Laser-line Oche for Dartboard

When I built the dartboard cabinet last year, I put a piece of tape on the floor to act as an oche (throw line).

As they say, there's nothing more permanent than a temporary solution, and a year later, the tape was still there, so now it's time to do something about it.

Years ago, back when I first started posting my projects on social media, one of my first Instagram posts was about a (now long abandoned) project to create a 3D scanner:

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In this process, a regular laser diode - like one from a laser pointer - is aimed through a transparent cylindrical object. This acts like a prism, refracting the light, creating a line.

The same principle I used back then, is what I'm using this time around. Although this time I'm using a piece of acrylic rod rather than being cheap and trying to use a stem from a broken wine glass...

The Diode

The laser diode that I'm using comes from an old Nintendo Wii lightgun accessory, and was the one I started using in the laser scanner project.

With all the plastic shroud removed, this is what is we're left with

 

 The Casing

I initially went down the rabbit hole of making a 3D printed case, but in a moment of inspiration, realised that a short section of copper pipe would be perfect.

The pipe is about 1.5 inches long, and we're using two end caps.

One simply has a small hole drilled for the wires to come out of the back

A plastic washer was used to create a mount for the laser diode in the pipe.

The second pipe end cap is used to create the lens assembly.

 

 

 

 

 

 

The lens assembly

A hole was drilled into the end cap, bevelled at the outside for a nicer finish. The hole should be no wider than the diameter of the acrylic rod.

A small piece of transparent acrylic rod was cut, and sanded to make a friction fit in the end cap perpendicular to the hole that was drilled.

You can see how the rod bends the light, making the drilled hole look square.

This lens assembly can be push fit over the end of the rod.

 

The wiring

The diode was powered by 2 AAA batteries, so I found a 3.7V phone charger as the closest contender for a power source. However, it's not just a case of connecting the diode to the charger.

It's important that laser diodes are driven correctly as current fluctuations can easily damage them. In some cheap laser pointers, control of the current is sometimes limited by the specification of the batteries that are used.

I was expecting this to be the case with this one, but after some probing, I determined that I was lucky, this laser contained some control circuitry (behind the yellow shrink-wrap in the diode picture).

So the only extra circuitry I had to add was a resistor to drop the voltage closer to the 3v that a battery would provide, and adjusted the resistance of the battery so that the current was also similar.

For safety I did this by starting with a high value, which provided virtually no light output on the diode, then reduced it until the brightness was suitable.

 

The mount

The mount is 3D printed (Source), and attaches to the top of the bottom compartment of the Dartboard Cabinet. The body of the laser is attached with a copper pipe clip, and is simply a case of holding the laser so the line is drawn the required distance away, and then the bolt tightened.

This can take a bit of trial and error, as the tightening of the bolt can unintentionally move the line.

 

 

 

The finished oche

 

Dartboard Cabinet

I got a dartboard for Christmas, which I have on the wall in my home office.

Darts is a great excuse for getting up and stretching your legs between video meetings, or while thinking over a problem, rather than just pacing back and forth.

However up until now it's simply had an old piece of hardboard as a backing, so thought it's time it got a proper cabinet.

The design is to have two compartments, the main dartboard cupboard (obviously!), and below that a small compartment which can be used as storage for the darts and accessories, and will open to provide a platform to help catch bounce-outs.

The Frame 

The frame is made from a reclaimed iroko desktop - I believe it was from an old school chemistry lab. It's about 5cm thick, so ideal for covering the thickness of the dartboard.

This was ripped down into 4 lengths to make the sides of the frame.

These are jointed using lapped mitre joints, screwed through from the back for extra support.

The divider between the main dartboard compartment and the lower storage compartment is joined into the sides with pocket screws.

The backing of the main compartment is hardboard, reclaimed from some dismantled hollow-core doors, simply pinned into rebates in the frame.
The backing of the lower storage compartment is reclaimed laminate flooring, which helps to add rigidity to the structure, again, screwed into rebates in the back of the frame.

I layered some cork over it, to try and prevent bounce-outs and reduce impact noise, although in hindsight I regret that decision, as the thin cork veneer seems to disintegrate at the slightest provocation. But seeing as it's there to catch errant darts, it's pretty much a consumable anyway.

The doors
The doors are iroko, edged with oak to add some contrast.

The fold down door for the storage compartment is reclaimed from a previous project which didn't pan out, and is already built in the same manner.

It also has a leather lining, again from a previous project - I don't know how well that's going to withstand some dart bounce-outs, but I don't think it's chances of surviving being ripped out are much better, so opted to leave it in.

For the storage compartment, a leather lace is used to create a limiter to stop the door folding down too far. This simply threads through a hole drilled in the divider and is knotted.

 

 

 

 

 

 

A simple latch for this is mounted in the side, made from miscellaneous brass hardware from the junk bin.

On the door side, the lace is threaded through more brass hardware (I believe a Chubb keyhole cover), and knotted. The knot is recessed into the door to hide it, and the hardware screwed to the door.

 

 

 

 

 

 

The handles

The handles for the doors are made of leather. This is done by creating a loop as shown below.

A hole is drilled through the thickest part (the 3-layer section). Between the second and third layer only, a small screw is placed with a washer.

The first and second layers are stitched together, and the handle screwed to the door. The hole in the first layer provides access for the screwdriver, as the head of the screw is hidden.

When that's done, the hole in the first layer is hidden by the rivet.

  

Finishing touches

In the back of the cabinet, keyhole hooks were recessed into the top and bottom of the frame. The sides would've been preferable, but the placement on the wall would have collided with cabling behind the wall.

A whole was cut in the centre of the dartboard compartment, this is to allow the existing wall mount to pass through - so the dartboard does still have a direct mount to the wall, which aids with it's positioning on the wall - we can make use of the calculations we did when it was first hung.

Finally, a couple of coats of danish oil were applied to bring out the pattern of the grain.

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