Blobs on Layer Change (Mendel90)

Hi Everyone,

I’m having a small problem getting prints on my mendel90 perfect, I am getting small blobs on my prints where the layer changes (see attached photo). I have been slicing with Skeinforge using the default parameters given by nophead, and using .3mm layers. I have tried messing around with the retraction settings in the dimension tab of skeinforge but changing them is having little/no effect.

Currently I have been running:
Retraction distance 1.5mm
Restart extra distance 0mm

Does anyone have any idea what values I should be changing and by how much? I have been changing them by +/- 0.5mm with no luck.....

Since I have my retraction set to 0.5mm it works much better for me. Maybe try going even lower? Or higher?

I had the problem that I was missing all the beginnings of a line so lowering retraction solved my problem, maybe making it higher for you will work?

Did you calibrate the steps/mm for your E-meter?

I am currently trying larger changes to the retraction distance; I have attached photos of 0.5 and 2.5mm. Visually there is a small difference but I find it quite hard to tell which one looks better.

On the subject of calibration I'm quite confident that the extruder is well calibrated, apart from this small issue my parts are coming out looking really good!

Once you go past the distance to reduce the pressure to zero it will make little difference. With zero retraction you should get strings across holes, etc. Increase it until they go away and add a bit of margin. A good test is two towers spaced apart.

To get rid of the blobs I think you need to alter the speed of the fast forward. I think it needs to be faster but not so fast it stalls. You might also need to play with the extruder acceleration.

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[www.hydraraptor.blogspot.com]

Ah ok the retraction distance makes more sense to me now.

When you say "alter the speed of the fast forward" is this done by increasing the retraction speed in skeinforge?

For the extruder acceleration i'm guessing I should increase the maximum acceleration and also the retraction acceleration, or is the retract acceleration not limited by the max acceleration?

"#define DEFAULT_MAX_ACCELERATION {4000,4000,150,5000} // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot."


"#define DEFAULT_RETRACT_ACCELERATION 5000 // X, Y, Z and E max acceleration in mm/s^2 for r retracts"

Thanks for your help!

Mk Wrote:
-------------------------------------------------------
> Ah ok the retraction distance makes more sense to
> me now.
>
> When you say "alter the speed of the fast forward"
> is this done by increasing the retraction speed
> in skeinforge?

Yes they seem to be both the same in Skeinforge although ideally you want retraction as fast as possible but I think the restart speed is more critical. You want it fast enough not to eject too much filament to make a blob before the axis starts moving, but not too fast the filament has not time to emerge from the nozzle and attach to the bed / layer below.

The extruder speed is also capped in the firmware so you might want to increase that as well.

>
> For the extruder acceleration i'm guessing I
> should increase the maximum acceleration and also
> the retraction acceleration, or is the retract
> acceleration not limited by the max acceleration?

I don't know exactly what the firmware does. Theoretically you should be able to accelerate faster when rewinding.

It is hard to set the acceleration because when it is too high the extruder stalls but unlike the axes it is very hard to see because the rewind and fast forward phases only last a small fraction of a second.

>
> "#define DEFAULT_MAX_ACCELERATION
> {4000,4000,150,5000} // X, Y, Z, E maximum
> start speed for accelerated moves. E default
> values are good for skeinforge 40+, for older
> versions raise them a lot."
>
>
> "#define DEFAULT_RETRACT_ACCELERATION 5000 //
> X, Y, Z and E max acceleration in mm/s^2 for r
> retracts"
>
> Thanks for your help!

Edited 1 time(s). Last edit at 05/17/2013 10:56AM by nophead.

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[www.hydraraptor.blogspot.com]