Another Sintratec kit built

[RomanG]

Interesting - Roman has just responded to a ticket I sent about the issue and he says the chamber temperature does not matter too much.

The first prints were done at the default values with the laser set at 550 mm/sec. With the melting that seems to be happening, I am now trying the laser at 600mm/sec and I have also change the hatching from 50 micron to 75 micron. I know I should not change more than one value at a time but with a print taking so long it will take forever getting things right. I still don't know how close my X, Y and Z values are going to be after the latest adjustment of the galvo drivers and I cannot adjust Z until I get a flat print!

the chamber temperature does matter. But everthing between 140-150 C is fine. But the surface temperature is much more important, a difference between 1-2 C can make the difference between a failed and a sucssesful print!.

Now I am really frustrated. Two more aborted prints today. This time I loaded the print chamber with four of the test pieces, in a similar pattern to that shown in Roman's photo below. All four curled up at the edges and were dragged into the overflow bin with some of the molten Nylon sticking to the blade. This happened using the default values of; surface at 170C and chamber at 140C. For the second print I upped the surface to 175C and the chamber to 150C. This time was slightly better in that only three were wiped out - not much consolation!

However, there may have been a slight clue in the second print as the 'cake' surrounding the prints was much more solid than in previous attempts. In the first few prints there was very little 'cake' and the prints were surrounded by loose powder. In the last attempt, at 175C surface and 150C chamber, nearly all the powder in the print chamber was loosely holding together. So, just how solid should the 'cake' be and does this point to my surface temperature still being too low?

This is an extract that accompanied the photo from Roman's response to my ticket:
Also check the following things:
-the Laser glass may not cover the IR sensor
- the tube of the IR sensor may not touch the sheet metal beyond it
- The frontal light shade has to be adjusted correctly. the shade of has to be aligned exactly to the backside.

The last point is the one that is confusing me. I don't see much of a shadow on my powder or in the photo. If the frontal shade needs adjusting does it mean a complete disassembly of the hood? Not looking forward to that!!

Print surface.jpg

As I already stated your temperature distribution has to be alright before you can get start fine tuning your prints. Here is what you should do:

-Do not use custom settings for starting. For starting use the standart PA12 settings. You can experiment that later. The custom settings are meant for people that exactly know what they are doing.
-As rudschul stated the front sheet of the lamp has to be perfectly aligned with the backside of the powder surface. If its to far, the back will get to hot and the front to cold. If you have h shadown on your print surface your front will get to hot and back to cold. To get an even distribution it has to be aligned perfectly.
- Preheat your printer. about 1.5 hours should be sufficent
- load a calibration print (only one in the middle) and force the printer into powder prep mode
- raise your powder temperature 1 C.
- wait for about 1 min and check the powder.
- raise temperature again
- repeat until you see your powder darken/ get burned
- reduce temp 1.5 C ------> This will be your printing temperature
- if you hit 180 C and the powder does still not get burned check your sensor position / laser glass. Something might not be right.

i think the most importent thing is that you have an object that you could measure. Try to get first a nearly good print and than try to adjust the x,y,z. With the grid have an orientation. Try the folowing values:
heat up: chamber 149,5 surfarge 166
printing: chamber 150 surfage 170,5
speed 550

These values are not perfect but a good starting point.

I strongly discourage from preheat temperatures over 150 C as this will degrade your powder in short and long term! Also you run the risk of overheating! The problem here is when you heat your powder with temps over 150 for a long time it might graded and turn black witch results melting your powder in the build chamber. This will cause serious damage to your printer.

Will just half of one degree make much difference when the temperature fluctuates more than that as new powder is introduced and is never very steady even when doing nothing? At 175C the first layers were better but still not staying flat.

I will have a closer look at the shade - difficult to get at though.

A little fluctuation is normal.