A heat exchanger tube sheet is a thick plate drilled with hundreds of parallel holes for the tubes. The challenge is not one hole — it is keeping all of them parallel, on-pitch and clean across a sheet that may be a meter thick.
Tube sheets carry the tubes of a shell-and-tube exchanger. Each tube passes through two sheets and must align so the tube slides in and the joints seal. The sheet is drilled from one face with parallel holes on a precise pitch pattern. Drift is the enemy: a hole that leans even a fraction of a degree over 300 mm thickness misses the mating hole on the far sheet.
| Approach | Best for | Notes |
|---|---|---|
| Multi-spindle gundrill | Ø10–30 mm holes | 2–4 spindles drill simultaneously; pitch by spindle spacing |
| Multi-spindle BTA | Ø20–60 mm holes | High feed, deep sheets, internal chip return |
| CNC with rigid boring | Prototype / thin sheets | Flexible but slower; pitch by program |
For carbon steel tube sheets (the common case), gundrilling a Ø20 mm hole:
For stainless or alloy sheets, drop Vc 30–50% and reduce feed to protect the drill from work-hardening.
Some shops drill the two tube sheets stacked — clamping both sheets and drilling through them as one unit. This guarantees perfect alignment between the two sheets (they share the same hole). The catch: the drill must stay straight through two plates and an air gap, and chip evacuation across the gap is harder. Drill through a sacrificial interface plate, or use through-coolant continuously, to manage it.