Drilling a long way through steel.

[WolfieParticipant @wolfie]

I have to drill a hole through a 2 inch block of steel. Is there anything I need to know or do I just go for it?

[WolfieParticipant @wolfie]

[JasonBModerator @jasonb]

Ideally use your mill with the vice fixed to the table, spot or centre drill then if you have one start with a stub drill then change to a standard jobber length drill. Back the drill out often to clear swarf and use some form of cutting fluid.

What dia are you looking at?

J

[Clive HartlandParticipant @clivehartland94829]

As jason describes and depending on the diameter use a series of drills, say if its 10mm dia. go through first with a 5MM drill.

Clive

[David LittlewoodParticipant @davidlittlewood51847]

Wolfie,

Jason's question is a good reminder that it helps if you give us all the facts with your quesion. Is it ordinary mild steel? What diameter hole do you wish to make? Are you proposing to do it on a pillar drill, a milling machine or a lathe? How critical is the location and diameter? Deep drilling (say more than 5 diameters) of small holes can be tricky.

David

[WolfieParticipant @wolfie]

Yeah sorry. It’s standard mild steel and the hole will be 8mm. I plan to do it on the mill with a 4mm pilot hole.

[mgjParticipant @mgj]

Gets a lot easier with a sharp , preferably 4 facet sharpened drill especialy for the pilot.

If you haven't got access to that, try buying a split point drill for the pilot – once you have a straight hole, the full size will follow it.

2" deep x 8mm. Wouldn't bother with a pilot on a mill – centre drill, lots of coolant and go with a 4 facet/split point. Just don't let the swarf build up (and jam the flutes) – that should keep even an ordinary drill pretty straight.

Why the split point/4 facet geometry – because it has a point on the tip rather than a chisel edge which tends to stop the drill from wandering.

Edited By mgj on 18/07/2012 22:09:40

[David LittlewoodParticipant @davidlittlewood51847]

Wolfie,

OK, shouldn't be too difficult. Make sure the 4mm drill bit is in good condition (and not resharpened) – it is important that the flutes are equal in length. Give a good start with a centre drill; follow up with a 4mm stub drill if you have one but don't worry if you haven't. Withdraw every few mm and clean the flutes, add some more cutting fluid. When you run out of flute, change to a 4mm standard drill bit and proceed likewise. If that runs oout of flute length – and you probably will, a typical 4mm jobber drill has a flute length of only 40-43mm – then you have a number of choices. Use a long 4mm bit, switch to a 5 or 6mm drill, or go straight to an 8mm drill; depends on how rigid your milling machine is. I think I would go for the latter.

If you need the hole to be dead on size and a nice smooth bore, only drill to about 7.8mm and finish the hole with an 8mm reamer (if you have one). Use with half the drilling speed or less, well lubricated with cutting oil, and keep rotating the reamer in the cutting direction as you withdraw it, otherwise you risk compromising its sharp edges. You didn't say what the hole was to be used for so you'll hae to decide that for yourself.

David

Edited By David Littlewood on 18/07/2012 22:14:59

[Ian S CParticipant @iansc]

Another name for a four facet drill is a crankshaft drill, used for drilling the oil ways in crankshafts, so go with mgj. I perhaps should not have, but I have drilled full depth to about 1/4" of the full length of the drill, not much holding in the chuck, if I'd had a long series drill I'd have user that. Ian S C

[mickParticipant @mick65121]

there's a distinct chance that a 4mm drill will wander when drilling through 2'' MS Why not double drill using a 7.5 first and follow up with the 8mm which will give you a size and much cleaner hole

[WolfieParticipant @wolfie]

Thanks all, mission accomplished with centre drill, 4mm and 8mm in turn!

[Author]

Posts