Like the others have said, the LR4 performance is light-years ahead of the LR2.
Here are a couple of specific responses to your questions.
First, you need a control board that can handle 5 motors. That is an absolute requirement since there are two pairs of motors on the Y and Z axes and another on the X axis. You also will need to be able to accommodate 5 endstops so that you can take advantage of the auto squaring. (But, in truth, you could probably work around this if you were to build the machine carefully, but, I doubt it would be worth the effort.
As for the board itself, the Jackpot is the latest and greatest, but the LR4 runs just fine on less sophisticated controllers like the SKR 1.3, which you can probably find for under $20. It’s firmware is Marlin but you are probably already using that, possibly along with Estlcam, in which case the switch will be very straightforward. You may want to add a display for convenience, which will be another $25 or so. (The Jackpot is around $65 so the total price is not too different, but you need to use your phone or PC for the display. But, the Jackpot is the future, so if you can swing it, you should)
As for your table, you can use it but your working width will be a bit smaller as mentioned. Since you said you haven’t actually done large pieces, that may not be an issue. There’s a calculator that will help you determine what your working width will be if you use your existing table.
As for hanging it on the wall, that is completely doable in one of two ways. The simplest would be to remove the gantry and storeit separately. This is actually very easy since it just sits on a rail on one side, unlike the LR2 which was essentially captured on both sides. Your just release the belts at the ends and lift it off. Re-installation would take less than 5 minutes once you get familiar with it…you would place the gantry at an appropriate place, attach the belts and square the machine. Looking at your wall, there probably enough space above your folded table to have a shelf where you keep the gantry.
Another option, probably not ideal but possible, would be to devise some method to lock the gantry onto the table when it’s folded. Since it merely rides on a rail on one side and on its bearings (think “wheels”) on the other, you would need to have a way to fix the gantry onto the table using some sort of clamping system. In that case, you’d probably remove the router and then it would be fairly easy to design this clamping system.
As for the other hardware, you probably have most of it from your LR2. You’d need all new belts and the linear bearings for the z axis. The pulleys and idlers are also new, I think, but you could re-use the 508 bearings. You might need some additional or different bolts, etc., but that is all pretty minor stuff. And, as I remember, LR2 required much less plastic than the LR4, so there’s that issue.
One thing to consider is that if you have not already dismantled your LR2, you could use it to cut the “strut plates” for the LR4. You’d need to have all your dimensions worked out, but that would save you some fiddling as you do the LR4 build. Alternatively, there’s a straightforward “bootstrapping" method that folks use very successfully.
So, for me, the decision would be clear. Go with the LR4. You can figure out the options as you go, but it’s really a much better machine. Good luck.
*******one more comment re: the height. The LR4 gantry is probably slightly taller than the LR2 was. The ends of the LR4 are fixed and will determine the clearance needed to hang the machine on the wall with the gantry in place. If you have trouble getting this dimension from the STL files, it’s a simple matter for someone to measure it, but my guess is that it would be around 10-12”. If memory serves correctly, with the LR2 in the lowest z position, there was still significant protrusion above the table surface, but maybe not as much?
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