Mounting Bracket Template

I have no connection with the manufacturer or suppliers of anything shown in this instuctable. This cctv camera is the second of its type I've installed and I've a third waiting to be set up at a remote location on a 4g router powered by a battery and solar panel but that will be a separate ible.
A couple of its down sides are the cables and mounting bracket. You need either a large hole in the wall it's mounted on 25mm/ 1"+ or you mount it on an external junction box then you can get away with an 8mm hole if you run it on wi-fi just for the power or 12mm if you're running it on an ethernet cable. Secondly you can't completely remove the mounting bracket from the camera to drill through it to position the holes. A camera dangling by a cable when you are at the top of a ladder holding a bracket in one hand and a hammer drill in the other isn't a good plan. Whilst it comes with mounting screws and plastic plugs to fit it to brick work what it doesn't have is a template of where the holes need to be. This is how I made mine.

Pair of compasses. Thin card or paper. Set of Brad point drills preferably 0.5mm size steps. Sharp pencil and a rule

This is simply a case of unscrew the support arm from the bracket. Yes I forgot to do a photo so this is the same state but after its mounted to the junction box. The problem is the rj45 conector is too big to go through the central hole. Fortunately there is a cut out in the foam rubber gasket that lets the bracret sit flush this also saves having to do any trigonometry to find the center point and radius of the circle the screw holes are on. You could manage without doing this step but it's a whole lot easier just to hold the bracket still if you're not hampered by the camera.

Why brad point drill bits? The shaft of the drill fits snugly in the bore for the screws and the Brad point gives you a nice neat center point.
Find the bit with the best fit in the bore for the screw this is why I suggest a set with .5mm steps in size. This turns out to be 4.5mm a 5mm wouldn't quite go and the 4.5 isn't quite tight.

Place the bracket flat on the card stock (I'm using a bit of cereal packet) and hold it firmly in position. Place the selected drill bit through the screw hole hold square and push firmly down to mark the card. Repeat with the other holes it is important you don't move the bracket between markings. Not thinking I gave the drill a twist as I pressed it down. With a Brad point this is not needed and could easily have been a problem

Use a sharp pencil. I've used a 0.5mm mechanical pencil as it gives a good fine line I suggest a pencil as you can get a finer line than you can with a biro. We used to use fine emery boards to make the points fine when I did technical drawing at school (pre CAD)

Measure between 2 points mark the centre and draw a line connecting it to the point opposite. Repeat with the other two sides of the triangle the lines only need to just cross the first line to find and confirm the centre point. This is now a usable template pin it to the wall with a masonry nail trough the centre and drill at the present marked points. But I want to duplicate it and drill a box lid so next step.

A good spring bow pair of compasses with a screw adjuster make for better accuracy but the basic set you get in a school geometry set will do. You can either measure the distance from the center to the point and set the compasses to the ruler. Or set the distance directlying from the template. This will give you the circle the right size to set the mounting holes on. Remmber drawring flowers with compasses at school this is the practical application of that.
I found the center of the junction box lid by drawing across the diagonals drew my circle. Marked roughly top centre and swung an arc that cut the center and both sides of the circle side. The points where the archive cut the circumference of the circle are used to swing two more arcs these should both cross the circle at the centre point of the first arc. This and the lower two crossings are the positions of the 3 mounting hole. All that is left to do is drill them and the center hole for the cable and bolt it all together.

Had I needed to punch a hole for the cable. Measuring where the center point was would have been difficult. I could have used trigonometry instead. Sine (S). Cosine (C), & Tangent (T). But which? Remmber SOH,CAH,TOA. We need to know H the hypotenuse. Which rules out TOA. We don't know the hight from the center between two points to the center of the circle the distance Oposite (O) the angle we know so we're not using SOH. We do know the length of the side adjacent to the known angle it's 25mm half the distance between two of the points where the right angle forms so we use the cosign of the known angle of 30° this is half the 60° of each corner of the triangle. We know this as all 3 sides are the same therefore all 3 angles are the same the angles of a triangle add up to 180°.
180÷3=60
CAH means: cosine= A÷H
Some algebra multiply by H moves the H to the other side of the =
Cosine×H=A
Divide by cosine leaves H on one side of the = and A÷cosine on the other. We look up the cosine of 30° or use a calculator (or a slide rule if you know how to use one whichI don't ) and it is 0.8660.
25÷0.8660=28.86
I measured it at 29.5mm as I was using a 0.5mm pencil I measured to the wrong side of a line. Using a 5mm drill as the bores were a lose 4.5mm gave me the play need to fit the screws ok.