The box will be built from high quality hardwood plywood panels 18mm x 610mm x 610mm (2ft x 2ft).  The Titan box was built from 500mm square acrylic panels with printed corners connecting the panels except for the base and back which were plywood, so I searched for ready cut pieces of plywood this size or larger and came up with the 2ft square sheets (a bit bigger than I really wanted but not by much).

This CAD model gives an idea of the arrangement of some of the parts within the box.  X and Y rails are aluminium extrusion "V" rail with the carriages running on them with matching ball bearing wheels.  The Z axis also uses "V" rail vertical pieces with 3D printed Z carriages running on them and supporting the print bed.  The Z carriages hold the bed level with any remaining deviation from truly level being compensated for in the firmware using Z probing immediately prior to printing.  I'll say more about the "V" rail system later.

These photos show the "V" rail arrangement.  The printer carriages use four wheels, two each side of the rail and separated along the rail to provide an accurately running carriage, constrained in all but the longitudinal dimension.  The 2nd photo shows a "Mini" carriage (gantry plate).  The carriages used in the 3D printer have the wheels much more widely spaced and the plates are 3D printed in thermoplastic (PETG).   In the CAD model above, the wheels are represented by cylinders on the Z carriages and are 150mm apart to keep the bed as accurately level as possible over the Z range.

Do you move the printers sound to your print bench or do you have more ventilation sites setup now?

with all that timber etc, I doubt you'll be able to lift it, let alone move it around.....

This printer will indeed be very heavy - I shall be fitting it with wheels (heavy-duty casters)!  I guess I shall be building it in my living room but where it will end up eventually remains to be seen. 

Regarding ventilation, I shall not be printing ABS on it as that has been superseded by more user and environmentally friendly filament types.

The printing capacity of this printer would appear to be more than I originally intended.  The increase in box size from 500mm to 610mm has resulted in a corresponding increase in the size of bed that will fit in and the available printing area.  So the 300mm x 300mm bed of the Titan is replaced by a 500mm x 500mm bed size and printing area of 400mm x 400mm.  By various means I think I can provide a printing height of approaching 400mm.  I can't say if I shall actually get these printing dimensions until I have worked out the design of all the parts.

I would strongly recommend having 3 leadscrews each driven by it's own motor. I use this method on my D-Bot and the bed is rock solid. If you are planning on using the Duet then get the Duex2 Or Duex5 expansion board to give you sufficient drivers.

You can also make the bed self-level itself

https://duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors.

Since the printer box will be on wheels, there will be space available underneath the base of the box.  This has enabled me to mount the Z drive motors below the base and not only simplify the construction but add a bit to the available printing height (I might as well get as much as practical).   As can be seen in the CAD model, the Z drive uses the standard threaded rods and a pair of stepper motors.  The substantial Z carriages keep the bed level.  The threaded rods are 8mm 1-start trapezoidal thread-form x 500mm.

+1 for the 1-start screws. Gives very fine z resolution.

3 hours ago, tekkydave said:

I would strongly recommend having 3 leadscrews each driven by it's own motor. I use this method on my D-Bot and the bed is rock solid. If you are planning on using the Duet then get the Duex2 Or Duex5 expansion board to give you sufficient drivers.

You can also make the bed self-level itself

https://duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors.

Yes, I remember that you did that Dave and if I find the bed is not held level enough I may go for your solution.  And yes, I shall be using a Duet control board.  I was originally planning on using 3 Z drive rods but with belt drive.  Decided it was too complicated and experiments with 4 rods on my Giant printer proved disastrous.  Three motors means an expensive add-on to the Duet so if I can get away with two motors I can save money.

EDIT :- For @tekkydaveChecked cost of Duex2 - £74-34.  This seems an inordinate cost just to add two stepper drivers.  Actually, really adding only one as the second extruder driver could be used for one of the Z drives.  If only Duet had provided 6 drivers instead of 5 it would have been covered.  Considering TMC2100 drivers cost about £8, spending £74 to obtain the same result does seem excessive.  I wonder if there's an alternative.  I can see the advantage of three Z motors.  I wonder if one could connect three motor coils in series like we do for two.

I found by previous mistakes that it is best to use the screws to maintain the plane of the bed and the z-axis wheels just need to keep it constrained in the x-y plane. My first iteration of the D-Bot relied on the wheels to keep the bed level. They were not very good at it

As I recall Dave the Z carriages had rather closely spaced wheels - my Z carriages have the wheels spaced 150mm apart giving much better control.  But the proof of the pudding...

The X and Y axes will be driven by the usual NEMA17 stepper motors with timing pulleys and belts in CoreXY configuration with one motor accounting for X+Y and the other X-Y.  This simplifies the construction and uses two motors at the front and four pulleys at the back of the box with two pulleys on each Y carriage.  The ends of the timing belts are attached to the X carriage.

This is my initial Y carriage design.  The X rail fits in the square slot (held with screw into the end) and ball bearing pulleys in the top and bottom slots.

I note you have managed to move the motors out of the enclosure (box) Gina. Are you provisioning for a heated & ventilated build chamber as a later development? If so, while a wooden structure is not particularly good at insulating it is supremely good for rapid modification e.g. holes for lights viewing windows fans and cameras!

I'll be interested to see how 'square' the XYZ linear axes turn  out to be relative to the bed. What are you planning for the bed anyhow?

Tony

I have no plans for an enclosed box - I do not plan to print ABS or other filament needing a heated chamber.

Since you ask I'll cover the bed now.  Or at least my initial thoughts.

A frame made of 20mm x 20mm aluminium extrusion 500mm x 500mm outside will have an aluminium plate on top 500mm x 500mm x 2mm.  On the underside of this will be a self-adhesive silicone heater pad rated at 1200W at 240v.  On top of the aluminium plate a glass plate will form the printing surface.  Here's a CAD model viewed from the underside.

Experience with machine tools suggests that for best accuracy bed levelling should be as rigid as possible and be a once in a blue moon (or less frequent) operation). Get it right, then leave it alone.

I agree, for my DBot, I've arranged a 4 point bolt down bed, which is a 6mm cast ally sheet, which I only need to re-level twice, both times due to replacing the PEI sheet.

14 hours ago, Gina said:

Yes, I remember that you did that Dave and if I find the bed is not held level enough I may go for your solution.  And yes, I shall be using a Duet control board.  I was originally planning on using 3 Z drive rods but with belt drive.  Decided it was too complicated and experiments with 4 rods on my Giant printer proved disastrous.  Three motors means an expensive add-on to the Duet so if I can get away with two motors I can save money.

EDIT :- For @tekkydaveChecked cost of Duex2 - £74-34.  This seems an inordinate cost just to add two stepper drivers.  Actually, really adding only one as the second extruder driver could be used for one of the Z drives.  If only Duet had provided 6 drivers instead of 5 it would have been covered.  Considering TMC2100 drivers cost about £8, spending £74 to obtain the same result does seem excessive.  I wonder if there's an alternative.  I can see the advantage of three Z motors.  I wonder if one could connect three motor coils in series like we do for two.

It's a good point but the Duex also adds lots of extra i/o which may or may not be useful. It has onboard 12v regulator which allows me to have a mix of 24v and 12v devices without resorting to buck converters etc.

Thanks Dave.  Yes, a 12v regulator would eliminate the buck converter - I too have both 24v and 12v devices.  I wonder if any of the extra I/O would be useful.  I'll see how thing go it's always an option for the future.

This printer will be bigger than I thought and yes, very heavy.  I thought I might be able to store it under the table but no, it's far too high.  Printers other than my Giant have been assembled on the living room table but Concorde is going to be heavier than the Giant and will also have to be assembled on the floor.  I was able to move the Giant out and into another room without wheels but not Concorde!!  My original thought was to have something like 50mm square internal corner blocks of wood to stiffen the box but this would add yet more weight so I think it will be 3D printed angle brackets.  Top rear brackets will also accommodate the Y rails and rear pulleys.  Bottom rear can be simple corner pieces bolted to the plywood panels.  Top front will be brackets to hold the XY motors and bottom front can be similar to the bottom rear.

19 hours ago, Gina said:

Yes, I remember that you did that Dave and if I find the bed is not held level enough I may go for your solution.  And yes, I shall be using a Duet control board.  I was originally planning on using 3 Z drive rods but with belt drive.  Decided it was too complicated and experiments with 4 rods on my Giant printer proved disastrous.  Three motors means an expensive add-on to the Duet so if I can get away with two motors I can save money.

EDIT :- For @tekkydaveChecked cost of Duex2 - £74-34.  This seems an inordinate cost just to add two stepper drivers.  Actually, really adding only one as the second extruder driver could be used for one of the Z drives.  If only Duet had provided 6 drivers instead of 5 it would have been covered.  Considering TMC2100 drivers cost about £8, spending £74 to obtain the same result does seem excessive.  I wonder if there's an alternative.  I can see the advantage of three Z motors.  I wonder if one could connect three motor coils in series like we do for two.

I got my Duex2 for £42.50 + vat (£51). At the time (Sept 2018) they had a special offer running.

That's considerably cheaper!!

Top rear bracket to hold box panels together plus Y rail and the rear pulleys.

Bottom box brackets.

Alternative corner bracket.