Tailstock guidance and the 'laws of physics'

[Troup]

Originally Posted by Limy Sami

That's what you get for living on the upside down bit of the world ............... but it still doesn't change the laws of physics.

By your reasoning, 'Scotty', it seems to me a Hardinge HLV must be right at the bottom of the lathe pecking order, below Raglan and WAY below Boxford.

The tailstock guidance would have to be about the worst imaginable, according to your take on the laws of physics.

To de-mystify those who didn't read the Raglan thread, I'm experimenting with a way of not hijacking a thread with a "live" query, with 'no-account' fist fights breaking out among the onlookers when the action gets a bit slow...

here's the link to the Raglan thread where this topic came up.

http://www.practicalmachinist.com/vb...66#post1228066

To save those who don't want to wade too deep, Limy's central premise was that any prismatic bed lathe trumps any flat bed lathe (an opinion I know is widespread in the US, so I don't expect much backup here!)

[jabezkin]

That you won't get any back up that is.
The strength of an object is never defined by a single plane.
I didn't read the thread. To decide something like that thinking is to say a tire can't roll when you look at the flat side, or a woman is good looking because she is wearing a blue hat.

Nope I don't agree, with either.

[Screwmachine]

An HLV is totally different than the Raglan bed. From what I can see the Raglan depends on the center opening for actually keeping the t/s straight, so to speak. Tiniest bit of wear there and you can twist the t/s all over the place.

An HLV has a dovetail bed. If there happens to be a bit of wear, the t/s may be slightly off center but it won't be skewed.

[Limy Sami]

Thanks guys.

Good try Troup ........ we live to duel again

[jim rozen]

Laws of physics:

1) F= ma

2) ya can't push on a rope.

3) experiments are ready to run, friday afternoon about four pm.

Jim

[David Utidjian]

Originally Posted by jim rozen

Laws of physics:

1) F= ma

2) ya can't push on a rope.

3) experiments are ready to run, friday afternoon about four pm.

Jim

4) Physics is what physicists do.... late at night.

-DU-

[CalG]

Alignment by square ways without gibs is never right!

But.... close enough for some .

[Screwmachine]

Originally Posted by CalG

Alignment by square ways without gibs is never right!

But.... close enough for some .

Watch out! The Myford crowd is preparing pot metal bullets!

[CalG]

Oh! Should it be "close enough for many"? ;-) Ducking!

[jim rozen]

"Alignment by square ways without gibs is never right!"

Well it worked out OK for Moore.

Jim

[Doozer]

Jim-
"2) ya can't push on a rope." *


* ...Unless it has no where else to go.
(like in a tube)

I think #5 is, You can't blow the ends off of a sausage. (relating to hoop stress)

--Doozer

[PhillipM]

Originally Posted by Doozer

Jim-
"2) ya can't push on a rope." *


* ...Unless it has no where else to go.
(like in a tube)

I think #5 is, You can't blow the ends off of a sausage. (relating to hoop stress)

--Doozer

You can in a tube....

[Doozer]

Phil-
Ya want to put the rope and the sausage in a tube? Sounds kinky.

--Doozer

[Mark Rand]

Originally Posted by CalG

Alignment by square ways without gibs is never right!

But.... close enough for some .

That's why Myfords have a gib on the tailstock!

In the specific case of the Hardinge, alignment is by two points on one side and one point on the other. This is good, in that it guarantees the tailstock can't rock. Might not be straight, but it's stable.

[jabezkin]

Well Troup;

Seems you were wrong. Most folks agree or are being silly. Otherwise folks would be taking

cheap shots and quoting Judge Judy to prove their point.:-)

[9100]

After 40 years of a couple of mills with square slides, they are fine for something like my Boston Digital 12-24 CNC mill where they are never clamped and the play can be adjusted out. On my Pal mill (Beaver with an all belt drive head) they suck. You have to clamp in two directions, requiring a total of three clamps on a slide, which they didn't provide, instead of the single gib needed on dovetails. For my next hand mill I got a BP pattern one. On hand equipment the only advantage I can see is that they are cheaper to make and the lower price soon fades into frustration.

Edit- I note in the Raglan thread they compare it to an SB light 10. I don't know why anyone would compare anything to one. Yes, I ran one that was in new condition for as long as I ever want to. Great machine if you enjoy a little music with you work, although the continuous squeals get boring, motor vibration prints on the work, and an utterly stupid tailstock design that interferes with the compound.

Bill

[Troup]

Originally Posted by jabezkin

Well Troup;

Seems you were wrong. Most folks agree or are being silly. Otherwise folks would be taking cheap shots and quoting Judge Judy to prove their point.:-)

I'm often happy to be wrong, and this is no exception.

....

Interesting that Limy S evidently took if from your first post you were agreeing with him!

I concede your first post was way cryptic!

This one's a bit clearer, but still easy to misunderstand.

You saying I'm wrong, and that people generally agree with me.

If I was a simple soul, I might infer they're wrong too

(OK just to be transparently clear, I realise that what you say I'm wrong about is not expecting much support for my contention)

[9100]

Originally Posted by Doozer

Jim-
"2) ya can't push on a rope." *


* ...Unless it has no where else to go.
(like in a tube)

I think #5 is, You can't blow the ends off of a sausage. (relating to hoop stress)


--Doozer

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

Bill

[Troup]

Thanks for all the responses

Not quite sure how 'square ways without gibs' came into the discussion - I haven't struck any serious machine tools with this arrangement.

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.
If the included angle was (say) 120 degrees, it would be more wishy washy; if it was 60 degrees, it would be less. If it was zero degrees it wouldn't be at all wishy washy: and that is effectively what we have with a flat bed

A flat bed tailstock has a narrow 'keel' with gibs. The guidance arrangement has a better aspect ratio (like a narrow drawer vs a wide drawer the same depth in a chest of drawers) than for prismatic and (especially) dovetail tailstocks.

If there is differential wear on the inside verticals of a flat bed, it's easy to correct as it develops by the occasional application of a stone.

If you're buying an old machine (as the OP was in the Raglan thread) and the tailstock ways are stuffed, it's a simple job to mill them straight and parallel. More difficult with a dovetail, most difficult (probably out of the question for most home shop guys) with a prismatic way.



I think the discussion of manual turret mill guideways is interesting. Might need another thread though. It would be interesting to trawl through rationales for the prevalence of box ways on the y axis (at least on machines more modern than the Bridgie) whereas it seems dovetails are still preferred for x axis.

[CalG]

Flat ways with adjustment . All thumbs up!

Works for more than MANY!

CalG