Re: Gonna try and beat a dead horse here...
Arch
>Hi David, I'll impose on the group and beat a horse that's not only dead, it's decomposed; Just some musings about applying principles of making holes in metal to making them in wood. Real machinists and woodturners may want to leave the room now! For those of us who didn't come to woodturning by way of the metal lathe, I'll trudge on.
In general, drilling has to do with making holes, while boring is opening out a hole by 'machining' with a cutting tool. Ex; In wood I drill with a twist bit, but I bore with a gouge. Think of boring as internal turning. (ok,I am also boring you with this post) Leaving out infirm lathes and chucks, knotty wood and other obvious causes for making poor and non-concentric long holes, there are two important considerations: the cutting bit iself, and the opening for the bit to enter the workpiece. As with most things in life, starting out is all important. A slocum or center bit is cheap and is ideal for making a good beginning. Its small tip clears a space for the drilling bit's tip and prevents it from slewing.
To make a deep concentric thru hole in wood, start with a slocum and drill a little past its shaft's full diameter. Drill thru with increasingly larger bits & extension shafts until the hole is large enough to bore with a D-bit. Maybe someone who can show pics and is blessed with better descriptive powers will discuss these very useful,cheap and easily made sizing and boring tools. (Drills & bits are just as much lathe tools as gouges & scrapers)
If a D-bit starts true and isn't forced, it will bore true an/or straighten wandering holes. Ex: gun barrels. Remember that you can reverse a long workpiece end for end and make opposing holes that meet truly. If the work was roughed out between centers and the opposing holes started with a center bit in the center punches, they will meet if a D-bit is not forced or chips allowed to accumulate. As an aside, I think that work held between centers that's removed and replaced will run truer than if held in a chuck of any sort.
This is a long to-do just to suggest trying a D-bit. Just be glad that I saved other earth shaking suggestions about drilling on a lathe for another post. Now you may wake up! Arch