Weird drill bits

[fizzy]

In amongst a huge selection of tooling I bought there are quite a few modified Morse taper drill bits.
Any idea what they are used for?

 

[Seadog]

Counterbores

 

[fizzy]

Counterbores

What are they used for? I am familiar with countersink.

 

[Seadog]

Boring a flat-bottomed hole to clear the head of a bolt, screw, or machine screw. Or to allow a hollow dowel to be fitted.

 

[jsf55]

Usually where a cap head screw goes, saw loads in Borg Warner

 

[fizzy]

They must be down deep then. I am familiar with a spot face bit to create a shallow flat hole.
I have loads of them in all sorts of sizes.

 

[Hitch]

Sometimes you dont have the right size when you need it... had to do this a few times over the years.

 

[pressbrake1]

One assume they’re just for counter sinks but they also drill a more accurate hole if made properly and guide better in cast iron.
Another use is on production machinery as they start on a pilot without chatter

 

[Agroshield]

Sometimes you don't have the right size when you need it... had to do this a few times over the years.

And off-the-shelf counterbores only come in specific (British Standard) sizes for the pilot/shank diameter, generally a very generous counterbore size. If you want a tighter hole (and who doesn't?), you have to roll your own.

The good thing is that they are very easy to convert back to a standard twist drill. A dedicated counterbore cannot be repurposed.

 

[pressbrake1]

They’re not for counter bores (can be used as such
They are for following pilot holes on uneven surfaces like castings
I’ve got a ton of them that came out of Colchester lathes

 

[JEZGUZ]

I've got quite a few but most don't have the flat counterbore on the larger diameter, I assumed they were self piloting drill bits( does such a thing exist?)

 

[bricol]

Usually where a cap head screw goes, saw loads in Borg Warner

And some people seem to feel the need to put every single cap head screw in a counterbore - when one will sit on the surface just as well as a hex head and therefore save a little bit of work creaking the counterbore . . .

 

[grim_d]

I’ve got a ton of them that came out of Colchester lathes

Me too.

 

[Agroshield]

They’re not for counter bores... They are for following pilot holes on uneven surfaces like castings

So why do these particular one he shows have a flat grind on the large diameter?

All the piloted drill bits I have ever seen for the application you describe have a point angle at the transition from pilot to major dia. (they are called drill + drill. The others are drill + countersink or drill + counterbore). For a through hole on a rough casting, the flat part may be a disadvantage both on entry and on break through.

 

[pressbrake1]

Flat is preferred on brake through on cast iron
I was there and saw the application myself
Carbide U drills have rendered them obsolete

 

[Morrisman]

I’ve made them, and used them, for spot facing bolt holes on castings or steel fabrications.