Centres and Centre Drilling (Haas ST-15Y)
Workpieces in the lathe cannot extend more than 4 to 5 times their diameter from the chuck or they start to wobble and whip. With care it is possible to make cuts at such extensions, but heavy cutting work needs to be supported by a live centre in the tailstock.
The tailstock is a hybrid manual-hydraulic design. The body of the tailstock must be brought forward toward the chuck, and then the hydraulic quill should be extended so the live centre tip rests securely in the seat created by a centre drill.
There is a high risk of crashing the turret into the tailstock, especially when it is extended and in position. Be very careful when moving the turret around the machine, indexing the turret, and proving out programs.
Centre Drilling
A centre drill has a 60-degree cutting surface which creates a perfect land for the tip of the live centre to seat in.
To be sure of cutting a deep enough seat for the live centre you can drill the centre hole to a depth equal to the diameter of the centre-drill's shank. For example, to drill a suitable hole with the 8mm shank centre drill typically loaded in the machine you should drill 8 mm into the end of the bar.
Drilling too deep can cause problems where the tip of the centre doesn't seat in the tapered section but instead rests on a ring of material. Drilling too shallow can cause the same problem, but nearer the end of the live centre tip. A small taper section cannot take as much load as a larger taper section.
Tailstock Pressure
Excessive hydraulic pressure from the tailstock can cause material, especially thin bar stock, to bow or flex. This can lead to inaccurate or bent parts coming out of the machine.