CVA Toolroom Lathe - Auto feed disengagement

[CarbideTip]

It was only when I took mine apart that I realized what the collar on the feed shaft was for.
There may be others out there unaware of this feature too!

I believe 10EE's have it as well, but the CVA implementation is a bit different.
So, for starters what does it do?

If you are using the power feed to move the carriage towards the headstock you can set the collar on the feed shaft to disengage the feed at a certain point. So if you get distracted the carriage won't crash into the chuck.

Here's where it happens:



The collar on the right is held by a grub screw and can be shifted laterally to set the disengage position.

When the carriage hits the collar the entire feed shaft slides left against a spring inside the cylindrical housing.
The grub screw in the housing has a plain round end that engages with the inner sleeve in the picture below:



The sleeve has a plain round bore so only drives the feed shaft by the cross pin and the slots at its left end.



When the feed shaft slides to the left the cross pin moves out of the slots in the sleeve and the feed shaft stops rotating.

Obviously this only works for carriage feed towards the headstock.

The rebuild of my CVA has meant finding spares so I've taken this mechanism apart on three different machines.
All were seized up, so I would suggest other CVA owners lubricate and operate this bit from time to time.

Here's one that was well and truly stuck!

 

[Cal Haines]

Yes, most 10EEs have a similar feed clutch. There are several different versions. It's really an emergency stop, NOT intended for routine use. I usually set the clutch on my 10EE so that the toolpost can't collide with the chuck. Most people don't realize that it's there and leave the movable collar all the way to the left, where it's inoperable.

The version of clutch on my machine can only be disassembled if the two witness marks are aligned. So if the clutch has ever been used, odds are the thing's out of alignment and the setscrew that allows the clutch to be disassembled can't be accessed.

Cal

 

[CarbideTip]

Thanks Cal.

I'm sure you're right that it's not intended for routine use.
I don't think the trip point would be very repeatable because of the way the mechanism works.
Like you, I've seen many machines where the collar is as far to the left as it will go.

Martin

 

[Earl Sigurd]

My CVA operators manual says the opposite, and "Repeats to 0.002" ".

The round pin however on both my machines had worn a flat - if the pin rotates not so repeat.
Easily fixed with new pin and touching up the disconnect part.

 

[daryl bane]

I don't know about the CVA , but the one on my 59 EE certainly lets you know when the carriage contacts the feed collar. Not something you want to do on a regular basis.

 

[CarbideTip]

My CVA operators manual says the opposite, and "Repeats to 0.002" ".

The round pin however on both my machines had worn a flat - if the pin rotates not so repeat.
Easily fixed with new pin and touching up the disconnect part.

Interesting that the manual says that. When I eventually finish my rebuild I will test that assertion.
My reason for being sceptical is that as the pin slides out of the slot, there will be a component of the feed shaft drive torque acting to assist the feed shaft moving to the left. A sort of positive feedback if you like. The heavier the cut, the more drive torque required and the larger the component of the force acting on the feed shaft.

Now if the drive pin had been made square that wouldn't happen.