I know what it is, but I dont know exactly what it is...

[Mark McGrath]

Most British makers used to stop No1 morse at 17/32",then 2 morse to 7/8",3 morse to 1.1/4" although there was one that went to 1.5/16".
The flat on the shank is called a whistle notch and it`s for security if you use the drill in an automatic.Stops the turret going back leaving the drill in the job.

[J Tiers]

As for the screw to hold the drill solid in tailstock......

This is probably a bad idea.

The issue is that the ultimate "holder" of the drill is not the tailstock ram, but the little pin or key that keeps the ram from turning.

No matter what sort of heavy clamp you hold the drill to the ram with, that little key is all that prevents rotation. Even a decent square key can be 'rolled over" is a bad jam-up. The "key" in a tailstock is often a drastically reduced size to fit in the assembly, far smaller than the key a similar sized arbor would have. That small key with limited depth in eitehr part is vulnerable to 'rolling over" and jamming up the ram. Or it may be just a little "pin" about 2 or 3mm diameter, ready to shear right off, or cut into the ram keyslot..

The best way to handle larger drills is to clamp a 'dog" to the drill shank, and rest the tail of the "dog" on the compound, or on a bar that you clamp to the compound or elsewhere. That way the tail can stay sullorted as it moves in and out, and the twisting forces are not transmitted to the little bitty key in the tailstock.

While Mr Fagerlund is correct that the taper should hold, that tends to fall flat when the drill is larger than the taper..... the leverage is such that the taper WILL spin, so external holding means is advisable.

About the tang holding...... I don't want to start a debate, the "tang drive" one is never-ending, but ........... If the tang were *really* intended to hold against turning, it would be at the FAT end like on a CAT taper, where the leverage is best. and not at the thin end where the tool has the mechanical advantage.
I have seen numerous tangs sheared off when defective tapers failed to hold......

[Toolguy]

Drill

The notch is called a whistle notch. It's for a setscrew to hold it in the taper. Some end mills have this also. You would not likely have a setscrew in your lathe tailstock. This is probably to hold the drill in an MT adapter for a radial drill press or an adapter for a mill spindle. If you have to change tools a lot or trying to hog out a hole to make time on production a big setcrew would be an advantage to keep the drill in the holder and not twist off the tang. The tang is usually considered to help in removing the tool from the taper, although it will drive the tool if not overloaded.

[jugs]

Jugs,

The pictures are massive (I like really big pictures), but here i a link to my photo bucket so you can see them..

http://i201.photobucket.com/albums/a...x/DSCF0094.jpg
http://i201.photobucket.com/albums/a...x/DSCF0095.jpg

Thanks for that - thought I'd gone blind

As mark says

The flat on the shank is called a whistle notch and it`s for security

Commonly found on milling cutters, less common on MT stuff