Parabolic Drills

[northwest]

They used to be, until the mandrel was broken and someone decided it would be quicker/easier/cheaper to machine the mouldings than repair the tool.

Idiots.

 

[Erie Fred]

Why are the holes not molded in when it’s made? Seems a bit daft

Because the draft angle required for a clean release would have the 5/8" dia. hole about 1" dia. at the other end.

 

[indy4x]

If I want a deep, precise hole I use a milling cutter.

Slot drills can be used for plunge milling but I prefer a pilot hole followed by a standard milling cutter. Milling cutters are so much more rigid than twist drills.

The pilot does not need to be perfectly straight but serves as clearance for the centre of standard milling cutter, which does not cut.

Depending on the diameter of the required hole, one can use either a solid carbide or cutter holder with replaceable inserts.

Not the fastest route to a simple hole but I don’t need to rush with anything where precision is required.

Have done similar on my lathe, drill bit in the tailstock, pilot hole then milling cutter and take it out to size

 

[northwest]

Have done similar on my lathe, drill bit in the tailstock, pilot hole then milling cutter and take it out to size

This works great but I have yet to find a milling cutter 800mm long.

 

[northwest]

This will give you some idea as to what I mean:



I have had one of these ground at the tip to give me a removable pilot so I can fit it more precisely to the bore the drill will follow
The smaller drills underneath these are unusual in that they are Parabolics and one of them I was recently given by @500e and not seen a tip like it, the one on the left:


Other cheap rubbish I use, solid carbide coolant through@ 8mm, cuts beautifully:




I buy them as I see them and that way, when I need one I am not in the poor house (quite yet) paying £200 for a drill. God forbid I destroy a carbide drill down a hole, I have done it with a reamer but that was relatively straightforward to extract, a carbide drill 8"long probably not so.

 

[500e]

Glad you think it is weird Graham, I think it is an aircraft tool but even a standard drill that speck is meany bags of gold as you noticed with link.
Have fun with it was given to me 3/4 years ago.