Drilling through pipe

[nigel jones 5Participant @nigeljones5]

[nigel jones 5Participant @nigeljones5]

I often have to drill a hole at exact opposite sides in pipe ( copper boiler shell ) up to 6" diameter. No matter how carefully I set everything up – clamped to the mill bed – I find it impossible to enter the pipe at one side and drill on through to the other side without it going skew to a fair amount. Drill is 5.5mm, use a good countersink and careful set up. Any ideas on how to improve things?

[Clive HartlandParticipant @clivehartland94829]

I would think the best bet is to make up a 'Jig' ring and accurately drill the two 5.5 holes and then offer it up to the boiler and drill one hole and put a peg in it and then drill the other.

Clive

[HopperParticipant @hopper]

I don't think there is much you can do to stop a 5.5mm drill wandering over a length of 6" or so. That's a very long, thin and inherently flexible drill bit. As Clive suggests you might be bettor off to drill it as two individual holes in two separate set ups using a jig.

[JasonBModerator @jasonb]

Don't think I would try and drill right through.

Mark horizontal ctr lines with a height gauge and distance from end for each hole then drill in from each side. Could tweak it a bit more by doing 5.0mm from each side then after the second hole change to your long series 5.5mm an run right through.

[vintagengineerParticipant @vintagengineer]

I would do as described below, except I would ream the hole to size.

Posted by JasonB on 02/07/2017 07:35:40:

Don't think I would try and drill right through.

Mark horizontal ctr lines with a height gauge and distance from end for each hole then drill in from each side. Could tweak it a bit more by doing 5.0mm from each side then after the second hole change to your long series 5.5mm an run right through.

[Brian WoodParticipant @brianwood45127]

Fizzy,

​I would go a bit further and state it is very nearly impossible to get a drill started accurately on the inside of a curved surface without it wandering about to a position it wants to settle into before cutting metal, especially a slender one.

​Clive Hartland is spot on with doing things better, but with correct alignment for the first hole and reliable 180 degree rotation to a new locked position, I don't think you will need a jig. You will though need a decent centre drilled hole to open up to size.

Regards
Brian

[Ian PParticipant @ianp]

If this is part of a boiler then presumably high precision is not really essential, but one simple way of finding two points diametrically opposite each other is to,

Get a long strip of paper and wrap it once round the outside of the tubs so one end of paper overlaps the other. keep the paper taut and use a scalpel to cut through both thicknesses so you end up with a strip the exact circumference.

Fold the paper strip in half with sharp crease. When you place the paper back on the tube with the cut ends butting, you now have two clearly defined indications of the 180 degree points. The axial position can be determined by measurements from the tube end (assuming its cut square).

I would think its easily possible to mark the two point to within a few thou.

Ian P

[nigel jones 5Participant @nigeljones5]

Thanks all – good to know its not me being crap as usual….plenty to ponder

[Ed DuffnerParticipant @edduffner79357]

Hi Fizzy,

Could you perhaps make a clamping jig a bit like a collet block with flat sides to enable drilling and maybe the top and bottom for other hole features? Just a basic square-shaped clamping frame, from MDF or plywood?

Ed.

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