same hole again

I need to drill and ream a 4 mm dia 55 mm deep hole in Inconel X-750, which is hard as something-or-other, a lot harder than even masonry nails though,
or perhaps just plain tougher as well, though it can just about be machined with newly sharpened HSS tools. Mind, I lose about 1/10th of an inch of parting-off blade every time I part off a 12 mm rod of the stuff, it needs sharpening twice, and facing one end of a 12 mm rod blunts a tool. But it's doable.
This darn hole doesn't seem to be doable. I have tried HSS, cobalt HSS drills (which it doesn't even deign to sneer at), Wickes carbide tipped "universal" drills (about 3 mm deep, after sharpening - the original drill didn't cut at all - then the tip fell off), TiN (which got me about 5 mm deep before the coating went) and have broken two cheap solid carbide drills (and two brand new centre drills).
Help! Any suggestions? Drilling in the lathe, coolant, anything else?
A good tough solid carbide drill is about the only thing I can think of that might have a chance - somewhere around 1/8" - 3.5 mm dia, and longish, though at a pinch a jobbers drill would do - anyone know of a supplier?
Any other tips for working with metals from hell?
--
Peter Fairbrother


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which
though,
machined
it's
drills
that
I thought Inconel was a copper nickel alloy, is this correct ?
drilling any hole more than 10 diameters deep is a challenge
Some materials harden as they are drilled ( especially stainless steels ), with these materials coolant or at least flooding with cutting oil is essential, and the feed rate must be kept high enough to produce a continuos swarf.
For a 4mm hole in a tough material you may only be able to run at 500 to 700 rpm if your not to burn out the drill.
If you do burn out the drill you will probably have hardened a "cap" of material at the bottom of the hole. The only way to deal with this I have found is to re sharpen the drill and then take a hefty / brutal " peck" at the hole, this should break up the cap, but it will blunt the drill at the same time.. :-(. So after the peck you need to re sharpen the drill *again*. Don't try pecking with a carbide drill as you could easily snap it...
I use insert tools for all my stainless steel turning work, the exception being parting tools... for now. I've got a holding blade, but no way of holding it on a T2 quick change tool post... ( Christmas ? :-) )
--
Jonathan

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Have it done on an EDM machine... Make friends at the local university...
Joules
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On Sat, 17 Dec 2005 03:11:00 +0000, Peter Fairbrother

It's a long shot with no guarantees, but I've had success in drilling HSS with Frhei Titanium Carbide tipped drill bits. The trick is to use very high speed and feed fierce enough for the swarf to exit at near white heat - at least 2000 RPM for a 4mm drill. The hard part is the initial penetration into cold material. It helps to make an initial indentation with a diamond burr so that the drill immediately starts to cut at a sensible radius.
If you're through hole drilling the workpiece needs backing with something of reasonably similar hardness. Without this the tip gets damaged as it suddenly breaks through.
Frhei are located in Cornwall Tel 01209 843654
Jim
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Gents,
We have used the Frhei bits to drill Inconel at work with nothing more than an electric pistol drill. Drill as per stainless in the instructions, and don't be tempted to drill a pilot and open it out.
Regards,
JohnP
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which
though,
machined
it's
drills
that
Slow speed, high feed and lots of lubricant. X-750 work hardens very quickly and a slow feed will just blunt the drill. However it isn't easy leaning on a small drill hard without breaking it. A drill jig guide would help as would starting off with a stub length drill until the hole is too deep for it. -- Dave Baker
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I would use a carbide drill, at very low speed (100-200 rpm) with heavy pressure, short pecks and constant supply of coolant. When drilling hard, or tough metals it is a good idea to grind the tip off centre, causing the hole to be slightly oversized, otherwise the flutes tend to wear down and you end up with a gradually tapering hole in which the bit will then jam and break.
I have drilled many holes in hardened steel (52-60Rc) using suitably sharpened, cheap carbide tipped masonary drills. These also have the advantage of not having any flute in contact with the sides of the hole.
I wouldn't put much hope on reaming such a deep hole properly, without a decent solid carbide reamer.
If you are in the South bucks area, I can probably get something done for you this week.
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I'm in Chalfont St Peter. For future reference and possible assistance (either way) where are you ? -- Dave Baker
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I'm just down the road from you, High Wycombe.
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