Lathe cutting a taper

[Chris MateParticipant @chrismate31303]

I bought a new CQ6133 lathe few years back. I worked around the taper cuttng problem, but are back at it again.

Note-1:Shimming & measuring=OK
-I Fitted a 16mm HSS grounded bar with 110mm stickout from 3 Jaw chuck. MY 3 jaw chuck had been modified to true adjust. So I adjust the chuck to run this bar without runout=OK.
-I managed to ajust/shimmed rear of bed inside bolt to .014″ shim. With this the .01mm Dial Indicator run true zero deflextion/taper along the HSS bar=OK.

Note-2:Cutting another Test Bar, setup as above=OK.
-As soon as I take a lightish cut with new insert(10mm shank type), I get a taper not good up to .1mm taper.
-Now I can duplicate this by pulling on the bar with one finger, I can pull it easily up to .1mm, with force up to .18mm.

Note-3:Checking headstock versus Spindle backplate versus MT5 versus face of backplate.
a)The spindle run 100% true(I was surprised), the spindle face run 100% true(I was surprised again).
b)Fit chuck & HSS Bar. Fit Dial indicator to headstock & measure from headstock to spindle, to chuck, to HSS bar. No movement with finger, zero. If I grab the bar with hand and pull as hard as I can, the deflection is minimal at less than.01mm, which certainly is not the problem I am looking for.

Note-4: Check headstock fit to Bed .
-The headstock is tight, I cannot tighten the bolt anymore.
-At this stage the bed is tight to the plate on cabinet, and run without taper from crossslide with shim, and without cutting or pulling.

Question: Where does this cause of the taper comes from-?

If you fit a bar to your chuck and pull on it, how much deflection do you get-?
-The pulling wih one finger to seems like similar taking a light cut.

If it was the spindle bearings, I would thought I saw that in the headstock/chuck/Bar test-?

[JasonBModerator @jasonb]

Note-1:
-I Fitted a 16mm HSS grounded bar with 110mm stickout from 3 Jaw chuck.

Note-2:Cutting another Test Bar, setup as above=OK.
-As soon as I take a lightish cut with new insert(10mm shank type), I get a taper not good up to .1mm taper.

 

To me 110mm of 16mm bar sticking out is not a good idea, Ctr drill it and use tailstock support

[bernard towersParticipant @bernardtowers37738]

your turning test should be done with a dumbbell shaped bar and with compound set to 5.75 deg. and then test cuts of tenths can be taken (3 or 4) then measurements taken.

[Chris MateParticipant @chrismate31303]

What puzzels me the most, is not cutting a test bar, but the fact that measured from the Headstock nothing moves(Hard pull), but measuring from crosslide it moves a lot(Soft pull), and that make sense to the taper it cuts under very light load…….I just cannot see where this is coming from yet. The bed cannot be that flimsy…..

From the headstock to the tip of the bar(Chuck & chuck jaws included) nothing moves, my 1st thought it was the spindle bearings, but it does not look that way.

[bernard towersParticipant @bernardtowers37738]

If you are going by soft pull and hard pull thats not very scientific you should let the lathe do the work then measure and yes a lot of latje beds are flimsy to a small degree. the twist can be adjusted with adjustable feet.

[Michael GilliganParticipant @michaelgilligan61133]

Slight digression, but I think it’s worth looking at Schlesinger’s design for a test mandrel … It puts the flexibility of all such items into the proper perspective !

Details are on p5 in the widely downloadable book.

MichaelG.

[Martin ConnellyParticipant @martinconnelly55370]

What inserts are you using? The long stick out relative to the diameter (slenderness ratio) of 6.8 is well in excess of most recommended values, typically 2.5 to 3 depending on the material being machined. Coupled with the relative bluntness of the majority of carbide inserts it will result in the bar moving away from the cutting tool at the free end. This will give a larger diameter at the free end than is turned close to the chuck.

As Jason said, supporting the free end is a good starting point, then use ground inserts rather than just moulded ones, using a well sharpened HSS tool with a small radius tip to minimise the pressure on the bar is also better than most moulded inserts. Finally for long slim parts a travelling follower rest will reduce flexing of the part but is a lot of messing around if you can avoid it and does not work in all cases, shoulders can get in the way for example.

Martin C

[bernard towersParticipant @bernardtowers37738]

i think we are at cross purposes here as the OP is concerned about the lathe turning tapered, no mention of tailstock use. these are two different things and adjustments made to alter things are different. the one for unsupported turning is usually bed twist and the second is tailstock misalignment.

[JasonBModerator @jasonb]

Not at crossed purposes but debating if it is the fault of the lathe or simply bad practice with so much stickout and “blunt” tools that is causing the taper.

But how far is reasonable unsupported turning. I’d not want to start twisting my bed to compensate for what is most likely to be the work deflecting away from the tool.

Before touching anything I would try it with some 30-40mm bar and sharper cutting tools on a warmed up machine. Only then if the same amount of taper is present would I think about looking further.

Though we have not been given any indication of which way the taper runs which could eliminate the work deflection if the dia is smaller away from the chuck.

[Dave HalfordParticipant @davehalford22513]

Note 1 good

Note 2 you don’t say what size this new test bar is, but it sounds like a light one. Using what you did anyone would get the same result unless you use a sharp GT style insert for aluminium.

Note 3 Of course, HSS does not bend. What you were machining before does bend. Had you taken a cut on the HSS bar with the carbide it would probably been parallel.

Note 4 good.

I think this was raised last time, but is the carriage locking lever too loose? If so on some machines (mine) the saddle can skew when drive is applied. Your finger held where the wiper meets bed will detect any sideways movement

 

[Dave Halford]

On Dave Halford Said

Of course, HSS does not bend.

A common misapprehension. Stiffness and strength are not the same thing. The modulus of elasticity of HSS is little different from that of mild, or any other steel.

[Peter Cook 6Participant @petercook6]

Some math.

A 16mm cylindrical steel beam rigidly supported at one end and 110mm long will deflect about 0.08mm under a pull of 25lbf.

For the same rod, based on simple geometry, if the supported (chuck) end deflects .001 (1 micron) the far end will show a 0.1mm movement. In reality the point around which which the composite unit of rod, chuck and front part of the spindle, pivot is probably another 100+ mm further back (half way down the spindle?). So .0005 mm of play in the front bearing will translate to your 0.1mm movement 110mm out from the chuck.

The lubricant film in the front bearing is probably of the order of 1-2 microns, and as the bearing is not rotating you may be squeezing the oil film out.

I suspect the 0.1mm movement you see with one finger pull is a reflection of a very much smaller amount of movement in the spindle bearing, and  the 0.18mm with a strong pull is a bit more of the same plus bending the bar.

[Clive FosterParticipant @clivefoster55965]

Concerning the possibility of deflection when turning the test area or user the weight of the test bar.

My preference is to use two delrin collars maybe 1/2″ – 3/4″ long fixed to the test bar as the reference. Turning forces are much lower than steel and the collars are relatively light reducing bending issues. Easily replaced when turned down too far without messing up the test bar. I have an (expensive) precision bar that fits in the headstock taper so turning that is clearly verboten. Sharp HSS easier than inserts on delrin. A third collar half way along may be helpful.

Thick wall tube is better than solid for a shop made test bar as being lighter than solid material and much less prone to deflect. Bar should be about as long as the lathe can handle. You will need carefully made filler pieces to take the centres. If I ever make another one I shall use a section of motorcycle fork leg.

I’d start by truing the tailstock using between centres turning of the collars to verify when it is actually true. Headstock end collar needs to be far enough along the bar to allow it to be transferred to the four jaw chuck.

Once the tailstock is true with no along the bed tilt and  both collars same diameter shift the bar to the four jaw and get everything running true again. Which may take a while. Probably best to use the outboard centre to support the bar in your newly aligned tailstock but on a shorter bed machine this may not be necessary.

When you have both collars verified as running true using an indicator you can start pulling, pushing and levering to see what is shifting under load.

Twist under cutting is quite common on smaller machines if they lack hold down gibs on both sides of the saddle. SouthBends being notorious.

Clive

[PeteParticipant @pete41194]

For a seemingly simple question, any answers are likely a lot more complex than far too many seem to think.

Leave that head stock and it’s fastening bolts alone, it’s the very last item you’d ever touch, and only after exhausting every other possibility by extensive testing to find where and what else might be causing that taper turning problem.

And you can only properly analyze where the problem, or sometimes more than one area that’s causing your issue by starting with a known baseline. Leveling the lathe bed to within a maximum of a very few .0001″ for accuracy. That’s your known baseline and everything else is then verified from it. If you can’t or won’t do that, anything else is just about wasted effort. And very few seem to actually understand what that leveling accomplishes. In reality, it’s the fastest and easiest method to remove any bed twist that may be present due to what any lathe is fastened down to. Visualize that lathe bed twist as slowly rolling the cutting tool tip either towards or away from the shaft being turned parallel as the carriage travels along any twisted bed ways. It’s effect is also greatly magnified just due to the elevation the cutting tool tip happens to be above the beds way surfaces. .0001″-.0002″ of bed twist can easily result in .001″ or more variation in taper along a shaft that’s being cut.

And no 3 jaw chuck is ever 100% accurate no matter what you think they are for run out since that’s only one measurement of it’s radial accuracy. There’s also the axial alignment affected by the non optional clearances within every 3 jaw or any other chuck type ever manufactured, and the inevitable variables each time any work piece is tightened within a chuck. In other words, how straight they hold any shaft so it’s directly centered on the tail stocks morse taper over that shafts full length. While it’s not impossible to align a shaft in both the radial and axial directions, it can take a very long time to do so. In my opinion, it’s just much easier to completely remove the effects any chuck might have.

As I said, accurately level the bed as the very first step, that isn’t optional. A dti can then be used and rotated using the head stock to swing that dti side to side to then verify or adjust until the tail stocks morse taper is in fact true to the head stock C/L of rotation. What that dti can’t do is check the tail stocks quills vertical alignment to the head stock C/L. Simple gravity effects ensure those measurements will always be incorrect. It’s pretty amazing just how much even a lightweight dti can deflect the .375″ diameter shaft on my small magnetic Mitutoyo base as it’s rotated in the vertical orientation, and even when everything is set up as short as possible. The side to side alignment can still be checked well enough though. https://www.youtube.com/watch?v=u08SfxVgxNg For the final verification of any lathes alignment, any indicator checks should always be considered as static checks only since they simply can’t load the lathe in the same way that actual cutting tests can do. The instant any tool on a lathe starts cutting, every part within the whole machine starts to deflect by variable amounts. And for that reason, any lathe bed I’ve ever properly leveled still required very minor adjustments to it’s exact level condition as compensation for the lathes deflections within it’s own parts. Properly understanding that those deflections are always present and will inevitably happen is key.

Secondly I’d very much agree with the others the shaft your trying to use is far too small in diameter compared to it’s unsupported extension outside your chuck jaws. During my final adjustments under those cutting loads, I always use a scrap of short and fairly large diameter ( 1.5″-2″) stock held in my 3 jaw lathe chuck. Then turn my own 60 degree point on it. That ensures it’s as concentric and true to the head stocks center of rotation as the lathes own head stock bearings will allow, and it also removes any slight inaccuracy effect a chuck might create. I use it and a dead center in the now aligned tail stock to then test turn a 2″-3″ diameter shaft the full length of the lathe bed while held between those centers. Fancy ground shafting isn’t required at all, common hot or cold rolled material will allow the proper dynamic cutting test checks you need. How you then purposely misalign your own lathe to compensate for those machine deflections depends on your exact lathe mounting set up and can’t be properly detailed with the available information in your post. I use hollow jacking bolts through heavy steel plates attached to both ends of my lathe bed as adjusters to remove any bed twist. Emco and I believe Myford as well as others used the same idea on there raising blocks.

But in theory, let’s say your lathe is now properly leveled and adjusted to turn parallel to less than a .0005″ variation in size over it’s bed length. Again that’s now a known baseline for a double check of the head stock alignment.

Properly aligned lathes including the best and most expensive in the world do not face parts truly flat. There all set up to face any part very slightly concave for a couple of very good reasons. Two accurately faced and slightly concave parts that are joined face to face can be put together without any rocking that a convex alignment would produce. Secondly, it allows the lathe parts to slowly wear towards that flat facing alignment instead of immediately starting to wear towards that highly undesirable convex facing. On a very well faced and with a good surface finish lathe part, you can even detect that misalignment just from the light reflections. You should see a pie shaped light reflection segment on each side of a faced part.

There’s two methods of producing that concave facing misalignment. And it depends on the lathe manufacturer for there choice about how it’s done. In general, but it’s not universal or guaranteed, North American lathe manufacturers tend to grind and / or scrape there cross slide ways to produce that very slight inward facing bias. European lathe manufacturers seem to purposely misalign there head stocks to point very slightly towards the operator and align the cross slide square or a combination of that misalignment on both the head stock and cross slide. With any far east machines, there’s no way to be certain between brands what method is used or even how well or accurately it’s even been done. But I never ever touch or adjust the head stock without 100% proven reasons it’s actually required. And so far, none of the 3 lathes I’ve owned have ever needed any adjustment to there head stocks.

But that’s not the end of the built in misalignments the better lathe manufacturers will use. As far as I know, most lathe manufacturers set up both the head and tail stock to point uphill approximately .001″ over 12″. That’s done as a built in compensation for work piece weight. And most of the better lathe manufactures will also bias the tail stock towards the operator by the same amount to compensate for cutting tool pressures.

Due to the very small amounts of built in head stock misalignment, it can be tough to accurately double check how well your lathes head stock is aligned. If I recall the numbers correctly, Dr. Schlesingers book Testing Machine Tools mentions a maximum of around .0015″ concave facing over a distance of 12″ on designated tool room lathes. So that’s over a 24″ diameter faced part. There’s a few possible ways of measuring how your own lathe head stock is aligned, but it depends on just how good the available metrolgy equipment and your own skills and knowledge are.

The easiest although not 100% conclusive of how much both the head stock and cross slide are misaligned is to take a full clean up cut across the largest lathe face plate you have. I’ll use an analog clock face as if it was attached to the lathes head stock and viewed from the tail stock for directions. Lets say you make a full clean up cut on your faceplate (under slow power cross feed if you have it) and with the carriage locked down. Most would start from the 9 o’clock position at the face plates O.D. and facing inward to the hole in the center of the face plate. Then with that done, retract the cutting tool away from the the face plate, then move the cross slide fully back towards yourself. Now set up a .0001″ or metric equivalent dti with it’s ball tip just past the face plates center hole. Zero the indicator. Now using the cross slide, gently move the indicator tip away from you moving from just past the lathes center hole out to the face plates 3 o’clock position. Whatever + – numbers you see are DOUBLE the lathes combined misalignment for the cross slide and head stock. Following the same path from the 9 o’clock position to the face plates center hole will tell you nothing since it would still show no deviation at all because your following the exact same path the cutting tool made. But this test will verify how much and in which direction any misalignment is. To be 100% certain of the exact amount of the head stocks misalignment against any wear or bias in the cross slide probably requires the use of a very expensive test bar in the head stocks morse taper. Possibly a bit less certain or exact, but a two collar test cut can be also made as a check for the head stock alignment once everything else is verified as being correct. Other than time and the use of a dti which most should already have, the face plate and that two collar test is free and will verify if the numbers are at least within the guidelines. If there not? Then the morse taper test bar or that two collar turning test would be the next step. Unfortunately and with any these off shore machines, absolutely nothing can be automatically trusted unless it’s been tested and personally verified as 100% correct first.

As just one example, I bought a brand new Sieg C6 lathe. It’s tail stock quill pointed uphill and above the lathes head stock C/L by just over .009″ in 2″. Add the length of a 1/2″ capacity drill chuck to that, and it instantly broke the tip off every center drill I tried until I re-machined and then shimmed it back to the correct alignment and vertical elevation. Most professional machinists using good condition industrial level machine tools usually don’t need to understand all that much about machine tool alignment. Even less so today with any new cnc equipment that’s set up, leveled and aligned by factory trained personal before it’s first used. For us, that’s simply not true, and the less were willing to pay, the more were required to understand about the subject. This is about the best information I know of that’s online. https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Schlesinger_Georg/Testing_Machine_Tools.pdf

There’s also one further item to understand about machine tool alignments that even less at the hobby level seem to even know about because it’s almost never mentioned in any threads about machine tool alignments. Any slide on any machine tool has 6 possible directions for misalignment. That can be a single direction or variable combinations of any or all 6, and can even reverse direction over any slides travel or not be constant. Fortunately and other than double checking how parallel any lathe is capable of turning every so often, most of these alignment test checks only need to be verified once and then many years later once any measurable part inaccuracies start showing up.

[bernard towersParticipant @bernardtowers37738]

And after all that we still haven’t made any bits!! sorry just a joke.

[bernard towers]

On bernard towers Said:

And after all that we still haven’t made any bits!! sorry just a joke.

Thanks, that made me chuckle! 🙂

Tony

[Michael GilliganParticipant @michaelgilligan61133]

Doesn’t add much to the discussion, but it’s good to see a Chinese manufacturer trying to engage with potential users:

MichaelG.

.

https://youtu.be/DAW6IMMGwFI?feature=shared

.

[Master of noneParticipant @masterofnone]

Excellent post.  I learned a lot! Thank you

[Pete]

On Pete Said:

Leave that head stock and it’s fastening bolts alone, it’s the very last item you’d ever touch, and only after exhausting every other possibility by extensive testing to find where and what else might be causing that taper turning problem.

.

.

.

Visualize that lathe bed twist as slowly rolling the cutting tool tip either towards or away from the shaft being turned parallel as the carriage travels along any twisted bed ways. It’s effect is also greatly magnified just due to the elevation the cutting tool tip happens to be above the beds way surfaces. .0001″-.0002″ of bed twist can easily result in .001″ or more variation in taper along a shaft that’s being cut.

I agree 100% with leaving the headstock alone. On my lathe the headstock is located by the Vs on the bed so can’t be twisted anyway.

I don’t understand how the tool movement is magnified by the saddle twisting. According to my simple trigonometry if the front of the saddle moves up by x then the tool bit also moves up by x and moves in towards the work by x, so no magnification.

Julie

[Howard LewisParticipant @howardlewis46836]

Surely the first thing is to ensure that the lathe bed is not twisted.

This can be cured by following the procedure laid down. Known as “Rollie’s Dad’s Method”, as advised by Ian Bradley in “The Amateur’s Workshop” and “Myford 7 Series Manual”. It also tells where to shim of make adjustments to remove the wist.

Until this has been done, DON’T fiddle with anything, you might do more damage than good!

Howard

 

[bernard towersParticipant @bernardtowers37738]

yes we keep saying it howard but no one is listening

[PeteParticipant @pete41194]

Sorry Julie, I was maybe a bit unclear in my explanation about that tool tip rolling into or away from the part during a longitudinal cut. Visualize it as an almost infinitely slow twist or thread along the lathe bed since that’s exactly what it is. Then add the distance across the lathe ways (front to back) With any bed twist and depending on it’s direction of twist, that results in the front bed way surface being either slightly higher or lower in elevation than the rear way, and a change in that same elevation as the carriage travels towards the head stock along that twist. With a correctly centered tail stock quill and a part turned between centers, the direction of a shafts taper instantly tells you which bed way surface is high or low and in which direction the bed needs any counter twist. Smaller at the tail stock end means the front bed way is high compared to the same bed way elevation at the head stock end as an example.

For our purposes, lets say the lathe uses flat ways like a Myford Super 7. With the lathe bed properly leveled in both the front to rear and tail stock to head stock orientations, you would then have a geometrically correct and flat X,Y plane within the accuracy limits of the level your using. When the lathe bed does have a twist in it, and due to the elevation of the tool tip above both front and rear bed way surface, that magnifies or rolls the tool tip either inward or outward to a shafts center line being turned as the lathe carriage travels along any twist that’s present in that same X,Y plane. You could also visualize it as placing a 12″ high height gauge on the cross slide of that Myford lathe. Any changes in elevation between either the front or rear way due to and along that bed twist will start tilting the top of that height gauge either inwards or outwards far more than the front or rear of the carriages measurable change in elevation. To a lesser amount and for those of us without those 24″ swing lathes, the exact same is true for the tool point for our smaller lathes.

I suppose anyone with a decent CAD program could measure up the important dimensions from there own lathe and have that CAD program easily spit out the real numbers for how much the tool point is moving into or away from the shaft being cut versus the amount of bed twist that’s present. But I first figured this out on my little Emco lathe just by indicating the amount I was counter twisting the lathe bed with it’s jacking screws verses the amount of difference I was seeing for the taper the lathe was cutting. I understood a whole lot less back then and just assumed there was a direct 1-1 correlation between how many thousandth’s of an inch I was counter twisting the lathe bed against how much taper the lathe was cutting. When that proved to be completely incorrect, it took a whole lot of further reading, searching online and that visualization before I finally understood what was really happening, and why such tiny differences in that counter twist produced far larger differences in the part diameter and it’s parallelism end to end.

One more example, lets say a 10″ swing lathe is being used. In round numbers, the correctly positioned tool point is obviously around half of that, or 5″ above the lathe ways. Now go check any set of sine tables for a 5″ sine bar. That could give you the rough answer for how much angle change the tool tip rotates through per .0001″ change in elevation caused by that bed twist. Those numbers still won’t be exact because the center to center distance between the front and rear bed ways is unknown, but it will still be close enough for that visualization purpose.

There’s a lessening of the effect that can also happen. For theoretical purposes, lets say the bed has been very accurately leveled, but it’s also worn an equal amount on both the front and rear way surface. And for this, lets say that bed wear is only starting to be present roughly 10″ away from the lathes head stock and increases the closer you move the carriage towards the head stock. In other words, there’s a taper worn into those bed ways the carriage moves into that increases in depth the closer it gets to the lathe head stock. Picking an imaginary number, let’s say the maximum amount of wear is .005″ at it’s most worn area. So logically the front and rear of the carriage and tool point will or could drop in elevation that same .005″. On something like a milling machine, that would be a serious problem for any parts finished accuracy. On a lathe, it can be hardly noticeable for the reason that the tool point is only moving directly down the radius of the shaft that’s being turned. Smaller diameter parts will show a more measurable change on there diameter that’s being produced than larger diameter parts will since the radius is much larger. “An infinitely large diameter is a straight line”. Bed wear isn’t something that has no effect or can be ignored, but as long as it’s not excessive, it’s actual effect on any shafts diameter or the amount of shaft taper it might produce is quite a bit less than any bed twist that’s present.

So it’s those very slight changes in elevation between the front and rear bed ways, the total distance between those front and rear way surfaces, and the elevation of the tool point above that bed twist that causes the tool tip to slowly roll into or away from the shaft being machined as the carriage moves along that twist.

But, and no matter how accurate the bed and all of the other parts have been manufactured to, or the absolute accuracy your level happens to have, that only gets you to a still very important but static condition, and that known baseline. I’d add that final and extremely small adjustments should always be made after real world depths of cut and your own average feed rates based on the lathe size and available HP, and directly measuring the shafts diameter along it’s length if those measurements might indicate further adjustments could be required. For that reason I always use a large diameter steel bar for my own test cuts simply because I’m trying to replicate as closely as possible how I’m usually going to be using it. I also think it’s more than common that almost any of us start out assuming machine tools are far more rigid than they really are. They aren’t, and that’s easily proven by anyone willing to set up a few indicators against various lathe parts such as the tool post etc, and just make a few test cuts. I’d guess that anything I’ve posted in this thread most likely seems like it’s far more complex and time consuming to do than it really is. It might be the first few times you try to do any of this. But I’ve already spent far more time just typing this out than what it would take me to actually do the basic checks on any lathe size that most of us would be using.

For myself and for multiple reasons, that basic lathe leveling, any other alignment checks or required adjustments aren’t optional. But anyone else needs to understand that at a certain point, the time and effort involved might start outweighing any further or even achievable gains. What’s good enough or has an acceptable level of accuracy for the parts were trying to produce should also be considered. Bernard’s very humorous but all too true point of “and after all that and we still haven’t made any bit’s”. 😀

 

 

[Pete]

On Pete Said:

…I suppose anyone with a decent CAD program could measure up the important dimensions from there own lathe and have that CAD program easily spit out the real numbers for how much the tool point is moving into or away from the shaft being cut versus the amount of bed twist that’s present.

That’s what I did. I drew an isosceles triangle with two sides at right angles, one horizontal side representing the width of the bed height and one vertical side representing the tool height above the bed. I made both these sides 125mm. The third side is not needed, but makes it easier to visualise the movement. The vertical movement of the bottom left point, representing the increase in height of one bed way is reflected pretty much one to one in the vertical and horizontal movement of the top left point representing the tool. The movements are not exactly one to one as the movements are in fact arcs.

I suspect that we are considering slightly different things. I only considered a single, small, step. Of course if the bed is twisted uniformally along its length then what one has is a series of steps per unit length. Even if each step is small the multiple steps will add up to a significant movement over a longer length, such as a test bar.

Julie

[Chris MateParticipant @chrismate31303]

Thanks for the replies.

Note-1:Chuck only.
I decided to start all over again, by lifting the bed at headside 1.3mm(Bolted) so if it wants to move slightly it can. I then insert a rod 110mm stickout 16mm and start machining it from chuck outwards till 60mm.
I then easily shimmed the right hand side of bed end .027″, which gave me a straight cut up to 60mm.
I decided 60mm is ok enough before I use the tailstock.

Note-2: Chuck + Tailstock use.
So after some thinking I came up with an idea of using the Wiggler in the lathe chuck to align the Tailstock. Took the tailstock apart, machined the grubscrew ends properly(4x grubsrews, 2 on sides 2 at rear). This tailstock adjust from the rear. I also machined the cast block inside where 2 side grubscrews make contact, it was just a rough casting.
-Back to the Wiggler use.
a)So I run the lathe with Wiggler in chuck, centre the tip which gives me the spindle centre, and then I aligned the Tailstock Live Centre tip to Wiggler tip…..Works like a charm visually.
b)Ok so now I made a Wiggler extention rod to take the wiggler tip up to the Live Centre tip with Tailstock slided to the end of the bed. I then run the lathe, the rod did not run 100% straight, but I purposefully left it like that, then I centred the Wiggler(Wiggler also has runout except the tip) tip with small ruler at the end of the tip, the tip now runs straight which again provides me with the Lathe Spindle centre……I then checked the tip of wiggler versus the tip of Live Centre 1mm apart and to my surprise they lined up perfectly visually, which was a surprise to me, did not expect that. So it looks the Heastock is not off course.
c) So one can use the Wiggler in the Lathe to visually check the Tailstock alignment with centre of spindle at as many lenghts from chuck as you want to see how the tailstock perform sliding over the bed by just reclamping the Wiggler Extention Rod at distance you want and repeat the process at tip every time.
—–On a very large Lathe I would have a steady rest to catch the Extention Rod if it should veared off centre without touching it(Safety)…. Due to how the Wiggler function, the rod did not have to run straight.
d)I also checked the Tailstock extending the tailstock spindle, it  extended true according to .01mm Dial Indicator.

So what do you think of using the Wiggler in this way for a quick initial visual alignment of Tailstock-?

 

[RobinParticipant @robin]

I went doolally with posh bubble levels and test bars until I got it down to one 12mm bolt, where the plinth rests in a steel cup on the concrete floor. It’s in the front right-hand corner.

Turning the screw clockwise widens the workpiece at the tailstock end. Not by much but enough.

450kg of freaking iron is bendy? -ghast-

It cannot be fixed, it is my lot in life to carry a 24mm spanner if I want precision parts 🙂

Robin

 

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