Neil:

May I ask where you get your ground stainless rod, please?

In Cura, I think you insert the maximum bed size and then it limits you, should you try to exceed those limits. I expect Neil will have simply inserted values for his table (if he uses Cura).

In the newest version of Cura you would choose the printer you have in the setup section and it will set the build table size automatically. With a little digging you will be able to find this setting and make changes to the build table size. Do so with care, prints will not come out like you intended if the print head or table hit the end of their movement as the stepper motors will chatter a bit and then assume they are at the right location while they are not.

I don't see how it would do this if the x and Y homes are off the build plate. I presume it can be done, since you obviously have.

I’m sure mine comes down on the z axis until it hits the limit switch – the bed is levelled on that pisition, so it should make no odds where the home point is, in reality.

… er …. well …. so does mine now you come to mention it. I had this fixation that the z-axis worked differently to the others.

Put it down to age, addled brain and forced isolation.

Wouldn't you know it …. just when you're locked in and can't get out to the opticians.

I'll leave now.

Neil.

I too have the same printer as you, and won a few extra mm by putting a bigger piece of glass on the plate; you rarely print on the corners anyway it's mostly the skirt editing the machine bed size in Cura > Machine settings got the datum back onto the glass.

I wonder if you had any success printing PETG? I've tried many combinations of settings and get rubbish results, I've now got a bin full of scrap and lost my original cura settings for PLA… I can print the CV19 headbands in PLA but dismal failure in the preferred PETG… I tried two different rolls so don't think it's the material.

Thanks (in advance)
Mark

Hi Neil,

Finally done with all the current batch of collars, etc. Thoroughly overloaded on wildlife conflict stuff, so..back the the workshop and FINALLY back on my oddball 3D printer…

Starting with the Z axis, which first start with the table and how its constructed. Can you explain you table construction a little please? There ais a flat 'plate' under the actual print surface I presume – Aluminium? and then is that reddish material a silicone flat rubber heater? Is that flat up against the surface below it, and is there some sort of heat insulator between? The I presume the print surface is a glass sheet – right against the heater – what thickness is the glass? I see spring clips holding the sandwich together – how well does tha sandwich maintain its thickness, ie, is there not a possibility of the Z gap to print head varying with heat, and time – do you use print head leveling and do you do that everytime before printing?

Please..

Joe

I only carry out Auto Mesh bed levelling if I know I have disturbed the printer, but I do home in Z onto the print surface at the start of each print.

Some print beds have PCB track heaters, either clamped as a sandwich to glass, or bonded to the aluminium bed.

Edited By Andrew Entwistle on 01/05/2020 10:33:59

Thanks Neil.

What sensor do you use for the auto-level process? And how does that process work on your printer? How many points ( a grid?) does the system check for height variation across the print platten?

Quite fun building this thing of mine – Of course , I believe I can do better than all the solutions out there, and proceed to waste a lot of time inventing the next answer to all problems….

So, while doing the Polar printer, I am also trying a DC motor worm-geared print head that is Induction heated, with no thermister sensor…

My aim is to fit the extruder head on the end of the SCARA arms, no Bowden tube, so the extruder has to be as light as possible, with as few wires as possible. Induction heating , if I get the concept to work reliably, will promote a light weight head.

Tests show some promise – I made some sample nozzles of 304 and 316 stainless steel, with a 10 turn coil around for the induction heater. The energy source is an 80 watt RF class E amplifier, driven by a 12 to 16MHz tuneable RF signal. The coil and nozzle are tuned to provide a matched load to the RF amp, when the nozzle is at 200degC . The frequency of the signal driving the amp changes from 12.2MHz when cold , to 15,8MHz when hot – this is changed in a closed control loop,  keeping max energy transfer to the load ( the nozzle..) . This is measured by a simple reflectometer ( SWR meter, for the Hams among us..) – when the ratio between reflected power and forward power to the load worsens, the frequency is changed to improve it. There is a sweet 'frequency' spot, which can be determined in a calibration cycle, at which the temperature is at set point. Then, keeping the frequency constant , if the nozzle heats more, the SWR degrades so reduce the amplifier output – the nozzle cools, and the SWR improves, until the curve goes the other way, where SWR degrades again, so increase the power till the SWR improves, etc – this provides SWR controlled temperature control, due to the curie effect of the heated nozzle.

The 304 grade nozzle gives the largest SWR change near 200 to 280deg C, so maybe the better alloy to continue test with. I would like to try some of the ferritic grades, but nothing in Namibia…

Probably going the be the most complicated 3D printer around, IF it actually gets to print anything!

Joe

Edited By Joseph Noci 1 on 01/05/2020 21:13:33