(for those not following the saga, I'm trying to drill and ream a 4mm dia 60 mm deep hole - and some other holes - in Inconel X-750)
Well I did my first hole - using a 7mm unpronounceable Frhei bit, which cost £6-odd, and needed sharpening three times - the first time because the carbide tip cracked. I reckon if it didn't crack I could get a comfy inch a sharpening, or maybe 8-10 inches per drill bit. Took four days. Reaming it to 8 mm took less than an hour, even allowing for cooling time.
One down! (I need three, one 8 mm dia, one 6 mm, one 4 mm, all 60 mm deep, cylinders for a very hp oxygen pump).
Encouraged, I tried the 5 mm "universal" carbide tipped bit from Wickes which someone here recommended - and unlike the first time I tried a Wickes bit, it seems to be working. I'm using a rather whizzy speed, maybe 1400 rpm, and a fair bit of force, and limiting the cutting action to a count of ten seconds before leaving to cool.
I think the first Wickes bit I tried before may have been defective, looking at it (the tip fell off) the braze doesn't seem to have wetted the insert properly. I've already done almost 30 mm in an hour with the new one, and am just thinking about to doing the first sharpening - but it don't seem to need it yet, though the shiny bits on the clearance part of the drill tip are getting longer/wider.
The Wickes bits seem somehow better that the Frhei bits - the tip material doesn't seem so brittle - though the famous Frhei braze did keep it's promise of being usable while very hot, and I am being very careful with the Wickes bit as far as overheating goes - I have no suds on the lathe, so I leave it to cool a lot, and then do other things like write this email and forget about the hole, which is what takes most of the time.
The Fhrei bits come with considerable negative rake, unlike the Wickes bits which are straight up-and-down - but I broke the Fhrei bit insert, and didn't break the Wickes bit's insert.
Maybe I'm just getting better at doing it?
(Wickes bits are about 1/4 the price of the Fhrei bits - but I'm only using them in one material, they may differ in different materials)
However the 3 mm hole I am also drilling, for the final 4 mm reamed hole I need, is still a problem - Wickes don't make a bit that size, and the ends of two 3mm Fhrei bits I bought (@ £3 odd ea) have both broken off in different workpieces, and I don't think the pieces are recoverable - not a real problem, I have more Inconel - but I lost two or three inches of good hole.
Got a few 4mm tipped masonry bits which I intend to grind in a little and reshape with no rake - but any other suggestions? I had some luck with a TiN coated 3.5 mm bit, but I can't find them in packets of ten, only as part of sets.
Ta,
bit drunk, bit spaced from pain pills, but hospital finally beckons, for an op next - this - Wed!!! Pain should be gone (after..). No more pills! My kidneys will leap up kiss me.
:) !!!