Cutting an ellipse with a lathe?

[Jon Welch]

I have a Femco TC-75 Lathe built in 1998 with FANUC 18T controles. I was asked if I could cut an ellipse, I've looked it up in the manual but no luck so I have no idea if it can be done with a standard CNC lathe.Has anyone done this and how. Thanks

 

[Andy]

Are you trying to cut a section of an ellipse in the lathe?

If so, then yes, you can cut an ellipse. The section of the ellipse you are cutting will be short line segments, or tangent arcs, or a combination of both depending how you program it with MC.

Andy

[Reece L Gibson]

Create your Geo,convert it to Arc's and go to code.

[Guest CNC Apps Guy 1]

There is an option on Fanuc Controls called "Polygon Cutting". I've never programmed for it. It may do what you're looking for, maybe not. I've always had milling on the lathes I've run.

 

Sorry I couldn't be more help.

[chris m]

With a regular 2-axis lathe, not likely as I don't believe there is any real synch between the X-axis and the spindle

[jeff]

I don't see why not,unless you are trying to do it the hard way.

[McRae]

Chris,

 

If you can sync the z-axis (for threading and tapping) why not the X axis. This is the function that James is describing - Polygon Interpolation on the fanuc.

 

See the pages on Jay's FTP under JPEG folder, 21-1 and 21-3.

 

Read this and it may give some insight.

[chris m]

quote:

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If you can sync the z-axis (for threading and tapping) why not the X axis

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The machine knows that you are threading or tapping because of the G codes you give it, during a typical X or Z G01 move i don't think that the machine is truly synched up; this is what I meant by that comment.

 

The Polygon stuff is unknown to me so I think I'll just shut up now...

[McRae]

Re-reading my post, I hope the language wasn't offensive - I was using this example as a case for what is possible.

 

Sorry Chris.

[chris m]

No offense taken

 

Just being honest with myself about my lack of knowledge on the subject

 

C

[jenks]

I have heard of an applications engineer with Joachim Machine of Indianapolis who was able to program an elliptical bore with an Okuma OSP700 control. I didn't see it, but was told about it by some of the other AE's.

[Jon Welch]

Polygon turning is explained in the FANUC 18M manual using an external two or three blade rotating tool attached to the tool turret in sync with spindle rotation. Two blades creates a square three create a hexagon.

 

[ 01-24-2003, 07:31 AM: Message edited by: Jon Welch ]

[tryon]

actually does anyone in here use that option?

polygon turning.

 

it something like 8 grand for the option so we didnt get it

[Richie21]

Polygon only refers to circular curves, not eliptical, by definition.

 

A circle is just a special case of an elipse.

 

An elipse is a mathematically defined curve and every point on it can be calculated.

 

Why not make a manual program, calculating x and z moves, and forget all the fancy MC software?

 

At the beginning time of NC, i wrote my own post processor in Radioshak TRS-80 basic language

for a pocketing routine, at any angle to the x or y axis.

 

I made the program ask me for length a,b, angle of pocket, cdia, cutter stepover, and then it spit out the numbers for x and y in incremental form.

 

 

I made my own tape, put it in the machine and

the program ran perfectly, putting six pockets

at various angles onto a 12" nylon part with 6 flats milled on a turntable, without even one error. It ran perfectly the first time.

 

I have not programmed NC in 20 years and wonder

whether this sort of manual programming is still

a feasable approach today.

 

Maybe I can give you an idea and you can tell me any handicaps I might encounter using this appraoch in todays programming environment. I am familiar with the cad cam programs, but only starting out to re -learn. I would not want to make such a program and try running it on a machine even if I know the postprogrammer format (template).

 

It should work, but there may be other factors I am not familiar with.

 

Rich

[tracy]

Okuma has a lathe which is capable of cutting elipses and other geometries not possible on standard CNC. It boasts the ability to cut a cork-screw shape from bar stock.

 

The X-axis is linked to the spindle rotation,

and I believe it has multiple beds and lead screws for each axis.

[LastCat]

One thing about cutting an elipse on a Lathe is, RPM's. Even though you could get a Lathe to cut an elipse, you still have the problem of Surface Speed. Depending on Dia of the part. Larger the part in the Lathe the lower the rpms. Smaller the part, the higher the rpms. And with a Lathe, the action of the tool in the turret in X axis would have to move so fast, you might not be able to keep up with the spindle speed. In a conditional scenerio, the turret would have an action as a sewing machine, to keep in time with the spindle rpms. Otherwise, a lower rpm, say 200-400, you then have less surface speed, which equals a poor finish, and possibilty of stalling the spindle.

 

My thoughts, cut an elipse on a mill.

 

 

Cheers

LC

[Guest CNC Apps Guy 1]

quote:

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My thoughts, cut an elipse on a mill.

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Well, I would wholeheartedly disagree with that statement. It is possible, Piston Manufacturers do it every single day. Just none of us here know how to do it that's all. Somebody in here HAS to know somebody that makes pistons.

 

quote:

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I have not programmed NC in 20 years and wonder whether this sort of manual programming is still a feasable approach today.

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It's feasable, just not practical in this day and age. With the complexity of parts these days, even a novice Mastercam programmer can outperform the best manual g-code writer and tie changes into that? Man OH, Man, not even a contest.

 

JM2C

 

[ 01-25-2003, 09:35 PM: Message edited by: James Meyette ]

[Andy]

James, Interesting you should mention piston turning machines (lathe?). I happen to have a 1945 piston grinding machine. Probably built to grind cast iron piston. We converted the machine to grind swage dies for a customer, which are 6" long shafts about .75 dia. in a cam like shape. I converted this mechanically operated machine to run off a 286 pc. (So we didn't have to be there to crank knobs and reverse feeds etc.) It actually works great for an old piece of junk. There is a slide for the x axis, which we put a stepper motor on, same for Z. However, the cam shape is still made by following a 6"dia cam template with a follower roll. So, because of this cam, it does not qualify for the discussion above, but I thought it would be interesing to mention.

Andy

[Guest CNC Apps Guy 1]

Hmmmmmm. Very interesting indeed.

[Eric S.]

I once watched a tv program that showed an oval-piston being machined for a Honda NR 500 (I think). I was amazed at how fast it was the lathe was spinning! Sorry they did no give any details on the type of machine though .

Sorry I know I am not any help here but I know it is posible! (and yes the tool was moving in and out as the part turned!)

 

[ 01-28-2003, 04:10 PM: Message edited by: Eric Sman ]

[McRae]

quote:

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quote:

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I have not programmed NC in 20 years and wonder whether this sort of manual programming is still a feasable approach today.

--------------------------------------------------------------------------------

 

It's feasable, just not practical in this day and age. With the complexity of parts these days, even a novice Mastercam programmer can outperform the best manual g-code writer and tie changes into that? Man OH, Man, not even a contest.

---

James...

This is a little overstated. I could Hand calculate and program a part in 3 minutes - the Novice pirate mastercam guy would have to have to post a thread on the forum, ask for a post, get hacked up because he is a pirate, appologize and apease the greatness of the SoCal gang and then finally Jay would take pitty and help the guy. By that time - I have already cashed the cheque from the customer and taken my wife out for a nice meal.

 

There are even things that mastercam won't do - I work with a guy that has a masters degree in systems design and he wrote his own cam software that will probe the part - find out how much material is to come off of it and it goes to town.

 

I have to modify the parameters page - regen-repost-reload into the machine-adjust offsets-cut the part... he changes one parameter at the machine and has things done before I even get in the next day.

[Jon Welch]

I would like to thank everybody fot there input and from that I gather the answer to my question is NO!

So now I go to plan B. I'll cut some clamp slots in this 18 inch X 18 X 28 block of aluminium, clamp it to a angle plate and mill it with 10 inch dia face mill surface conture.

 

Thanks guys

 

Jon Welch

[Eric S.]

I am still curious... had anybody here turned an ellipse on a lathe? There must be someone!