On 24/01/2019 at 20:25, Gina said:

Gina, the variation in 'error' across teh plate is tiny - are you sure you recalibrated the zero point? - Surely there ought to be a start point showing up as green.

Yes, you're right, LH bottom should be green.  Z homing should set the start point unless I'm missing something.

This is a bit better.

Another.

53 minutes ago, Gina said:

Another.

Now looks like tilt rather than distortion.

Yes.  No problem as the error is tiny and easily compensated by the firmware.  In other printers I have had a slope of 5mm across 200mm and the firmware still coped fine.

I am now thinking of replacing the inductive Z probe with the Precision Piezo sensor that works by probing with the nozzle.  This will give more accurate and repeatable results, avoid all the setting up required for inductive probes and avoid Z probe setting up when changing hotends (Concorde has interchangeable hotends).

Been working on this on and off but not yet managed to separate the nozzle touching the bed from all the other vibrations.

Arranged anti-vibration mountings for the Z stepper motors and also a new X carriage with better piezoelectric sensor mounting and now eliminated Z motor vibration triggering the sensor.  Now the hotend fan is triggering it instead so I need to isolate that.

Been having lots of problems with the Z drive - very noisy and tending to stall one side or the other even at quite a low speed - so decided to dismantle the Z drives and see if I could find the problem.  Tested the threaded rods for straightness and they are fine.  One problem is that the printed Z carriages have warped and the wheels are loose on the Z rails.  So I shall need new Z carriages anyway.  From what I can discover and discussions, I think the main problem may be the accuracy of alignment of the threaded rods with the nuts on the carriages.  To make alignment easier and save myself a lot of work I think I may add more cash than effort and order some ready made parts.

I would want two sets - one each side.  There are other useful parts too such as top and bottom plates that hold the rods precisely in ball bearings but aluminium parts are quite expensive at £10.50 each (so 4 off would be £41) and I think 3D printed ones would be good enough.  This is a system designed for precision in CNC machines and with the taller gantry plates just the job for the Z axis.  Firstly though, the smaller and cheaper gantry plate.

C-Beam Gantry Plate  £11.00

The double gantry plate is longer that the standard one which is only 60mm between wheel centres and would give better resistance to twisting.

C-Beam Double Gantry Plate  £16.50

C-Beam Linear Rail – Cut To Size  £13.62

I'm already using NEMA23 stepper motors for the Z drive so it all fits.

I have implemented this method of Z drive using C-Beam Double Gantry Plates.  With the overall height of the drive (except for motor) being just under 500mm the Z range is 300mm.

With the heating problems with the 400mm square print area I have decided to abandon this size of print bed and go for the 300mm x 300mm as used in the previous Titan printer.  In view of this and the inaccurate plywood panels currently used in the box and having found a source of cut-to-size hardwood plywood, I have decided to make a new box slightly smaller in footprint but slightly higher.  As a result of all this the build volume will be around 300mm cube (just under 1ft cube).

Decided that buying cut-to-size plywood was both expensive and not guaranteed to be exactly what I want and also preferred to use what I had so decided to buy a good quality circular saw and fine cut blade and do it myself.  The saw will have plenty of other uses too.  I was able to cut the box panels down to exactly the size I wanted and rebuild the box.  Everything had turned out to be precisely to size and I have been rebuilding the printer.  It is now almost complete and ready to work - just need to replace a connector on one of the motor cables.

Some diagrams and photos.  Firstly, top view diagram of the printer box and bed.

This is a cross-section of the bed.  Top is a borosilicate glass build plate, then silicone heater pad (not shown) followed by 12mm thick PU for insulation and to ensure good contact between heater and glass.  This is supported by a 6mm thick plywood panel and the whole lot held together with 3D printed framing.

Here is a photo of the bed assembly.  The plywood bed base is bolted onto two rails of aluminium extrusion.  Between these rails are two more which will be attached to the Z drive units.

Here is one of the Z drive units (C-Beam with gantry plate, wheels and trapezoidal screw system) with a piece of extrusion attached to the gantry plate.

Here is the partly assembled printer, showing the box, X and Y rails and Z drive units at the sides.

The Z axis is driven by two NEMA23 stepper motors (as shown in a diagram in a previous post) which go below the base of the printer.  To allow for these the printer is supported by four castor wheels  which also make moving the printer easy.

Here is a photo of the current stage of build.  Not finished yet and needs some cables connected and everything tidying up.  The blue cylindrical part in the bottom centre takes the filament reel, with the filament being carried in a PTFE tube up to the extruder.  Between extruder and hotend is a new improved version of the Precision Piezo piezoelectric probe that works by sensing a light touch of the print bed against the nozzle when Z homing.  My attempts at using the bare piezoelectric disc and amplifier were less than totally successful - I'm hoping this will be more reliable, the design certainly looks much better.

A connector got pulled off one of the motor cables whilst moving thing around and I seem to have mislaid the metal bits that go inside to make up a new one.  Meanwhile, I've been testing as far as I've got.  The following items tested and working.

1. Hotend heater
2. Heatbreak cooling fan
3. Bed heater
4. RH XY motor
5. X endstop
6. Y endstop
7. Z drives

Replaced connector for RH XY motor and now that motor is working.  I now have the X and Y homing working fine but having a problem with the Z which is probably something wrong in the homez.g and homeall.g code.

This printer has been working well until just recently when I've been having problems with bed adhesion.  I need to take and post an up-to-date picture as I have added parts cooling, filament feed and support for the umbilical cable bungle plus some tidying up.

I've just given the bed a service.  Cleaned the glass, taken the bed unit apart and checked the brackets etc.  Then I adjusted the Z drives to get the bed as level as possible as I believe the auto-levelling works better if the bed is reasonably level to start with.  I adjusted the LH drive by a few tenths of a mm to give the best levelling as indicated by the results of the Mesh Grid Compensation.  The borosilicate glass plate is not flat but I've reduced the maximum error.  Here are the Automatic Calibration Results top view.

A check with an IR thermometer has shown that the bed surface temperature varies quite a lot over the area.  Also, the thermistor is reading over 20°C higher than the bed surface.  With the thermistor reading 120°C the bed reads from around 80°C to 102°C.  Maybe a new heater and borosilicate glass plate are indicated.  It's a mains voltage heater and not cheap!  OTOH this could be why the filament id not sticking to the bed.

1 hour ago, Gina said:

Maybe a new heater and borosilicate glass plate are indicated.  It's a mains voltage heater and not cheap!

Surely a new thermistor is indicated? The controller will just be underpowering the bed if it's getting false readings.

The thermistor is part of the heater pad.  Anyway, the bed surface temperature is very uneven so I think the heater is on it's way out so I've ordered a good quality (Keenovo) heater pad for about £56 due to arrive on a slow boat from China sometime next month.  Meanwhile, I've increased the bed temperature to a nominal 140°C.  Bed is reading around 90°C to 100°C in the area in which I'm printing.

Print seem to be going alright with the increased bed temperature.

Here is a photo of the printer I've just taken.