What sort of drill bits, and where would I find them, to drill flat bottomed holes in steel?  I suspect that there is some sort of machinist bit which will do this but I have never had any training in this skill and can recognize a lathe 4 out of 5 times and a milling machine 3 out of 5.

 

Flatly,

George M. 

I assume you mean in steel, not wood.

 

Center cutting end mills will "drill" a flat bottom hole, but they aren't the greatest thing on average. If I had to use one, I'd 1st drill the hole with a standard bit to remove most of the material in my drill/mill, then change over to the center cutting end mill and "dill" out the last little bit.

Do a search on "lathe counterbore"  and I think you will find several options that could be used after drilling most of the hole with a standard bit.

I have a book by Alexander Weygers where he makes a bit to flatten plier bosses where the two halves meet.  It looks like a wood cutting paddle bit with a center pilot.  He made it out of mild steel with case hardened edges. 

 

He also had one using a large bolt into which he filed flutes on the top face.  The hexagonal corners ended up the outside diameter edges of his "bit".  Again, he case hardened it before use.  One neat aspect of the whole thing was that he used the drill press to turn the bolt head against a file clamped in a vise.  That way he was able to perfectly flatten the face, and reduce the bolt diameter to what he wanted.  Slow speed and correct file orientation appear critical here.

 

I've been meaning to give it a try some time. 

May I inquire as to the reason it matters if the bottom of the hole is flat?

Milwaukee, end mills. We use them in mag based drills to fit engineered steel parts. Very common and you can usually get them at welding supply outfits. They are carbide inserted and a bit pricy but they work slick.

Peter

If it is a standard size hole that could be started with a fractional drill, drill to the depth using your depth stop(so you do not go too far), then go with the same size flat bottom end mill.  Again, use the depth stop.

Dear Ronin,

 

Actually, I want to make shallow, flat bottomed holes to mount semi-precious jewel cabochons (domed, not faceted stones).  For example, cab garnets in the terminals of a penannular brooch.  Some of the materials may be rather thin and I don't want to punch through with the tip of a standard twist drill.  Also, a flat bottom may be polished up a bit to reflect up through the stone better.

 

Thanks to all the responses, I will chase them down.

Though not a jeweler by any means, I have taken a few workshops and classes. Never seen cabochons set by that method, all work for stone setting done by stock removal/polishing with a hand held Foredom tool, or built up from soldered strips and plate.

 

Try looking at the Ganoksin Project online, lots of jewelry tutorials by professionals, both in print and video formats.

Granger should have them!

Take a regular old twist drill and grind it to drill a flat bottom hole.  You have to start with a standard pointed drill first to locate the hole though.  I do this all the time when drilling gun barrels to make threaded blind holes for sights.  It allows that maximum amount of threads in an otherwise shallow hole.

Take a regular old twist drill and grind it to drill a flat bottom hole.  You have to start with a standard pointed drill first to locate the hole though.  I do this all the time when drilling gun barrels to make threaded blind holes for sights.  It allows that maximum amount of threads in an otherwise shallow hole.

 

That is what I do too. I use them for counterboring for hex socket/allen screws and also for flat bottoming the socket in rivet making tools amongst other things.

 

You spin the ordinary drill bit against the grind wheel to take off the 120 degree angle point and make it flat ended. Then you can just take off the trailing part of the flute to create clearance behind the cutting edge. Takes a few seconds. I will post photo if that would help.

 

What metal are you working with? Are you glueing in the stones? I would have thought that drilling in order to leave a wall thin enough to push over with a burnisher would be a bit tricky. When I was making cabochon stone settings I was working in sterling silver but used to buy the softer  Fine or Brittania silver especially  for the ease of pushing it over the stone.

 

Alan

Petere76 said "milwaukee end mills" but the correct term is "Annular cutters" made by Milwaukee, Haugen, Jancy and others.  You could use those after drilling first with a regular drill bit to get a flat bottom, another thought is a custom ground cutter in a boring head (again after drilling the hole to desired depth with a regular bit)

Here are a couple of images of flat bottomed drills from the drill drawer. My apologies for the lack of close-up focus.

Alan

Aw Alan, you should have said something , I would have shown you how to sharpen a drill.  :) 

 

  How's that for cheek?

Ian I think your remarks are a bit twisted....

Alan






See what I did there?

:)

Getting a BIT off topic here gents...

Well, after all it is a boring subject.

Do a google search for D-bits. They are dirt cheap, easy to make in the shop from drill rod and they work extremely well.

 

There's a pretty good description of how to make them half-way down the page at:

 

http://modelengineeringwebsite.com/Holes_part_3.html

 

Silver steel is the British version of drill rod and is water hardening. Modify your HT to suit the available material.

Dear Ronin,

 

Actually, I want to make shallow, flat bottomed holes to mount semi-precious jewel cabochons (domed, not faceted stones).  For example, cab garnets in the terminals of a penannular brooch.  Some of the materials may be rather thin and I don't want to punch through with the tip of a standard twist drill.  Also, a flat bottom may be polished up a bit to reflect up through the stone better.

 

Thanks to all the responses, I will chase them down.

 

For what you intend to do with them I would look into a slot drill or centre cutting end mill. I gather you are only going about 1 - 3 mm deep so a normal drill bit sharpened flat will not give the finish that you seem to want. You will need to use them in a ridged machine to be able to use them properly like a mill drill unit. Most small drill press units will have to much movement in the spindle for proper use. Have fun hope to see some posted results of what you come up with.