Drill Heads

A number of drill head types are used for centre hole drilling. The selection of the drill head to be used for a particular application is usually governed by considerations of access during the drilling process:

Straight drill head (medium-speed electric motor):  This drill head is shown below is used for most measurements with free access.  The collet diameter is 7 mm (increasing to 10 mm further from the cutter), which allows a reasonably close approach to step-up features.  Long series (or extended) drilling cutters can be used with this drill to allow closer approaches to higher step-up features.

stresscraft drawing and dimension of straight drill head using in residual stress testing
stresscraft straight drill head extended drill position example
stresscraft example drill example for difficult access scenarios
stresscraft residual stress measurement example in turbine disc

Large Mechanical RA drill head (medium-speed electric motor): This was the first right-angle drill head produced by Stresscraft (~1999).  It can penetrate to a depth of 200 mm at a diameter of 60 mm; the use of shortened drilling cutters and a modified clamping screw can reduce the diameter to around 50 mm.

stresscraft mechanical right angle drive high speed drill dimensial drawing
example of stresscraft mechanical right angle drive inside air turbine hubl
example of stresscraft mechanical right angle drive inside aero engine front bearing house
example of stresscraft mechanical right angle drive access to rear flange
Example of stresscraft mechanical right angle drive inside bore radius

Mechanical RA drill head (medium-speed electric motor):  This drill head is a development of the larger Stresscraft design, the size has been reduced in order to achieve access to smaller component details (rather than simply within disc bores).  The range of applications has been increased by the addition of an optional RA adapter which provides for large offsets (49.5 mm dimension from drill holder to drilling cutter axis).  For aerospace engine components, this drill head finds applications in small disc bores, on the inner sides of flanges and within F1 engine pistons, cylinder blocks and heads.

stresscraft offset mechanical right angle drill head dimensional drawing
example of stresscraft offset mechanical right angle drill head under flange access
example of stresscraft offset mechanical right angle drill head rear flange access

Air-turbine right-angle drill head (high-speed):  This drill head is for use in places of restricted access (e.g. in smaller hub bores, inside disc drive arms, on the reverse faces of drive flanges, etc).  The image shows the drill head held by a universal swivel arm; a number of other arms (straight, curved, small fixed right-angle, etc) are available to suit required applications.  In addition, other adapters are available for soldering to tubes for special applications.

stresscraft air turbine adjustable angle drill head high speed dimensional drawing
example of stresscraft right angle air turbine configuration inside narrow channel
example of stresscraft air turbine straight drill head configuration under flange on narrow ledge
stresscraft air turbine with adjustable angle drill head

Miniature offset drill head (medium-speed electric motor):  The offset drill head is used for drilling 031-size gauges in bolt holes and piston pin holes, under ledges, etc.  The gearbox within the drill head and flexible drive from the motor provide the offset at the drill axis.  The minimum recommended diameter of the target hole is around 11 to 12 mm

stresscraft miniature offset drill head dimensional drawing
stresscraft type A 031 strain gauge installed inside 13mm diameter aero engine bolt hole
example of stresscraft miniature drill head drilling installed strain gauge inside aero engine bolt hole
example of stresscraft miniature drill head drilling installed strain gauge inside aero engine bolt hole