Tailstock guidance and the 'laws of physics'

[jabezkin]

Troup;
Some folks read something expecting to be right, so that's what they get out of it.

Ever talk to someone and you realize he is just thinking about what they are going to say next, instead of listening to what you are saying?

They are to sure of themselves, no respect for the dialog. Nothing wrong with confidence, but folks say so much no one ever hears.

I'm guilty as anyone.

'Course with me, most folks think I'm being silly when I'm being serious. And think I'm being serious when I'm being silly.

Unless you listen................:-)

Later
Rob

[JST]

Originally Posted by Troup

IN the context of an old machine, if I was fixated on tailstock alignment, I would definitely prefer a flat bed over prismatic or inverted dovetail.

The inverted dovetail shares the same guide faces between the carriage and the tailstock, so it seems to me the tailstock is likely to be misaligned by the increased wear in places where the carriage traverses under load.

A prismatic tailstock way is, at least, not shared with the carriage. However on smaller lathes I think it is misguided (pun not intended) to assume the wear will be the same on both faces of the prism. All wear is abrasive wear, and the only load is the self-weight combined with the operator's muscle power in shifting the tailstock. My observation is that the latter is directed largely towards the operator, and consequently the rear face of the prism sees a lot more wear than the front, and the only theoretical advantage of the prism is cancelled.
As a prism wears, the alignment location can quickly become quite 'wishy washy', especially if ledges and ridges develop, even when these can barely be felt.

Haven't seen that problem...... Tailstocks get moved a great deal less than carriages. At least one maker made a special type way to compensate for cutting pressure on the prismatic carriage ways (leBlond) but that was never particularly saluted by others.

Personally, I think the one part of the tailstock which receives the most wearing action, and has the least ability to adjust, is the ram. A round plug in a round hole....... A stupid design, really.

Must be loose to begin with, or it won't move, which means it starts out imprecise. ANY wear makes it looser and less precise/accurate, and there is no reasonable way to compensate for wear. As it is extended farther, it simultaneously is less well guided, leading to loosey-goosey sloppy movement.

there is a strong tendency for the guiding surfaces to become bell-mouthed, and when that happens, there is nothing to be done but boring, sleeving, and grinding or re-making the ram. Which will begin to deteriorate with the first movement, and slowly slide downhill again.

[Conrad Hoffman]

Dunno, but I want things to be kinematically correct, at least to some degree. Then it's a matter of, "how does it wear?" IMO, both my little Logan at home, and the HLV at work are kinematically correct to a reasonable degree. The Logan, however, has small bearing areas and will wear asymmetrically on it's prism way. The HLV stands a better chance of wearing predictably and in a less harmful way, not to mention doing so under high production conditions.

What I really want to know is why lathe design was always split up between two groups of people- smart ones and idiots. The smart ones apparently did the carriages because they always have wipers to push away the crud. The idiots are always assigned to the tailstocks. Along with the above mentioned post-in-a-hole, tailstocks rarely have wipers. I've often seen more wear on the less used tailstock, than on the carriages, just because everything gets ground between the ways and tailstock. The HLV has a really huge scraped bearing surface on the tailstock, but it can also do a lot of damage to the bed if stuff gets under there. An oil reservoir wouldn't hurt it either.

[CalG]

I've seen HLV's fitted with compressed air lines to the tail stock base.

Pull the trigger, and the piece floats like a feather. The small hiss of air flushing away the nasty stuff in it's path.

Clean air and an inline oiler might be a good combination for many motion applications.

Air bearings!

And you are so right. The dedicated V and flat ways for the tailstock on the Mazak 16 in in the shop are in a lot rougher shape than the similar ways for the carriage. (which has a mechanical pump in the apron to keep fresh oil behind the wipers). been that way since I got the tool 20 years ago.

Good design/ bad design.

CalG

Oh Oh Way OT.

[Troup]

Not really OT - the whole point is what's good design for tailstock ways to minimise misalignment arising from wear; if the design minimises wear to those ways, mission accomplished, no?

I have a flat bed Myford my dad bought before my hair took the first migratory steps southwards.

In 35 years of continuous use the main wear to the bed was a shallow trench to the top of the front bedway, in the strip traversed by the tailstock only.

My surmise is that this represents a combination of abrasive wear and the fact that, since the human spine is not good with torsion, we unconsciously protect it by pulling predominantly towards us as we pull the tailstock towards the job.

Interestingly, the vertical inner faces, where the keel runs, were so unworn that I didn't touch them when I remachined the bed, even though it would have been a trivial exercise.

The tailstock on that lathe maintains the best alignment of any lathe in my shop, (half of which have prismatic ways; they are the worst despite in one case being hardened and in the other massive.)

I love how, by a small addition to the hardware (to capture the clamp, when unclamped, so it opens up only to a running clearance) the tailstock on the flatbed Myford can be made fully guided when unclamped - great for reaming, tapping, diehead threading, small hole drilling, and for towing the tailstock with the carriage for power feed of a drill or threading appliance.

This mod also keeps swarf from getting into the slide. However I'm keenly aware that a wiper would be a great addition. I fitted one to the tailstock side of the carriage, most satisfying 'improvement' to a lathe I think I've made...

It's annoying that the least loaded item on the bed has the potential for the greatest wear.

An HLV would certainly be a great candidate for air injection, with that huge flat area...

[misterT]

Actually Colchestor lathes DO have wipers on the tailstock also and i have not seen heavy wear on any of them. In fact I just worked on one that had been bought at an auction that had been heavily abused for over 25 years. It did show a lot of wear in the bed but not by the tailstock. With a lot of work, creative alignment and leveling We were able to get a decent finish without a significant amount of taper in under six inches. Which met the customers requirments and actually suprised me, when I first saw it I didn't think we would get anything usable truned on it. I have seen a few cases of excess wear in the tailstock barrels. Usually in very dirty shops that do a lot of large bore drilling, where the barrell gets coated with chips and fine metalic dust. Long strings can get drawn back into the tailstock by the tang slot if the operator doe not clean it.

[jabezkin]

We had air on all the HLV tailstocks, 10 psi and an oiler. Left the air on all the time. Lock the tailstock and it shut off the air. It became second nature to unlock, move, and lock.

There is almost NO wear. In the mid 80s we got a new HLVH to replace a TFB that was from the 50s. It had not had an easy life.
When doing work with enertia welding, we would put a 45,000 RPM air motor on a MT in the tailstock, run the spindle in the other direction, each with a titanium piece.
The tailstock was floating on air so....
Slam the tailstock toward the headstock and watch the sparks fly!!

A lot of wear on the ways with welding slag but the other end of the ways was fine.

[JST]

My Logan has tailstock wipers, and moving the T/S is like pushing a wagon... it just glides. Oiled wipers work fine.

No wiper for the ram though.

I'd not get so upset about the T/S ways when the ram may be as sloppy as a Chevy shift lever from wear.

[Mike C.]

1943 American Pacemaker... four V ways. Tailstock is not moveable by hand. It weighs as much as a small car. Ram is 4" in diam. .002" taper over 6ft. Crossfeed and compound dials calibrated diametrically, so .0005 accuracy with compound at 60 degrees. 18 speeds 20-1200rpm with 25hp on tap. That's how you build a lathe. Chuck up Myford and turn off square corners.

[jim rozen]

"Chuck up Myford and turn off square corners."

Hey. That's MY line!



The HLVH tailstock, now that's really a design error. The huge surface area
makes it prone to 'lockdown' when the oil squeezes out. Hence the air
sometimes put to the underside. It's a bug, not a feature.

The tailstock rams, that's a good point. I've never seen a tailstock with
anything other than a round ram. EXCEPT for turret lathes of course. The
one I have, flat ways with gibs. But the same lathe comes with a ram where
the clearance between the fixed and sliding parts, cannot be seen with a
50 millionths reading dial gage.

Yes it wears out. STuff wears out. Machine tools in the end are consumable items,
and the wear issues cannot be eliminated - only reduced.

Jim

[donie]

The laws of physics, yes indeed.
I have seen many Monarch EEs where, the tailstock base is worn, causing the center to point down and to the right, facing the chuck, when the machine is otherwise in good shape.
The cause is, dragging the tailstock along the ways by its hand wheel. The angle of pulling and pushing forces the base into the V way causing undo wear.
This can be avoided by grabbing the base at the rear between the ways, and with two fingers under the nose, lift slightly when moving the tailstock.
Peck drilling can still be done just fine, just with a slight more effort to protect your fine lathe.

[number 2]

Originally Posted by Conrad Hoffman

Dunno, but I want things to be kinematically correct, at least to some degree. Then it's a matter of, "how does it wear?" IMO, both my little Logan at home, and the HLV at work are kinematically correct to a reasonable degree. The Logan, however, has small bearing areas and will wear asymmetrically on it's prism way. The HLV stands a better chance of wearing predictably and in a less harmful way, not to mention doing so under high production conditions.

What I really want to know is why lathe design was always split up between two groups of people- smart ones and idiots. The smart ones apparently did the carriages because they always have wipers to push away the crud. The idiots are always assigned to the tailstocks. Along with the above mentioned post-in-a-hole, tailstocks rarely have wipers. I've often seen more wear on the less used tailstock, than on the carriages, just because everything gets ground between the ways and tailstock. The HLV has a really huge scraped bearing surface on the tailstock, but it can also do a lot of damage to the bed if stuff gets under there. An oil reservoir wouldn't hurt it either.

The HMT lathe i run at work has both tailstock wipers and way lube from oil nipples on the base. I cant speak high enough of HMT, their lubrication systems and machine performance are excellent, in my opinion. FWIW, id buy a HMT before a Colchester. I was using a brand new Colchester Master? i think yesterday. Horrid machine.

[Troup]

Seems to me you raise a good point. I've often mused that it would make entirely more sense for tailstock rams/quills/barrels to be square, with short witness diameters the same at each end to facilitiate setup for regrinding, and full width wedge gibs on two sides... in every respect except cost.

Imagine the torque transmission, for one thing. It would be prodigious - and none of that pesky slop which can let drills grab...

The rams as well as the bases should have wipers, seems to me. Sure you cannot eliminate wear, but in situations as lightly loaded as tailstocks on smallish lathes, if you keep 'em lubed and the surfaces clean, the rate of wear will be so slow as to be a non-issue, unless the lathe's doing eight hour days - unusual for a manual lathe in smaller sizes.

As for " Tailstocks get moved a great deal less than carriages" ... that depends. Apart from clearing chips from drilling operations, the tailstock needs to be cleared out of the way frequently on fiddly boring jobs to take measurements, and some lathes do more of these than external turning.

My 'cute' wee Myford gets used a lot for drilling very small, very deep holes, often in tricky materials. The combination of a nicely made, small diameter, three start (fast lead) tailstock screw with ball thrust bearings, and a relatively light but well guided barrel, makes it ideal for sensitive drilling (try that on your Pacemaker!)

I'm tempted to make some sort of spider wheel arrangement to tow the entire tailstock up and down the bed for chip clearance, applying the force centrally and low down. A rack in that position would be a liability for chips.
I'm thinking maybe an endless wire might have merit, and would allow positioning the spider wheel in a convenient, stationary location.

In the meantime I just couple it to the carriage by ad hoc methods (using an end stop I made for repetition turning, positioned between chuck and barrel as shown below), and use the carriage traverse, which is OK but still a bit tedious in comparison with a large diameter, high geared spider. But I think the best thing about the latter would be the ability to use it for ALL tailstock position changing, with the reduction in wear as well as convenience.

Getting back to Pacemaker tailstocks, while doing the Tim Taylor "I'm a bimbo for power" routine, you forgot to specify, Mike, what form the wipers take, and where.

[Question Boy]

Originally Posted by 9100

You may be able to confine a rope to make it transfer thrust, but you cannot comb a hairy ball smooth.

Bill

What just happened?

QB

[JST]

Originally Posted by Troup

As for " Tailstocks get moved a great deal less than carriages" ... that depends. Apart from clearing chips from drilling operations, the tailstock needs to be cleared out of the way frequently on fiddly boring jobs to take measurements, and some lathes do more of these than external turning.

I'm thinking that you often do two or three passes turning and then may or may not need to move teh T/S to remove the part when done, or for fitting, measuring,, etc. Between centers you usually do not, but it's possible for other things if the part is in a collet and is rather longer than the part sticking out..

Certainly for deep drilling, you will probably be sliding it a lot. No question about that, unless you use a drill holder on the toolpost.

A square ram could be gibbed on two sides, and kept nice and snug with little slop.

Since wear often accelerates as alignment gets bad, keeping the alignment might mean less wear overall.

[rjibosh]

Here's a little lighter fluid to throw on the discussion. Although it doesn't address box ways directly, it is enlightening in a Rules of Physics kind of way.
Rick

[Mark Rand]

Having an oil nipple on the tailstock is very useful, to be able to oil the ram from the centre and push any dirt out. Without it, applied oil is as likely to carry dirt in as not.

[9100]

Originally Posted by Question Boy

What just happened?

QB

Are you referring to the disappearance of my post, which later resurfaced? I assumed that I had been "moderated" because he assigned some lewd association to it. There was none, in fact it was an almost verbatim quote from an article on topology. The axiom is that if you cover a sphere uniformly with hair or similar fiber, you cannot comb it into a uniformly smooth covering, but must have a cowlick somewhere.

Bill

[swarf_rat]

A Mori Seiki lathe (or the licensed version by Whacheon) has wipers on both the tailstock ways and the ram. They are heavy enough to require a bit of grunt to move, but are no easier to move with the wipers absent.

[gwilson]

Maybe this was said. The HLVH has closely fitted steel plates on the tailstock and carriage that are supposed to squeege away any trash .