forstner bits

[timegoesby]

What are the advantages of these? I see them advertised in Screwfix.

[Rob]

Advantages over what?

They cut flat bottomed holes. Good for blind mortices.

[Elessar]

Presumably advantages over spade bits. I get rounder holes(!), and overlaps are much easier when making a freehand mortice if you don't have a drill press.

[Elessar]

Let me rephrase that. A Forstner bit always makes a perfectly round hole. With a spade bit I get something that looks like a Spirograph outline, if you remember that.

[Peter Ashby]

The ability to overlap is one of the main pluses, if you are drilling for a through mortise the flat bottomed bit is no help but being able to overlap is. They do give nice clean holes too though.

Peter

[impvan]

If you drill a through hole (e.g. for passing a cable through a joist) you don't get the ragged edges where a flat bit would break through. That way it's easier to draw cables BOTH ways through the hole.

Problem with the screwfux ones is that they're so badly ground that at least one in each set will only burn a hole and not cut one. And they're near impossible to sharpen. Best get them individually from the likes of Axminster; they ain't expensive.

[Peter Ashby]

Agreed, Axminster also do short pattern Forstners specifically to help in getting access for drilling joists.

Peter