Valve Seat Machining,
one century of evolution and... the solution!

The lapping of powder metal valve seats, or of some cast iron valve seats, brings about unavoidable chatter marks. Chatter marks are very harmful to a valve since gases escape through them while the valve is shut.

The machined valve seat will consequently deform rapidly and its seal will never be adequate. Chatter marks result from the carbide form tool scrapping a large surface of a material with a grainy structure made of different materials (such as powder metals, nodular cast irons...).

Traditional valve seats machined with the lapping technique (form tools), all present undulations, measuring hundredths of millimeters, that are the direct result of irregular cutting efforts on a 360° rotation. The resultants of changing cutting efforts transmit irregular forms on machine spindles that will flex more or less depending on the machine and will yield irregular shapes. This phenomenon, well known by operators of manual machines, is compensated for, when large visible defects appear, with quick and forceful pressure on the spindle command.

The above results in considerable spindle efforts and, while it can help smooth out small defects, it can in no way rectify the geometry.

These undulation, inherent to the very principle of machining by lapping, have unquestionable consequences on valve sealing and require further lapping of each valve on its valve seat to obtain an acceptable seal. Valve lapping, so far accepted out of necessity by engine builders and their customers, has long been banished by engine manufacturers and anyone seeking the minimu8m quality required by current engine generations.

Valve Seat Machining by Interpolation,
FIXED-TURNING^®, definitely eliminates all defects shown on Drawings 1 and 2.

Micro-chatter marks and undulations are virtually impossible to generate. Single point marching does not allow the formation of such defects. One only needs to consider machining on a lathe to convince oneself. Machining with a turning tool traveling on two interpolated axes generates a circular micro-groove, perfectly round. The depth of the groove and the interval between 2 grooves is controlled by the numerical control of the machine, yielding the finest achievable surface finished. Much like cutting efforts, reduced considerably (300 times and more), surface finished defects are reduced to levels that rank FIXED-TURNING^® at the very top of quality scales defined by leading OEMs.