What size drill bits in hollow chisels?

[ken carroll]

For a typical 1/4", 5/16", 3/8", 1/2" hollow mortise chisel set what are the diameters of the respective
drill bits?
Is there a "standard"?

Need to figure out what sized collets to buy for a horizontal borer to do mortises.

Thanks!
ken

[Jamie Buxton]

The bits for hollow-chisel mortisers are typically the same diameter as the chisel, or a tad larger. This diameter is only at the tip. The spiral shaft of the bit is substantially smaller, so it can fit inside the hollow chisel.

I'm a little confused about your mention of a horizontal borer. If I understand them correctly, they generally use something like a straight router bit, running at router speeds. And the table slides back and forth to make a slot. The hollow-chisel bits run at drill-press speeds, and only plunge into the work to bore a square hole.

[ken carroll]

They can be used as slot mortisers, or as in the case of my old piece of iron as a hollow chisel unit.

It's the shanks I am interested in, and to partially answer my own question:

1/2 and 3/8" chisels have 19/64" shank drills
1/4" have 3/16" shanks.