How critical is the exact placement of the tonearm

Thanks Richard, that tolerance was what I was looking for.

Less than 0.5mm is about right. You have some room to compensate by changing overhang via moving the cartridge back or forth.

Good luck!!

It's hard for me to believe anyone could drill a hole that large in an armboard and get it within .01969 of an inch.... Then get the armboard mounted that precisely... I'm not saying it's not critical, just the nature of the drill bit that size.

I don't believe anyone said the hole had to have that tolerance. There is play within the hole to adjust the arm to that tolerance which can be achieved with micrometers and other measuring tools. The actual drilled hole would have a much greater tolerance. Then again you would be surprised how accurate a drill press can be - let alone plowing it out with a Bridgeport if you wanted to get ridiculous.