Originally Posted by
jono5axe
Very interesting thread for me, as I am just about to build a 4000mm long composite gantry. I have been procrastinating back and forth about it, and maybe just to use steel, but am pretty committed by now to doing it in composite. I therefore list my plan below, for the purpose of getting everyones comments. All comments and ideas gratefully accepted - to ensure I am not overlooking something....
- Composite gantry beam 4000mm long x 600mm high x 400mm deep [RHS - rectangular hollow section].
- Construction: Sandwich construction - 5mm foam core, internal laminate = 2mm quadraxlial glass fibre, external laminate = 4mm quadraxial carbon fibre & glass fibre (50%/50%), with transverse internal gussets/bulkheads every 300mm (bonded in).
- Resin system = epoxy, infusion, room temp.
- Method: vacuum infusion + hotbox post cure cycle. [make up core material as C-Section, lay-up inside C-Section, bond in transverse gussets, close C-Section by bonding on last side panel, vacuum infuse external laminate in one hit].
- Thermal expansion goal is to achieve approximate equivalence with concrete [13x10-6 m/(mK)] and steel [12x10-06 m/(mK)], as side frames are steel and machine base is concrete floor. Thermal expansion co-efficient of epoxy GRP = 36x10-06 m/(mK), epoxy/carbon = 2x10-06 m/(mK).
Metal threads will be achieved by either/or
1) 50x8mm steel flatbar laminated into the core of the sandwich construction, or,
2) Drilling beam and bonding in threaded inserts (with plexus/crestabond/etc)
Datum faces (machine beds) for 35mm linear rails & 24x24mm gear rack will be produced by one of the following methods, either/or:
1) Shimming components in place and then back-filling gaps with "Chock-it" [CHOCKFAST ORANGE (PR-610TCF)], or,
2) Epoxy-concrete machine beds, molded on a 4000mm long flat table produced with self-leveling epoxy (make flat table mold using self-leveling epoxy, lay in the epoxy/sand/fibre mix on the table mold, place the gantry beam on top to bond the epoxy concrete machine beds to the beam.
??? forgotten something?...
Like I said, all comments and ideals thanks very much.
Regards,
Jono