Made with Meccano parts. See below for details.
Fig 1 - The complete tool with a Mecarep
145 type Ø 7-1/2" Flat Ring in position for spot drilling an extra
8 holes using a 16DP pinion.
1. Convert two Cheese headed bolts as shown in Fig 1 - Top left.
2. Drill the centre hole in the Part 1 (BZP) strip 3/8" Dia clearance for it to revolve on the boss and serve as the position indicator (left Fig 2 below) and fit the converted bolts with nuts as shown.
3. Referring to the coloured no 1 strip Right Fig 2 Below:
1. Drill two x 8 B.A. clearance (Ø 3/32") on 1/2" PCD each side of the centre hole with the pinion clamped in position using a short axle rod as a dowel in the centre.
2. Fit 2 x 8 B.A. x 1/4" long Screws and nuts as shown - Note Make sure that the pinion is positioned with the roots of the opposite teeth relative to the Meccano holes in the strip as shown
Fig 2 - Not to Scale