[sdantonio]

I'm just a simple country physicist (to paraphrase McCoy from Star Trek - for those of us old enough to remember the original series when he used to say "I'm just a simple country doctor...").

I have 3-axis, for the sake of the discussion lets call then x, y, and z (which could just as easily be forward/backward, left/right, up/down.

I'm assuming that one stepper/one axis (lets say x) can move in both the x and -x directions. Likewise for the other axis too.

If I can do all that with 3 steppers on a 3-axis board, then why would I ever need a 4th axis? I'm trying to envision a time when I would ever need a 4th axis to see if I should build that ability into my forst CNC router.

As I used to tell my students back when I was teaching. There is really no such thing as a stupid question. There are just questions that make everybody else in the class point at you and giggle.

[Bloy2004]

A forth axis, from my limited experience is usually a rotary one.
Suppose you wanted to use the machine to engrave, route, or in general cut material from a round or cylindrical object. The forth axis would rotate the object in sync with the other three axes. The X (up, down) travel would need to be great enough for the rotary forth axis to be set up on the table under the x axis.

I'm sure many will elaborate on this and indicate many other uses for a forth axis.

[whateg01]

sdantonio,

As an example of a time where a 4th axis would be handy...

Using a three axis machine your tool is only able to access the workpiece from one direction. Let's say you had something that you needed to access from the top and then the side. By using a 4th axis, you can rotate workpiece (or the tool) to come in from the side instead of the top. There are also machines (typically very expensive) that use 5 axes. And I suppose there are conceivably machines that use more than that.

Dave

[mxtras]

A 4th axis on a mill is typically used to perform rotary milling - like milling a helix for example. It's a handy thing to have to make nifty stuff and for some parts it is required - such as a shifting spool for a transmission.

I am sure we can scrape up some fine examples of stuff you can make with a fourth axis that would be very difficult or impossible by any other means.

And yes - five and six axis machines are common. Finding a truly competent programmer for them can be a nightmare.

Scott

[dighsx]

The way I understand it is like this:
Think about a 4th axis like and its path like the shape of a dome over the work piece. And that the cutting tool can run perpendicular to all points on that dome. With a setup like this you could engrave a salad bowl or make a 3D bust of someone.

I've also seen 4th axis that work like a lathe and spun the work piece. Think of making an engraved candle.

And if you really want to get confused add both the spin and dome axis to the same machine.

I had a heck of a time getting my head around all the axis stuff. I've even seen a 6th axis. But 6 axis’s are the limit because the 7th axis is time and the closer you get it to the heavier the work piece becomes. Or I've read about an 8th axis that's called the quantum axis, the theory goes that it's all the axis's at the same time. You just can't look at it.

Ok I'll stop with the physics jokes.

[whateg01]

sdantonio,

Here is a link to a page that describes the some uses/benefits of multiaxis machining.
http://www.delcam.com/powermill/5-axis.htm

Dave

[jeffs555]

Jay,
In order to do your dome or bowl example, while keeping the tool perpendicular to the cut, you would need 5 axes. You need one axis to tilt the tool or the work, and another to rotate either the tool or the work.

Jeff

[dighsx]

Jeff,
Yeah I thought of that about 10 minutes after I posted.

[ViperTX]

...say what....if you keep your cutter stationary and rotate the object being cut....the cutter is perpendicular to the surface....

[dighsx]

For the salad bowl example I was thinking more of a cutter that could move up and down but also rotate 360 on the horizontal plane and 180 on the vertical plane. Here's an example of what I mean. They have a good picture of the cutting head towards the bottom. As a side note I wouldn't mind having this cnc machine. Maybe you could get it to change the oil on your car:
http://www.cncmotion.com/titangallery.htm

[ynneb]

Lets answer the question pictorially.
How would you do this with a 3 axis router?
The 4th axis as said before, rotates you work piece around.
The fifth axis will give better reach into the work.
It goes like this, X,Y,Z are linear axis, and A,B,C are rotational axis.
This is the best pictorial explanation I have seen
http://www.rainnea.com/cnc_a2.gif

[whateg01]

Very cool machine if they have a photo of it on their website.

http://www.5axismodels.net/

I can't seem to get the link to work on my computer here at work. Actually, it redirects to a page to load flash8. I'll have to try it again at home tonight. But this is a link to a company called 5Axis Models that makes models (not those models ) for the automotive industry as well as high end hot rod builders. I have seen the machine on tv shows like "Rides", I think. Very cool. I am hoping there is a photo of it on their website, but right now, I can't find out.

Dave

[tauscnc]

Below is a picture of a candle I cut using the 4th axis as a 3rd axis. Yes, it does get more confusing Click the links below.

While it is rotating it is plugged into the Y axis. So really it is still three,....but if you had 4 axis cam and know how to program it this would be a working example of a 4 axis modle.

A perfect example of 4 axis machining is cutting a turbine blade.


CANDLE USING A 4th AXIS


HERE IS THE MAIN PAGE FOR THE CANDLE

taus