Another Sintratec kit built

[rudschul]

yes, Sintratec try to help where they can do.
@fred_dot_u: You will not need to fill the chamber completly. For calibration i think about 3 cm powder will be enough. At the beginning you will have to calibrate your temperature. If you have a lot of warping mostly your print will go autamaticly into trash. :-)
Keep aware the the glass is clean and is not between your IR sensor. If this happens your temperature will not be correct.

[RomanG]

Replacement driver and switch arrived today so I was pretty keen to get them fitted. Had to earn some brownie points first though before I could play. I first checked the driver was working by rigging it up without mounting it to the chassis. Yay, it was working and the Y axis galvo was doing its thing However, there was a bit of a problem with the new driver - the mounting holes were threaded 4mm not drilled as clearance as the original ones were but as the bolts are captive, between the two layers of aluminium and insulation, there was no way of getting the driver attached. It was clear they had to be drilled out 4mm. This I did, being very careful not to get any swarf into the electronics. That done, the driver and switch were positioned and fitted.

Next the printer was fired up and I could finally do the calibration. The galvos needed a lot of adjustment to get the pattern right but I got there in the end. Probably have to wait till tomorrow to get some powder in and a test print done.

It's not clear from the instructions but I am assuming just a small ammount of powder can be used without having to fill the powder chamber? Can anyone confirm?

Hi Mike its nice to hear that you are finally up and running!

You can calculate the powder like this:

You need 1 cm for every 100 layers (0.1mm layer high is standard) Also you will need additional 2 cm. 1 cm is for bed preparation and 1 cm is for cool-down. Also i suggest you put 5 mm to 1 cm more just to be sure.
So for the calibration print (5 mm) you will end up with about 3 cm space you need in the build chamber

For the feeding chamber this is a different story. you have to keep in mind that the density of the powder chances when sintering. From about 0.5 kg per liter to about 0.9 to 1 kg per liter (depending on the sintering strength). This means that you actually have to apply more powder to compensate. This means the feeding chamber will move about +25% the distance of the building chamber.

If you apply that knowledge to the calibration part you end up with 37.5 mm.

have fun printing if there are any more questions feel free to ask.

[Mike Francies]

Thanks for the reply Roman. Below is a copy of a ticket I have just sent regarding my test prints.

Printer is now operational and I have been attempting the test print. First print was not good enough to measure in Z as the first few layers were deposited in the waste powder bin having been wiped out by the blade. It was good enough to measure in X and Y and these were way out, measuring just 34mm x 35mm. I unbolted the top and adjusted the galvo drivers by quite a lot and did a re-print. This time the print went fine with no layers lost. However, the X and Y were still a long way off at 36mm and 38mm - too much for the computed scaling. I have now altered the galvo drivers again and the test pattern is now overlapping the print chamber. Is this okay? Another test print planned for tomorrow. The quality of the print is disappointing with the bottom surface being convex and the top surface being very concave. Again, I cannot check the Z scaling because the surfaces are not flat. What is causing this? The surface seems very molten as the laser fills in the surface. Should I speed up the laser, widen the hatching or raise the surface temperature?

Maybe other could chime in with their thoughts too.

[rudschul]

What is the color of the powder before the laser get active?
the convex bottom problem is a sign of warping and you have to change your temperature setting and to check that the IR sensor is working right.
Warping happens while part of the matierial fall under a spezic material temperatur and the material shinks at different point of the print. I hope you understand what try to say. My english is not so good.

What is your chamber temperature? (i take heat up 149,5 Printing 150) What is your surface temperatur? (166 / 170,5) What was your heat up time?

[Mike Francies]

Hi Rudschul, colour of the powder is difficult to ascertain but it doesn't seem to discolour at all. I appreciate what you are saying about the warping and the difference in temperatures but I am using the default settings that Sintratec have set though I do realise these are only starting values. Heating up takes one hour forty five minutes and the chamber temperature is 140C and the surface temperature is 150C. When printing the surface temperature rises to 170C.

When sintering, the powder really does appear to melt and become molten rather than just fusing together. To me it suggests the laser needs speeding up but as I am at the very early stages of playing with this technology, I am open to suggestions.

[rudschul]

140 C for the chamber is definitive to less. The shrinking of plastic happen at a specific temperature. The chamber temperature has to be highter than this temperature. With every layer you cool down your print. If you cool down to much shinking will happen and than your print is bad or destroyed. Roman told me that he uses alway 150C chamber temperature. Which printing speed do you use? I use 550,0 the default value.

[Mike Francies]

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!

[Mike Francies]

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

[rudschul]

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.

[rudschul]

yes this is important:

The frontal light shade has to be adjusted correctly. the shade of has to be aligned exactly to the backside.

You remember the L-Peaces near the lamps. The L-Peace of the front lamp makes the shadow. You can loosen the screw and move the L-peace