Power Feed Randomly Skips a Beat

[David2011]

The lathe is an 11x26 G9972Z. When turning with power feed the carriage randomly takes brief pauses that result in lines around the workpiece. Sometimes it will go 3” perfectly; the next pass it might pause 3 to 6 time, for just 1 or 2 revolutions of the lead screw and then it proceeds normally. There’s no pattern to the pauses. Just wondering if anyone has seen this before I open up the apron.

 

[Smithdoor]

The lathe is an 11x26 G9972Z. When turning with power feed the carriage randomly takes brief pauses that result in lines around the workpiece. Sometimes it will go 3” perfectly; the next pass it might pause 3 to 6 time, for just 1 or 2 revolutions of the lead screw and then it proceeds normally. There’s no pattern to the pauses. Just wondering if anyone has seen this before I open up the apron.

I had lathe did skip it well used and need a new shaft .
The surprising is it would keep going after the skip.
Look for a worn part

Dave

 

[Jubil]

Does it have a clutch on the feed rod? Clutch may need adjusting.

Chuck

 

[jcp]

Could also be a sheared key in the gearbox or lead screw.

 

[Suzuki4evr]

Had that problem and I needed a new hex drive shaft and the bushing was also worn so I made up a new one and had it wirecut.

 

[Jake M]

... Sometimes it will go 3” perfectly; the next pass it might pause 3 to 6 time, for just 1 or 2 revolutions of the lead screw and then it proceeds normally. There’s no pattern to the pauses....

You've kind of nailed it down right there.

I think you ONLY have a leadscrew, no power shaft, but it doesn't matter. Whatever shaft you're driving from, if it does not stop, but the carriage does stop... Then it's inside the apron. Or behind the apron, depending on how you consider the rack gear and pinion,...

Something's loose, something's broken, something's worn, or something's out of adjustment. You might have some tactile feedback when it happens, or maybe not, which could give you "some" clues as to the nature of the failure... The problem could be several things, but you already know where you're going to find it.

The only thing I can think of that you might do before you take it to bits is to consider the clutch/engagement mechanism for the power feed. I do not know the answer, but if there is an adjustment there, a friction clutch or a sliding gear, or heck, even a loose pin in a lever, making a poor engagement, that "might" be addressable without disassembly. Have a look at that of course, but I think you're goin' into that apron.

 

[jcp]

Look at your parts breakdown for the apron, part number 403 and 404. The key wears out and so does the keyset in the worm gear. Been there, done that.

 

[David2011]

You've kind of nailed it down right there.

I think you ONLY have a leadscrew, no power shaft, but it doesn't matter. Whatever shaft you're driving from, if it does not stop, but the carriage does stop... Then it's inside the apron. Or behind the apron, depending on how you consider the rack gear and pinion,...

Something's loose, something's broken, something's worn, or something's out of adjustment. You might have some tactile feedback when it happens, or maybe not, which could give you "some" clues as to the nature of the failure... The problem could be several things, but you already know where you're going to find it.

The only thing I can think of that you might do before you take it to bits is to consider the clutch/engagement mechanism for the power feed. I do not know the answer, but if there is an adjustment there, a friction clutch or a sliding gear, or heck, even a loose pin in a lever, making a poor engagement, that "might" be addressable without disassembly. Have a look at that of course, but I think you're goin' into that apron.

I was already fairly sure that the problem was inside the apron. There’s a single slotted lead screw that uses the slot to drive turning and the half nuts only for threading. The engagement is a gear on a sliding shaft; nothing fancy like the clutch on American mid sized lathes.

 

[David2011]

Look at your parts breakdown for the apron, part number 403 and 404. The key wears out and so does the keyset in the worm gear. Been there, done that.

I had kind of focused on those two parts just from study the drawings. At about $24 for both I think I’ll go ahead and order them before taking it apart. There does seem to be some binding associated with the skips which would be consistent with those components being worn. Thanks!

 

[jcp]

There does seem to be some binding associated with the skips which would be consistent with those components being worn.

There usually is some binding on the carriage travel....I should have mentioned that.