How to keep small drill bit from wandering?

You also probably want to use machine screw length drill bits, not the usual "jobbers' length", which are longer and more likely to deflect.

Not sure that you should start with a very small bit, either, as they are more flexible, and thus more likely to wander. I would use the recommended center drill (or a spotting drill) to define the point, then switch to a drill of the desired final size.

There can be inconsistencies in cast iron, which will induce a drill bit to wander as well, and a long, small one is more likely to do so than a short fat one.

You would be a bit better off drilling in a lathe, as the rotating workpiece tends to even out the wander somewhat.

Or set up a fixture to drill through a drill bushing to stabilize the bit -- and drill *one* workpiece at a time. The longer the hole, the greater the chance that the bit will wander out of spec. You were drilling through two workpieces in series? I'll bet that the hole which was off center the worst was the second piece below the first in each case.

Yes -- accumulated chips in the flutes can sometimes induce hole wander too.

Good Luck, DoN.

jt wrote: I was trying to drill some 3.3mm holes in a bit of cast iron a bit less than 1" thick (clip) I started with a much smaller bit, (clip) ^^^^^^^^^^^^ I think you may have made a mistake in pilot drilling with a much smaller bit. When you apply drilling pressure to a very small bit, you can easily cause it to bow, so it will start to wander. When you follow with a larger bit, it will take the path set up by the small bit. I would suggest that you drill to the full tap-drill size on the first pass. Cast iron is easy to drill, and if you take it slow, you can probably get a straight hole.

I think all the other things you did to line it up were good.

Or a "spot drill"

Gunner

"What do you call someone in possesion of all the facts? Paranoid.-William Burroughs

Hi, was your drill bit new?

A used bit can sometimes develop more wear, or a chip, on one flute and this would cause the bit to tend to walk off.

Lewis.

Don't try to do several layers of the metal when drilling. You will quickly wander and the lower pieces will be off badly. First, clamp the work to where the hole needs to be put. Center drill and then use the full sized drill without moving the piece. You will have a possible chance at that point of the drill actually going fairly straight but you never know. Better, if you really want to do the job with a really straight hole is to use a gun drill rather than a regular jobber's bit.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works evevery time it is tried!

Typical cast iron has anomilies in it, such as pockets of slag, core sand, and variations in hardness that can "encourage" the bit to wander. Twist drills are almost never used for deephole drilling because of their tendency to wander.-Jitney

I'd say to drill from the mating face on each part separately, to the outer face, not from one outer face through to the outer face.

And like he said, center drill, then full size drill. No intermediate drills, or if you use them, not full depth, very shallow. Cast iron has a skin that can deflect the drill. The stiff center drill will get through the skin.

Yours,

Doug Goncz, Replikon Research, Seven Corners, VA Unpublished work Copyright 2003 Doug Goncz Fair use and Usenet distribution without restriction or fee Civil and criminal penalties for circumvention of any embedded encryption

On Sun, 13 Jul 2003 23:04:18 -0300, "jt" wrote something ......and in reply I say!:

Apart from all the other stuff, I would suggest placing the drill bit as deep in the chuck as you can, then gradually extend it as you go.

Not recommended practice all round, bit in the "RAG" (rough as guts) engineering side of things, it may do the job.

Nick White --- HEAD:Hertz Music Please remove ns from my header address to reply via email !!