finding the exact center of a small (<10mm) dome

[trialuser]

Anyone got any tips please.
just had 3 attempts, cocked up 2!
currently I'm doing it by eye, marking with a marker and then with a ball burr prior to drilling. Looks ok at this stage but when drilled is ever so slightly off.
I'm marking on the convex side.
perhaps I'm just cr@p, perhaps I'm too fussy - no I'm cr@p!

[mizgeorge]

Much easier to do before doming! I just use a caliper to mark the radius from three places on the circumference and the spot in the middle of the marks is the centre.

[Goldsmith]

Do you have a pair of steel dividers in your tool collection, if not you should have, like these;http://www.silverlinetools.com/products/d79/s631
With these you can set them at an approximate size to the centre of your domes, then holding one arm of the dividers to the edge of the dome mark an arc across the centre, twist the dome a little then scribe another arc, then twist again and repeat the process, this will either give you a small circle in the centre or if you have guessed right a cross in the centre, making it easy to mark the centre for drilling.

James

[trialuser]

Thanks both - got it sussed now.
Easy(ish) when you know how!