I have done plenty of deep drilling using the following "knife & fork" technique.
Use a new or well sharpened drill.
Centre drill very accurately - the tinyest problem at the start just gets worse. Also be sure your tailstock is accurately aligned.
(Once I drilled an 18mm hole down 1.2m of 30 diameter stainless and the drill came out the side about 1.15m into the job - amazing - it was a bad start and I knew it but pressed on regardless - lesson learned)
Start with an undersize hole and true it with a D bit or boring bar to drill size to act as a guide for the size drill.
Peck drill as far as you can go with your drill.
Turn down the shank end and silver solder into an undersize extension shank. (if you need your lathe for this then you need to make an extended drill first.) Step turn the shank and make part of it a press fit into the extension for accuracy's sake - you can also get away with locktite - slightly undercut the turned down portion of the shank (you can't press fit locktite) to leave a small annulus for the locktite between two small bands of press fit diameter at the start and end of the turning.
http://www.homemodelenginemachinist.com/showthread.php?t=15958&highlight=shooter+elbow+engine&page=4
Carry on peck drilling to depth / through.
On a lathe it is easier to unclamp the tailstock and pull it back to clear the swarf - push in, relock and continue drilling - every so often you are going to have to rewind the quill back to the start.
Drill in suitable size pecks so that the drill does not become swarf bound - if you break it off the game's over.
For a through hole you can also drill from both ends - that way it is accurate at the ends but you can't be too sure about where they meet in the middle.
You can also get drill wander down the core of the bar you are drilling due to spin casting errors (in cast iron) and similar corkscrew graining down the centre of continuous cast strands and even aluminium extrusions. In short lengths this manifests as the exit hole being off centre - in a long hole it can be corkscrewed.
http://www.homemodelenginemachinist.com/showthread.php?t=15958&highlight=shooter+elbow+engine&page=6
Where I have had this problem I have drilled first and then mounted the oversize O.D. part on a mandrel to finish turn the O.D. true to the bore.
Regards
Use a new or well sharpened drill.
Centre drill very accurately - the tinyest problem at the start just gets worse. Also be sure your tailstock is accurately aligned.
(Once I drilled an 18mm hole down 1.2m of 30 diameter stainless and the drill came out the side about 1.15m into the job - amazing - it was a bad start and I knew it but pressed on regardless - lesson learned)
Start with an undersize hole and true it with a D bit or boring bar to drill size to act as a guide for the size drill.
Peck drill as far as you can go with your drill.
Turn down the shank end and silver solder into an undersize extension shank. (if you need your lathe for this then you need to make an extended drill first.) Step turn the shank and make part of it a press fit into the extension for accuracy's sake - you can also get away with locktite - slightly undercut the turned down portion of the shank (you can't press fit locktite) to leave a small annulus for the locktite between two small bands of press fit diameter at the start and end of the turning.
http://www.homemodelenginemachinist.com/showthread.php?t=15958&highlight=shooter+elbow+engine&page=4
Carry on peck drilling to depth / through.
On a lathe it is easier to unclamp the tailstock and pull it back to clear the swarf - push in, relock and continue drilling - every so often you are going to have to rewind the quill back to the start.
Drill in suitable size pecks so that the drill does not become swarf bound - if you break it off the game's over.
For a through hole you can also drill from both ends - that way it is accurate at the ends but you can't be too sure about where they meet in the middle.
You can also get drill wander down the core of the bar you are drilling due to spin casting errors (in cast iron) and similar corkscrew graining down the centre of continuous cast strands and even aluminium extrusions. In short lengths this manifests as the exit hole being off centre - in a long hole it can be corkscrewed.
http://www.homemodelenginemachinist.com/showthread.php?t=15958&highlight=shooter+elbow+engine&page=6
Where I have had this problem I have drilled first and then mounted the oversize O.D. part on a mandrel to finish turn the O.D. true to the bore.
Regards
