</font><blockquote><font size="1" face="VERDANA,ARIAL,HELVETICA,TAHOMA">quote:</font><hr /><font size="2" face="VERDANA,ARIAL,HELVETICA,TAHOMA">However just one more thing, can anyone say why pins slide upright? </font><hr /></blockquote><font size="2" face="VERDANA,ARIAL,HELVETICA,TAHOMA">New pins and newer pins have flatter bottoms. Older pins have been *******d around and the bottoms get worn. Flatter bottoms, more difficult to knock down.
Pins are also built within parameters. Here in the US, the USBC (old ABC) demanded these parameters. If the pins are built more bottom heavy (say at the lowest end of the parameter) then they are harder to fall.
Pin decks (where the pins stand) are supposed to be flat and level. But there was be a slight tilt and still be within USBC parameters. This effects pin fall also.
Then you have the oil. Oil gets carried down to the pin decks. Its stripped off there with a chemical. How often and what strength chemical used is up to the center. When the backends/pin decks are dirty pins slide more. This is more then likely the most influence on whether pins slide or fall.