Grooves in Irons - Another Question for Our Engineers

After wading through the relatively new leglisation: max. groove width - 0.035" / max. depth 0.020" I got to wondering, as one does. When I place a golf ball on the face of an iron - to the naked eye - the ball appears to fail to give any impression that it actually penetrates the grooves at all. Though obviously it would if the grooves were widened. How far, if at all, is a ball actually penetrating the grooves?

If any penetration is taking place this is presumably lessened the harder the ball is struck due to ball side flattening?

This question also has implications concerning the sharpening of grooves. There would appear to be little point in sharpening grooves until they are completely worn out if the ball is not actively penetrating.

To me, spin appears to be primarily loft and swing speed generated. (Or by using an advanced chipping technique - striking the ball with the leading edge). For example, it can be a struggle to reduce ball revs. to under 3,000 r.p.m. even using a SMOOTH FACED 6 degree driver.

Please convince that the present obsession, in some quarters, with grooves has any performance significance in the real world.

Grooves are there specifically to move water/debris from the face to allow the ball to impact the face without there being anything between them.

The generation of additional spin is a byproduct of its main purpose.

Brian, Thanks. Accepted and noted. So am I right then in assuming that the R. & A. have attempted to reduce the effectiveness of grooves as it considers it more fair for players not to have a clean strike?

On most premium golf balls the Iomer resin skin is around 0.070" thick (sometimes made up of two parts but accurate as a general rule) which is soft but resilient (elastic). So when hit at speed with a club will deform partly into a square groove and therefore generate spin. The key is that the skin does not deform enough to fill the groove but just enough to grip the surface. By changing the groove shape to a 'V' means that the skin does fill the groove and effectively spits itself out (as with most tapered shapes. The result is less grip and therefore less spin.

To increase spin rates on wedges the faces are now often spin milled or etched to increase the friction to gain more spin.

Thanks Tim,

Yes I can imagine that. It would be interesting though to see a photo. to prove that it actually happens. I can also imagine that the resin exerts less leverage against a 'v' indentation groove than it would against a 90 degree 'u' shape groove.

The other interesting science facet is how long the ball actually sticks to the face at impact. But I will not draw any analogy with drivers as the R. & A. have quite a vicious 'because we say so' umbrella rule which effectively allows them to rule any iron head illegal without citing a specific engineering breach:

'If claims of excessive spin are made by the manufacturer, or if there is strong supporting evidence of excessive spin, then the club would be deemed to be non-conforming.'

(Appendix 11, 5a.)