Gallery, Projects and General > How do I??
snapped centre drill
Stilldrillin:
That's quite true Sparky!
Anyone who has any drilling finesse. Will feel the drill chatter, as it opens out the small diameter, before settling into making it's own hole......
David.
ieezitin:
Spotting drills makes a concentric hole to drill through the zero axis of the job. Center drills are for prepping for a job between centers giving the lead angle for the taper nose. A two for one. The end of a center drill is a spotting drill.
spotting drills give the concentric axis and taper for the drill to follow, a drill bit will follow an askew lead if off center, hence why spotting drills are short or stubbed, a sturdy force over less length.
QED.
Anthony.
sparky961:
--- Quote from: ieezitin on December 06, 2015, 07:50:34 PM ---The end of a center drill is a spotting drill.
--- End quote ---
While technically this may be true, this statement strikes me as a bit misleading to those with less experience. The end of a centre drill is way too small and fragile to use for every day spotting of hole locations. Not to mention that if you penetrate the material deeper than the cutting lips of the small point, you've defeated the purpose of spotting/"centre drilling" in the first place.
Does it work? Sure it does. I'll even use a centre drill to spot holes if it isn't too critical and I have one sitting right there beside me.
Would I trust it for anything I wanted to be absolutely "spot" on? Nope.
But I'm digressing horribly from the original topic of this thread. In this instance the best reason not to use a centre drill is that you're making an operation more risky than it needs to be. If you break off the tip of a centre drill occasionally, that's par for the course. Been there, got the T-shirt. If, however, you break off the end of a spotting drill in a part..... well, worrying about the drill wandering off a few thousandths this way or that is the least of your problems.
An option I favour that hasn't yet been mentioned is to use "stub length" or "screw machine" drills. They are much, much more rigid than their "jobber" counterparts. Most of the time you aren't drilling more than a few times the diameter anyway so the extra length is just extra length. They're stupidly expensive to purchase, but making your own set by cutting a regular length set is excellent practice in drill bit sharpening. With care, properly sharpened stub drills can be used on their own for all but the most critically located hole.
awemawson:
Don't forget that if you do cut jobbers drills down to stub drill length, the diameter won't be accurate as drills taper slightly to create clearance. They will cut slightly under size.
Arbalist:
--- Quote from: sparky961 on December 06, 2015, 11:04:35 PM ---
--- Quote from: ieezitin on December 06, 2015, 07:50:34 PM ---The end of a center drill is a spotting drill.
--- End quote ---
While technically this may be true, this statement strikes me as a bit misleading to those with less experience. The end of a centre drill is way too small and fragile to use for every day spotting of hole locations. Not to mention that if you penetrate the material deeper than the cutting lips of the small point, you've defeated the purpose of spotting/"centre drilling" in the first place.
Does it work? Sure it does. I'll even use a centre drill to spot holes if it isn't too critical and I have one sitting right there beside me.
Would I trust it for anything I wanted to be absolutely "spot" on? Nope.
--- End quote ---
Agreed. I've had holes go off centre on very small parts in the Lathe by starting holes with a centre drill. Using a spotting drill proved far more accurate for me so I'm not sure the point is the same. Many folks, particularly newcomers don't know what a spotting drill is though much less have several in the cupboard. I should add that unlike some I don't use mine for deburing or countersinking, I use a countersink for that!
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