How well mounted is your drill press? How little throw are you using between the chunk and your work piece?Are the two flats on your workpiece precisely parallel? Are they precisely normal to the axis you're trying to drill?If the flats are not normal to the axis, then you need to make a jig in which to mount the workpiece onto the drill press' baseplate.
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Illustrating Kelseymh's pointYou could also start with a smaller drill and drill a pilot hole. Then go onto the larger drill.Make sure the drill is correctly sharpened with both cutting edges being equal.make sure the bearing in the drill machine are good with no play.
Maybe too much force in drilling is causing the bit to deform and drill slightly curved? Match cutting speed to the material.
can u explain the bit "match the cutting speed"
eg. http://www.wisc-online.com/objects/ViewObject.aspx?ID=FAB1102 or http://en.wikipedia.org/wiki/Speeds_and_feeds or http://its.fvtc.edu/machshop1/drillpress/cutspeeds.htmThis one summarizes in a table: http://www.fnal.gov/pub/takefive/pdfs/Drill_Press_Speed_Chart.pdfEvery material should be cut at a different rate. Chances are good your drill is going too fast, as wood can go much faster. Slowing it down a bit and maybe adding lubricant (I use bar soap), ought to help.
Here's a picture of a V block jig for drilling the parts.
What's the surface finish ? It looks like it might be a cast component.
actually surface finish was to bad so v do milling to get the flat surface and than drill as the part is smal(2 cm),while mounting the part workers do mistake(some 1 or 2 deg shift takes palce) so we get drilling errors.. so we want to eliminate this problem for ever,using some error profing techniques...like sensors or some thing...plz help us to resolve this problem..
This needs a jig to hold it then. Can you post a picture of the part ? A jig with 4 points of contact, and a clamp might be the best way to do this.
There could be a couple of reasons your hole isn't square to the end face.1) The end face is not perpendicular to the length of the bar2) Is your drill press' table perpendicular to the chuck?You shouldn't need a jig to hold this, a vice with a notch should suffice so long as 1) and 2) are correct.