Drilling and tapping cast iron.

I'm fitting an aftermarket injection system to the old Rover which uses a lambda sensor. The cast iron exhaust manifold has provision for this (for US versions fitted with a cat.) but isn't drilled and tapped on UK ones. I don't have the required tap, and maybe not the tapping size drill either. Is it easy enough to do - I do have a pillar drill - or is it best left to a workshop?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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London SW

Shouldn't be a problem with the correct tapping drill size - pilot drill first - lowish speed.
(ex-toolmaker)
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Drill with a sharp HSS bit. Tap carefully; back off and cut again if there is any sign of binding. Cast iron does not need lubrication, but, if you have coolant on your machine, flood cooling does help.
Colin Bignell
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So buy the necessary drill and tap. You might only need a taper tap, as you can stick the whole length of the tap through into the manifold. Buy the drill, as drills are cheap and exact tapping drill sizes are a good aid to getting a good thread. If it's some archaic Rover thread, try a model engineering supplier like Chronos. Ideally a thread in CI will be something coarse pitch like Whitworth, UNC or the rare metric coarse series, but I guess you're stuck with whatever the sensor uses.
It's usual to tap in a back-and-forth motion, but this is just to break the swarf up and if the CI is doing that anyway, you might not need to.
Use some cutting fluid too. It's not essential on cast iron (the free graphite lubricates), but it doesn't hurt when doing awkward bits by hand. A drop of engine oil will do (and you have some confidence there's no lambda-unfriendly additives in there).
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In article

It's a brand new wideband Bosch sensor and I'm pretty certain it's an M18 thread. Not sure my pillar drill will take a drill that size - unless one of those reduced shank types.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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PS - If you don't know the tapping drill size, say what thread it is and I'll look it up in Machinery's Doorstop
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Dave Plowman (News) wrote:

I have all the taps and drills if you get stuck. Whip it round and we'll can do it on the milling machine.
--
Dave Baker



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Thanks very much for the offer, Dave. Remind me of where you are?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Cast iron is relatively easily drillable and tappable, but IIRC you need a very hard steel bit, done slow with a lot of lubrication as cast iron will shatter, not flow, if peak stresses are exceeded.
In other words, do it in very easy stages..
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