Hello, after having totally failed to print large part on the Fisher (diam ~140) after a full day of essay, I have built a new bed by cutting 2017 aluminum sheet thickness 3mm.
2017 is relatively soft and very easy to cut with a jigsaw. I had to take some time with the grinder to somewhat clean the plate and the look is not the best.
I insulated the positioning/probe balls with wood plug, with 1.5mm model plywood glued as counterplate on both sides.
At the end, I removed the wood pads atop springs. They were installed to have same height and load, but were preventing easy fit with the spring not sliding well under them (use paraffine for easy sliding).
The cost is quite low and it have taken maybe three /four hours of work, in any case, a lot less than the time I expensed because my original bed was not flat.
From the very start, I got problems with my first layer and having a reasonnably flat bed was a real relief. Nearly no survey of the first layer and now I can start the print with minimal check and go doing something else. That is a big change.
So, everything perfect ?
I experienced something new, I had warping on PETG. While I had warping on long PLA parts, I never get any warping on PETG before. That was easy to check because I printed the exact same part with same Gcode file before and after the bed change.
I assume that because of the thermal conductivity of the aluminium plate, it cool the buildtak to ambient temp which then loose some adherence.
So, using an aluminium plate shall in principle be associated with a heated bed.
I did not intend to build yet a heated bed, so I tried the 'poor man' heat bed with a lighting spot (40W, then 60W) . With 40W, the bed temperature did'nt go very high, maybe 40°C.
It works reasonnably well, however, I had still some warping on a few long part (before I go to 60W). One constraint is that you need to start the lamp at least 20 min before your first print.
I think I may have done it simply in plywood. Plywood may not be ultra-flat, but in any case, much more than the original bed. That may be worth a trial.
The problem is that the buildtak cannot be removed from the plywood, while it could be from the aluminium or acrylic bed.