What are bits for flat-bottom holes in metal called?

I need to drill flat-bottom holes with a drill press and I can't find any bits designed to do this in metal. What are these bits called?

Counterbores. You will need to drill the hole to near finished depth and then run the counterbore down to finish it.

dbooksta said:

I need to drill flat-bottom holes with a drill press and I can't find any bits designed to do this in metal. What are these bits called?

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flat bottom drill bits. my company has many sharpened that way and left that way. when sent in for resharpening they are left as flat bottom drills. if we need one a siz we do not have we have to tag it please resharpen as flat bottom drill. they need a hole already made. they only machine the cone shape flat at bottom of a hole

In a pinch, assuming common diameter, a pilot hole drilled, then finished with an end mill plunge-cut can get it done.

Not sure if you're talking about production items (seems you'd probably not have to ask about flat bottom hole making if you were setting up production, so I assumed you are not) or just making a thingamajig one-time.

Apparently, OSG makes flat bottom drills. They claim that they won't walk off center, can drill half a hole on an edge and at regular drilling speeds. They are limited to 2xD though.

JNieman said:

In a pinch, assuming common diameter, a pilot hole drilled, then finished with an end mill plunge-cut can get it done.

Not sure if you're talking about production items (seems you'd probably not have to ask about flat bottom hole making if you were setting up production, so I assumed you are not) or just making a thingamajig one-time.

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This method is one that I've used a lot but it did cause me some problems once. The call out was for a flat bottomed hole that allowed for a small chisel point in the center when generating the drilled hole before flat.

However, I got myself into trouble once doing that and parts had to be reworked. This was because the small reverse taper on the face of the end mill was more than the flatness call out IF I did not use the minimum chisel diameter they allowed for on the print.

Ironic, a smart designer trying to help knowing about the end mill use allowing the chisel point and we screw it up!

Their CMM caught the error. Fortunately, as I said, they were fixable and now I always circular interpolate flat bottom holes with a small enough end mill to avoid that.

flat bottom drills i use are sharpened flat on bottom. they do require a hole already there. i often see 20x length to dia ratio flat bottom drills.
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any tool whether drill or end mill and be resharpened flat on bottom but you have to specifically ask for it.

Allied Machine and Engineering Corp. sells flat bottom spade drills.

JNieman said:

In a pinch, assuming common diameter, a pilot hole drilled, then finished with an end mill plunge-cut can get it done.

Not sure if you're talking about production items (seems you'd probably not have to ask about flat bottom hole making if you were setting up production, so I assumed you are not) or just making a thingamajig one-time.

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Just need this sort of thing for one-offs and prototyping. Often I'd be quite happy with a brad-point bit, but I can only find those for wood, and even then they often have an angle (often slightly inverted) on the flats around the point.

bw_4000 said:

Allied Machine and Engineering Corp. sells flat bottom spade drills.

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We do have Flatbottom drills from 3/8- 2-9/16 for T-A's and up to 5" diameter as a universal spade. The OP does not specify diameter or depth of the hole, so I am not sure what to offer. While you can drill from solid with these tools, it is better to drill almost to depth with a regular drill and just finish the flat.

(Alied)
[Flat Bottom (FB) Geometry Flat Bottom Drill Inserts Made Under U.S. Patent No. 6,135,681 Euro Patent No.: 1 210 196 DE,GB,IT,FR Canadian Patent No: 2,341,367 Other International Patents Pending Allied’s Flat Bottom geometry is used to flatten, or square, the bottom of pre-existing holes. Tools with this geometry are normally sized the same diameter as the hole.]However, this style tool (when used with short length holders) may also be used to counter bore holes smaller than the tool diameter. The patented geometry provides
efficient and stable cutting action. For a Flat Bottom Drill Insert without chipbreakers, please specify using -FN. Available in the Y through 4 series.
Grades: Super Cobalt, C2 Carbide
Sample Item Number: 152T-0112-FB]


Likely any flat bottom drill or the like will tend to walk about at stating on a drill press. putting a flat bottom to an existing hole may be home made with putting a flat to a std drill or bought..An end mill use on a mill can start and finish a flat bottom hole. For production an end mill can be ground dead flat and center cutting with an OD land like a drill of carbide or HSS for very ling life...but with the OD circle land it can only plunge straight in (axial).. it can not plane mill going to the side.

May also be looking for the term "spot face", where you have a small pilot first since centercutting is harder on tooling and rarely necessary.

I've always known them as "spring pocket drills" for doing what their name describes in stripper plates.

We always piloted drilled to a dia. greater than the spring pocket drill's web thickness to full depth then finished with previously mentioned tool. Obviously, this leaves the drill point dimple in the center, which to you may be a no-go.

The best working ones we ground out of old, shortened-up core drills.