I was once looking at my wrist and thinking how hard would it be to make a DIY watch strap buckle. As it turns out, it is a surprisingly simple task. It probably took me less than an hour to make and I have something original and durable.

Step 1: Supplies and Tools

Supplies

Aluminum flat bar – the width dependence on the width of your strap. I am using a 20 mm wide and 2 mm thick piece. e. g. https://www.amazon.com/Pieces-ALUMINUM-FLAT
Steel wire or nail – 1,2 mm in diameter
Regular spring bar

Tools

Hacksaw
Fret Saw
File
Sandpaper
Vice
Drill press or cordless drill
Drill bits – 1 mm, 1.5 mm, 3 mm

Step 2: Draw the Shape

I used old an old buckle as a reference, therefore I just traced its shape on a piece of flat aluminum bar. You, however, can draw any shape, just make sure that you have enough clearance on the inside. You can see the exact measurements of mine on the picture.

Step 3: Cut Out the Inside

Now you can remove the material from inside of the buckle. I used a fret saw because its blade can fit in the corner, therefore I can cut the back side as well. To make it easier you can drill a 3 mm hole in the corner. You could also use a hacksaw and drill out the back side.
After most of the material is removed you can work to the line precisely with a flat file. Lastly, clean everything with a 240 grit sandpaper.

Step 4: Dril Holes for the Spring Bar

Support the lugs of the buckle with a scrap piece of wood. Drill a 1 mm hole in each lug to accept the spring bar.
A drill press is the best tool for the job but you theoretically could do it with a cordless drill as well. 1 mm drill bit is quite fragile so be careful and take your time.

Step 5: Cut the Part and Clean It

You just cut off the piece you need for the buckle with a hacksaw.
Hold the piece in a vice, clean it with a file and chamfer the sharp corners.
Lastly finish the whole piece nicely with a 240 grit sandpaper. You can go to higher grits if you want, but I was going for a brushed look so 240 was enough.

Step 6: Grove for the Buckle Tongue

Mark the middle of the buckle with calipers and make a groove with a small rounded file. This will accept the tongue and make the connection nicely secure.

Step 7: Make the Tongue

You take a substantially longer piece of 1.2 mm wire than you will need at the end (20 mm should be enough). Using pliers you will bend over the last 3 mm of the wire. Next, you will flatten the area a little bit with a hammer.
Then using a drill press and a 1.5 mm drill bit you will expand the hole which is created when you fold the material. This hole will then accept the spring bar.
Now you can assemble the buckle mark how long you need the tongue to be, cut off the excess, and clean it with a file.

Step 8: Assembly

Now you can simply put everything together. Regular watch spring bar is going to connect the buckle, tongue, and strap together nicely. It is a good idea to use a spring bar tool, it makes the process easier.