every now and then I have to drill 2 holes in opposite sides of a piece of tube about 34mm OD. It's not amenable to drilling all the way through as they're offset by 3mm along the length of the tube.
Now, obviously, tube being round the first centre-punch mark can be at any arbitrary point around the diameter - the problem is finding the diametrically opposite spot for the second one.
any thoughts?
through as
Block of aluminium, bore to suite tube, drill both holes right through, thread over tube, drill one hole, put pin in, turn jig over, drill second hole.
AWEM
Indexer or rotary table are the most obvious. But a height gauge (scriber) with a pin in the already existing hole (to get a reference), the tube in a Vee-block and a bit of math is another solution.
Nick
Get vee block - drill hole accurately in the bottom of the vee - make up dowel to fit - drill hole - turn over - drop on dowel.
Handy if you also side drill vee block for screw to hold dowel - this way you can have a series of standard size stepped dowels.
-- Regards,
John Stevenson Nottingham, England.
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You could always resort to traditional old fashioned marking out. It is at least worth knowing how to do this.
Set the tube in a v-block on the surface plate. Adjust a scribing block to roughly centre height. Scribe lines on each side of the tube. Now rotate the tube in the v-block, approximately 180 degrees until one of the scribed line lines up with the scriber. Now move the scriber to the other side of the tube. Unless you are exceptionally lucky, or are not doing it right, it will not line up. Adjust the scriber by a *quarter* of the error. Repeat the process until you are satisfied. It should not be too hard to get it spot-on, which is usually good enough.
On or around Sat, 13 Jan 2007 23:27:43 +0000, Charles Lamont enlightened us thusly:
for what it's doing, within 0.5mm will be good enough.
Tried drilling at a 10-degree angle, but the drill moves off-centre and puts the hole out of place, hence drilling 2 holes.
This helps if you have not caliper. But if you should have one: Set tube in Vee-block, touch the top of the tube with your scriber. Read the height off your scriber and substract half the tube's diameter off the reading.
Nick
In article , Austin Shackles writes
If you need to drill at an angle into any surface, you could try starting off with the appropriate-sized slot drill, preferably a short one not long series.
David
On or around Sun, 14 Jan 2007 10:23:43 +0100, Nick Mueller enlightened us thusly:
That's got to be the simplest one yet. wonder why I didn't think of it.
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