Re: Router plan made from steel

Dave:

Well, this is an interesting topic. In machine frames we don't
stress materials anywhere near the yield point except for perhaps
ball bearing contact surfaces.

So the property that matters for structures is the stiffness, and
to a lesser degree the vibration damping properties, dimensional
stability, wear, etc.... Cast iron is king for this.

Given the choice between aluminum and steel, go with the steel.
It's stiffer, cheaper, expands less, and wears long.

Although I can't recall the title, a book I've read on the subject
suggests that built up steel structures for big machine tools are
almost as good as cast iron for damping properties owing to the
joints.

Your intuititon that the same design in steel will be stiffer is
correct. The extra weight doesn't matter - a 2" square bar in
aluminum and steel of equal lengths will sag about the same amount
from their own weight.

Dave Kowalczyk
Mercer Island, WA
Author of TurboCNC --> http://www.dakeng.com

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<davemucha@j...> wrote:
{snip}

>
> I don't think the materials used for machines and the structural
> specs would become off topic.
>
> Aluminum is stronger than steel on a pound for pound comparison,

but

> aluminum is often 4 to 10 times the cost.
>
> I would hope that one of our structurial guru's would comment on

the

> differences. But, on the surface, I would think that steel would
> offer a more ridgid structure when the designs are similar. also,

I

> would think that aluminum would be a lot larger for members to
> achieve the same strenghts.
>
> but, I also agree that a complete design is better than using one
> based on one metal and building it with another.
>
> The Axuus unit looked like it was an all steel platform and only

used

> aluminim for the risers on the gantry. One thing that table did

not

> appear to have were any members to prevent racking. Probably not a
> problem for wood or plasma.
>
> My design was very similar, 2 inch square steel tubes, 3.16 wall

for

> most of the frame, some 2x3 square for some parts. I also followed
> Les's advice and laid in a corner to opposite corner brace. It was
> made by laying a length on the table, and cutting it on the angles,
> then pieceing it into the sections and welding. that made my

design

> look very similar, but with the addition of a large X on the table.
>
> Getting married and moving into a smaller shop set my building of

my

> table back a little more than I hoped.
>
> Dave
>
> ps: plasma is a VERY smokey process and some form of smoke
> handling/removal is needed to keep the shop from getting too

filled.

> for more discussion, we covered this in depth about a year ago.
>
> Dave