Drill hard cast iron 1.7mm 10ba clearance

[Peter VennParticipant @petervenn53369]

I have a casting of the Chimney on my Adams O2 which I’m building and it is fully machines and ready to mount on the smoke box. However I have found it impossible to drill the base of the casting to accept 10 BA bolts to hold it on. ordinary HSS bits don’t touch it and I ordered some cobalt 1.5 mm and 2 mm drillbits but they don’t seem to want to touch it either!!

Does anybody have any suggestions about how to soften the casting enough to get a drillbit through it?

[bernard towersParticipant @bernardtowers37738]

Put it in your BBQ

[JasonBModerator @jasonb]

Fire or BBQ, get it to red heat and hold for an hour or two and then let it cool SLOWLY in the ashes overnight.

[John HaineParticipant @johnhaine32865]

If it’s that hard I wonder how it was machined?

[Anonymous]

Use a carbide drill.

Andrew

[BazParticipant @baz89810]

I agree with Andrew, use a carbide drill but belt and braces job, give it a good cooking in the BBQ as well. If it doesn’t work you will need to find someone with a spark eroder.

[John Haine]

On John Haine Said:

If it’s that hard I wonder how it was machined?

Often the way with castings it is the thin parts like the skirt around the bottom that cool too quickly and become hard. The top having a machining allowance on the thicker flange would not have suffered the same problem. And milling & turning can be done with carbide inserts that most workshops have to hand, it is drilling and tapping where the usual HSS has a problem.

Couple of photos to illustrate the problem, the darker areas around the edge and in the corners are where the metal is hard as it is the extremities that cool fast and chill

Flange faced with carbide but how to tap it?

With the use of heat, soft enough after treating.

Another example the hemi head on this cylinder end was chilled around the thin edge, the rest was OK. Just about managed to turn it with GT inserts, swarf was a long string of fine blue swarf not the usual swarf from CT until I got to the non chilled area

If anyone wants to read the science behind it then this post on MEM is quite informative.

 

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, when I had a Parkray, I used to do what JasonB has said, and letting it cool slowly overnight in the hot ashes, always made cast iron nice to machine. Although white cast iron doesn’t, but I wouldn’t think your chimney is made of white cast iron.

Regards Nick.

[Peter VennParticipant @petervenn53369]

Thanks to all who contributed to this thread. There are clearly two opinions: one is to heat treat the casting and the other is use a carbide drillbit. I have now sourced carbide drill bits from MSC engineering and I spoke to a girl in the technical department today who was incredibly helpful and I discussed the problem with her. I’ll see how I get on when the drillbits arrive but I’m aware that I need a rigid set up to drill for drilling because they are very brittle.

[JasonBModerator @jasonb]

And ideally a carbide spot drill to get a good location for them to start cutting rather than skidding about on a cast surface.

[bernard towersParticipant @bernardtowers37738]

Its all very well to get to get carbide drills but what if you need to tap holes????

[Anonymous]

The title says 1.7mm 10ba clearance; so no requirement to tap and a carbide drill will be fine.

Andrew

[bernard towers]

On bernard towers Said:

Its all very well to get to get carbide drills but what if you need to tap holes????

It’s lucky he wants a clearance hole!

 

Jasons point about the drill skidding around is important.  Drill needs to go straight in perpendicular – or breakage is likely to occur.  With it so hard and quite tiny, I might well have invested in a carbide spotting drill if I was doing it.

[JasonBModerator @jasonb]

Thats why cooking your castings works for all occasions, Carbide taps can be had but very expensive.

On the recently completed Clarkson, having heard that their castings had a reputation for being hard I did a couple of test cuts on some chucking spigots that seemed OK with carbide but a couple of other thinner parts seemed hard when given the old file test so I played safe and cooked the lot and had no problems with HSS drills, taps and the odd hand ground special shaped HSS toolbit, though most turning and milling was done with inserts.

A sack of scrap wood was cheaper than a single carbide drill bit and I would have needed a couple of different sizes plus a means to tap holes. Too small to thread mill on the CNC.

[Peter VennParticipant @petervenn53369]

Here is the promised update on drilling the casting.

I ordered 2 pure carbide drillbits from MSC Industrial Supplies in the West Midlands and they arrived today. Wow!! What a difference! As soon as I touched the casting, it just went straight through all the holes that hadn’t really got started with the other drillbits like a knife through butter. My thanks to everybody who gave tips, and at least it saves sticking it in the barbecue (we’ve actually run out of Charcoal). Also my thanks to Nicole Clough at MSC Industrial Supplies who gave me some technical advice and the whole attitude of that firm was so helpful and I thoroughly recommend them!

Onwards and upwards!!

[BazParticipant @baz89810]

Pleased to hear that it all turned out successfully for you Peter.

[David George 1Participant @davidgeorge1]

Glad it worked out well for you. It is great when members let us know if fail or succeeded.

David

[old martParticipant @oldmart]

You have to treat solid carbide drills with great care as they are much more brittle than hss, but not only will they cut through hard cast iron, but through case hardening and the holes are exactly to size, no reaming required. Never use one freehand, or on unclamped work, especially in a drillpress.

[MacolmParticipant @macolm]

I find a diamond or carbide point (from Aldi or Lidl set, etc) makes a sufficiently good spot to centre a small carbide drill, even if only run at drill press speeds. It usually only need to be 0.1mm deep, just enough to be “uphill” all round.

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