Drilling a hole in a plastic casing

Yorky

I need to drill a hole in a 70watt sodium light casing to install a photocell. The diameter needed is 18mm so I believe I will need a hole saw and arber. I have nenver used one of these before so any advice would be appreciated, such as:

What type of saw should be used ie are there different types?
How much longer should the drill bit be than the actual saw?
Can it be operated with a standard electric drill and the fitting braced by bodyweight?

Any further tips/instructions would be appreciated.

GreeBo

you might be better off using a dremmel (etc) and grinding out the hole until its the size you want.
You can get grinding bits that are tapered so you can make the hole as big/small as you want.

trying to use a hole saw for 18mm will be hard, if you can even get one.
You can get regular drill bits that size either...

Yorky

You can get grinding bits that are tapered so you can make the hole as big/small as you want.

Thanks, what does this look like?

Would it not make the sides of the hole sloping also?

You can get regular drill bits that size either...

This might be the simplest option. The chuck aperture is only 13mm on my drill but the drilling capacity is higher - would the actual drilling part of the bit
be a larger diameter than the chuck part?

What sort of drill bit should I use for plastic?

tribesman

You could use a spade bit. They are available in 18mm and would drill through plastic even though they're mainly for wood.

http://images.google.ie/imgres?imgurl=http://www.toolbarn.com/images/bosch/sb1011.jpg&imgrefurl=http://www.toolbarn.com/product/bosch/SB1021/&h=303&w=320&sz=6&hl=en&start=2&tbnid=QBl9at-0p1FGlM:&tbnh=112&tbnw=118&prev=/images%3Fq%3Dspade%2Bbit%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DN

Yorky

I've got an 18mm spade bit but thought it would smash the plastic rather than cut through it.

GreeBo

The would look something like
this

How thick is the plastic you are cutting through?

tribesman

Yorky wrote:

I've got an 18mm spade bit but thought it would smash the plastic rather than cut through it.

I've used one to bore a hole in a plastic electrical box. It didn't shatter it and the hole was fairly clean.