Regular Ripples w/ Power Feed on PM-1130v

[mikkmake]

First of all, I'm unbelievably grateful to all of you for jumping on this problem with me. Thank you.
Here's where I'm at tonight.

Passes, Feeds, and Materials
Disclaimer: Many of these passes have crap finish for other reasons. I'm not talking about the overall finish here, that's a totally different topic; I'm specifically investigating the ever present, regular, ripples.

Boy am I blowing through bar stock on test bars. Gotta order more metal. Sticking with free machining steel and 6061 aluminum for now. If I ever get this resolved, I'll have fun with the brass (so pretty but sooo $$$).

Every pass used the same HSS tool. I've replicated this using some other off the shelf tooling with the same results.

500ish RPM, Manual Feed, 6061, .020 DOC -- Work piece was about .500
I'm not well practiced in manual feeding but it's clear that the pattern didn't show up. I did feel as the pinion transitioned from one gear to the next. This tripped up my smooth turning from time to time. Generally, OK.

500 RPM, .010/rev, 6061, .020 DOC

300ish RPM, .0025/rev, 12L14, .020 DOC

Here are two more passes on the 12L14 but I forgot to write down which was which on the feeds. Both were faster than the slowest which is .0025. As I see it, both of these also clearly show the pattern.

​

Measuring the Ripples​

I took this super lovely pass in 6061. It is glassy smooth to the touch apart from the ripples. I put a tenths DTI on the carriage and ran it over the surface. I measure between 5 and 9 tenths between the low and high spots consistently. I can repeat this measurement on the surface plate if we want to remove the carriage as a source of measurement error.

Other observations and Feedback from Precision Mathews​

At their suggestion, and in line with the post from "the other forum" I did some inspection of the rack and pinion while under power. I was unable to see anything visually wrong. I snuck an indicator in and was able to measure about 1.5 thou of runout/wobble on the pinion shaft about .25 from the gear. Hard to know if this is having an impact.

Applying pressure to the hand wheel either helping or opposing the direction of motion doesn't seem to make a difference.

EDIT: The pattern is apparent when power feeding away from the chuck as well.
EDIT: Tail support also makes no difference.

PM also suggested swapping out some change gears to see if there is some eccentricity in them somewhere. I'll try that when I get back next week.

One more test I should try out is a manual spring pass after a power feed pass. This just occurred to me as I was writing so I'll add that to the test list for the next session.

Here's a video running at .0025 in steel. The wine you hear is another annoying issue I'm experiencing with the VFD. That I've solved with ear plugs.

I'll try just about anything at this point. I'm really impressed with this lathe all around but this power feed issue is really making life tricky. I discovered it during initial adjustment when I was working on bed leveling and tailstock alignment. Both are operations during which I was hoping to leverage power feed for consistent cuts.

That's all I have for now.
Regards,
Eilif

 

[mikkmake]

Whoops, I forgot one pass. @macardoso here's the .005 pass. Not as prevalent but still there and can be felt.

I'm generally expecting the finish to be kinda bad or kinda good but mostly random. The regularity is the most perplexing part.

 

[macardoso]

Let me try and summarize. Please correct if I am wrong.

1. Ripples present when power feeding carriage
2. Ripples present at any tested power feed rate. (0.0025"/rev and up)
3. Ripples present in all tested materials
4. Ripples are between 5 to 9 tenths in amplitude
5. Ripples are NOT present when using the threading leadscrew to power feed
6. Ripples are NOT present when manually turning a fine finish
7. Absence of ripples is a requirement for proper operation of the lathe
8. You lathe has a 3 phase spindle motor.

Here are a couple random thoughts

1. Ripples are likely NOT caused by variations in the ways
   1. You'd see them
   2. Ripples are not caused by manual or leadscrew feed
2. Ripples are likely NOT caused by any gearing in the headstock
   1. Those gears power both the leadscrew and feed rod. You'd see issues in both.
3. Your lathe is equipped with a 3 phase spindle motor and VFD. This *should* resolve any harmonics issues people complain about with single phase motors.
4. Try and snug up on the carriage gibs. It should have a light drag to it but not be tight. If this is loose, there might not be much keeping the carriage from bouncing around. Don't forget to oil all sliding ways including the ones on the bottom side of the bed. Lathes have a lot of ways.
5. Try and snug up on everything on top of the carriage. Make the setup as rigid as possible.
   1. Cross slide gibs
   2. Cross slide locks
   3. Compound slide bolts
   4. Compound slide gibs
   5. Compound slide locks
   6. Tool post mounting
   7. Tool mounting
   8. Minimize tool overhang
6. The passes you are taking seem light. This seems to indicates the issue is not with rigidity.
7. Can you measure the pitch of the crests of the ripples? This might help indicate where in the gear train the issue might lie.
8. Measure the travel of the carriage after exactly 1 handwheel revolution.
9. Try to measure the travel of the carriage after exactly 1 feed rod revolution. Disconnect the lathe from power and rotate the feed rod manually while carriage power feed is engaged.

I still think the most likely culprit is something in the apron gearing, but I don't think we have tested enough to eliminate all other possibilities yet.

 

[Christianstark]

"Here's a video running at .0025 in steel. The wine you hear is another annoying issue I'm experiencing with the VFD. That I've solved with ear plugs."

Can you share your programmed settings in the VFD? Is it Hitachi? There may be a very easy fix for this.

Edit - Also, is there a repeatable cadence to the ripples? Are they always the same length or does frequency change depending on feed rate?

 

[mikkmake]

"Here's a video running at .0025 in steel. The wine you hear is another annoying issue I'm experiencing with the VFD. That I've solved with ear plugs."

Can you share your programmed settings in the VFD? Is it Hitachi? There may be a very easy fix for this.

It's straight from the factory. I have a VFD manual that came with the lathe but I didn't program anything myself. Here's exactly what I know about the drive system so far. https://www.precisionmatthews.com/shop/pm-1130v-lathe/

The booklet that came in the crate with the lathe says it's a Delta (not the delta woodworking tool brand), MS300. I don't have any more information as I'd have to lift and rotate the lathe to see the back. There appear to be parameter settings available in the manual but I don't know what any of it means.

 

[Christianstark]

It's straight from the factory. I have a VFD manual that came with the lathe but I didn't program anything myself. Here's exactly what I know about the drive system so far. https://www.precisionmatthews.com/shop/pm-1130v-lathe/

The booklet that came in the crate with the lathe says it's a Delta (not the delta woodworking tool brand), MS300. I don't have any more information as I'd have to lift and rotate the lathe to see the back. There appear to be parameter settings available in the manual but I don't know what any of it means.

See if the booklet has an option to view and edit "Carrier Frequency", and if so what is it set to currently? A good place to try to get a reduction min whine is 12kHz.

 

[Illinoyance]

If the feed pinion does not engage the rack properly the feed rate will be irregular resulting in banding. The pitch of the banding would be the same as the pitch of the rack. Quite common on older machines with worn beds.

 

[Christianstark]

Can you hold a banded piece up to the rack? Do the bands exactly match the stagger of the feed rack?

 

[mikkmake]

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

1. Ripples present when power feeding carriage
2. Ripples present at any tested power feed rate. (0.0025"/rev and up)
3. Ripples present in all tested materials
4. Ripples are between 5 to 9 tenths in amplitude
5. Ripples are NOT present when using the threading leadscrew to power feed
6. Ripples are NOT present when manually turning a fine finish
7. Absence of ripples is a requirement for proper operation of the lathe
8. You lathe has a 3 phase spindle motor.

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? IDK

Ripples are likely NOT caused by variations in the ways

Agreed. This lathe is brand new. Ways look pristine.

Ripples are likely NOT caused by any gearing in the headstock

I agree but I haven't actually changed out any gears yet. Was hoping to get the lathe adjusted in and gain some experience before messing with the change gears.

1. Try and snug up on the carriage gibs. It should have a light drag to it but not be tight. If this is loose, there might not be much keeping the carriage from bouncing around. Don't forget to oil all sliding ways including the ones on the bottom side of the bed. Lathes have a lot of ways.

This is going to sound silly but I can't actually find any carriage gibs that appear adjustable. The carriage lock grips the ways from the underside. Can't tighten this or I'd break everything.

While I'm here...
The cross slide and top slide don't seem to have the usual gib adjustments I've seen before and the adjustments do not match the photos in the manual. There are two gib retaining screws on the end of each slide that seem to move the gib slightly but don't appear to be cams by design. Tightening the daylights out of them does stiffen the slide a bit.
The top slide has a single screw and pin which does tighten up the slide. The cross slide may have a similar screw and pin but it is obscured under the linear scales for the DRO. These may be the slide locks but if they are, they are very coarse or, in the case of the cross slide, inaccessible.

The exploded diagrams in the manual show the lathe as delivered while the photos do not.
Am I missing something on slide adjustment?

Here's a photo of the retaining screw on the cross slide. A similar screw can be see in the top right of the photo for the top slide.

Can you measure the pitch of the crests of the ripples? This might help indicate where in the gear train the issue might lie.

Measure the travel of the carriage after exactly 1 handwheel revolution.

Try to measure the travel of the carriage after exactly 1 feed rod revolution. Disconnect the lathe from power and rotate the feed rod manually while carriage power feed is engaged.

These will come in the next update tonight or tomorrow.

The hunt continues!
-Eilif

 

[mikkmake]

One more thing!
A camera on the pinion did not show anything obvious -- it's moving fairly slow. I put an indicator on the pinion shaft as close to the pinion as I could. I measured about 1.5 thou of eccentricity on the shaft.