I've started threading up the XY cords and think I may have discovered a flaw in my design using the Core XY system.  With the Y carriages at the front ie. Y = 0, the X carriage can be in any position.  This means that as the X position is moved from 0 to 200mm the cord winds up onto the right-hand drum and there will be a small error due to the geometry of the cord.  Minimal error would be obtained if the cord is at right angles to the X axis when X is centred ie. X = 100mm.

Now to look at the geometry.  Taking the calculation above the total cord range on each drum is 4mm corresponding to 400mm (diagonal movement,  200 X and 200 Y).  The movement we are considering is 100mm from the reference. meaning 1mm of cord sideways movement.  The minimum distance from pulley to drum will be about 20mm.  Referring to the diagram below (not to scale), the horizontal line represents the case where the X = 100mm, the origin represents X = 0 and the hypotenuse of the triangle is the cord run with X = 0 (or 200mm).  The error is the difference between the adjacent side (horizontal) and the hypotenuse (angled).  In this case the vertical side, the movement of cord on the drum, will be 1mm and the adjacent side 20mm. 

Applying Pythagoras, "the square of the hypotenuse is equal to the sum of the squares of the other two sides", the hypotenuse is sqrt of (1^2 + 20^2) = √(1 + 400) = √(401) = 20.025 giving an error of 0.025mm.  This is negligible, so my worries were unfounded   But I had to check.

XY cords threaded but need slight adjustment - job for tomorrow - I'm off to bed   So tomorrow the first job is to fix the drum settings and then it will be time to take some parts from my Pilot printer.  The print bed parts, Mega/RAMPS and LCD unit.

Cord threading is a tricky job!  Found I hadn't allowed enough length on one of the cords so had to replace it.  Then I got it crossed over in spite of plenty of light.  This job is showing my age - shaky hands and poorer eyesight, but I'm lucky compared with some of my friends   Have no fear, I shall conquer it!!

Done it

Took Mini printer off the table and put the Pilot printer on it.  Then I noticed something I had completely forgotten about - X and Y end stops   Hope I'm not losing it  

Think I'd better sort out the X and Y endstops before other things then.

I'm hoping this printer will produce more accurate prints than my Pilot printer which it will replace.  I can use a nozzle of 0.25 diameter and small layer heights.  The Pilot goes out of calibration and suffers from the Y axis being by moving the print bed.

Printed a bracket plate for the Y endstop.  This will be attached to the Y rail.

Y endstop fitted to rail - also shows a Y carriage, pulleys, motor etc.

Designed and now printing the X endstop bracket.  This will be attached to the X rail and the endstop will be operated by the extruder motor casing.

X endstop attached.  A little adjustment to the run of the cords is needed, I see.

That's all the endstops taken care of.  The print bed and the runs of cables would seem to be next.

Started stripping down my Pilot printer for parts.  Undoing the hard work I put into that brought a bit of a lump to my throat but it has to be.  It's being replaced with what should be a far better printer and I can't keep too many 3D printers.

I shall be using the print bed glass plate and bed heater plus the Arduino Mega + RAMPS + LCD control unit initially but I have a Duet Wi-Fi control board that I intend to use in the final construction.  This new control board provides a number of improvements including smoother running, more precision, faster printing and much easier control (and remote) from a web browser.  I might change the bed heater for one with nearly twice the power and hence faster heating. viz. 20 X 20cm,400W@240V,w/3M PSA & Thermistor,Silicone Heater Pad,3D Printer HeatBed.  This also saves on a high power PSU.

The print bed heater is a silicone pad of 200mm square and 220W meaning current of 18.33A and I use a relay to control it since that is too much current for the RAMPS.  It's also too much for the Duet - just.

Is that correct? 220W on mains voltage is around an Amp, isn't it?

No, I meant my present heat pad which is 12v.  The mains one is something I'm thinking of getting (on a slow boat fro China).  I'm afraid I didn't make myself clear.

Drums for XY are 15.83mm diameter and the Z is 10mm.  Adding the thickness of the cord gives 16.31 and 10.48.  The Z drive gear ratio is 33:8 so the drum diameter is effectively 10.48x8/33 = 2.54.  Motors are 200 step per revolution and cord movement is Pi x d so steps per mm will be 200 / (Pi x d) but that's whole steps so for 16x microstepping, micro-steps per mm = 16 x 200 / (Pi x d) = 3200 / (Pi x d) or 1018.6 / d.  So micro-steps/mm for XY = 1018.6 / 16.31 = 62.45 and micro-steps/mm for Z = 1018.6 / 2.54 = 401.02.

Extruder E3D Titan :- hobbed pulley measures 7.8mm diameter, gear ratio 3:1, motor 0.9°/step (400 steps/rev).  For 16x microstepping, micro-steps per mm = 16 x 400 / (Pi x d).  With the 3:1 gear ratio this gives micro-steps per mm = 16x400x3 / (Pix7.8) = 783.53.

5 hours ago, Gina said:

No, I meant my present heat pad which is 12v.  The mains one is something I'm thinking of getting (on a slow boat fro China).  I'm afraid I didn't make myself clear.

Ah, I understand now

I seem to have lost a post (or never uploaded it).  The above figures were inserted into the input fields of the RepRapFirmware Configuration Tool which generates all the g-code files required to set up and calibrate the printer firmware.

Connected the Duet board to my Win 7 laptop with supplied USB cable and been setting it up using Repetier Host to send g-codes.  Had to download and install driver for it.  WiFi all set up and I have it working via Firefox on my Linux Mint desktop.  Have uploaded the G-Code files I downloaded from the configurator web site.  I think the next stage will be to connect it to the printer and ATX PSU.

Been looking into the positioning of the various parts still to add such as the Duet control board and ATX PSU.  The back would seem the appropriate place.  I think I can get the PSU in if I move the print bed forward a bit.  An ATX style PSU meets the electrical requirements nicely though rather on the big side.  I've worked out that everything on this printer works fine with 12v with the possible exception of the print bed heater.  Also, the ATX PSU has the advantage of easily turning off the main power after printing, automatically from g-code.  The Duet board can be mounted higher up, clear of any exhaust hot air from the PSU.  It seems unlikely that the Duet will need fan cooling if its mounted vertically with plenty of space for air circulation across the back of it.

I think I may need a plywood panel on the back of the printer on which to mount the PSU and Duet.  Originally I was thinking of mounting the electronics on the top but I would prefer to have the PSU further down to stop the printer being top-heavy.  Since I no longer want an LCD control unit at the front the electronics can go at the back - just the Duet board in this case.  XY motor cables and Y endstop cable can be fitted into the Y rail grooves to go from front to back and with the Duet board at a similar level, the motor wires can be shorter than otherwise.  The extruder wires will have to go up to a support near the middle of the top as will the filament and its holder.  Have yet to sort this out.  May be a sheet of plywood or extrusions.

11 hours ago, Gina said:

I seem to have lost a post (or never uploaded it).  The above figures were inserted into the input fields of the RepRapFirmware Configuration Tool which generates all the g-code files required to set up and calibrate the printer firmware.

Connected the Duet board to my Win 7 laptop with supplied USB cable and been setting it up using Repetier Host to send g-codes.  Had to download and install driver for it.  WiFi all set up and I have it working via Firefox on my Linux Mint desktop.  Have uploaded the G-Code files I downloaded from the configurator web site.  I think the next stage will be to connect it to the printer and ATX PSU.

Make sure you upload your config gcode files in the settings area. If you upload them in the 'Gcode Files' area they will just be available to be printed. Might be a good idea to download the supplied files before overwriting them. Select all files via the tick box at the top, then right click on one of the files. It should let you download as a zip.

Ahh...  I think I may have done that wrongly then - thank you for that.

Yep!  Wrong...  Ooops.  I'll correct that.  Settings > System Editor seems to be where the setup files are.

That seems to have worked alright - downloaded the files in a ZIP and uploaded the g-code files, rebooted then disconnected and reconnected USB to allow WLAN comms.  Now have the new g-code system files replacing the originals.  Now to remove the setup g-code files from the g-codes for printing area.