For my example of the Jacobs Machine I have used waste pieces of mild steel which i got from a metalworking company.
So i didn't follow the construction plan and choosed greater dimensions for the three components of the machine.
After reading the articles of Chris Robinson i upgraded the normal gear train by the differential gear train.
This version was able to cut gears in good quality until a diameter of 8 cm. Beyond this the cutting was running mechanical unstable and the cutting process was often interrupted.
The cutting of a 127 teeth gear in modul 1 was a difficult affair. I contacted Chris Robinson. He confirmed that this little machine could deliver good results up to modul 1,25.
After a further check of my machine i decided to introduce four impovements for better results with big gears:

1. A counter-Bearing for the gear-cutter
2. A counter-Bearing for workpiece-axis
3. Different heavy flanges 8cm / 6cm / 4,5cm / 3cm / 2cm in diameter for a better fixing of the gear blancs.
Some quick-release axles and many adapters for different bore diameters.
4. Correction of to much play of the worm screw

The aim was to correct the mechanical instabilities when cutting big gears. The attached pictures will show you the four places for my uprade. The simplest and most effectiv step was the correction of the play of the worm
by using some adjusting washers.
The link of the video will show the cutting of a big gear modul 1,25, outer diameter 140 mm with 110 teeth.
The video is showing the cutting process at a depth of 0,9 mm, later you can see the last cut, depth 2,7 mm.
After the upgrade improvments the cutting could be finished with a great reduction of mechanical instability and without any interruption.**LINK**

Here i have a better looking Video:

Edited By Neil Wyatt on 03/08/2018 17:49:55