heartless wrote:

The problem I have with using g-code to set preheat temps is that it starts both the bed & hotend at the same time, but the bed usually takes much longer to heat up, leaving your hotend hot and waiting (and drooling filament) for extended periods - this can, and does, lead to clogging.

I, personally, prefer to preheat the bed manually, then load and slice my model(s) while the bed is warming. Then, once the bed is hot, heat up the extruder and then hit print. But to each their own.

+1

++1

The problem I have with using g-code to set preheat temps is that it starts both the bed & hotend at the same time, but the bed usually takes much longer to heat up, leaving your hotend hot and waiting (and drooling filament) for extended periods - this can, and does, lead to clogging.

I, personally, prefer to preheat the bed manually, then load and slice my model(s) while the bed is warming. Then, once the bed is hot, heat up the extruder and then hit print. But to each their own.

+1

That is a good explanation, I think I get the idea now.

I just loaded a sample STL, and run the Slic3r. In the G-Code editor I found this code:
M190 S115 ; set bed temperature
M104 S200 ; set temperature
G28 ; home all axes
G1 Z5 F5000 ; lift nozzle
M109 S200 ; wait for temperature to be reached

Is it correct, that this code will take care of pre-heat (no manual setting)? I mean, M190 and M104 will set the temperature, and M109 will make sure that the print starts when the temperature are reached?

yes, that should work, but the temp settings themselves should be specific to the material you are using

M190 S115 ; set bed temperature - this is setting bed temp to 115C

M104 S200 ; set temperature - this is setting hotend temp to 200C

The problem I have with using g-code to set preheat temps is that it starts both the bed & hotend at the same time, but the bed usually takes much longer to heat up, leaving your hotend hot and waiting (and drooling filament) for extended periods - this can, and does, lead to clogging.

I, personally, prefer to preheat the bed manually, then load and slice my model(s) while the bed is warming. Then, once the bed is hot, heat up the extruder and then hit print. But to each their own.

I just loaded a sample STL, and run the Slic3r. In the G-Code editor I found this code:
M190 S115 ; set bed temperature
M104 S200 ; set temperature
G28 ; home all axes
G1 Z5 F5000 ; lift nozzle
M109 S200 ; wait for temperature to be reached

Is it correct, that this code will take care of pre-heat (no manual setting)? I mean, M190 and M104 will set the temperature, and M109 will make sure that the print starts when the temperature are reached?

In a perfect world everything can be programmed in with g code and it will work fine.
Manual overrides are something from the machine tool industry. The machine is dumb and will do what it is told. So the programmer does his or her best to program the machine. In the days of old cnc machines were operated by experienced machinists who could hear and feel if things were going the way they should. So the ability to increase or decrease feed rates and spindle speeds is a good thing. 
The same with.3d printing  we are programming our printers in g code via a CAM program we refer to as a slicer. We do our best to put in the best info possible for the best results.  Now we run the print we as the operator can see how the print is coming out. the machine has no idea. so the ability to adjust flow rate of plastic speed of the movements and nozzle and bed temp can come in handy.
Experience  is needed to know what a good print looks like. And there are limits to the manual control  for instance one number of perimeters are set  and infill is set and the slicer does its magic these can not be changed unless you go through the whole slicing process again.

1)
So I always need to pre-heat before printing (either by g-code or manually)?

2)
Why would I want to only pre-heat a little (not meeting target temperature)? If I pre-heat a little and start printing, I assume the printer starts printing before meeting the correct temperatures and giving bad prints?

3)
Should I in fact pre-heat to the desired temperatur, and then start printing?

4)
If I use manual heat to reach the desired temperature, what is the temperature settings for in the printer settings? Aren't they overruled by the manual settings?

A matter of preference It is nice to know when the thing will start and not have to wait.  but YOu need to remember to preheat.
Auto g cde is nice as yu will not forget to turn the heaters on but IMHO waiting for it to start can be unsettling.

To start with, I am using latest version of Repetier-Host. In this software I have configured Solidoodle specific settings (printer and slicer settings) according to suggestions found in this forum - so far so good.

Some of these settings are in 'Printer settings' where I can set my default extruder/bed temperatur. According to my logic, when I start a print, the printer should first start when these temperatures have been reached. However - when I uploaded a sample STL file, and pressed the start button, the printer startet to print immidiatly. At that time the extruder and bed were still on room temperatur.

What am I doing wrong here? How do I start a print correctely to ensure that the temperatures have been reached?

Br
Lemme