Problems with PRE-echo on models

[DenysNazarenko]

Hi, Have a nice holidays everyone!

I have a big problem and we try to solve this with support with no luck. I need community help.

The problem related to echo that appears on every embossed or corners detail.
First I think that echo appears with high speed and related to table shake.
But after experiments I note that echo appears before line is finished.
_Before_ every corner.

Could you please help in following -
1. Print example in attach with M2 MakerGear and send me the photo of the right corner.
(please rotate by x -90)
2. Give some ideas how to fix.

I use Simplify 3d and I try to reduce the speed, align the bed and many other things like tighten the screws.
So I need to know does this problem with every M2 or just with my.

[jimc]

i downloaded it. ill print this a little later but right off the bat i will tell you one problem is that this is a tiny piece and i can see by your photo that the part is getting heat soaked. basically each layer doesnt have enough time to cool. you cant figure out why the corners are doing that until you get this to print clean. that has to happen first. i think 90% of your problem is everything is too hot. if you printed 10 of these at the same time then i bet the part would look 100 times better. to add layer time you can also turn on 6 or so skirt perimeters then for the # of layers put 9999 in there. this will make the skirt the same height as the model.

[ErikAkia]

I agree with Jim. The overall surface quality is way down and is probably the small part syndrome.
I did print this part. I was not sure from the pictures the orientation you used to print this, so I did both. I already needed to print another small part so threw these in to help.
I did get some harmonics in the flat side but they are so small you can not even tell they are there when you hold a flat edge to it. The pictures shows it but that is because I was using my new PETG yellow which is translucent so you can see several layers into the part.

IMG_2106.jpg (46.22 KiB) Viewed 12513 times

IMG_2107.jpg (64.42 KiB) Viewed 12513 times

IMG_2108.jpg (66 KiB) Viewed 12513 times

IMG_2109.jpg (68.89 KiB) Viewed 12513 times

IMG_2110.jpg (57.23 KiB) Viewed 12513 times

[jimc]

ok i printed this too. i did it in black pla since that is what you were using. here it is printed with my settings. i used a 3 outline skirt, 10mm offset and it was printed the height of the model. this was just to give cooling time. i cant print your gcode to compare because i have a different hot end. this was printed with no support. if your all dialed in you should be able to print clean like this. this model is a bit deceiving in size. its only 1cm x 2cm..so really tiny.

test.jpg (164.04 KiB) Viewed 12510 times

[DenysNazarenko]

Hi,
Jim and Erik thank you very much!!!! You saved me from madness!

Yes you right the part is small and my experience not so cool as yours so my part looks ugly.
I create this small model for fast test.
But I get this echo problem with very large models too. It's easy to see the echo with embossed text
or hole. Of course your settings bit hide a problem but even on your prints I can see the echo.
(I show it with arrows).

Echo.jpg (189.27 KiB) Viewed 12496 times

I try to fix this echo by replacing RAMBO with Arduino Mega but get
the same problem. Since you have the same problem it can be related to firmware or
to the model of the engine that use M2 inside the printer.
So on given moment I think that I should try other firmvare than marlin or change the engine.
How do you think?

Also I attach gcode test for the square. This is hand written g-code print the square. After print
you will see the step before every corner. Please note that my g-code print model in one direction but STL
parser can print in both directions and this will bit hide the problems since steps will be from
both sides of the corner after each layer so it will be difficult to see.
But if you can use gcode or use one direction print then you can see the step.
Problem related to that printer changing direction for few micrometers before other direction was finished. This why we get echo _before_ corner or hole.

square problem.jpg (33.36 KiB) Viewed 12496 times

[jimc]

The echo you see after a direction change is very common and almost every printer will do this to some degree. This is the reason for the development of a core xy movement system that you will see becoming more popular in printers as time goes on. This echo has nothing to do with gcode, electronics or firmware. Its mechanical. It comes from a vibration in the machine from a sudden direction change. It can be reduced but not eliminated. You need to lower your acceleration settings in the firmware. The default is 3000 so try it at 1000. in s3d lower your xy movement speed and your perimeter print speed to maybe 30%. Of course make sure your belts and everything is tight on the machine. Also make sure your bed leveling screws with the springs are as tight as possible while still giving you a level bed. Beyond that it is what it is. You will not remove that 100%. 60% maybe.

[ednisley]

This why we get echo _before_ corner or hole.

Have you previewed your G-Code to make sure that the nozzle is moving in the direction you think it is, so that the mechanical ringing occurs earlier in time than the motion change that causes it? That's the usual definition of "before".

Having the effect precede the cause seems unlikely, but I'm willing to be convinced.

I preview G-Code using http://gcode.ws/, which allows stepping vertically by layer and horizontally by command within each layer. I predict that when you follow the nozzle around the model, you'll discover that mechanical ringing occurs after the platform changes direction at corners. The ringing won't be visible in the preview, of course, but you will get a good view of the ideal path defined by the motion commands.

It will help if you post your hand-written G-Code, along with close-up and well-focused pictures, so we can take a look at it.

[DenysNazarenko]

Hi Ed,

This is the reason why I'm attach the G-Code. you can spend 2 minutes to check. And yes I'm sure that problem appears _before_ corner but not after.

Hi Jim,

Your suggestion is very good for vibration. But I want repeat once again that echo appears _before_ corners. Yes. For the fist view it's looks like vibration I think so for few weeks but after I discover this problem and also note that some other printers even from china don't have this problem. For prof I will ask to print this part on the most cheap printer that has my friend.
On given moment you can take a look this video and check the speed -
https://dl.dropboxusercontent.com/u/720 ... G_4959.MOV

btw. I was try to print all this as slowly as possible but this is _not_ vibration.

[ednisley]

you can spend 2 minutes to check

The G-Code preview in http://gcode.ws/ shows the nozzle moving counterclockwise around the outside of both models, as seen from above the platform. The problem appears to happen when the axes decelerate before the corner, then accelerate afterward.

On both the X and Y axes, check the setscrew holding the belt pulley to the motor shaft: I think you'll find at least one screw has come loose. Apply threadlocking adhesive and tighten the screws against the flat on the pulley.

If the screws have been loose for a while, the motor shaft or the pulley ID may be scarred enough to prevent you from tightening the setscrew at the proper position on the shaft. Remove the pulley, use fine needle files to remove the scars, then reinstall.

Severe backlash due to a loose belt pulley produces effects that depend on speed, acceleration, and path geometry, but it's a good thing to check when the print quality abruptly changes for the worse...

[DenysNazarenko]

Hi Ed,

We check setscrew many times.

I'm not sure at 100% but if imagine that problem with setscrew then we should get the model smaller size than it should. size will be smaller according shift in setscrew. Also this can be problem for shifted layers.
For example we try to print the line with slack in setscrew from 1 to 4 point-
1___2___________________________________________________________3.....4

1 - start print
The extruder shuld be in position 2 but since we have the slack the extruder stay in 1 point and only just start own move.
at the 4 point extruder should be finish but it stay in 3 point.

You can repeat this for more complex form like square etc. you can't get the pre-echo in this way.