The most rigid 4-5 axis design

[Zathras]

Guys,

Eventually I would like to build a 5 axis CNC machine to mill Al alloys but a 4-axis will do for my purposes for now. I am aiming for maximum rigidity in the design with, of course, the largest working volume. Prob go for open loop stepper control.

My Q is what is the most rigid type of design?
This site has the most common design types;
http://engraving.majosoft.com/html/body_choice.html

But this is what I think is the best design;
http://69.13.114.130/techspex/millin...illing_id=4041


Thanks!!

[mxtras]

Can't see your second link.

I think the most rigid design is like a planer mill where the table moves under a fixed bridge structure - the Y and Z and all other axis are mounted to the bridge. This style take up more room, but has the ability to be made more rigid than a moving column in my opinion.

Scott

[Zathras]

Thanks for the reply.

I'll try the link again;
http://69.13.114.130/techspex/millin...illing_id=4041

This is the Hermle c40U
Some have described this as "trunion" type.

Any one else care to comment?

[jdownie]

Try this cached link...

http://72.14.207.104/search?q=cache:...%22+4041&hl=en

or...

http://www.hermle.de/fs_hermle.php?sprache=en&page=168

[Zathras]

Thanks for the input and correct links guys.

mxtras:

I would have put it second on my list. Fair enough. You'd know better than me.
You mean like the pic?;

[mxtras]

I was refering to a bridge mill like this:
http://www.xyzmachinetools.com/pages/money.html

Scott

[Evodyne]

Hi guys! This has been on my mind lately too. I've pretty much decided to try this (all comments welcome).

Sliding table under a fixed gantry. The table either is or incorporates a flat (horizontal) rotary table. The entire Y-axis raises and lowers as a Z axis. This is to combat the long moment arm from a conventional Z-axis with a rotating router. The router/spindle would rotate 180 degrees relative to Z so that the cutting tool can move from horizontal along the X axis to vertical and on around to pointing back along the X axis again.

Anyone see any flaws or weaknesses?

Evo

[Stevie]

Here's my gantry mill I'm building; it's taken a back seat while I forge ahead on my new lathe; but it is quite a bit more on than this pic
If someone needs a more updated photo I'll shoot one

[Stevie]

The entire Y-axis raises and lowers as a Z axis.

Evo

Needs matched ballscrews and drive systems to work right and even then it's tough to make sure moton is matched end to end in Z

[mxtras]

Evodyne -

I see no flaws with your logic. I used to run a massive Cincinnati that was configured the same way (with the exception of the pivoting head). I think this layout offers numerous advantages over a gantry - rigidity being one (for a bridge mill in general).

I like the simplicity of Steve's design. I am envious!

Scott

[Stevie]

more details of the mill; with the Z axis now


rails are THK RSR25mm for Y and Z SR25 for X
Travels are 21.375" X 14" Y 9.5 Z

[mxtras]

Nice and clean work, steve. I really like your work.

Scott