Robert Speck Ltd


Formdrill Style Selection
We have a range of formdrill styles to suit different applications.
For threaded holes it is desirable to have a slight coning in the bore of the formed bush, as the forming tap forces its way in to form the thread, the thinner wall at the end of the bush exerts pressure onto the tap, to ensure a correctly formed thread. If the bush bore is cylindrical, thread forming will tend to stretch the bush open.

Thread forming gives 20 - 25% more thread strength in a formdrilled bush than can be a achieved with a cutting tap.

Standard or Flat
Initial material displacement is back towards the outer surface until the formdrill point has penetrated the inner wall; from there material is displaced forward to form the bush that we aim to achieve. The small amount of back formed material that is left on the outer surface can either be :-

A) rolled over to form a neat collar around the hole - this method uses the basic drill form and no material is removed,


B) if a flat outer face is required the ‘flat’ style drill should be used. This incorporates a cutter into the formdrill body and cuts the surface flush.



Long or Short Formdrills

A ‘short’ formdrill is normally used in material thickness up to 1/3 of the thread diameter, ie up to 2mm for an M6 thread.

Long formdrills are used for thicker materials nominally up ¾ thread diameter (please see charts for more detail).



Long drills are also used to create cylindrical bushes for use as shaft supports or soldered connections.


Long Flat
Short Flat
Tool Holder

A specially designed tool holder is an important element of the thermal drilling system, having the following functions:

Morse taper fitting for machine spindle


Disc heat sink distributes heat from tool and prevents it traveling to the machine spindle bearings


Collet to (A) Ensure accurate rotation of the tool (B) gives close contact with tool shank to conduct excess heat away


Threads are produced by using a cold forming tap.

Again no material is removed

Formtaps produce a stronger connection than using a cutting tap. The operational method is the same as normal tapping, but with a production advantage of no swarf.


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