Accurate drilling

Munroast · 26 Dec 2022

I suppose it is a little bit ball shaped, a turned peice of wood, 2 inches across. I want to drill a hole 'precisely' (+/- 0.1mm) exactly through the centre. I would like to start from both sides and meet in the middle (to avoid break out)

Any clever ideas ?

freddiemercurystwin · 26 Dec 2022

Make up a jig? Do you have a drill press?

Munroast · 26 Dec 2022

yes several, including one with very fine x y adjustments. But still difficulty holding the item, then getting precise starting positions and angles.

conny · 26 Dec 2022

To avoid breakout you could drill right through with a small drill first. This will give you your centre points on each side.

freddiemercurystwin · 26 Dec 2022

Does this help

How can you go 'precisely' (+/- 0.1mm) exactly through the centre of something that isn't circular or a sphere? As conny says I can't see how you'd do it without drilling all the way though first with a smaller bit.

Justin Passing · 26 Dec 2022

Got owt like a V block?

Notch7 · 26 Dec 2022

Munroast said:
yes several, including one with very fine x y adjustments. But still difficulty holding the item, then getting precise starting positions and angles.

maybe drill 3/4 of the way through one side, turn over and stick the turn piece on a dowel sticking up, that way you will be registering your 2nd hole off the first

I guess you need a saddle to support it.

if you had like a timber Vee block set vertically, you could drill some small holes in it and put in some wood screws positioned to suit your datum points on your turned piece -then you could adjust the screws in and out until youve got it vertical, then use your X Y vice to adjust for centre.

virtually impossible to drill with 0.1mm accuracy on timber -the natural material will contain differing densities and grain directions so stopping a drill wandering would be very difficult.

If you really want it accurate, you will need to spend a fair bit of time jig making

Munroast · 1 Jan 2023

The need for accuracy is created by wanting a 3mm hole though a M6 threaded bar, it needs to be pretty central. The threaded bar will eventually be inside a wooded knob and the 3mm hole will need to go though that too.

So instead of trying to drill the knob with the threaded bar inserted, I decided to drill the threaded bar first, then as per the image below, align the drill with the hole, slide the wooden knob over the threaded bar then drill through the wood to meet the hole.

I used one of those stumpy drill bits, they're designed not to wobble off course, and the drill is a small milling machine fitted with a quaulity chuck, its pretty dam concentric.