Placing it into the rough cut 11” hole I had already cut, it was clearly going to need a bigger (and more perfectly circular!) hole.

The Walther’s turntable needs a 12-1/2” diameter hole. On my trackplan I superimposed that size hole where I had the smaller hole and it was a tight fit, but it did fit.

It is a good idea to read the instructions: closer reading reveals that the turntable needs a 12-5/8” hole. As usual – everything ends up taking a bit more space than you initially plan.

First I needed to draw a really accurate circle on the plywood. Normally this is no big deal but there’s a hole in the plywood where the center needs to be so I clamp a piece of ¼” plywood over the hole from below.

Next I need to mark the center of the circle. The approach tracks to the turntable are already laid out and their centerlines should cross exactly at the center of the circle. Using a flexible clear plastic ruler I draw lines out and where they cross will be the center of the new enlarged hole.

Drawing the first line.

Drawing the second line. Where it crosses the first is the center for the new hole.

From the center just marked I use an inexpensive compass and a sharp pencil set for a 6-5/16” radius to gently mark out the new circle’s outline. This kind of compass works fine as long as you use very little force.

Drill a starter hole for the saber saw.

Cut the hole

Somehow I forgot to take any photos of this step. Maybe it was because I was holding the saw with both hands!

Anyway, I carefully cut the hole with a new blade in the saber saw and with a little bit of shaving the new hole works great.

The edge of my plywood base for the yard area is now dangerously close to the edge of the turntable so I immediately add some pine 1×3 facing boards and use a cargo strap to hold them while I glue and screw them in place.

The plastic lip of the turntable is exactly the same thickness as the ties under my track. Since my track is riding on cork roadbed I need to raise the turntable to match the track height. The easy way to do this is to run a ring of roadbed around the turntable hole to use it as a riser. Then I just cut away the bevel where the approach tracks come in.

I still have to actually assemble the turntable but I’m moving on to laying the track first.

The plan was to scratchbuild the turntable but those of you who have done this before know: it’s really easy to build a turntable badly. Fortunately, I realized this immediatly after casually cutting a rough 11 inch diameter hole in the main track sheet of Tiburbon.

First: a rough hole will not do the job.

Second: it became clear that a precisely built and aligned pit, bridge, and approach tracks are required or I will be very sorry indeed.

Third: since this turntable is in the IMMEDIATE foreground of the scene it must be tidy looking.

Enter the Walthers 90′ Turntable kit (unpowered) on sale for $31.98.

I’ve had spotty to poor experiences with Walthers plastic kits but I figured for $32 I’d get at least a few pieces I could use. So far it looks great. Simple and tidy. With some easy modifications will turn smoothly. I plan on turning by hand since the table is right at the edge (will I regret this?).  

I’ll have to enlarge the existing hole but it basically fits and now I can turn a USRA 2-8-2 Mikado if I want. I’ll post details on cutting and installation soon.