Grinding new gear and wurm . To get the best fit . A mixture of diamond dust and oil .

What is the speed at which you perform this operation? (Lathe RPM)

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Vive la Marque !!

190 RPM

In the Bugatti GP book, steering chapter, it mentions that there seems
no reason to machine all the circle of teeth as only a small area is ever
used..could this be the reason, to run it together precisely and properly ?

Both directions?

_________________
Vive la Marque !!

For sure both directions . You can hear it if one side is ready , the sound is changing .
Some gears need one hour some all day . With this grinding in you get the best possible steering .

Molsheim did not need this rude method to compensate for bad machining.
Bugwrench

should I be surprised about your post ? I'm sorry, I'm not. It is more or less normal.
Dont worry `, I help you to build up your technical knowlige a little bit .
If you buy a gear grinding machine today , like the number one , it is a Schleifring . We talk about 750 000€ . But even this expensive machine , can not make the quality like grinding in with diamond dust . In the industry today , it is still normal for high quality gears to grind them in . There are special machines for . The translaten from German , Gear grinding in machines , some call it Lapping machines . Used in for example measurment devices or auxiliary gearboxes from jet engines . Or in all places where you need high quality gears . Very common today is lapping piston pins in special piston pin lapping machines .
What quality had a gear cutting tool in 1930 ? And what quality was a gear cutting machine able to do in 1930 ?Did you see one ? If you take a original Bugatti steering gear and grind it in like you can see in the picture above ,only for 1 minute .You can see the quality from 1930 . How many spots are touching and how many not .I like to have the minimum play at the steering wheel as possible , and easy and soft to turn , you not ?