This kind of design “works” only if you make the overall dimension MUCH larger. It is an overall more efficient design but bmovimng material does not add streght of stiffness. You would need to do something like scale the beam up to maybe twice its size then cut away half the metal.
The first step should be to look for a material with the best stiffness to weight ratio you can afford. Then if you change the shape, you woiuld have to go outside of the current 4x8 dimensions. “Strength” is not just the tensile strength of the material but, that tiimes the cross sectional area, and then you multiply by the distance from a kind of “center line”. The problem is cost. The machine has the aluminum extrusion likely because it was the loest cost reasonable solution. They could have used a high grade of tool steel machine into a truss frame but that might cost more than some cars. My suggestion of carbon fiber has because the materials are not super expensive but what you pay for is the huge amount of labor Whatever you do it will cost a bunch more then that extrusion. So be sure to have it modeled using finite element analysis. You hate to spend $10K or more only to find iot made thins worse. > On May 14, 2024, at 3:21 AM, Gregg Eshelman via Emc-users > <emc-users@lists.sourceforge.net> wrote: > > A triangular tube with an isogrid pattern cut into it to reduce mass without > sacrificing stiffness. Could have it laser cut with slots on the fold lines > to make it easy for a sheet metal break to fold accurately. The design could > have tabs and slots to interlock on the joining edge. Then TIG weld along the > bend slots and joining edge. Weld it like they do top fuel dragster frames, a > little bit here, a little bit there - to eliminate warping. > > Or it could be possible to design three panels to bolt together and to the > gantry using tabs and Rivnuts. > > The round holes at the vertexes of the triangles wouldn't need to be cut, > except in places where you'd want Rivnuts to mount things. > > For isogrid design there's the 1973 book > https://femci.gsfc.nasa.gov/isogrid/index.html Page 42 of the PDF has the > dimensions for the panels used for walls and floors in Skylab. The photos in > it are mostly useless since the PDF was apparently produced from a microfiche > of a FAXed (or early non-greyscale photostat) copy of an original printed > copy of the book. > > In some dusty, forgotten file cabinet there must be an original printed copy > of > Isogrid Design Handbook - NASA CR-124075, Rev. A, Feb. 1973 > > A triangular tube is more twist and bend resistant than a square, > rectangular, or round tube, and it is lower mass than a square or rectangular > tube. Even less mass with all the bits removed to cut an isogrid. > > On Monday, May 13, 2024 at 02:49:51 PM MDT, Todd Zuercher via Emc-users > <emc-users@lists.sourceforge.net> wrote: > > Anyone have any brilliant ideas to stiffen a woefully inadequate cross beam > on a gantry router without adding too much mass? What is there now is a 4" x > 8" rectangular 3/8" walled extrusion that is 145" long. > > Under normal jogging commands the two servos control the ends of this gantry > reasonably well, but while the axis is homing the thing shakes and wobbles > terribly bad. Also If I put a dial indicator in the center of the bridge and > hit the bridge forward or backward it will flex and wobble enough to displace > the dial indicator +/-0.03 and it takes nearly a dozen wobbles to dampen it. > But on the ends the servo's only have a few thousandths of give. > > I'm less concerned about the actual stiffness and more worried about > dampening the wobble. > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
