DIGITAL MACHINEDESIGN DESK / DFM-02

Holes & blind threads

Separate bore depth, full thread depth and fastener engagement.

DESIGN INTENTUsable thread depth is not drill depth.
01Drilled hole: define the endpoint
Section of a blind drilled hole. Diameter D is across the clear bore. L runs from the top face to the end of the cylinder; a separate arrow extends to the drill tip.

L stops before the drill point

02Blind thread: reserve bottom space
Section of a blind threaded hole showing complete threads, incomplete lead and runout, bottom clearance, and the drill point below. No allowance dimensions are prescribed.

Complete thread first, tool allowance below

WORKED EXAMPLE / mm

Hole ratio = full-diameter depth / bore diameter

18 / 6 = 3:1 | 60 / 6 = 10:1
03Check the assembled joint

Engagement is the overlap of mating threads, not drilled depth. Required overlap depends on loads, materials and the fastener.

CAD: check bolt overlap in the assembly.

04Give chips an exit

Blind and through holes need different chip strategies. Tool geometry, coolant and cutting cycle must match the actual hole.

CAD: use through holes where function allows.

05Use available sizes when suitable

Standard drills can simplify tooling. A required fit may still need reaming or boring; nonstandard sizes do not always need interpolation.

CAD: keep the required fit, not an arbitrary size.

06Make passages cleanable

Cross holes can leave burrs inside the part. Include access for deburring, cleaning and verification of critical intersections.

CAD: locate intersections with cleanup in mind.

WHAT THIS DOES NOT PROVE

Specify complete usable thread depth. Set lead, runout and bottom allowance using the selected tool and chip strategy.

BEFORE RELEASE Protect fit, loads, sealing and required material sections when changing geometry.
  • State thread standard, size, pitch and class.
  • Distinguish through holes from blind holes.
  • Dimension required complete thread depth.
  • Confirm actual mating-fastener overlap and loads.
  • Allow tool-specific bottom clearance.
  • Review intersection burrs and cleaning access.