Do It Right!
I was able to slightly elongate an existing hole (from 40mm round to 40mm x 45mm oval). It was centered at 230mm, I eased it bigger (toward the spindle only) to allow my 225mm arm to be properly located. (rear Acos Lustre GST-801).
It’s base plate covers the entire hole, but you can always make a thin hardwood or metal spacer or find a very large washer.
The arm’s hardware on threaded post tightened it properly from below. If a 3 screw Jelco type surface mount like my Blackbird, you can rotate so the screws find fresh wood. My left side Mission arm was tapped for machine screws from below. I drilled the holes all the way thru and made it like a Jelco Surface Mount, painted some wood screws black, done.
My 12.5" long arm, I rotated the removable rectangular arm board and drilled a new hole for it’s small diameter post and surface mtd. base. I made a 1/8" recessed plug for the old hole (simply taped in place from below so hole can be used if desired) and put a 45 rpm adapter in it to make it appear purposeful.
Elongating the hole: I clamped 1-1/2" thick wood on top of the arm board, so the new hole thru that 1-1/2" would guide the bit as it passed off-center thru the original hole, easing one edge only.
It was fun solving things, and knowing they are correctly located personally.
The 3rd arm on the left: I had to find an arm with a very short counterweight section, luckily the seller knew how to measure and give me the needed answers, there is only about 1/8" clearance when the arm is parked and the thick dust cover is on. Small diameter base was needed, it just fits very close to the wide rim of the JVC TT81.
I was going to move to a CL-P3 3 arm plinth, at the last minute, I got an answer from the seller in Hong Kong. I realized, I could not put my 12.5" Blackbird arm on the right side arm board of the CL-P3, because they modified the plinth and arm board, cut it’s shape and moved the armboard cutout inwards closer to the TT, to make room to add the 3rd removable arm board on the left side. My 12.5" arm is too long for it, it only fits on my CL-P2. Dumb luck, I got a lot of that.
