Another drill sharpening question.

mmcmdl said:
Here's some dreamers . .250 has over 8" of flute length . Not sure who has them these days as I haven't looked for them . Perhaps someone on here has a resource .
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At first i thought you mistyped the word Reamers but after the second post im now not so sure and am starting to think maybe you are referring to a "Combination" Drill and Reamer Bit AKA a "Dreamer?"
 
Sacaps said:
I'm trying to drill a water jacket into a piece of copper. The hole diameter is dimensioned at 6mm and plugged with a 1/6-27 NPT brass fitting.
The depth of the hole is close to 195 mm. As the diameter is not critical, I start with a .250 diameter drill. (Close to tap drill size for the plug) and gradually step down sizes the deeper I get. I eventually have to insert my 5.2mm drill at the 140 mm mark. The problem is the drill drills undersized. As it goes in the copper will actually grap and break the drill. Now we have a scrap part.
How does one go about sharpening a drill so as it drills oversize?
Thanks.
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Drill the holes to diameter or as large as possible, tap holes when finished.
I realize that copper is often a difficult material to tap but many thousands of holes are tapped in copper every day.

As far as your original question about making a drill bit make a larger hole why not just start with a tool that makes the desired sized hole?
Would this not be easier.
Also do not tap a tapered pipe thread any further then the gauge line on the plug gauge.
 
Thanks for the responses. It is not a matter of just starting with a proper size drill. I find that the copper tends to close up on the drill and bind as the depth increases. I have been setting the quill stop and only increasing the depth buy a fraction of a millimetre each time before pulling the drill out of the hole and removing the chips. Lots of cutting oil and patience.
Attached are the two lumps I have to drill water jackets through.288260
 
That looks like an awful job.
I suspect that you do not have a mill with enough Z to peck these parts?
 
Hanging the parts off the side of the mill clamped to an angle plate. Must raise and lower the table when I run out of Quill travel.
Good fun.
 
Get rid of the rake on your drill if you can. Dont just set your quill stop then drill. Keep tension on that quill stop as you drill so just rotate your quill stop as you keep tension on it. The flutes are acting like threads being pulled into the part then pulverises itself. Let her fly with the Rpms.
 
markba633csi said:
Agree w/ Mark: little to no rake on the drill
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Rake is the angle behind the cutting edge of the drill.

Very carefully dress this edge until it's parallel the long axis of the drill. Flat, not concave. Only needs to be a few thousands, more than the amount of cut. Then the bit won'd 'dig in'.
 
Would a gun drill help. Long depth accurate holes are what they are for.
 
I wonder also if you didn t step down your drill size not giving your drill a chance to shear the cut. Have you tried the power downfeed?
 
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