ANODISING TELESCOPE PARTS

Anodising aluminium telescope parts needs only a basic knowledge of chemistry and electrical engineering technical know how.It is the sort of knowledge that you get from your school education.The components required are a DC power supply,dilute sulphuric acid,a piece of lead sheet metal or stainless steel sheet metal,a 1 gallon plastic open topped container,and a metal saucepan with water based anodising dye in it.The plastic container is part filled with dilute sulphuric acid.A length of 10 amp wire is connected to a piece of sheet lead or stainless steel via a bolt in the metal,the wire being wrapped around the bolt head.This metal needs to be about 3 inches wide and long enough to go from the top of the container to the bottom of the container,so that the wire end itself does not go into the acid.This is called the cathode and this is connected via the wire to the negative terminal of the DC power supply.The positive terminal on the DC power supply now goes via wire to the aluminium job you are going to anodise.The job is then placed in the tank of acid but not the connecting wire.A current passes through the acid between the job and the cathode and a gas is liberated from the surface of the cathode.If this state of affairs is left for a time of approximately 30 minutes then the surface of the aluminium job will have changed.The surface will have changed colour to a slate grey appearance by the formation of a complex aluminium hydroxide chemical coating.This coating is porous and can accept coloration by a special dye.The job is removed,washed in cold water then taken to the metal pan with the dye in it.The dye is preheated to a temperature of 60 deg centigrade.On immersion the job is left in the dye for several minutes.On removal and after washing and drying you have an anodised and coloured piece of aluminium.

Snags.....

The power supply needs to be adjustable from zero to 30 volts at a current of 5 amperes.

The acid concentration for startup needs to be approx 100ml of concentrated sulphuric acid mixed into 1 gallon of water very slowly while wearing safety spectacles or goggles.It must be remembered that the dilute acid is a skin irritant and eye protection must be used at all times during the anodising process.Washing water must be nearby and it is necessary to protect clothes from splashes.Protect hands with plastic gloves.Lots of ventilation is required in the anodising area.A good non glass storage bottle is needed for the acid when not in use with a plastic funnel used to get it back in the bottle.The acid can be obtained from garages and is normally used for car batteries.

All connections to the anode or job need to be of the same metal ie aluminium or they will dissolve rapidly in the acid so croc clips are useless.One of the easiest methods is to screw a piece of thin aluminium rod into a tapped hole in the job then connect the wire to that outside the acid using a croc clip.Thin aluminium rod can be cut from 16swg sheet metal.

The anodising current for most jobs needs to be kept between one and two amps during the anodising period so you need an ammeter.

The aluminium job must be clean and free from any oil or surface contaminant.

You need anodising dye , use the internet to buy it as it is difficult to obtain but not expensive.The dye comes in the form of a powder which you mix with water.Remember those plastic bottles one and a quarter inches diameter that you used to get 35mm roll film in,two of those filled with dye powder into a gallon of water is a general mix.Remember also it is very difficult to remove the dye from your skin,use plastic gloves always.

My power supply was constructed using a mains variac that turns the a.c. voltage up and down to a transformer.The output of the transformer goes into a 20 amp rectifier bridge.The DC output has a capacitor of 1000 microfarad across it 60 volts rating and that is all.This was built into a steel box for safety.You can use two car batteries in series and use power transistors to control the current,there are many methods including using power transistors to make a constant current power supply.A cheap power source can be a battery charger but the voltage is lower and it still has to be made variable voltage some how.Simple power supplies can be made as the following circuits.Circuit1----Circuit2etc.In circuit1 this is a simple constant current supply set at two amps.This is set by a combination of the voltage of the zener diode and the value of the resistor in the emitter of the 2n3055 power transistor.The second circuit consists of a variac or variable mains transformer turning up and down the mains input supply voltage to a mains to 30 volt step down transformer rated at 150VA.With this you use the variac to set the current in the anodising circuit.As the temperature changes in the acid bath the set current can change so with this system you have to constantly monitor the current with an ammeter and adjust as necessary.If you look at suppliers on the internet it is possible nowadays to even buy a power supply with electronic meters built in that is marketed as a variable voltage bench power supply for under £40 UK so in many cases it is not worth the effort of building your own if that form of expenditure is low enough for you.If you took articles to a professional anodising company the cost for one job would pay for your home brew set up.