Distance between the hotbed glass and extruder nozzle

Hi there,

I'm building prusa i3 Rework from scratch. Sourcing parts locally and from the internets.

I'm looking at the calibration instructions and it says to fold paper in half and run it between the nozzle and plate - and adjust as needed.
I'd like to ask what paper to use, but i know from working in the printing industry for almost 20 years that this is a silly way to measure things. Paper weight is usually not equal to paper thickness. And is usually not even uniform thickness, unless the paper is specially calibrated paper.

I will probably use a feeler gauge for this and would like to know the distance between the nozzle and the plate in metric system?

Relax... No need to be overly precise here.
If you are lucky, you'll get your bed level within 0.1mm difference. So no reason to perfectly adjust nozzle height at one spot.

Make yourself familiar with your z-endstop adjustment or related firmware parameter and adjust nozzle height by "gut feeling".

Honestly asking the distance between the nozzle and plate is like asking "how long is a piece of string" There is no exact number.
It should be about a paper thickness (probably 100 micron). But to add o_lampe's reply - it's something that you need to learn and it will be different depending on filament type, what you use on the bed for adhesion (blue tape, kapton tape, buildtak etc). I use paper as you get to feel the tension or lack of it. It takes time, but you get to know what is the right tension for the right filament. If it's wrong it's a simple adjustment (or should be) and you try again.

With a properly built printer the z height adjustment should be a set and forget. I printed a number of things this weekend in ABS, I checked the z height once at the home position before I started and that was it and that was only because I had moved the printer.

Edited 2 time(s). Last edit at 02/28/2016 01:14PM by SteveRoy.

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Thanks for the replies,

Ok, i will start from 100 micron and work my way from there.

Just another thought. Do these things need a pre-heating before they start printing? (Of course, thermistors need to say they are at the right temperature)

In my experience from the digital press, their fusers might need to "warm up properly" before the first print even adheres to the sheet.
This means the first print for the day is usually crap, but the second print from the same job is good. Heat in the fuser rollers is evenly distributed. Are these 3D printers suffering the same problem? (Looking at the heatbed)

Edited 2 time(s). Last edit at 02/28/2016 01:36PM by Veesta.

The preheating might be something to consider.
I rarely get a print done at first try. Maybe because the heat has to spread out evenly in the hotend or on the bed?
Marlin has a preheat menu, worth a try next time.

Just thinking here,

Thermistor in the heated bed is connected directly to the heating element.
This element is able to get to the target temperature sooner than the glass element on top of it.

Actually, the glass is cooling the bed. It takes more time to heat to the target temperature.

What if you moved the thermistor from the heating element to the glass element instead? Thermistor would then measure the real bed temperature instead of the heating element temperature.

Problem is the distance between the heating element and the glass and Thermistor only measuring the temperature of the heater.

These two might even need some thermal paste to transfer heat. (like CPU coolers)
Or just glue these two with a thermal silicone, so they act as one element? (Thermistor on top)

Edited 1 time(s). Last edit at 03/01/2016 12:53PM by Veesta.

Quote
Veesta
Hi there,

I'm building prusa i3 Rework from scratch. Sourcing parts locally and from the internets.

I'm looking at the calibration instructions and it says to fold paper in half and run it between the nozzle and plate - and adjust as needed.
I'd like to ask what paper to use, but i know from working in the printing industry for almost 20 years that this is a silly way to measure things. Paper weight is usually not equal to paper thickness. And is usually not even uniform thickness, unless the paper is specially calibrated paper.

I will probably use a feeler gauge for this and would like to know the distance between the nozzle and the plate in metric system?

I'm with you I am also in the printing industry and I think people have no idea how many different papers there are. What I have been doing is leveling the bed using any kind of paper sometimes 20# bond sometimes 80# cover whatever. Then I printed this adjustable end stop [www.thingiverse.com] and I will use that to set the distance. I usually just use a single thickness of 20# bond but I have found I will need to change it depending on the material and the time of day so I will just tweak the adjustable end stop until it works the way I want.

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Newbie with Folgertech 2020 i3.

Some thoughts.
When you set the gap you put the material thickness in the Z offset for your slicer. This allows the software to know where the bed is. So it doesn't mater how thick the paper is as long as you put the thickness in the slicer.
Common paper is generally taken as about 0.15mm thickness so for common folk!!!! its recommended to use paper and put 0.15mm in the offset. (On the assumption you don't have special measuring equipment)
Since there is variability in both setting the gap and material thickness you want a first layer thickness set to be significantly greater than the paper so that the error is relatively small.
So if we used paper and set the offset to -0.15 we should have a first layer height of about 0.3 so that an error of 0.05 doesn't make a big difference to the print. if first starting I would suggest not using a first layer less than the paper thickness +0.1 (So 0.25 in this case)
If you measure the paper and can set it accurately you can use very low layer height including less than the paper thickness, but a low layer height can lead to other issues if you have a width factor over 100% to try and get squidge.
You are free to use anything instead of paper as long as you know the thickness and put that value in the Z offset.
Hope this helps.