Drilling plastic

CasperCaster

When drilling plastic pickguards for small holes, such as for a mini switch I generally get a nice clean hole. However, when drilling for a larger hole, such as that required for a pot, the holes are often not as accurate as I would like.

What am I doing wrong? What type of bits are you using to drill plastic cleanly and what speed? Are you starting with a small bit and then going up in size, or going straight in with the final bit size?

And whilst we are on this topic, how do you cleanly countersink holes? I'll need to countersink a few pickup and switch mounting holes in the near future and would like to do a neat job. 

Thanks in advance. 

Modulus_Amps

Are you using a drill press or a hand drill?

Are your drill bits sharp? don't force a bit through it needs to cut through the material.

You can buy countersunk bits for the holes.

ICBM

You need to drill a pilot hole the size of the flat tip on the larger drill bit you need - that stops the large bit wobbling and producing a 50p-piece shaped hole.

It's also better to use a reamer to reach the final size rather than a drill bit, so ideally you need to drill to just smaller than the final size, then ream the last bit.

Mark1960

Generally speaking as ICBM said above, with the addition of slowing the drill speed down the bigger the bit is, For the counter sunks buy a hand counter sunk tool, I find it gives the best results.

Corvus

Centre-pop, pilot hole, drill with scrap backing like ply or MDF (ply doesn't dull bits so much). You can buy 'automatic' centre-punches or pointed hand punches dirt cheap.
If hand drilling clamp the plate + backer, doesn't need to be mega tight but helps steadiness plus frees up a hand.

Countersink bit's best in a pillar drill, or you can get 'manual' ones with a handle. For a drill press get something decent like Famag not the cheap no-name ebay stuff. If they're even slightly not true you get chattering and holes like hexagons.
With a drill press you can set the table up to make the countersinks all the same depth and look dead neat.

Roland

For wood and plastic I use brad point drills, or for larger holes a Forstner bit. For both I like to start with a centre punch to stop the bit wandering, and if necessary a pilot hole, then drill at a slow speed. I don’t like flat bits because they’re prone to produce holes which aren’t round. They can also grab the wood or plastic and make a real mess of it.

Both brad and Forstner bits will drill a small centre hole, then score the outside of the main hole. Using a backing sheet can leave a rough edge which needs filing or reaming. It can also lead you to press too hard, deforming the plastic. Instead you can score the hole outline by drilling from the back, then turn the plate over and drill from the front, leaving a clean edge on both sides.

WiresDreamDisasters

All this talk of holes and reamers... I'm very excited.

Corvus

Will have to agree to disagree on the backing board, but ways to skin cats and all that. To me it gives a clean cut similar to drilling wood, and a little leeway if you have a dull or crappy bit or drill too slow & heat it up, both which can give a frilly edge on the way out, and no depressing the plastic when you start in it.

SteveRobinson

Roland said:

For wood and plastic I use brad point drills, or for larger holes a Forstner bit. For both I like to start with a centre punch to stop the bit wandering, and if necessary a pilot hole, then drill at a slow speed. I don’t like flat bits because they’re prone to produce holes which aren’t round. They can also grab the wood or plastic and make a real mess of it.

Both brad and Forstner bits will drill a small centre hole, then score the outside of the main hole. Using a backing sheet can leave a rough edge which needs filing or reaming. It can also lead you to press too hard, deforming the plastic. Instead you can score the hole outline by drilling from the back, then turn the plate over and drill from the front, leaving a clean edge on both sides.

This is what I do.

CasperCaster

Thanks to all of you for your input. I don't currently have a pillar drill, so on the next dry day I'll take the Workmate outside and experimanet on some scrap material and see what works best for me - plenty of things to try. With regard to the holes I wish to countersink, those are already drilled - it's the pickup and switch mounting screws on a modern Strat pickguard that I want to countersink so that I can use vintage style screws, so I'll order a countersink tool and give it a go.