Cutting Large Sphereical Radius....pre-CNC ?

Last year I worked on some large bearing-housings from a power-plant.
This would be the outer component.
Split of corse, but they must have been bolted together......
and I picture must have been on a 36" Bullard or larger.

But what would have been the method / attachment, Used to cut
the sphereical radius inside the housing?
I envision an arm that would extend from a fixed point in the table center
and hold a cutter, the arm then being swung verticaly by ram movement.

Natural I could be over-complicating this, as it was surely done often
and may have been some very simple arrangemnt.

Thanks and have a good Week-End.

M1M

Assuming they were ground to finish, then probably roughed out with a hydraulic tracer. That would be my guess anyhow!

Gregor

Not sure how it is done on a production basis, but if you need one, you can mount it on a rotary table that is tilted relative to the spindle.

Tracer. My dad made high-accuracy hemispherical shells this way back in the '60's.

Regards.

Finegrain

OOps, my bad,

Finegrain said:

Tracer. My dad made high-accuracy hemispherical shells this way back in the '60's.

Regards.

Finegrain

Click to expand...

Thanks!
I guess I was thinking pre-tracer, but surprisingly, tracers go back
quite a ways. I worked in a shop that had a Rockford open-sided Planer.
It had a hydrolic tracer with a roller-stylus. The old Master said
"It duplicted prop-blades, and was incredibly accurate".

M1M

Re propeller blades, remember when there was a big flap about someone selling some big CNC mills to the Russians? It never saw a public statement, but a friend told me that the reason there was such a fuss was that up to then there was enough difference in the Russian submarine propellers that the individual sub could be identified by sound signature. The CNC machines were so uniform that we lost that advantage.

Bill

On a VBM, we used a pivoted arm in one ram driven by the other ram.

Find radial and axial center with the left ram, attach link on arm to right ram, feed up with right ram, end of bar with tool describes/cuts a radius. Very accurate.

That was about the only fine feed I ever used on a larger VBM.

Cheers,

George

I'd do cart-wheels , but it I'd end up in the E.R.

gmatov said:

On a VBM, we used a pivoted arm in one ram driven by the other ram.
Find radial and axial center with the left ram, attach link on arm to right ram,
feed up with right ram, end of bar with tool describes/cuts a radius. Very accurate.
That was about the only fine feed I ever used on a larger VBM.

Cheers,
George

Click to expand...

Good O'l George:
I had a strong gut feeling, I was look'n at a cut that had been
acheived manually. Or that by the apperance that the housing
was just too Old. Or both.

I can picture exactly what you are describing.
On a Bullard, (only one ram) I picture a table-center mounted vertical shaft.
Protruding from a supportive cone, and a horizontal pivoted joint, affixed at
the center hight of the work-peice. The jointed arm swung by the ram-motion.......
inscribing the radious in the same fashion.

Thanks so muchly George !!
Phil

machine1medic

Gmatov discribed a 2 ram machine with a pivoting arm on one ram not on the chuck like you drawn it The other ram provides the downfeed
That way you can give infeed without messing on the pivoting arm
You could then start turning with the ram which holds the pivoting arm off center Then the last cut should be with the pivoting arm centered

Like you drawn it the pivoting arm needs a extra bearing to make it possible for the chuck to rotate

Peter from Holland

I think it was the sale of programing that was the problem. Russia already had the cnc machines.

"Good O'l George:" is right! Insight to past successful problem solving is critical if we intend to hand down hard-won innovation.

This is a perfect example of a rare, (in the majority of modern machine shops) machine, being optimized for a particular need, presented by the guy who ran the machine. It don't get no better than that! ...'cept maybe w/ photos..

Sad when you think of the millions of remarkable innovations that got no farther than the shop they happened in, only to be laboriously re-invented over and over again, and worse, simply lost forever.

Enter the internet, the perfect solution to disseminate that portion of the body of knowledge that remains. That and the dwindling supply of guys like George.

Not only does George's knowledge pinpoint a little known, proven method, it's inspirational, expands our thinking out of the box.....

.....like it did here. Phil, I'm guessing you don't have a VBM lying around, thus the inspired work-a-round in your drawing.

It's obvious that you've simply established the loci with your drawing, which you would then flesh out to a working drawing.

Risking being thought of as (more) anal, I'd add an anti-torque element and clarify the bearing, (plain, big, heavy and preloadable) on the pylon.

Now, the question of tool advancement in the radial plane, while the machine is running....ooooh....

...up from the heavy pylon bearing, a centered, horizontally pivoting dove tail tool slide, and as you show, being occillated by the Z feed. Tool advancement then controlled by the one remaining movement of the spindle, rotation. Tight amplification from tool slide, back to spindle rotation with means of incremental manual input?

You do have a contract for a million of these, right Phil? good, you know, like bevel gears and short lead screw....oh lordy....

I think that the few that recognize the huge practical value of say a good VBM, (one in Nevada right now, on Craigs list) at scrap prices, also feel some of the desperation that I feel as old iron fever strikes hard, wanting to save it all and truly sad that we can't. No degree of rationality can quell the desire for a huge museum like working shop that won't support it'self.

....as if the few remaining fine artists sob in abject misery as the world scrambles to turn their easels, brushes and paint into valueless confetti....digital camera soooo much the superior.... no one cares....progress...

ramblin' robert

Robert Campbell Jr. said:

"
....as if the few remaining fine artists sob in abject misery as the world scrambles to turn their easels, brushes and paint into valueless confetti....digital camera soooo much the superior.... no one cares....progress...

ramblin' robert

Click to expand...

Despite being devoid of artistic talent, I hang around with artists a good bit. There are still a lot of people putting oil paint on canvas and doing charcoal drawings. There are plenty of pieces done with the modern techniques, but I don't know anyone who thinks they have replaced classical methods. They regard the new ones as having been added to their available tools. OTOH, computers have destroyed the old ad agencies. Now every office has someone who makes some pretense of doing computer ad art. Photographers who used to make much of their livings doing the 2" square head and shoulders of Lucy Schmoe who has just been promoted to third assistant sales manager and wants to see her picture in the company newsletter now have to find other means of support. One of my ad man friends actually got down to working for a telemarketing agency before he found a new gig.

Bill

The jpg is just a conceptual representation.

Enough to get the point accross.
The method George describes is awsome, but if we go manual
it'll be more in the Bullard catagory (no second Ram).
They might even find a CNC* * * in the right size / price range.

Then it will only have been a pleasant excersize.
And neat that it fished up a real example.

I realise that lateral tool presure needs to be considered.
And that the pivot is free to have it's axis spin inside it.
Kind of a fun deal. Thanks for contributing Guys.
M1M

* * *Unlike with milling on large horizontals, I really have no passion
for CNC turning, it is just a smart move for the shop
if they find one. Lots of CNC turning guys allready

As for pencil sketch'n I still go thru tons of paper per year.
And nut'N better than a dry-erase board for shop brain-storming.

cutting radii on manual machine

To make some Pullmax Doming dies with a larger radius than my Holdridge Radius cutter would go I mounted a pivot to the head stock behind spindle then I mounted a pivot to the carriage cross slide and put a link between them . I set cutter on cl then aligned link parallel to the ways . so when you crank cross slide screw the link woul move carriage right or left . in this manner I made radii up to 20+ inches . these were on the end of a bar . to turn large radii on the side of a bar I am mounting extra slide to saddle that is controlled by a link perpendicular to the ways . I need thissecond one for English wheel wheels Ken

machine1medic said:

Good O'l George:
I had a strong gut feeling, I was look'n at a cut that had been
acheived manually. Or that by the apperance that the housing
was just too Old. Or both.

I can picture exactly what you are describing.
On a Bullard, (only one ram) I picture a table-center mounted vertical shaft.
Protruding from a supportive cone, and a horizontal pivoted joint, affixed at
the center hight of the work-peice. The jointed arm swung by the ram-motion.......
inscribing the radious in the same fashion.

Thanks so muchly George !!
Phil

Click to expand...

THAT, is some slick snot ! i don't think i'll forget that one any time soon. thanks !

(just beginning to learn the tricks of larger boring machines and loving it!)

Well, we never had one with a center mounted bearing post. That would have to be a very snug fit both axially and radially to hold 2 thou or less on the sphere.

I assume that your Bullard has a side head, 4 position turret? The ram on that will reach far enough over the ID of the bearing seat to use for the feed control. That side head does feed up and down.

I haven't done this job for near 30 years. It is not all that clear, any more. If I recall, the trick is to get vertical center, make a trial cut, maybe 1/16 at the crest, measure up and down from that cut area for center. This is not super critical. Turbo generators have up to an inch of float in them. They pull to electrical center.

As I said, 30 years ago, but I believe to get size, measure, back off center ram, feeler to adjust DOC, raise tool, back to zero, cut. As long as your pivot is on center, it doesn't mater the length of tool, it will cut a spherical bore. Off center either way will cut an oval, orientation depending on whether you are left of center, egg laid on its side, right of center, egg on end.

These seats fitted into endbells that weighed up to 25 ton. Bearings were anywhere from about 30 to 48 inches in diameter spheres. Bearing journals up to 36 inches. 200 ton rotor takes some steel to hold it up. And these spherical seats were just 6 or so inches wide..

BTW. They were a good paying job at my mill. No hurry to ge it close. They wanted it right. The oil feed hole came up thru the bottom of it. If the sphere was not true, oil pressure would be lost.

Cheers,

George

Now I have to ware a Dunce Cap

gmatov said:

I assume that your Bullard has a side head, 4 position turret? The ram on that will reach far enough over the ID of the bearing seat to use for the feed control. That side head does feed up and down.

I haven't done this job for near 30 years. It is not all that clear, any more. If I recall, the trick is to get vertical center, make a trial cut, maybe 1/16 at the crest, measure up and down from that cut area for center. This is not super critical. Turbo generators have up to an inch of float in them. They pull to electrical center.

As I said, 30 years ago, but I believe to get size, measure, back off center ram, feeler to adjust DOC, raise tool, back to zero, cut. As long as your pivot is on center, it doesn't mater the length of tool, it will cut a spherical bore. Off center either way will cut an oval, orientation depending on whether you are left of center, egg laid on its side, right of center, egg on end.

Cheers,

George

Click to expand...

I plumB forgot about the side-head.
Again I can articulate your method in my head, and there's no dout
that it will work just fine.
YES dead center is critical, but comeing out of injection-mold building,
finding the sweet-spot is every-day buisness.

I salute you George.

Phil

PS:
I feel another "Paint" sketch coming on.
Maybe tomorrow..............G'nite