Is it proper to use extra long drill bits to bore a hole say 8" deep? Or should I bore from both sides using a 4 jaw or collet for repeatably to insure a straight bore?
Only a reamer that I know of , and if my machine is set up straight and the drill bits straight I'd go from one end , if you machine is questionable do drill from both ends to the middle.
Gun drills are what you are looking for, you will find them difficult to use in a hobbyist setting as they require high pressure thru tool fluids to work well. They are also not inexpensive by hobby standards.
Information may be found here http://www.sterlinggundrills.com/deep-hole-gun-drills-function.php
used a high pressure car wash pump to make a high pressure coolant system. got the gundrills off ebay, cheap there. You need very fine feed, just a few tenths per revolution of the lathe. You can install a variable speed drive on your lead screw or use a CNC lathe here.
What size is the material you want to bore? And how accurate do you need the hole to be? Those answers, along with what tools you have, will determine the best approach for you.
The gun drill is definitely the way to go on that small a diameter. The setup to run it is not to difficult.
I originally used the coolant system on my lathe to drill with. I have since switched to air and oil.
A harbor freight pressure regulator air tool oiler combo. I run 60psi air pressure and adjust the oil flow as needed. Chips really fly so some kinda guard is nice.
I have found gun drills on ebay for cheap...usually around the $20.00 range. Sizing is hit and miss. Not always able to find the size immediately but within a week usually can find what I want.
Dulltool17 makes a good point and that way works well. I have gotten cheap gun barrels and turned them in that fashion. One end will be on center and the downhole end would be .030 off. Turning between centers fixes this quick and easy.
When drilling deep holes where I want the entrance and exit holes to be centered, I will drill from each end with an undersized drill. Once the drill breaks through the opposite side, it will tend to follow the other hole. Drilling in multiple steps will usually true the hole so the final pass produces a straight hole.
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