Ammco 7000 disc brake lathe cross feed stops intermittently. I notice that the handwheel has jerky rotation.

https://www.autoess.com/manufacturers/ammco-4000-brake-lathe-parts

The cross feed drive shaft is connected to the cross feed spindle via a coupling that resembles a universal joint that is threaded onto the end of the cross feed spindle. Either one of the roll pin holes in the drive shaft coupling has worn and the roll pin fell out or it has broken, or the coupling could have came un-screwed from the cross feed spindle. Remove the 4 bolts that hold the cross feed gearbox on and slowly pull it away from the machine and you should see the coupling I'm describing. My guess is that the roll pin broke or fell out due to wear. You can buy a new drive shaft and coupling or drill and install the next larger roll pin. Either way you should download a parts list for your machine. Just search for it, they can be downloaded free.

Not enough rigidity, wrong speed, wrong feed rate, wrong depth of cut, wrong or dull tooling...

Most likely you have a stripped out "disc feed screw."
This is a common problem I see several times a month in the field.
The stripped out portion of the screw is near the end of the feed range obviously.

If you need parts or more questions answered....

Buy Sell Used Brake Lathes Brake Lathe Parts

Yes, an Ammco 3000 brake lathe can be converted over to a 4000 model--most any year 3000.... preferably the later years after 1970.

The problem with some of the early 60's models is that the cross-feed bore is not perfectly perpendicular to the spindle.

If you convert one of these models, you will cut the rotor at an angle and then jam the machine.

Later models can easily be converted.

You will need...

1) A complete disc feed gearbox.
2) A driven pulley (the big one) set-up for a with a pin drive.
3) A complete spindle lock assembly for the Infimatic gearbox.
4) Possibly need a longer guide bar for the cross-freed. If you have a round guide bar, this is possibly long enough. If you have a "Double-D" guide bar (flat on each side), you most likely will need a longer bar.
5) A complete twin-cutter, with tool guides, tool holders, knobs, etc.

We have all the parts you need for a conversion--or we can convert it expertly for you...

Buy Sell Used Brake Lathes Brake Lathe Parts

There's a lot of reasons why a brake lathe chatters during a cutting operation. They range from lack of maintenance, adjustments, cutting speeds, wrong cutting tools and so on and so forth.

Be a little more specific.

What kind of machine are you using?
What are you cutting? (rotors? drums?)
Are you using the proper silencers?

Come back with some answers please.

Buy Sell Used Brake Lathes Brake Lathe Parts

I think that you really need to source the manual for that machine.

I am a brake lathe technician.

To change the drive belt on an Ammco 4000, you must first remove the 90 degree angle PTO (power take off) gear assembly which is driven off the back of the big pulley. Two small allen head screws hold it tight.

Pull the PTO gear assembly out of the disc-feed gearbox. If there are colored shims between the gearbox and the PTO assembly, you must make sure not to loose. If they drop off, be sure to replace them with a dab of grease.

Rotate the red knob at the back of the machine and the motor assembly will unlock and rotate upwards. Replace the drive belt.

To adjust the drive belt tension properly--loosen the 3/4 inch nut on the back of the machine, and the motor will drop down. Tighten the 3/4 inch nut and then rotate the red knob back until the belt is taught.

Replace the PTO gear assembly--making the rotating part with the protruding pin is centered on the big pulley. Tighten the allen head cap screws.

Turn on the machine. If the PTO is making noise--you have not correctly is correctly. Repeat the centering process until the machine runs without rattling or vibration.

The problem isn't clearly explained. but the main shaft bearings go bad after awhile and it's one day thier good the next job their bad.

If you live near a machine shop any lathe operator can steer you in the right direction, or you could call them. I'm not certain if Ammco is still in business. I had the same machine in my shop in 1976, not the same model # of course, but a model with the stand.