Problem drilling UPVC sliding patio door to fit lock

[bathjobby]

As the subject says; fitting one of these locks and drilling the hole in the door for the locking bold to fit into is a problem.
I was expecting the sliding door frame to just be extruded UPVC and hence easy to drill the hole to take the locking bolt. After drilling through the outer skin, there is obviously a heavy duty aluminium frame inside which resists drilling.
So my 2 minute job is on hold until I understand a little more.
Any advice; is this normal, do this, do that, etc, will be greatly appreciated.
Would normally post an image rather than asking you to follow a link but I couldn't get it to work this time.....
http://www.screwfix.com/p/patio-door-lock/13541?_requestid=574066

 

[Burnerman]

You are correct, your patio door has an aluminium frame inside the upvc.
It is however easy enough to drill, using a correct size and sharp (new) HSS jobber drill bit.
Always drill a smaller hole than needs be, and work upwards until the screw (self tapping type) bites in firmly.
Watch for the glass panel! The panel typically extends 10 to 15mm into the frame from where you can see.
John

 

[bathjobby]

Thanks for the response Burnerman.
I didn't understand the last part of

Always drill a smaller hole than needs be, and work upwards until the screw (self tapping type) bites in firmly.

Its the large hole for the bolt that I'm refering to, everything else youve told me makes sense. Have I missed something ?
Thanks again.

 

[Burnerman]

Oh I see - its the shoot bolt hole you are talking about. In which case, drill a pilot hole as accurately as you can, and then use a drill thats 1/2 a mm bigger than needs be.
John

 

[bathjobby]

Thanks again John.
I stopped drilling into the aluminium frame as none of the product reviews of the lock had mentioned it so I thought maybe I had something different. They all said things like; 'took 2 minutes to install'. Well this bolt hole is going to take longer than that to drill, even with the new bit I bought and not having drilled a centre hole first (was only expecting extruded plastic) the centre of the hole in the alloy has drifted a mill or so. This has left a slightly larger and irregular hole in the plastic which I can probably cover with the bolt hole cover but my concern was, as I couldnt see the size of the alloy frame, was I in danger of weakening it or breaking/disconnecting some parts of it with the drill.
Thanks again but still seems strange all the reviews say 'fitted in 2 mins' !

 

[Burnerman]

Screwfix 68824 is the one I fit, but the bolt only locks down when its fully depressed, if you get my drift.
This one penetrates into the frame about 30mm so is good at resisting door 'jacking'.
John

 

[bathjobby]

And for whichever type of bolt lock you use, its normal to have to drill right into the doors internal aloy frame ?
Cheers.

 

[Burnerman]

To aid security, yes....I position them where water can't ingress of course, and fit one top and bottom.
On my own doors, I have an angle bracket fixed to the sliding door inside, and another one on fixed frame inside.....resting on these angles is a length of square section tubing long enough to keep the door tightly shut - there's no way the opening door can be slid.
John