Presto 6N crank: how it works?

[boryo]

I'm trying to figure out how the handle works. From the right side of the 6N overhead it is clear but on the left side where the feedscrew is connected to the gearwheel that is driven by the worm gear. I checked probably every photo in google but no results.
Looking at the wiki I think that the feedscrew is tightly pressed to the gearwheel so when the gearwheel spins it passes the motion to the feedscrew.
On the other side when you turn the crank the motion is passed to the feedscrew but because of the big resistance of the gearwheel the feedscrew slips on the left side and this is how it makes leadin, leadout and space between songs. Am I missing something?


Thanks,
Bob

[rsimms3]

On a 6N feedscrew there is a keyway on both ends, one for the hand crank on the right side and one on the left side for the one way ratcheting mechanism. It's just like a ratchet you use for nuts and bolts. As the worm gear turns it engages the ratchet at the geared speed but because it's a one way system turning the crank you can advance the feedscrew faster than the worm gear.

See this post for a picture of the interior showing the ratcheting system -
https://www.lathetrolls.com/viewtopic.php?f=1&t=2587&p=48796&hilit=ratchet#p48794

And watch EpicenterBryan's video discussing his mods to a Fairchild lathe and use of a one way bearing, similar to the ratcheting system on the Presto but through great planning, Presto's advance the feedscrew turning the crank clockwise instead of counterclockwise.

https://youtu.be/uuxxkbP41hE?t=2m48s

[boryo]

Exactly what I was looking for!

Thanks,
Bob

[boryo]

Is it possible the ratchet mechanism of 6N to fit on 6D? I found some photos on the net of 6D with ratchet but not sure if it depends on the serial number or it is modified.

[rsimms3]

The short answer: yes.

The long answer is more complicated and basically involves swapping out the entire handle side portion of the overhead due to the way it's constructed OR find a 6D ratcheting mechanism that could be directly swapped out AND the matching feedscrews. You'd be better off buying a whole 6N overhead than finding suitable replacement parts.

This is the ratcheting mechanism you'd be looking for to install on a 6D:


Feedscrews - Top 4 suitable alternate screws made in Canada by McCurdy, 5th screw from top is Presto factory 6D feedscrew, and bottom 3 are Presto 6N screws.


6D feedscrews rotate on a beveled center, the handle is secured with a setscrew on the opposite side of the gear mount:


The 6N ratcheting mechanism has a shaft that goes into the handle, the handle mounts from the outside with two screws, the ratcheting shaft goes from the inside through into the handle. See my previous post that linked to the exposed 6N ratcheting system and the below picture for reference.

6NRatchet.jpg

[boryo]

Thank you very much for the detailed pictures! Probably I will try a motorized solution.

Thanks,
Bob