I ned to drill (& tap) a large hole in a 70mm stainless steel elbow to fit an air temp sensor
However I can't make a dent in it! I thought I'd start small (4mm) and then use a stepped drill to open it up, but when I had it under the
drill press all that happened was the drill bit started to bend.
What sort of bit should I be using? Is there a particular technique?
Regards,
Dave
Was it bending because it was simply sliding round the curve? I wouldn't expect that sort of tube to be very thick or particularly strong, it
would just be a problem to keep the drill bit straight.
Perhaps a centre punch to make a dent so the drill bit didn't stray? And check your bit to make sure it's actually sharp?
[Edited on 30/10/13 by Slimy38]
As above, use a centre punch to make a start mark for the drill bit. Might also be a good idea to use a centre drill to produce a pilot hole for the larger drill bit.
Def center dot it and make sure you use a new / high quality sharp bit
Should go easily enough then
The slowest drill bit speed, lots of lubricant and steady pressure. If it starts to squeal, stop, you've blunted the drill bit and are hardening the stainless.
Cobalt 5% drills are recommended and slow drilling speeds.
Cannot see you tapping a thread and it being any good without you having a bung welded in.
I,d be inclined to put it into the side of the top hat, loads of meat to hold things there.
quote:
Originally posted by mark chandler
Cannot see you tapping a thread and it being any good without you having a bung welded in.
I,d be inclined to put it into the side of the top hat, loads of meat to hold things there.
two things - when I was making sumps in stainless I bought specific stainless bits (cobalt I think), and also just the right lube. No amount of
punching and standard drills will make a dent - they'll just skid right off. If you don't use a proper cutting oil (that doesn't break
down under the tremendous pressure at the cutting head) then things will blunt quickly. My local nuts and bolts and stuff shop sold the cutting oil in
an aerosol for about £10. WD40 won't cut it (ahem).
Then, you need to buy a stainless tap. I couldn't get anywhere with a good conventional tap, and I found there are specific stainless taps. Cost
me about £5 from ebay.
Doesn't stainless work-harden when you drill it too quickly/get it hot?
I remember we found this out after one guy went through 3 drill bits trying to bore a hole on a lathe in a piece of stainless bar.
Good quality bit, lube, slow and steady!
I would be inclined to sub this out to a machine shop. A guy near me does lots of small jobs for little money.
Thanks all for the advice. I've gone off on a tangent instead. On the back of the hat (you can just see it) is another threaded hole which is
larger than the 3/8" NPT of my sensor. However digging through the garage I found a brass adapter which fitted. I needed to put a small notch
in the bonnet to clear the wiring, but I can now get the bonnet closed 
However I've got this thread bookmarked for the next time I'm
thinking about drilling such a hole.
Regards,
Dave
quote:
I found a brass adapter which fitted. I needed to put a small notch in the bonnet to clear the wiring, but I can now get the bonnet closed
Why not put the sensor in the aluminum alloy airbox?
quote:
Originally posted by britishtrident
Why not put the sensor in the aluminum alloy airbox?