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Another drill sharpening question.

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Sacaps

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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.
 

tq60

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For copper you need a sharp but controlled cut.

Sharpen the cutting edge but have the relief behind the edge so it cannot take a deep cut.

Now constant pressure so it stays cutting as copper may work harden.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 

mmcmdl

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Use a taper reamer if you want but it's not neccesary . I think you mean 1/8-27npt though . Just drill the correct size hole and tap it . The tap provides the taper if that's what you trying to achieve .
 
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Sacaps

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Sorry, 1/16-27 NPT. It's not the tap that's the problem. The hole us almost eight inches deep and the copper closes up on the drill binding it in the hole.
 

hman

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When learning about drill bit sharpening, I was told that uneven flute widths can cause the drill to cut oversize. Don't know if that will help you, but you might want to try it. Also - I didn't see any mention of lubricant in your post. Lard oil is supposed to be good. Years ago, I often had to re-drill a ~#60 hole in a copper part because it kept getting closed over by an arc we were generating. Lard oil made a world of difference.
 

mmcmdl

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Try a Guhring drill . Made for deep hole drilling . I'll supply pics in the morning .
 

mmcmdl

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Heres a pic of some Guhring parabolics . Long length and they cut great . Expensive too . This length would get you in 7" or so ( clearing the chips the last 2" ) , and then you could send an airplane length drill down in there to finish . MSC or Grainger most likely sells longer drlls than this set also . I also have " dreamers " that would reach that depth with no problem , but I haven't seen these lately in catalogs .
 

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mmcmdl

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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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RJSakowski

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As to your original question as to sharpening a drill to cut oversized, make one of the lips longer than the other. To create an oversized hole, you will need to drill without a pilot hole.

Another way to bprevent the binding would be to use a two step process. Drilla short distance with and undersized drill and open the hole up with the final diameter drill. Then repeat the process untill full depth has been reached.

195 mm in copper is some serious drilling. I would expect to see the drill wandering. If it is a through hole, drilling from either side would be easier. If you are drilling a passage and perfect alignment isn't an issue,, I would drill to just short of breaking through and use a smaller diameter for the last few mm. Then follow through with the final diameter.
 

markba633csi

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Copper is a very tenacious metal like brass, it tends to grab the bit- need drills with less rake for that
 

Latinrascalrg1

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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 .
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?"
 

P. Waller

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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.

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.
 

Sacaps

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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
 

P. Waller

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That looks like an awful job.
I suspect that you do not have a mill with enough Z to peck these parts?
 

Sacaps

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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.
 

MarkM

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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.
 

T Bredehoft

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Agree w/ Mark: little to no rake on the drill
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'.
 

rgray

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Would a gun drill help. Long depth accurate holes are what they are for.
 

MarkM

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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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