Hey All, I am trying to decide which design to go with for my X-axis/gantry beam. The length of the X-axis beam will be 56" (with roughly 50" unsupported). This will be used for wood, plastics and aluminum. I have narrowed my options down to the following: 40mm x 160mm aluminum extrusion (made up of two 40x40 v-slots with a 40x80 v-slot C-beam stacked vertically between them) with a 1/4" x 6" x 56" steel/aluminum (haven't decided yet which one) bolted to the back side. Solid 3/4" x 6' x 56" 6061 Aluminum Plate Which would be more rigid? The solid 3/4" aluminum plate would cost about $50 less that the extrusion/steel plate option and about $100 less than the extrusion/aluminum plate option. And that savings does not include the cost of all the hardware needed to bolt all the extrusions and plate together, so there would actually be much more savings when all is said and done. Thanks for any advice! Shawn
Consider a chunk of 6x2x1/4 rectangular aluminum tubing. Second suggestion would be based on the built up concept above but skip the C-Beam in the center and put another aluminum plate on the opposing face. The solid aluminum plate would be the option I would suggest you avoid. It has the least resistance to torsional twist of the group. One issue to watch is thermal expansion. Steel and aluminum have significantly different coefficients of thermal expansion and with the steel rails bonded to the aluminum rails you may have issues if the build is located in an environment with substantial temperature variation.
Yeah another design I drew up was to sandwich the extrusion between to aluminum plates but I am trying to keep within a budget so I am looking at all angles. I will look into the rectangle tubing as well. Great point about the thermal expansion properties. I had not thought of that. Thanks!
The thermal expansion issue got me thinking. The gantry sides that the beam will be mounted to are steel. So I guess I need to look into doing a steel beam instead? If so, what size would be sufficient? I feel like that would start to get pretty heavy.
Alright so I modified my original design. I now have a 40x40 extrusion framing sandwiched between two 1/4" aluminum plates. The total size is roughly 2" x 6". I assume this would be more rigid than the solid beam? Regarding the thermal expansion issue between aluminum and steel, I am curious if I will have issues mounting this beam to my steel gantry uprights? The mounting surface of the gantry uprights is 3" x 6". If this could be an issue, what would I need to do to remedy it? Thanks
I have been researching mating dissimilar metals and the issues of thermal expansion as well as galvanic corrosion. I am not too worried about the galvanic corrosion mainly because it is in a somewhat controlled environment. I may apply a zinc primer coating to the mating surfaces or maybe a piece of zinc sheet between them. Has anyone on here had this issue with mating aluminum and steel? Not sure how much expansion I would have with such thin pieces of aluminum. I would also think that the open spaces inside the extrusion would help absorb expansion a little. And the fact that the room temperature does not fluctuate too much I would not expect too much expansion/contraction. I am thinking about using Belleville Springs when attaching the two pieces to help absorb any expansion. Am I on the right track?
Looks good. The spacing between the uprights is not the issue here. The problem is the interface between the aluminum and steel rails. (ref: Thermal Expansion of Bimetallic Strip - YouTube) But if you are in a reasonably temperature stable environment it shouldn't be an issue. It's just not the kind of design I would recommend in a shed with a 100 degree (F) temperature swing.
