Saddle causing .150 taper 3” off chuck no tailstock need help.

Cadillac

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Put a indicator on the flat way of the saddle. Have to point riding the flat way while taking a cut and see if there’s movement in the cut. You shouldn’t get more than acouple TENTHS of movement on any sliding surface if not NO movement. Good luck
 

RJSakowski

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Follow up: Well I’m still contending with the issue. The manufacturer has been very slow to return calls and today I finally was able to put a parts request in although I have to wait to get a quote back in a few days it’s a painstakingly sloooowww process. In the interim I removed the compound slide and installed a machined piece of 4140 that has removed .22mm or .0085 so it has lessened the taper by 50%. Rather than two sheets of paper thick of taper it’s now one. It’s still too much for some parts I need to make that slide together. The next thing to do is to replace the y axis lead screw and nut. If that doesn’t fix it then a new carriage top. If that doesn’t work then I will call a local repair shop to come out and see what they can do. I suppose the lead nut could be moving that much under load it’s really hard to tell I cannot get anything to indicate that tells me I’m having an issue. I did cut a piece of tool steel and a piece of 6061 and both tapered identically so that was a good sign I suppose that it’s not affected by material and it’s a mechanical issue. After all this I think it’s time to upgrade to a 16” lathe if after a year of use we are wearing these parts out this fast. I would hope to get 3-5 years before replacing mechanical components.
Turning a taper should not be affected by the cross feed lead screw or nut. Nor should the tailstock be the cause if not using the tailstock center.

Turned parts will tend to have a slightly larger diameter at the tailstock end, the amount dependent upon tooling geometry, condition of the cutting edge, the depth of cut, the material, and the diameter of the stock. Since the tailstock end is smaller in diameter, this isn't the cause of your prob;lem

Aside from that, there are only two conditions which will cause a turned taper. The headstock is misaligned or the lathe bed is twisted. The effect of headstock misalignment is fairly obvious. Rotating the headstock in a horizontal plane will bring the part closer or further from the cutting tool as the carriage moves away from the headstock, depending which way it is rotated. Some lathes like the Sherline actually rotate the headstock to purposely cut tapers.

The carriage rides on the vee way at the front, being prevented from lifting by small plates at the front and back of the carriage that ride on the under side of the ways. The vee way determines the distance of the cutting tool to the spindle centerline. If the bed is twisted, if corkscrews which will raise the front edge of the carriage and drop the back edge or vice versa. Since the cutting edge is several inches above the pivot point, the effect is to move the cutting edge closer to the spindle axis. The effect increases as you move away from the headstock causing a taper to be cut.

There is also a slight shift in vertical position of the cutting tool which moves the cutting edge up or down depending upon the direction of twist. This effect is usually minor compared to the lateral movement although it will increase if the cutting edge is significantly lower or higher than the horizontal plane though the spindle axis.

By the same token, if the headstock were rotated in a vertical plane it would have a similar effect, raising or lowering the toll relative to the spindle axis as you moved away from the headstock.This would be extremely unlikely unless the headstock was removed from the ;lathe or there had been a severe crash.

Considering that the lathe had been performing satisfactorily in the past and that you have not seen any serious change in level and the amount of taper that you are experiencing, I would suspect the headstock has shifted. It is possible that the mounting bolts were not tightened sufficiently and a crash could have caused a shift. In any event, I would check that first. I would position the carriage close to the headstock and lock it in place. I would mount a faceplate with a small boss about half the cross feed travel distance from the centerline. Mount an indicator on the crossfeed and rotate the faceplate so the boss is at the front and more or less horizontal with the spindle axis. Zero the indicator on the boss and mark the contact point with a Sharpie. Rotate the boss to the rear and move the indicator with the cross feed to intersect the mark on the boss. A difference on readings would mean that the headstock is not perpendicular to the cross feed travel and, by inference not parallel with the ways.

There are some caveats. The assumption is that the carriage cross feed travel is perpendicular to the carriage ways The second is that any degree of twist is not affecting the measurement. This is probably a safe assumption since the effect of the twist is least with the carriage near the head stock.

Here is my faceplate modified for this measurement. The boss is a bolt with the head slightly domed and polished.
FacePlate .JPG
 

bretthl

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Just a suggestion ... mic the work piece at 1/2" intervals and plot the diameter vs distance. If it is a straight line trend then it may be, as others have suggested, a head stock alignment problem. If there is a shift in the trend (not a straight line) then perhaps the problem is in the carriage or ways.
 

stupoty

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Hay , hows it all working out for you at the moment? Have you managed to nail down your issue yet?

Stu
 

pacifica

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I think I would do this first:
. Along with the face plate test by rjsakowski, check runout in spindle bore, level lathe,turn a test piece of 1.5 to 2" steel that is 10" long(no tailstock) and go from there(align headstock?).
 

petertha

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Misaligned headstock & related taper cutting problem has been discussed quite a bit. I know I have posted & included these same pics just cant find the link(s) right now. There is a very fast & accurate way to verify.
First - do your lathe levelling due diligence
Second - buy a MT3/cylindrical test bar like this inexpensive ($50) import I bought on Ebay. They are cylindrical ground & plenty accurate. If you have an MT socket like MT5/MT3, plug that in the spindle, then the test bar so it is extending cantilever. No chuck is involved. No tailstock is involved. No material cutting is involved. Mount DTI to saddle, run down the test bar along the horizontal plane. What do you read? If its pointing in or out (anything but zero) you will be cutting a taper longitudinally and a cone in cross feed. Its as simple as that. You need to correct this by loosening your HS bolts & carefully adjust the shimming/jacking bolts so the HS rotates in so the bar is parallel to bed axis. The screws are uber sensitive so just crack them & re-measure.

While you are at it, repeat test with DTI along the top of the bar. Is it pointing up or down? Trickier to solve but same basic problem.

Only when this is remedied can you introduce the tailstock into the picture.
 

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petertha

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ps - I notice several of the same vendors also offer MT5 ended cylindrical test bars if you want to go that route if your spindle is MT5. This eliminates the MT5-MT3 intermediate sleeve, but I would assume they are pretty ground accurate too. My tailstock is MT3 so it can serve double duty there. Basically its acting as a big long lever exaggerating any angular deviation.

For example (no affiliation)
https://www.ebay.ca/str/atoztoolstore/Lathe-Test-Bars/_i.html?_storecat=18372947012
 

stupoty

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ps - I notice several of the same vendors also offer MT5 ended cylindrical test bars if you want to go that route if your spindle is MT5. This eliminates the MT5-MT3 intermediate sleeve, but I would assume they are pretty ground accurate too. My tailstock is MT3 so it can serve double duty there. Basically its acting as a big long lever exaggerating any angular deviation.

For example (no affiliation)
https://www.ebay.ca/str/atoztoolstore/Lathe-Test-Bars/_i.html?_storecat=18372947012
I'm really tempted by a test bar, I was thinking of getting it in MT3 and have a sleeve so I can put it in the MT4 head stock and my tail stock.

I wonder how much difference their is between sleeve brands for run out ?

Stu
 

Rex Walters

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I'm really tempted by a test bar, I was thinking of getting it in MT3 and have a sleeve so I can put it in the MT4 head stock and my tail stock.
If I could only afford one, I'd buy the larger test bar for the headstock. A sleeve is probably accurate enough but will more than double potential errors (two mating surfaces for grit/burrs/whatever to cause you to pull out your hair).

The tailstock is far less critical IMHO. Drills and reamers will tend to follow their own path anyway (you'll need to use a boring bar regardless for accurate holes) and the tailstock is adjustable for cutting/not-cutting tapers when turning between centers. The spindle taper you want dead nuts aligned to the bed ways in both dimensions (horizontal and vertical, maybe ever so slightly pointing higher toward the tailstock — a few tenths over 12" at most).

A taper test bar isn't a mandatory tool unless you have reason to distrust the accuracy of your lathe (or are planning to rebuild it). It's kind of a one time use tool. (But I own both!).
 

petertha

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The tailstock is far less critical IMHO. Drills and reamers will tend to follow their own path anyway
That's the beauty of being able to plug same MT# test bar into either head or tail stock. You can similarly check TS alignment by mounting a DTI in the lathe chuck & turn it around the OD. Yes, you can also do this with a regular dead center, but what the longer bar is providing is extended cantilever length so its going to exaggerate the angular discrepancy: up/down/left/right. Yes big drills & reamers might find their own drilling holes & such but its still better to have the TS aligned. Turning between centers depends on this. No sense having a 0.0002" live center when teh TS is in or out 0.002". Another example, after breaking 2 teeny carbide center drills in tool steel it finally dawned on me to check the TS, sure enough it had migrated off a couple thou. Actually that's not quite true. What I learned is that just tightening the TS down against the displacement grub screws while adjusting can drift it (on my particular lathe). So now I leave an indicator ball on the bar as I'm setting it up & just tweak it down while the needle is giving me constant reference.

Yes it probably goes without saying you have to clean any mating surfaces, particularly between rotating parts. Setting up the machine is the one time you should be extra diligent unless you want to repeat this whole process. HS alignment is a PITA. Maybe I got lucky but before committing to the MT3 test bar I put a tenths indicator on the MT5 ID taper of the spindle, measured nil runout. Inserted the MT5-MT3 socket adapter, exact same thing. Pulled & clocked it a few different ways, same thing. So I trust it.
 

stupoty

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If I could only afford one, I'd buy the larger test bar for the headstock. A sleeve is probably accurate enough but will more than double potential errors (two mating surfaces for grit/burrs/whatever to cause you to pull out your hair).

The tailstock is far less critical IMHO. Drills and reamers will tend to follow their own path anyway (you'll need to use a boring bar regardless for accurate holes) and the tailstock is adjustable for cutting/not-cutting tapers when turning between centers. The spindle taper you want dead nuts aligned to the bed ways in both dimensions (horizontal and vertical, maybe ever so slightly pointing higher toward the tailstock — a few tenths over 12" at most).

A taper test bar isn't a mandatory tool unless you have reason to distrust the accuracy of your lathe (or are planning to rebuild it). It's kind of a one time use tool. (But I own both!).
Yeah , I think you are right about the sleeves, I have had my head stock off before but it does sit on the ways for alignment so I might just use the button on the face plate method fof double checking it and call it good.

Although a shiny test bar ? who could resist that ? I will just keep my eyes peeled on ebay unless I find plenty of spare cash in my pockets for some reason :)

(although the power hack saw motor rewind is priority for cash injection currently)

Stu
 

Rex Walters

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You can similarly check TS alignment by mounting a DTI in the lathe chuck & turn it around the OD.
I might be misreading, but whatever you do, do not rotate a test indicator around the horizontal axis such that you perform some readings with that dial facing up and some with it down. Gravity absolutely will affect your indicator reading significantly.

It’s a common mistake but easily proven to be terribly imprecise - Richard King demonstrates this effect at the beginning of all of his classes:


I also still prefer dedicated test bars for headstock/tailstock rather than a single bar and an adapter sleeve. But your process sounds great if you only have one for the tailstock.
 

petertha

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Good point, I should have clarified I'm measuring tailstock in/out relative to operator which is the typical jackscrew offset adjustment relative to bed axis. So I assume the DTI would be seeing the same gravity forces in those 2 orientations where the face is vertical but pointing either towards or away from operator on either side of test bar centerline. But maybe that cant be trusted either? I'm going to repeat that Richard King test at home. I've read about it but never seen it demo'd live like that. Very interesting.

Actually, full disclosure, I have one of those Edge test bars that I use for TS adjustment. I bought it subsequent to the MT test bar. What can I say, I'm a tool junky LOL. The DTI stays in same position from heatstock ring to tailstock ring so the DTI sag issue isn't there. You can also DTI off the top of the HS ring & then compare to TS ring. My TS is about 0.001" high which I'm told is normal.
 

darkzero

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Although a shiny test bar ? who could resist that ? I will just keep my eyes peeled on ebay unless I find plenty of spare cash in my pockets for some reason :)
Those things are pretty cheap on ebay. MT3 bar is like $33 shipped all the way from India. I paid like $60 shipped for my MT5 bar. Been sitting in the tool box for years though but at least it's there. :big grin:
 

john.k

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I d be checking that the saddle wasnt fouling some part of the bed ,or gap,and forcing the ways apart as it moves forward..................I checked a similar happening once,and the problem was the small piece of rack attached to the gap was oversize.
 

petertha

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... whatever you do, do not rotate a test indicator around the horizontal axis such that you perform some readings with that dial facing up and some with it down. Gravity absolutely will affect your indicator reading significantly. It’s a common mistake but easily proven to be terribly imprecise - Richard King demonstrates this effect at the beginning of all of his classes:
Well I finally had to try this for myself. I have 2 new-ish Mitutoyo DTI's. One is 0.0005" the other 0.0001". When I hold them by the body or by the dovetail mounted boss adapter & rotate in by hand, the dial goes nowhere in any rotation. It sits in the exact zero position. Do you think this is a fair comparison to Richards demo or should the needle be loaded?

Seems to me I tested this once upon a time too clocking around an accurate dead center with DTI in chuck & needle on OD. Pulled out the dead center rotate 1/4 turn, rinse & repeat. Same setting looking at the underside measurement with a mirror. I just don't recall the needle moving under gravity but I wasn't really looking for the effect either.

I haven't yet mounted it to a mag holder & plate yet like video, that will be next. But now isn't that introducing potential drift of the indicator holder arms & assembly into the equation vs the DTI in isolation? Sorry if this is off topic. I know this has come up before, just cant find the link.
 

Rex Walters

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Do you think this is a fair comparison to Richards demo or should the needle be loaded?
I’m don’t know what percentage of the gravity effects are with the indicator itself vs the holder arm assembly. I even asked this very question during the class this week.

I wouldn’t be at all surprised if it isn’t almost entirely with the holding assembly. But since you always need some sort of holder assembly regardless, and there are many better ways to indicate the tailstock in, I’d still avoid rotating an indicator.

Richard said Stefan G. did some testing of this sort with various indicator holders to see which were most rigid with this type of testing, and that (quality) old-school rod and flexture clamp type holders were way more rigid than flexible mounts of any type.
 

stupoty

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I’m don’t know what percentage of the gravity effects are with the indicator itself vs the holder arm assembly. I even asked this very question during the class this week.

I wouldn’t be at all surprised if it isn’t almost entirely with the holding assembly. But since you always need some sort of holder assembly regardless, and there are many better ways to indicate the tailstock in, I’d still avoid rotating an indicator.

Richard said Stefan G. did some testing of this sort with various indicator holders to see which were most rigid with this type of testing, and that (quality) old-school rod and flexture clamp type holders were way more rigid than flexible mounts of any type.
I was surprised the Noga flexed that much over the relatively short distance, next time I am at a loss I will try this with my rod and clamp type holders and see how flexy they are.

Stu
 

john.k

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I have found that a lever type gauge solidly mounted on a square bar ,held in a 4 jaw ,has negligable gravity effect,and can be ignored,.........however a dial gauge mounted on two angled rods to a magnetic base attached to the chuck face will have several thou gravity effect............and in one case ,an owner decided his tailstock was 005 high!.......,and had the base surface ground,on the evidence of a dial gauge.
 

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It’s been one month since Uguessedit has replied to this thread. We’ve since gone down quite the rabbit hole with him absent. I wonder what’s happening with the machine in question.
 

petertha

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I’ll upload some pics from my camera, but here are my findings. New & tight Noga mini DTI mag base. I chose it for test#1 because its the smallest one I have. Mitutoya 0.0001” DTI. Installed on a 3x5 chunk of steel. About 2 thou preload & needle zeroed sitting upright. Rotate the steel base 90-deg I get about 0.0002” deflection. Rotate it 180-deg so completely inverted, get about 0.0010-0.0012” needle deflection. So it’s real. My guess is a longer arm mag stand and/or a heavier Dial Indicator vs DTI may well exaggerate these findings. My gut feel is 99% of this is ‘gravity effect’ is attributable to the indicator holder assembly itself because when I grip the DTI by the short stub arbor that comes with the kit in a lathe collet & spin around a dowel pin I get no measurable difference. So that has eliminated pre-load & inversion on exact same DTI. The only remaining variable is the holder assembly. Maybe if you absolutely have to go inverted then consider a bolt-together holder vs the hydraulic or tension lock style. I'll try my longer Noga next.
 
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petertha

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I know this is detracting from the thread, but I'll post my pics & re-post elsewhere under something like Gravity vs indicator holder.
Noga Mini + Mitutoyo 0.0001: Level = 0.0000, 90-deg = 0.0005 - 0.0008", 180-deg (inverted) = .0011
Noga 14"? + Mitutoyo 0.001: Level = 0.000", 90-deg = .0042", 180-deg = .0055" (suspect a smidge more because it didn't return to zero & there might be some flex in my bar).

Conclusions
- I think the DTI by itself might not see much gravity effect, but the contribution of the DTI holder assembly sure can.
- if you have to use a holder, best to find something significantly more rigid. Or else find some independent way to DTI reference in an angled/inverted position. Reading DTI values at different rotation clock positions is a no-no.
- assembly weight is the enemy here. I suspect a dial indicator would be worse because it weighs more than DTI
 

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bretthl

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I know this is detracting from the thread, but I'll post my pics & re-post elsewhere under something like Gravity vs indicator holder.
Noga Mini + Mitutoyo 0.0001: Level = 0.0000, 90-deg = 0.0005 - 0.0008", 180-deg (inverted) = .0011
Noga 14"? + Mitutoyo 0.001: Level = 0.000", 90-deg = .0042", 180-deg = .0055" (suspect a smidge more because it didn't return to zero & there might be some flex in my bar).

Conclusions
- I think the DTI by itself might not see much gravity effect, but the contribution of the DTI holder assembly sure can.
- if you have to use a holder, best to find something significantly more rigid. Or else find some independent way to DTI reference in an angled/inverted position. Reading DTI values at different rotation clock positions is a no-no.
- assembly weight is the enemy here. I suspect a dial indicator would be worse because it weighs more than DTI
I’m confused. I thought a dial test indicator is used to take a relative measurement. So unless there is flex in the arm caused by the spring tension from the indicator itself then things should be okay.
 

petertha

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Yes, that's the whole issue. Flex in the apparatus that is holding the indicator, not so much an issue with the indicator itself. Think of it this way - if you press your finger on the articulated arm, the indicator registers displacement. Well gravity is like your finger, its a force acting on the mass of the arm assembly. Its moving under its own weight vs. the assumption that it stays locked in position. So the indicator cannot distinguish this displacement from something that is out of round.
 

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Ive bought a lathe like this. It also had a bad taper that I could not get rid of .I had it reground by a very dubios character.He said it would take six weeks but I had to physically remove it six months later.He took a six meter lathe and because his grinder wasnt long enough he ground it from both sides and blended it in. But thats another story.
The remark about the gap should be looked at. I would try a three jaw chuck in a 4 jaw to push it away as far as possible from the headstock and try taking two cuts from the tailstock and headstock side and then compare.
Just out of interest when I removed the headstock I was shocked to find there are no vees under the headstock. But what shocked me about it is that instead of being scraped in you could clearly see that they had used an angle grinder . There were actually big gouges taken out.
 

Illinoyance

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Many lathes have jack screws that are used to align the headstock to the bed. See if your lathe has them.
Before checking for, and correcting taper issues be certain the bed is not twisted. Check it with a precision level.

Use a test bar as shown in the video. Relieve the middle of the bar leaving a collar about 1/2" wide at the outboard end and next to the chuck. Take a light test cut across both collars (without disturbing the cross slide) . Measure them. If there is a difference, use the jack screws to bring the headstock in line with the bed. It will take several attempts. Adjust, make a trial cut, measure, repeat until both collars are the same diameter after a test cut.

After you have the headstock true to the bed it is time to address the tailstock alignment. Make a test bar with a center in each end and a raised collar at each end. At the headstock end leave room beyond the collar for a lathe dog. Set up the test bar between centers and drive it with a dog. Make a test cut across both collars (without disturbing the cross slide). Measure the collars. Adjust the tailstock until a test cut produces equal diameters on the collars. Save the test bar. In the future you can set the test bar between centers then set an indicator to zero on the collar nearest the headstock, them move the carriage and see if the indicator reads zero at the tailstock end. If it does your tailstock is dead on. If not adjust the tailstock to get the indicator to zero. You might have to repeat that check a couple time to get both collars to read zero.

The sequence of tests and adjustments is critical.
1. correct twist in the bed, commonly refereed to as leveling the bed.
2. adjust the headstock so the spindle is parallel with the bed. A bar held in the chuck should show no taper when turned.
3. Adjust the tailstock using the two collar method.

The tool used to make test cuts should be HSS and very sharp. Test cuts should only be a few thou depth of cut. Heavy cuts or carbide inserts will deflect the test bar making it difficult to achieve good results.

I am now in the process of aligning the headstock on my Nardini. I had about .020" taper in 6". It is a time consuming job.
 
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bretthl

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Just out of interest when I removed the headstock I was shocked to find there are no vees under the headstock. But what shocked me about it is that instead of being scraped in you could clearly see that they had used an angle grinder . There were actually big gouges taken out.
I don't think any Asian made lathes have head stocks that rest on way vees.
 

Illinoyance

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The quality of Asian tools can vary all over the map. A lot of it has to do with the quality control the importer has in place. I suspect many importers care very little about the quality of machines they sell.
 

bretthl

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Yes, that's the whole issue. Flex in the apparatus that is holding the indicator, not so much an issue with the indicator itself. Think of it this way - if you press your finger on the articulated arm, the indicator registers displacement. Well gravity is like your finger, its a force acting on the mass of the arm assembly. Its moving under its own weight vs. the assumption that it stays locked in position. So the indicator cannot distinguish this displacement from something that is out of round.
If you don't move the indicator base/arm the gravity acting on the arm should not change.
 
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