Making holes in a boiler tube?

[Bo’sunParticipant @bosun58570]

Good morning,

I need to cut two holes, 0.50″ & 0.40″ dia, in a 2″ dia x 20swg copper boiler tube.

My plan is to use a 1/2″ slot drill for the first hole and a 10mm slot drill, followed by a 10.2mm (0.402″) drill for the second.  This will be done on my milling machine with a close fitting wood core.

Is this a good plan, or are there any other suggestions out there?

Clearly I don’t want things to go awry, as the copper tube wasn’t cheap.

 

[JasonBModerator @jasonb]

Step drills work well and there lack of helix makes them less likely to grab

[Roderick JenkinsParticipant @roderickjenkins93242]

End mills don’t cut well on convex surfaces since the first cut is on the centre of the milling cutter.  I cut holes in copper tubes with a step drill or cone drill – much less dramatic than other methods.

HTH,

Rod

[Bo’sunParticipant @bosun58570]

Thanks guys,

A step drill will work for the 0.50″ dia hole, but the 0.40″ dia hole?, unless there’s a 0.40″ dia step drill out their somewhere.

I’ll use a 10mm dia step drill followed by the 10.2mm dia twist drill.

[Chris GunnParticipant @chrisgunn36534]

Bosun, the twist drill may snatch as it goes into the 10mm hole. I would do this in the miller, and lock the quill, and make the cut by raising the bed, if you have this type of miller. If not try not to make the cut freehand as the drill could dive in and distort the hole.

Chris Gunn

[ChrisLHParticipant @chrislh]

Just something which may not matter for your job but using a cone drill on a convex surface will produce a mildly elliptical hole in plan view.

[Bo’sunParticipant @bosun58570]

Chris Gunn,

I was planning to do this in my mill anyway.  I’m banking on removing 0.20mm (slow feed) with a twist drill not being a problem.  Unless anyone knows better.

ChrisLH,

I’m not sure I understand.  Surely, as the cutting tool is round in section, and the drilling operation is perpendicular and tangential, the resulting plan view will also be round.  Or am I missing something?

The plan is to use a step drill, not a cone drill.

 

Lube or no lube?

[JasonBModerator @jasonb]

0.2mm is a file job or a few times round with a de-burring tool. Or can what goes  in the hole be made 10mm? Tinman’s reamer would also take that last 0.2mm off easily

Cone drill will be marginally elliptical as it is cutting a bigger dia at the crest of thetube than it is at the sides. Not usually an issue with a step drill

 

Bit of soluble oil or full fat milk

[Bo’sunParticipant @bosun58570]

Thanks JB,

I haven’t looked yet, but I think my Tinman’s reamer will bottom out on the inside wall of the tube.  However, my small cone drill in a collet tap wrench may be OK.

Yes, maybe I’ll remake the boss that goes in the hole (not enough material to hold to re-machine the spigot).

 

[JasonBModerator @jasonb]

Assuming the boss has a hole in it, just make a simple arbor and retain with a screw so you can turn down the spigot. If it is already threaded then just hold something with a matching thread in the 3-jaw an dscrew it on, even the tap will do

[Bo’sunParticipant @bosun58570]

Thanks again JB,

Why are the simple solutions staring you in the face?

[Nigel Graham 2Participant @nigelgraham2]

Given that a step-drill is the favoured method, and assuming these holes are for bushes, I would make the holes to the nearest step then turn (or alter) the bushes to suit.

Since you’d probably struggle to find an Imperial-sized step-drill these days, and they usually advance in 1mm or perhaps 0.5mm steps – the nearest are:

1/2″ Use the 12.5 or 13mm steps (respectively 0.492 and 0.512 inch)

0.4″ (an odd size anyway): 10 or 10.5mm (resp. 0.394 and 0.413 inch).

[JasonBModerator @jasonb]

Plenty of imperial increment step drills available, go look at ebay, amazon or many others.

[Bo’sunParticipant @bosun58570]

Thanks for all the help guys,

Step drilling worked a treat.  And thanks JB, I used an ME tap as a mandrel to resized the bush spigots.

Now to the silver soldering.

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