfectly centered as long as both pins stay in contact.

Put the drill bit into the insert before starting the drill, this will reduce the amount of wear on the plastic inserts. Use the jig to guide the bit. Repeat on both boards and you'll have perfectly centered holes to accept dowels. For me, I find the 1/4" insert gets the most use.

Step 10: The Finished Product

This was a fun project, and being able to create the tools I need has been really rewarding. I'm definitely keeping this one handy, and it's so easy to modify for whatever your specific needs are.

Thanks for reading!

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You can also find me at:

YouTube (all my DIY videos)

Instagram (What I'm working on @greatlakesmakes)

My Website (Geek out on some engineering know-how)

Facebook (be my friend?)

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    1 Questions

    1

    Very nice project and well defined. Can you, please, share the the 3D print files we can use to build this jig? Thanks

    14 Comments

    3D print an insert with the hole the diameter of a pencil, and then you can also use it to draw a straight line through a long board :)

    5 replies

    The pencil would work well - but I'm very unconvinced about how a PLA insert will stand up to more than one or two sessions with a drill bit. I would find a hex bolt with an appropriate size top. Cut off (?almost all?) of the threaded part and then carefully drill a hole through the top. That way you'll get a metal insert which will suffer minimal wear.

    I plan on machining some aluminum inserts once my lathe is up and running. You could also press in a piece of tube or a bushing as someone else mentioned above. So far, they hold up pretty well; and even if they wear out printing replacements is really quick.

    How about using drill stop collars/collets instead? They are already the size of a drill bit, are toughened so will not wear, and threaded so with careful alignment of a hole in the insert can be screwed together

    That sounds good! A far better solution to mine! Might give that a whirl when I've finished casting my bells....

    I like this! Actually gives me another idea for a modification :) Thanks!

    Good tutorial on using Fusion 360 as well! How long do the inserts last? Thanks for posting, nice design.

    1 reply

    The 1/4" insert is getting the most use right now, I've put several dozen holes through it so far. As long as you don't rock the drill back and forth, they seem to hold up well enough... and it only takes about 15 minutes to print a replacement if I need one.

    In addition to making an insert for a pencil as @Yonatan24 suggested, I would recommend adding some metal bushings to the insert to slow down the wear caused by the drilling. You can buy pretty cheap bronze bushings with flanges that would install easily for pretty cheap at most hardware stores. otherwise awesome project & Instructable 10/10

    bushing.jpg
    1 reply

    I looked at using bushings, but didn't one to have to buy separate bushings for each size, maybe if I could find ones where the outside diameter is the same and I can drill them to match - otherwise it's extra cost and extra work :-/

    I do plan on using some aluminum hex stock to machine the inserts once I get my lathe set up.

    Super cool little jig. It would be cool to add a tick mark that indicated on the edge of the board where the center of the hole will be. Since you probably use just a few common thicknesses of wood, you could just add the common ticks.

    1 reply

    That's a clever idea, I could probably put a notch on one side for 3/4" stock and on the other for 1.5" - have to see how that works out. Thanks!