Needling hammers

Could someone give a brief account of the process used when needling hammer felts? Particularly, what is the angle or attitude of the needle relative to the face of the hammer? Thanks a bunch.

I'm answering my own question here......I found a downloadable pdf document file from Renner with pictures that tell all.....you may want to check it out if you have similar questions

Renner makes piano actions, hammers and such