I have been asked to design and build a large raised level pond that is wheelchair friendly. It has a very small free board of 70mm from water surface to top of the raised sides. It will need some accurate building work, I realised that the best way to go would be to use a rotary level to draw a laser line all the way around to survey in the edges.

As this is for outside use my thoughts were that a green laser was essential for visibility..... the cost of such a device online was prohibitive so I put my thinking cap on to work out a way to make my own, low cost, version.

Step 1: Design Thoughts

The professionally built laser levels all have the line projecting from the top of the unit, I decided to turn the whole thing on its head as using gravity would save me from having to design a complicated gimbol unit to level the projected line.

To help gravity along I wanted this to have some weight to it so I chose brass, a nice dense metal, for the chassis. To make it even heavier I decided to mount all control and power on the chassis too, no trailing wires or plugs and sockets.

Step 2: Parts List

The first Items I had already in stock but I will suggest suppliers I have used in the past.

1.2mm Brass offcuts

Brass tube of a size to suit your laser module

Silver solder, soft solder, fluxes
Various screws, nuts and washers.
Super glue

Small piece of front surface 3mm plastic Mirror

Green laser module Deal-extreme-laser-module

Small 3v dc motor (with gearbox removed) reichelt-small-dc-motor

2 x single channel remote control relay units & 2 button remote fob Deal-extreme-remote-relay

4mm D shackle shackle

4mm x 40mm Carabina

I used reichelt, for the outstanding electrical parts. reichelt home

2 x AA-battery-holder

4 x AA li-ion rechargable 3.7v batteries

Step 3: Tools Required

I am fortunate that I have a fully equipped workshop and I will make good use of Lathe mill and drill, this build can however be hand built with the following.

Hand drill and bits
Hacksaw
Heavy tin snips
Files various
Gas torch
Large soldering iron
Bench vice
Wire wool ( cleaning for soldering)
Emery cloth

.....and whatever else you can see in the mess that is my workspace :)

Step 4: Other Design Thoughts

There are many very good reasons for using brass for the chassis,

it can be easily cut drilled and formed when annealed
It can be silver soldered (high temperature)
Soft soldered (low temperature)
Super glued (room temperature)
it is very stable once work hardened
It looks nice

It doesn't need to be painted

The idea of the chassis is to make it as thin as possible so that the section of the circle not lit by the laser is as small as possible, wires from the motor run up through tubes either side of the main support plate. The design also allows for "tweeking" to get a flat line once the build is finished.

I decided on using a remote fob to turn it on and off as it uses quite a lot of battery power (More of this later).

Step 5: The Electrics

The wiring turned out to be quite complicated due to the fact that remote control relays need a minimum of 6 volts and the laser and motor need a maximum of 3 volts.

The starting point is to use 4 of the 3,7 volt re-chargeable batteries with the same size as AA batteries.
Modifying a pair of twin battery holders to get both required voltages turned out to be the answer.

Step 6: Remote Relay Supply 7.4V

The relay boards can be run from 2 x 3.7volt batteries in series giving an output of 7.4 volts, the only modification to the holder is that I inserted a small slide switch in the top to allow the power to be turned off, this is the only switch required. This is the right hand holder in the second picture.

Step 7: Laser and Motor Supply 3.0 Volts

The laser and motor can be run from 2 x 3.7volt batteries in parallel giving an output of 3.7 volts.

The contacts need to be modified to move both springs to one end and both positive terminals to the other end, in addition I added an IN4001 rectifier diode in the positive feed, this has the effect of dropping the output voltage by 0.7 volts so that we get the desired 3.0 volts.

Step 8: The Chassis

There are no dimensioned drawings for this as a "one off" it was all done by the suck it and see principal.

The main plate was made long enough to attach a motor, a laser and a hanging up arrangement and had to be wide enough to attach the battery holders.

The spine needed to wide enough and long enough to mount the relay boards, the piece of tube needs to be a good fit on the laser module.

The motor plate was silver soldered to the main plate, the laser tube and the spine were soft soldered in place.

I also soldered the tubes for the motor wires along the junction of the main plate and the spine but these could be super glued in place.

Step 9: Covering the Motor and Its Wiring

I wanted a nice clean design with no visible wiring, the afore mentioned wiring tubes hide the motor wires as they pass the laser and ensure that the area of the chassis that the laser hits is as small as possible.

The motor cover is a simple fabrication of brass sheet, bent into shape and silver soldered together, it protects the motor and hides the wires.

Step 10: Covering the Laser Driver and Its Wires

I made a cap for the top end of the laser out of a small piece of tube with one end blocked off and two short pieces of tube inset for hiding the laser wiring. This was all soldered together and is a good fit into another piece of tube that slides over the back end of the laser module

Step 11: The Rotary Mirror

This is by far the hardest bit to get right I can only tell you in a few words what to do.

The mirror needs to mount at exactly 45 degrees, it is mounted on a piece of round brass 8mm diameter with a hole in it to fit the motor shaft.

. I cut my brass rod by hand, holding it in the vice, using a hacksaw and a set square with a 45 degree side to get it as close to 45 deg as I could. I tickled it up with a fine file until I was happy with the angle.

A small piece of plastic mirror is then stuck on top with superglue. and filed to the finished round shape.

On final assembly I used a dot of superglue to stick the mirror mount to the motor shaft.

Step 12: Adjustable Mount

The assembly is symmetrical left to right so it hangs perfectly straight in that plane. Weight front to back is not at all even which is why I cut an 8mm slot in the top of the chassis to make the hanging point movable to get it to hang correctly.

To make the pivot I found a short M8 brass nut and bolt, thinned down the head and the nut and drilled it through to the size of the shackle, 4mm in my case.

Step 13: Testing

The frame could have been tweeked if needs be to get the line correct but I found there was no need, I set it up using a water tube....(no photo's of this process I am afraid as my computer died after a windows update and those photo's were lost :( I will describe it below).

Mrs rog and I filled a length of tube with coloured water, set the laser level running then took one end of the pipe each to compare the height of water to the laser line out to the sides. (it was within 6mm over 20m). There was an obvious high to the front, low to the back thing going on so I moved the hanging point until it was evened out. The last test is to have one end of the tube right next to the laser and the other out as far as possible. This is where any error in the 45 degree mirror shows most, my build was slightly out but is near enough for my purposes.

Here is a quick video showing it in operation, the camera doesn't pick up the line as well as the naked eye.