Bulging, Rounded Corners From Bowden Style Printer

[wirlybird]

I have a new printer, F410, it is a Bowden style printer. My first Bowden.
It is doing a good job and I am using the printer vendor supplied FFF for my PLA brand.

One thing I see is that on my test part the corners on the square part are bulging and rounded. Also on the round part on top of the square section the "corners" are very bulging there too. The "matt" finish one is the problem part. The shiny one is from a different printer and is how the part should look.
These are pictures 1 and 2.

Picture 3 show top surface scarring on the Bowden machine.

I have been doing some reading on this issue and it seems to be something a Bowden setup can suffer from.

Not blaming S3D here! Looking for suggestions on what I might try to improve the prints.

Thanks for any ideas.

[horst.w]

A bowden style printer needs a lot of retract , more than a direct extruder does.

Direct Extruder situation: when the print stops (for layer changing e.g.), the pressure is interrupted instandly. in most cases a retract is not needed.
Bowden extruder, same situation: caused of much play the filament is meandering inside the bowden and presse out material even when the extrusion stopps.

What to do?
Heat up the nozzle and extrude some material while the nozzle is now cooling down. Stop extrusion when it is cool enough and mark the point on the filament where it is entering the extruder. Than open the extruder screw, the filemt is jumping back now. The difference between your first mark and the new entering point is the length to retract .
For my Mankati with 70 cm bowden I need 5,5 mm retract and the best restart distance is round about -0,13 - -0,15 mm (negative).

All other settings are identical.

H.

[wirlybird]

Printer manufacturer has their S3D profile at this:
Retract distance - 4.25mm
Extra restart - .05mm
Speed - 400mm/s

They say they test heavily to design a profile for a filament so I don't want to vary to much from it yet. I have a lot to learn about a Bowden.

Right now I am testing speed and temps to see the effects.

Thanks for the info.

[horst.w]

Clearly, its depending from the lengt of the bowden. And also from the inner diameter of this hose and from the filaments diameter and some other parameters like temperature, print speed also as retracting speed, multi, viscosity .... . Therefore general advices are not possible, it needs to collect own experiances.
Mankati has designed in 2013 / 2014 the printer for 3 mm filament, so the bowden has an inner diameter of 3.2 mm. But meanwhile filaments standard is 2.85 mm what requires more retract distance than real 3.0 mm filament. The point is, the extruding pressure must be stoped.

The only one problem I have with the Mankati is to print flexible filaments. I'm not able to do it . Therefore I bought a 2nd printer -A8 - , that was much cheeper than a new equipement for Mankati. And I'm very satisfy with it.

H.

[wirlybird]

I appreciate the insight.

The part in the picture with the problem is printed at 100mm/s (this is a default speed for their profile and it does pretty good).
If I drop to a more standard 40mm/s then the print is pretty good.
So in my testing so far the speed is the main factor.

As I work on this I will see how an increase in retraction distance affects the corners.

It will be a process as I learn about this machine.

Thanks again for the insights.