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Tripod bolt adapter

Why

Often it is needed to affix a custom device to a photographic tripod. Cameras commonly come with such threads in their bottoms. Other devices, not so often.

The photographic equipment uses usually the UNC 1/4-20 thread (0.25 inch outer diameter, 20 threads per inch), or, the bigger and heavier cameras, the UNC 3/8-16. The latter one is fairly unusual in the field of consumer devices, though.

Metric threads are way more common, both as bolts, nuts, and taps. Another common mounting standard is a plain hole. An adapter between a metric thread and the 1/4-20 one is therefore needed.

How

A M8 bolt was chosen as the initial platform. The 8mm diameter of its outside is sufficiently small for common uses, often used in various things/devices already, and the inner diameter of the thread is just a bit larger than the outer diameter of the 1/4 thread.

A M8x10 bolt was chucked into the lathe, using a M8 nut as an adapter to protect its thread. Its head was machined flat, to remove the protruding letters marking the steel grade and achieve a flat mating surface.


M8x10 bolt

M8x10 bolt, nut

Bolt head facing

Bolt head facing

A small hole was predrilled in the center of the head. This hole was then used to guide the drill bit when drilling the 5mm hole. The hole can lead through the entire length of the bolt, or be just 12-15  millimeters deep and blind if a through-hole is not necessary. (Some difficulties were encountered when almost through the bolt. Probably the steel was hardened there during its manufacture. This was not encountered during making the blind holes.)


Hole predrilling

Hole predrilling

Hole drilling

Hole drilled, end machined

Hole drilled, end machined

The bolt was then placed to a vise and the 1/4-20 thread was manually cut through the hole, using the three-piece set of taps.


Thread cutting

One bolt was destroyed during this operation. Probably due to excessive torque or a material fault or an inaccuracy, the thin wall of the hole, weakened with the threads on its both sides and with the stress concentration in their edges, sheared.


Torn-apart bolt

Torn-apart bolt

Torn-apart bolt

A new bolt was picked and drilled, and the thread cutting operation was successful at the second attempt.


Successful thread

Successful thread

Successful thread

The bolt was then chucked in the lathe again, and its ends were machined. The head-end got the hole coutersunk to facilitate easier mating with the tripod-side bolt. The tail-end was faced flat, the inner side of the hole was slightly countersunk, and the outer side was chamfered in 45-degree angle as well.


Machining of end

Machining of end

Final adapter

Final adapter

Final adapter

Final adapter

Blind and through-hole adapter

Blind and through-hole adapter

Blind and through-hole adapter

The adapter can be used with e.g. certain pipe sleeves, some of which have a M8 female thread in their base. These adapters can be used for tripod-mounting of cylindrical objects, e.g. a microphone.


Pipe sleeve and adapter

Pipe sleeve and adapter

Pipe sleeve and adapter

Pipe sleeve and tripod top

Pipe sleeve and tripod top

Pipe sleeve and tripod

Microphone in the holder on the tripod

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