Regular Ripples w/ Power Feed on PM-1130v

[mikkmake]

Clarification on the Gibs and the obscured lock pins from Precision Matthews.

for the gibs, you loosen the screw at one end, and tighten the other to move the gib back and forth. It's one long wedge, so one way will tighten, the other will loosen. The screws just need to be snug once adjusted. They break easily if tightened down too hard. The gibs should be adjusted just enough to keep the slide from wiggling or moving in any direction other than the one intended. More than that will just wear out the gib.
The lock pin is used to keep the slide from moving. Don't use it to adjust the motion of the slide, you'll just wear out the center of the gib. However, when making a powered cut there's every reason to use the lock to keep the slide from moving.
The cross slide does have a lock screw that is indeed hidden behind the scale. I don't know why they do this, but they do.

Still hunting for the carriage gib on the exploded diagram. It's gotta be somewhere.

Mike at PM votes carriage rocking. He makes a compelling argument.

The carriage is clamped to the lathe bed in the front and back with a gib strip in the back. If any of those are loose, this could also allow the tool holder (the whole carriage actually) to rock, so it's worth check those too.
The fact that the lead screw doesn't show this effect argues for this being the cause. The half-nut clamps firmly around the screw and would prevent the carriage from moving in an odd direction. A bent feed rod would contribute as well, but once again, if the carriage is properly secured, it wouldn't cause an issue.

So tonight is gib night now that I understand how they work on this machine.

 

[Christianstark]

Clarification on the Gibs and the obscured lock pins from Precision Matthews.

Still hunting for the carriage gib on the exploded diagram. It's gotta be somewhere.

Mike at PM votes carriage rocking. He makes a compelling argument.


So tonight is gib night now that I understand how they work on this machine.

I would tend to agree with carriage rocking. What causes it is another mystery.

I will ask again, can you take a piece of rippled stock and match it up to the tooth pitch on the carriage feed? If the tooth feed is a direct match, you may be experiencing rocking as the pinion riding along the carriage feed lateral gear maybe tightens and loosens agains the teeth. pulling the carriage down and the tool slightly away from the stock. As the tooth moves further, that pressure is relieved, causing the carriage to rock back.

That being said, I do wonder why that might only be during power feed, so maybe the issue is with some eccentricity or poor gear mesh of the gear that drives the pinion during power feed.

 

[mikey]

Thanks everyone for the ideas! I'll hold off on messing with the VFD until the ripples get sorted out.

1. Correct
2. Correct -- Only tested .0025, .005, and .01, the feeds that are set up as standard.
3. Correct
4. The amplitude does seem to vary a bit. I can explore more here. I took an objectively WAY TOO heavy cut and the ripples were significantly less present.
5. Correct.
6. Very likely correct - I'm crap at manual feeding.
7. For a brand new lathe, I expect the power feed to function successfully, yes. Can I make parts using entirely manual feed, yes.
8. Shop power is 120VAC single phase. I know very little about motor control. If the VFD is turning that into 3 phase? ID

Seems to me that if the lathe finishes/turns clean when manually feeding then the issue has to be with the power feed rod or gears that drive it. The periodicity of the problem would point to the gear that drives the hex shaft in the head stock or the drive gear in the saddle. I don't see how it can be anything else given the responses you made above.

I would look to see if the gear that drives the hex shaft is tight and is in good shape. If it is, then I would pull the hex shaft and check it for straightness. Then if that fails, I would pull the saddle apart and look at the drive gear in there.

 

[macardoso]

Alright, I don't own a PM-1130V so I'll be including pictures of my lathe (an ENCO 110-2033, 12x36) but mechanically they should be similar.

Saddle Gibs:
My lathe has fixed gibs on the operator side, behind the apron, and adjustable flat gibs on the rear of the carriage.

Image 1: Headstock side fixed flat gib, located behind apron. Rides on ground underside of Vee way. Verify fully tightened.

Image 2: Tailstock side fixed flat gib, located behind apron. Rides on ground underside of Vee way. Verify fully tightened.

Image 3: Rear adjustable flat gib, located on the backside of the carriage. Rides on ground underside of flat way. Loosen the jam nuts, snug the adjustment screw, then tighten the jam nuts. You should feel a light drag on the carriage while sliding on well oiled ways.

Image 4: Same as the above the picture, but zoomed in on the adjustable gib.

Cross Slide Gibs:

Image 5: Cross slide tapered gib adjustment screw, operator side. There are (2) gib adjustment screws, one on the front operator side of the cross slide. Loosed the one in the rear of the lathe, then snug the front one up. There should be light to medium drag on well oiled ways. Lightly snug the rear screw. Do not over tighten as this can warp the gib.

Image 6: Compound slide tapered gib adjustment screws. Loosen this screw. Then snug the front one up. There should be light to medium drag on well oiled ways. Lightly snug this rear screw. Do not over tighten as this can warp the gib.

Image 7: Front side tapered gib adjustment screw on compound slide. Tighten to increase friction/rigidity.

Lock the cross slide and compound slide locks.

 

[pdentrem]

Does your handwheel disengage from the rack or is it always in turning when power feeding?
I found that if I maintained a constant tension on the handwheel there is a difference. My handwheel will slowly turn until the handle is at the top and then suddenly start down the hill, putting tension on the gear rack and change the amount of backlash present in the system. Try power feed but put a light drag on the wheel as it turns and see what happens. A dial indicator will show a speeding up and slowing down that is timed with the handwheel.
The only fix is to tighten the gibs on the carriage to add a little no drag to maintain the backlash that was taken up when the powerfeed was engaged.
Pierre

 

[mikkmake]

I don't want to let the thread go too cold.
I've tried a million and one things. The thing that appears to have an impact was tightening the carriage gips. Man, that was a pain in the butt. They are very inaccessible. Thank you @macardoso for your detailed guide on that process. Someday I'll take off the back splash guard and adjust the gibs without screwing up my back leaning over the lathe.

I can still sometimes see the ripples in surface finish but they are no longer measurable. The jam nuts aren't as well adjusted as I would have liked so I'll revisit the gips every few months.

For the question of pitch, here is the ripples compared with the rack.

There is no tightness or disengagement as a turn the carriage hand wheel. After watching Quinn (Blondihacks) crash and repair her pinion shaft I think it's very unlikely mine is bent.

 

[bretthl]

Sounds like you have chased down a lot possible adjustment issues. Have you tried changing your tool grind? I seem to remember having the same pattern on steel stock using a HSS tool bit with too sharp of a nose radius. Not saying that is the cause, just something to check out. Figuring out HSS grind, feeds-speeds-DOC by material was a steep learning curve for me (and I'm still not there).

 

[tweinke]

I don't want to let the thread go too cold.
I've tried a million and one things. The thing that appears to have an impact was tightening the carriage gips. Man, that was a pain in the butt. They are very inaccessible. Thank you @macardoso for your detailed guide on that process. Someday I'll take off the back splash guard and adjust the gibs without screwing up my back leaning over the lathe.

I can still sometimes see the ripples in surface finish but they are no longer measurable. The jam nuts aren't as well adjusted as I would have liked so I'll revisit the gips every few months.

For the question of pitch, here is the ripples compared with the rack.
View attachment 396968

There is no tightness or disengagement as a turn the carriage hand wheel. After watching Quinn (Blondihacks) crash and repair her pinion shaft I think it's very unlikely mine is bent.

Did you ever come to a resolution on the ripples

 

[Winegrower]

As another random opinion, and though it might be a problem with the photo, those rack teeth seem poorly formed and not identical looking. It’s possible whatever tool made the rack had some periodic error in it…maybe inducing a slight velocity variation in the carriage Z travel which could create a varying tool load with slight X axis deflections. Some gib looseness would make this more noticeable. This defect would support the no ripples manually, yet ripples under power feed.

Can the rack be replaced separately?

 

[Jake M]

I see this is an ongoing issue, have you solved it? One thing I notice, you were seeing a regular "amplitude", or height for the variation, but I don't see where you've measured a wavelength. Can you get a dial indicator on the carriage to measure carriage travel, to get a distance from high spot to high spot?

I was lead (almost immediately) to this for several reasons. Because you have no issues with the lead screw, and no issues with hand feeding, you can rule out a lot of things. In particular, the carriage slides along the ways just fine, without the undulations. Unless it's in one particular drive mode. And because you tightened the gibs, and WERE able to reduce the undulations, but not eliminate them. That just screams that something is acting on the carriage, forcing it to move in ways it otherwise doesn't. And, because you said at one point, something to the effect of you could feel the pinion gear switching from tooth to tooth (or something to that effect). That (probably) shouldn't be the case, but I dunno..... However, the feed shaft drives the carriage a given distance per revolution. With that information, the "wavelength" of the undulations in the work could be compared to the pitch of the rack/pinion gears, and/or "math'ed" a little in proportion to the gear ratio(s?) for the feeding mechanism inside the apron, and narrow the causes down to the items which are capable. Or, if you were to determine that the "wavelength" of the undulations changes with the feed rate you've selected, you could actually rule out the carriage/apron area and you'd be able to see if it were something back at the headstock end of the feed shaft. Although with the gib tightening results, I'd bet it's at the carriage area, because your evidence really points to something applying force to the carriage assembly in an unusual/abnormal way.