Need a perfect 8mm hole - to ream or bore?

[HankMcSpank]

Ok, I'm now actually workjing on the bit that needs an 8mm hole - HELP!

So the story so far. I need a backplate for a pickup wider. I eventually take delivery of 100mm length of 60mm dia round aluminium bar - & I cut 35mm off the end (with a hacksaw - I've a bicep like Popeye now) . I then true it up in my 4 jaw ...it took me absolutely ages - top tip, make sure the jaws are inserted the right way for the size of the piece becuase for all the jaws sorta gripped the piece in their original way...and the piece went in ok, the jaws were almost totally out their holder - their threads hadn't sufficient purchase into the chuck, meaning the jaws were locking up as I tried adjusting them)

Anyway, so the first part went well (turning down about two thirds of the overall length down to about 20mm thereby making a flange type of arrangement (aren't engineering forums great - you get to use all sorts of double entendre sort of words )

All this left me to do was drill a simple hole through the middle of the workpiece - piece of p!ss me thinks - hah, not at all - AAAAAAARGHH. You'd think it would be easy, but what I got was a hole that was all over the shop - and that was starting with a centre drill.

I removed the centre drill & then put a normal drill - the thing bends flexes like a b1itch (not a double entendre - just a bitch) - am I meant to use a special type of drill ...maybe stubbier, shorter?

So anyway, I stop after drilling in to the piece about 5mm, panic and instead of using a 7.5mm drill , (I need an 8mm hole)...I slap in a 6.5mm drill - it bends about like a bendy thing in Bendy Convention....no worries thinks me - I'll kick this holes backside & play my trump card - my Micro boring bar!

So after making up a shoddy boring bar holder (I'm too tight to buy a proper one), I start using that, thinking it would be a dream/breeze - AAAAAARGH. This things starts flexing a litoo - I've had to abort the mission for this evening on account I'm ready to torch my lathe - but what's the score with boring bars - is there a technique I'm missing?

If I get a chance I'll post a photo later.

[Robin Hewitt]

So after making up a shoddy boring bar holder (I'm too tight to buy a proper one), I start using that, thinking it would be a dream/breeze - AAAAAARGH. This things starts flexing a litoo -

Either the tip angle is wrong and it's rubbing below the cutting edge
or
The tool height is wrong, slightly above centre is better than slightly below
or
The cut is too deep for the whip in the shank
or
You haven't got a good grip on it
etc