Arca Swiss Mount for Small Cameras

The Arca Swiss dovetail mount is the most popular camera mount for professional and advanced amateurs. The Arca Swiss ball heads are very popular with nature photographers. All of my tripods are fitted with some some of head topped by an Arca Swiss type dovetail clamp.

This presented a problem when I decided to try out some small mirrorless SLRs. The spare mounting plates I had were all too large for the small bodies, and covered the battery and SD card door. So to remove the SD card I had to unscrew the mount so that the door could be opened. So much for quick change.

This is a simple machining project, none of the tolerances are very tight. If you are a photographer with a lathe and mill, you can make your own. Maybe you have a friend who has a milling machine and a family that needs to be photographed. Maybe you have a machine shop and a friend who needs a mount. Items made in the machine shop are always good for bartering.

The mount uses a simple male dovetail fitted to the camera. The tripod size has a matching female dovetail that acts as a clamp. There is quite a bit of range on the female clamp, so the tolerances of the male part are not too critical.

The drawing above demonstrates the method I used to measure the dovetail on an official Arca Swiss mount. Using pins or wires is a common method for measure the width of either a female or male dovetail. In this case two pieces of brazing rod (0.093" in diameter) were places on the reference surfaces of the dovetail. The outside distance on the pins was measured and recorded. At this point you could refer to The Machinist's Handbook and some trig, but instead I simply drew the position of pins and dovetail in AutoCad. The goal was to find the depth of cut needed to make a correct size dovetail.

As you can see in the photos, the mounting screw on the baseplate is quite close to the access door for the battery and SD card. The center of the mounting hole is about 0.625" from the edge of the door. The width of the dovetail is determined by the dovetail itself, but the length is waht ever you want. I choose to make the mount 1.75" long, with the mounting hole centered on the width and 0.625" from the edge.

I used Fusion 360 to draw up the plate. You are free to modify the drawings as needed to fit your camera. It would be possible to use the Fusion 360 drawing as a basis for making a 3D printed version. If you decide to do this you should probably use either a button-head cap screw or a flat-head screw. Modify the counter bore to suit. Both the button-head and the flat-head would provide more material under the screw head for strength. I used a socket-head cap screw because that was what I had on hand. The screw needs to be modified, more about that later.

I used 3/8" x 1.5" 6061-T6 aluminum. I cut off a piece just a bit longer than the 1.750" length needed for the finished part. The length is not critical, use whatever length suits your need. The ends are squared-up in the mill. It is set high enough on parallels so the dovetails can be cut. This means you need at least 0.200" above the vise jaws.

Start by putting marking fluid (magic marker works great) on the front and rear edges. The dovetail cutter is 45 degrees. My cutter is 1-3/8" in diameter, but a smaller one would do as well. Set the cutter Z axis to the required depth of 0.198". Advance the cutter toward the work until it just scratches off the marking fluid. Zero the Y axis and make the cut at a depth of 0.140". Do not go deeper the 0.140". Do the same for the backside.

Using an edge finder locate the edges of the part then move the piece until the spindle is in the correct location for the mounting hole. The hole will be drilled and tapped for a 1/4-20 UNC screw, the standard camera mounting screw. Your hole may be in a different location depending on the needs of your camera. Drill the hole through with a #7 drill bit. Tap the hole with a 1/4-20 UNC tap. I use spiral taps and tap under power, you should use whatever method you find comfortable. The hole is tapped so that the mounting screw is captured and is not likely to get lost.

For a 1/4" socket-head cap screw, use a 1/2" endmill. Cut the counterbore 0.275" deep. The counterbore brings the screwhead below the bottom surface of the plate to prevent interference.

If you use a button-head or flat-head screw, cut an appropriate counterbore or countersink.

At this point the machining of the plate is complete. Round off all sharp edges and chamfer the through hole and counterbore edges.

I used a 3/8" long 1/4-20 socket head screw. I was able to securely clamp the screw head in the 3-jaw chuck. Using a parting tool, I cut back the threads under the head. They were cut back to the minor diameter of the threads for a length of about 0.125".

If you use a button-head or flat-head screw, the method is a bit different. Use a screw about 1/2" longer than needed. Secure about 3/8" of the threaded end in the 3-jaw chuck. You may want to support the head using the tailstock. Cut the threads under the head back as above. Make sure the threads are cut back far enough so the an unthreaded portion will be visible on the top of the plate (see photo). Back off the tailstock (if used) and cut the screw to the finished length.

You may find the threaded hole in you camera base is quite shallow. If the screw is a bit too long, grind it back. Make sure the plate will screw down firmly to the base of the camera.

Note how the access door can be opened far enough to easily extract the battery and SD card. It's a good idea to make several dovetail plates and keep them around for mounting other cameras or flashes. (especially if you had to borrow the dovetail cutter)