Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.
Rich_Carlstedt wrote:Somehow most machinists use center-drills for starting holes. Center-drills are for use of a dead or live center --period...
Harold_V wrote:I'm not suggesting that using a ball end mill doesn't work, but I'm also not about to agree that center drills are not for starting holes.
Like Harold, I must challenge this.
I have been machining stuff since around 1960 and was taught to use a center drill to spot a hole. No one, including the toolmakers I frequently worked with in the 1970s and 1980s, ever suggested a ball mill would be a better tool for the purpose. No question a ball mill can help one "move" an out-of-position hole. However, a ball mill offers no greater hole spotting accuracy than a proper-sized center drill in the same machine.
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Music isn’t at all difficult. All you gotta do is play the right notes at the right time!
The only times I use a centerpunch, and that's all I use, is with a handheld drill or the cheapy drill press. Just those places that +/- a 32nd, or more, doesn't matter.
Mr Ron wrote:This brings up a related thought. When center punching prior to center drilling, do you use a p***k punch alone or follow up with a center punch?
These days, I exclusively use an optical center punch, unless working with thin sheet metal. The one I have creates a sufficiently deep mark that no additional punching is necessary prior to drilling. The days when I could accurately spot a hole with a conventional center punch are long gone. Something about being old and having an old man's vision.
I use a prick punch on sheet metal so I can get adequate punch depth without seriously distorting the part.
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Music isn’t at all difficult. All you gotta do is play the right notes at the right time!
Mr Ron wrote:This brings up a related thought. When center punching prior to center drilling, do you use a prick punch alone or follow up with a center punch?
I sometimes use a prick-punch to mark the crossing of scribed lines and then follow up with a punch because I can reliably find the crossing-point with the prick-punch by feel. This gives me an intermediate level of accuracy between wood-working quality and +-.001". For the latter, of course, scribed lines are just a sanity check so there is no point in punching.
Mr Ron wrote:This brings up a related thought. When center punching prior to center drilling, do you use a prick punch alone or follow up with a center punch?
The school of thought in this regard is that a prick punch has a finer point, as well as a diminished angle, so location is easier to establish, with greater precision. Once prick punched, it is considered acceptable practice to then center punch, which broadens and deepens the location, which it is assumed would then make a drill start on location.
I am somewhat unusual in that I never use a punch for starting a hole unless it is hand drilled. It's too easy to lose location by punching. If one hopes to achieve precision and is at the mercy of working to a layout, it's much easier to simply use a wiggler with a sharp point. That's assuming one can clamp the work piece. Pick up the location with a wiggler, then use a spotting drill or a center drill to start the hole. With modest care, one can hold locations within ± .005".
I rarely use a drill press. I prefer to use my BP for drilling holes, so I use the screws, and do not need a layout.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
Due to the split point, yes, you likely can rely on the drill to cut on position, especially if you choose screw machine drills. They're stiff enough to drill where they're pointed. I am not suggesting that they would satisfy critical tolerance work---but you should be able to expect reasonable locating.
Don't know if many of the readers have ever considered what the web of a drill does, but it (normally) doesn't cut. It presents a drastic negative rake to the workpiece, which displaces the metal (under the web), which is then removed by the lips. That raises cutting pressure considerably, but that issue is eliminated with a split point or a pilot hole.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
We are talking about the sharp point wiggler, not the ball end edge finder, right?
Is the pointy wiggler used rotating or still?
I center the point by pushing with rod until i feel no vibration and it actually seems to resist being offset once the center is attained. How do you do it?
We are talking about the sharp point wiggler, not the ball end edge finder, right?
Correct!
Is the pointy wiggler used rotating or still?
Rotating. That's the only way you are ASSURED that the tip is the centerline of the spindle. If you get it running true, then stop the spindle, so long as you don't bump the tip it makes no difference. The exception to that is if the tip is eccentric to the shaft, at which time you may not have the tip dead on center, which would be verifiable if it was spinning.
I center the point by pushing with rod until i feel no vibration and it actually seems to resist being offset once the center is attained. How do you do it?
I use my finger. It's perfectly safe to do so unless you're a clutz and make contact with the sharp point. Been using a wiggler for almost 60 years now (same one) and it has never happened.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
Many of the machining texts I used when in high school showed using a center drill as the start of a precisely located drilled hole. They also showed using a cape chisle to relieve the side of a center drilled hole if the center drill was mislocated. Relieving the side of the center drilled hole was supposed to cause the drill to come back to the desired location for drilling the hole.
I wasn't until I started programming CNC that I used 90 degree starting drills for the purpose of locating the drill start, but also to programmed depth to leave a chamfer on the finished drilled hole.
