Re: Router plan made from steel- alum vs steel

Take a look at http://groups.yahoo.com/group/CAD_CAM_EMC/ in the
photos. You do not need to join. I built this steel gantry router and
use it every day. I was going to offer plans but never updated the
drawing to reflect minor changes I made during the build process. I
can tell you this, weight is not the problem, but friction is (lead
screw type). The gantry assm. on mine weighs 178 lbs, but only 108
lbs is the gantry framing The rest is (bearings,rails, motors, lead
screws etc.You will not save much weight by using alum for the
gantry frame. As far as getting a true flat surface for mounting
rails I just bedded epoxy to the framing by using a level as a mold.
As far as welding goes just clamp or bolt the assmys. together and
take them to a welding shop. Look at the photos of mine and you will
see little welding is needed. Most is in the Y Z assmy.

Frank

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "David A. Frantz"
<wizard@e...> wrote:

> Hi Everyone;
>
>
> I'm begining to believe that there are to many guys named Dave
> responding to this thread :)
>
> Dave; you do hilight some important points. I look at it this way
> Steel can be a fine base for a machine, but it will take more

effort to

> get the stiffness required based on weight. There is not a huge
> difference in cost either once one considers the effort required to

keep

> the steel frame from flexing. One could always throw a lot of

metal

> into a steel structure and hope for the best but then costs will

sky rocket.

>
> When it comes to off the cuff engineering with steel, with respect

to

> something like a router table, you best friend will be lots of
> triangles. I'm sure this is how many a home grown router is
> implemented. For me though I would have more confidence in a
> combination of aluminum extrusions and aluminum plate given equal

lack

> of real mechanical engineering and a fixed budget.
>
> Maybe its me, but you are talking a great deal of effort and

resources

> required to weld up a steel frame and end up with it striaght,

square

> and level. Most of the robotic frames, fabricated from welded

steel,

> that I've seen are usually milled or planed after fabrication.

Not

> many of us have the resources to do that on a router platform. I

could

> see where a well designed frame welded up out of steel would be

nice,

> but I doubt that there is a well designed frame floating about in

the

> public domain. That is a frame that has been verified through
> computer simulation. If there is I'd be the first to give it a

serious

> look.
>
> The alternative is a design that has been independantly implemented

by a

> number of people and has field proven itself. This is most

likely

> what the original poster is looking for.
>
> Thanks
> Dave
>
>
> turbulatordude wrote:
>
> >--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dave Kowalczyk"
> ><dkowalcz@d...> wrote:
> >
> >
> >>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
> >>
> >>
> >>
> >
> >
> >There are merits to most everything. the neat thing about some
> >aluminum extrusions for frames is that one can often find some
> >extrusion that is not just a hollow tube, but an X interior with
> >slots on the outside to bolt things too. advantage aluminum.
> >
> >steel is easier to find and easier to weld. advantage steel.
> >
> >alum does not rust. -> alum
> >easier to drill -> alum
> >
> >pound for pound, aluminum is stronger, but it is also lighter so

it

> >means a thicker piece, often a lot thicker. advantage....

er.....

> >depends.
> >
> >but, as the originator mentioned, aluminum is not universally
> >available so in some places steel is really the only choice.
> >
> >also as since the steel is often much heavier, the gantry will
> >probably weigh more and therefor have some inertia problems for

both

> >accel and decel.
> >
> >but when at a steel yard it is odd to look at a 20 ft long x 12

dia

> >solid steel bar bend under it's own weight.
> >
> >
> >Dave
> >
> >an one thing I did on my design was to make the table stand large
> >enough to accommodate full 4' x 8' ft sheets as a storage rack.

I'm

> >not sure if the extra weight would make it more stable or the

heavier

> >weight would make it harder to move. more tradeoffs.
> >
> >
> >
> >
> >