Ron Yost wrote:
Is it just me, or are there others wondering what these machines are
intended for?
How can the apparent goal of self-replication (of a largely metalic
machine) be accomplished by squirting layers of hot-melt plastics? Or carving foam??
They're fascinating to watch .. but other than rapid-prototyping (making
plastic
models of things), and/or as a conceptual challenge, of what utility are they
for getting -real work- done???
For some, it may be an intellectual challenge, only. For modelmakers and RC airplane
folks, small lightweight parts may be perfecly usable as is. And, for people with the
ability to do lost-wax casting, these parts may be the mold patterns for either sand,
lost wax or investment casting.
Things have to be really beefy to do heavy, yet precise, work in steel, and I don't see how eliminating mass is going to work at all for us home-
shop types doing metal. Plastic bearings wouldn't last long at all, either.
Yes, and it is with constant dismay that I see yet another newbie coming in and
saying he's going to build a machine with 1/2" Thompson shafting that will mill steel
blocks a foot on a side.
Yes, I know a tripod is a very strong structure. And I do get the concept of the things. But, there has to be mass somewhere, doesn't there?? How can
a decent spindle holding real milling cutters hang off spindly legs?? Or
is there a 'scale' thing here I'm not getting?
Well, mostly. Mass is a cop-out when sufficient stiffness can't be obtained.
Really, stiffness is the first goal. But, looking at a Bridgeport machine, for instance,
it should be pretty obvious that spindly struts can't maintain the stiffness required
unless things are quite overconstrained. That's why the 6 legs of the Stewart platform
help, when the adjacent struts are loaded against each other. Secondly, it is rarely
necessary to use 1" diameter end mills (and larger) on smaller parts. The only real
requirement for them is when reaching DEEP into a cavity. A smaller cutting tool
spinning much faster requires much less stiffness of the machine.
But, if you want smooth cut surfaces on hard materials, spindly legs are not likely
to help achieve that goal.
Jon
