Cutting a Hole.

Most if your holes drilled will be in the normal range of 1mm to 13mm. For this purpose a box of normal twist drills can be bought from most tool supply shops. If you are not too hard on these drills, they will last you a long time and you can buy single replacement drills to keep your box full.

Using a recognised cutting compound/fluid also from tool suppliers will help keep your drills sharp. Using too much force when drilling can make the drill too hot and burn out the cutting edge giving you a blunt drill. You can sharpen your own drills on a bench grinder, but this is best only for people that have been trained as drills have a precise cutting angle and also Safety when using a grinder. If your drill is sharp and you use the correct force whilst drilling, you should see two equal spirals of metal swarf coming off the drill tip! If you ever see light grey smoke coming from the drill tip, your drill is getting too hot, so dip the tip again in cutting compound to cool it.

There is a engineering formulae for the drilling speed for cutting , but you will have to look up the cutting speed for the Material being cut, which also can be found in engineering handbooks. Some metals are harder or softer than others and so have there own specific cutting speed. For all you Technical addicts out there, the cutting speed for normal Carbon Steel is around 28metres/minute.

The formulae for drilling speed is-

Cutting Speed (Material) x 1000mm DIVIDED BY 3.142 x Diameter (Drill)

So for drilling normal carbon steel with a 10mm diameter drill-

28 x 1000 Divide by 3.142 x 10

This equals 891rpm (revolutions per minute)

This is too long a method for every drilled hole , so experience will take over once you have drilled lots of holes and start to get an expert! A general rule of thumb is the bigger the drill the slower the speed. Most modern drills Electric/ Battery have a high and low speed range and a variable speed trigger. This allows you in high or low range, to vary the speed, by how much pressure you use on the trigger. Practice a lot and learn by experience.

When you start to drill a hole the drill can slide around and move its start position. So when you have marked where your hole needs to be, use a dot punch/ centre punch to indent the spot. Your twist drill will grab in this point and you will drill exactly where you wanted your hole. Practice and learn by experience.

Bigger holes will be drilled with either a step drill or in most cases, a hole saw. Hole saws use the same size mounting (arbour) but you will need one saw for each hole diameter. Remember once again the bigger the hole diameter the slower the cutting speed.

Warning! Cutting bigger holes with too fast cutting speed makes the cutter tend to grab! This is a very bad experience as it tries to twist your wrist grip and your arm, Painfull! you will certainly know if this happens! Drilling good clean holes will soon become second nature, but always remember Safety and wear goggles when drilling. Trust me I do talk from experience!

Remember you only get one pair of eye's.