Be careful if you modify the pier so as not to create a sloppy attachment of the mount base into the pier. In mounts where the bolts are on the side of the mount base (like on the 1100 GTO), oversize mounting holes (or slots) can result in a situation where the mount could shift under the load throw off your polar alignment.
Put the mount into Park 3 and you will see what I am talking about. With the counterweights and scope attached, the weight is centered out beyond the north side of the pier. This cantilevered mass wants to tilt the whole mount downwards, and if it is not securely bolted to the pier it will shift.even if you think the bolts are tight. In my old 8-inch pier, the bolt holes are oversized enough that it allows the mount base to tilt about 1/16-inch. This is a shift of about 1/2 degree ! I have reduced the chances of the mount shifting by using high performance NORD LOCK wedge lock washers on the bolts that attach the mount to the pier, but a better solution would be to use a flat surface adapter so that the mount attaches to the top of the pier rather than from the side. Another option might be to replace three of the six side bolts with tapered dowel pins. Doing this would absolutely fix the mount base to the pier and not allow it to tilt under load.
TSR Global Manufacturing Support
PO Box 2000
Orange, TX 77631-2000
Phone: +1 (409) 882-2799
From: "Robert Berta" <biker123@...>
Date: 01/22/2020 10:48 AM
Subject: Re: [ap-gto] Rotating pier adapter #Polar_Alignment
Sent by: firstname.lastname@example.org
Seems you could just drill extra holes in the pier tube to allow more position options. You could also machine slots in place of the holes on the tube and use washers and bolts to clamp once rotated. that would give you perhaps another total of 10 additional degrees adjustment besides the existing azimuth adjustment in the mount. A machinist could easily build an adapter for what you want.
I am a hobbiest in machining and have a metal lathe and milling machine. When I leave my home observatory and go in field I designed and machined a cap that fits on a modified Meade Giant Field Tripod that takes the flat plate adapter and allows me to rotate the entire assembly if needed to reach the range covered by the mounts azimuth control. The Meade tripod has the advantage it can be adjusted for uneven ground easier than a traditional pier and that was why I went that way instead of a pier.