A dog clutch is used for threading in a number of high end lathes e.g. the Hardinge HLV-H.
The CGTK dog clutch is shown here:?
CGTK copied it from my site but it looks like he mis-understood how to engage the clutch which likely led to it failing.? Compare the first picture on my site:? ? to the first picture on the CGTK site and notice the spring on the rod which engages the clutch. This is missing on CGTK's version - this spring is important since it allows minimal force to be applied to the clutch while waiting for the spindle to rotate into position for the dog to engage.? Applying the full force of the trigger directly to the clutch likely caused the engagement mechanism to fail.? My dog clutch has not failed in the 15 years it has been in place, although it does need oiling every 3 or 4 years else it becomes slow to engage.
There is nothing wrong with using a thread dial for imperial or metric threading. But the original poster seemed to be preparing to build a metric thread dial which needs 3 interchangeable gears to cover all metric threads.? My point was that a dog clutch is relatively easy to build compared to cutting gears and making the numbered dial and the associated holder.? Plus the dog clutch works for imperial and metric. And it picks up the thread in one spindle rotation, no waiting for the dial to come around.
John
GadgetBuilder