Max size CoreXY Laser cutter, mechanical considerations

Hi People!

Been a long while since posted anything! Got a new itch that have to scratch; I want to build a metal laser cutter as I am presently building Precious Plastic machines and it hurts to have to order most of the parts from half a world away, as the cost of outsourcing locally is over twice the amount of ordering externally... I hope to also be able to offer cutting services as a possible extra, but is not at the moment a considered reason for the build,.. if it happens that get some extra work, then great!

So I can buy locally 1x2m metal sheets, and taking into account the margins for the mechanics, I was thinking of going straight to using 1.5m 20x80 v-slot vertically orientated for both X and Y, as revising CoreXY kinematics, I realise I can make a raised XY gantry that is open on both X and Y (raising the gantry on 4 "feet" on the corners above the bed), so could place the sheet in from any side.... as yet I don't think I will be cutting anything much over a meter, but later on was thinking of adding some decent measured stops to the bed, so could slide the sheet very precisely if I ever need to do a cut larger than the axis permit.. (supporting any overhanging sheet outside the bed)

So my greatest worry obviously is accuracy and repeatability, I want to use a 500w (air cooled) or 1000w (water cooled) fibre laser, so will need to move the laser focusing head around as accurately and repeatably as possible (cuts can be down to 0.1mm wide, maybe less), so was thinking of going with the widest steel reinforced belts that I can find, maybe 15mm, but at least 9mm wide - the belt length for a CoreXY is about 4x the lengths of movement, so 1.5m x 4 = 6m long belts! I am pretty sure Nema23 will be more than strong enough with a Duet control board (I want to be able to add possibly a rotary axis later on), and would do a couple of days of run-in, just sending the head all around the machine, to get rid of any stretch before actually cutting anything..

Linear movement would be on at least 12mm wide linear rails (maybe 16/18mm), I have yet to refine the XY carriage connections, but was thinking on the lines of a 6-8mm thick T shaped aluminium (or CF if I can afford it and find a decent way to cut it!) support, 1 each both above and below the X axis v-slot, so 2 at each end of X axis, then can put 2 linear rail carriages on the Y axis profiles, spread out one at each end of the top of the "T" (total of 8 carriages, 4 linear rails, 1 above and 1 below on each Y axis profile), and the bottom of the "T" fixed to the X axis profile (with a shim the same thickness as the linear rails fixations), and should be super rigid.. I would be using a crossover CoreXY set up, as I would like to eliminate any possibility of racking the Z axis by having both sides connected at the same height (obviously 2 linear rails to slide the Z carriage along the X axis, but also not sure if to simply use the v-slot 1st and 4th slots to position the rails, or go "all-out" and put the rails above and below the v-slot to obtain the maximum distance between fixings, again to promote rigidity, but this would interfiere with the T shaped profiles mentioned above, so would lose X range)

This might sound like over kill, & this setup could probably be pretty solid for a CNC, but from what I have learned, the laser head can weigh up to 2kgs (and maybe a bit more with water cooling, this is why not sure whether to bother with water cooling by using a 500w max air cooled laser), and the laser needs to move a lot faster than a CNC, so need to consider moving that much mass quickly may flex thinner profiles... I would be connecting everything on the head via a hanging ceiling hose support over the center of the machine, not cable chains, as I wish to keep the laser fibre curvature path as wide as possible, and also can be a lot shorter than running 2x 1.5m cable chains along Y and X, however still have to check how much looseness/droop there may be for the fibre optic cable when in the center, maybe a flexible cable tube would help, but would have to look for fatigue points anyway

If anyone has already made something CoreXY of this size, I would love to get your direct feedback, as I am conscious that belt stretch can be a problem at this size, and from what I have learned I hope that wider stiffer belts and a pre-stretch run-in period can reduce this issue enough to be able to get repeatability of at least 0.1mm, and preferably 0.01mm (as a 0.1mm cut with 0.1mm repeatability could conceivably by up to 0.1mm off, and if I have to repass, this would almost be a new cut!)

Also a (lower) priority is "dismountability" (the ability to dismount the machine at some point), to transfer somewhere else, using a possible maximum door size of 80cm x 200cm as the max size of the "dismounted" machine components.. the whole gantry for example would be able to stay together as would fit sideways thru a doorway, but the bed (was thinking steel welded for strength and rigidity) maybe not.. AFAIK, 10mm thick steel plate is about 78kg/m2, so the machine must be able to take at least 200kg resting on the bed without deforming the gantry anchor points..

Sorry (as usual) for the long post, would love to hear opinions and keep refining the design specs, so I can actually start some designing in CAD soon!

Cheers!
Andy

 

Hi Peter! How you doing!

I have looked into Plasma, but it does not convince me, the cuts are uglier and need more cleaning, and am restricted to conductive materials.. also, more importantly, I am investigating water jet guided laser, as a future upgrade to this laser cutter, so plasma is not going to work for me at all..

What I really need to confirm is the mechanical CoreXY side of things... I have made a CoreXY 3D printer in the past, build volume 35 x 35 x 35cm, and it goes great, even has a direct extruder on the X carriage, so I am not intimidated by the kinematics, just that at the scale of the printer, belt stretch is not a thing at all, but at 1.5m x 1.5m it will be, so would like others input if had experience with such a large CoreXY machine...

Hope you've been doing good during the pandemic!!

Cheers!
Andy