Having realized that SBR20 rails are 45mm wide I scrapped the 80x40x4 box section in favour of 50x50x4 – should have checked that before designing the thing I suppose. I then plugged the figures into the gantry stiffness calculator and, if I understand it correctly, I should be getting a maximum deflection of about 50μm with a 30kg gantry. The assumed the maximum span was 750mm where as it will actually be more like 665mm. I’ve not studied engineering though so I might be reading the spreadsheet completely incorrectly – don’t take my word for it!
Although the gantry stiffness calculator is really designed for the gantry portion of the system these no reason it can’t be used for the X-axis rails here you just want to ignore the X-deflection portion.
After seeing this design I reduced the number of bed supports and thinned them down a bit, they are now 50x25x3mm. I needed to reduce the weight a little as this is going to be installed on an upstairs floor which already has a fair bit of weight on it. My calculations indicate the frame weighs about 85kg so far but that doesn’t include the multitude of fixings and brackets I’m going to need.
To keep down the mess I’ve added 2mm aluminium sheet on the sides and ends. I plan on making the ends hinged so that I can work on longer pieces if needed. The bed is sacrificial a sheet of ply or mdf.
The length of the X-axis has been reduced slightly to 1480mm with the rails being 1450mm. This is so that I can hopefully get all for long rails out of a single 6000mm piece of box section and save a little money. The reduced cutting length on X doesn’t worry me as I was only aiming for 1220mm.