Printing Holes

[jameshs 42]

Not sure if this is how to do pictures!

 

I am trying to print two small 'holes' voids in the side of an object - it is to take a clip in the side wall of a small box. one side prints brilliantly - because the head stops and dos not cross - imagine a C where the good opening is on the opening of the C and the bad opening is opposite - because of the stringing it does try to leave this one out, but stringing and a slight amount of oozing means that this opening actually gets filled.

Is there a trick I am missing ?

Slicing in Cura

The wall thickness is only 0.5

Nozzle 0.4

Stock Setup (have had machine 2 weeks

While PLA

220 degrees

Print Speed 75

Layer height 0.1

Retraction speed 60, distance 4.5

Speed 100

min layer time 8 seconds

I played around with a lower temp setting - 210/215/220 and below 220 I had artifacts (curling) from not getting proper adhesion on the first layer - whereas I get good adhesion (painters tape) at 220

I lowered feed by increasing the diameter of the filament (it is 2.87 ave and I have put in 2.84 for normal extrusion - when I increased the diameter I did not have enough extrusion to actually achieve good layer adhesions and the thing fell apart.

Am I trying something too hard - I was thinking that maybe I should do a dimple in stead of a hole as then I am just diverting the head?

It can clearly achieve the bridging as it does one side perfectly - but not the other.

I am just really trying to learn all the defaults on a simple box before I move to more complicated stuff - 40 boxes printed so far - drawn in Revit, into 123D Design, out to STL and into Cura!

love the machine!

Should I keep trying to go with the hole/bridging - or go with a dimple?

James

 

[illuminarti 18]

Your photos aren't showing up. I think it will be easier to diagnose once there are photos. :-)

 

[jameshs 42]

My error - I had not 'finished' uploading the photo.

I think it is now here?

 

I could be wrong

 

James

 

[illuminarti 18]

Ok, I see the picture now, although its a bit fuzzy. :-)

It looks like it's not even trying to print a hole there. If you look in the layers view in Cura, do you se it really trying to print in that area? I suspect there's something wrong with your STL file and how the hole is defined, such that Cura doesn't see it as a hole. Can you share the STL file?

Are any of the 'fix horrible' advanced settings turned on in Cura? Those might be deliberately trying to close the hole up.

 

[gr5 2,095]

I played around with a lower temp setting - 210/215/220 and below 220 I had artifacts (curling) from not getting proper adhesion on the first layer - whereas I get good adhesion (painters tape) at 220

 

1) Wiping the blue tape with isopropyl alcohol (found anyplace that sells bandages) will DRASTICALLY increase the adhesion to the tape. Try it.

2) There's nothing wrong with printing the first layer at a higher temperature and then lowering the temperature manually either with Cura or with an ulticontroller. It's pretty straight forward and simple.

 

It looks like it's not even trying to print a hole there.

 

This is *not* a difficult print. You will learn about difficult prints later, lol. I agree with illuminati here - are you sure it's not *trying* to fill that hole? Look at the gcode view - blue lines are non-extruding passes. You might need to visit the 'fix horrible' checkboxes.

You could reduce stringing by reducing the pressure of the filament in the print head which is easiest to do by lowering the print speed. Both Cura and Ulticontroller let you set the % print speed - when it gets close to the top lower it to say 30%. When you are printing at high speed you get high pressure at the nozzle and it's hard to stop the PLA from oozing out.

Also you will get less stringing at lower temperatures as the PLA is more like toothpaste and less like honey:

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/

Your filament and UM will vary so do the test I did in the top photo to determine how much stringing you get at various temperatures. Its an easy test and only takes about 10 minutes.

 

[jameshs 42]

so this will sound dumb - how do I upload gcode - the album viewer would not let me?

I had a look at it in the Gcode viewer gcode.ws and the hole is definitely there.

Will post a screenshot next post.

James

 

[jameshs 42]

here is a picture of the gcode

the issue is that the blue blobs produce pla blobs, and that the thin green line produces strings, which form a thin, but effective wall.

so it is seeing it - and I rotated the model - and it did the same thing to the rotated side, and printed the other side well - so it depends on how it slices it.

I can try the adhesion tricks - so are we saying that I need to have the lowest temp possible for void/bridging and (in my mind) a higher temp for good lower layer adhesion?

Can I have a lower layer temp like I can have a lower layer thickness? ... or does that require a manual editing of the gcode?

Thanks

James

 

[gr5 2,095]

You could have just looked at the gcode in cura. Be default cura shows the model as a 3d object you can pan, zoom, rotate around (right click drag, both click drag, shift right click drag).

In the top right corner is an icon to view in other modes which can be very helpful. One of them is "layers" which shows the gcode visually in 3D. You can select the layer you care about with the slider and zoom in and around the problem or questionable area with the 3D mouse movement.

 

[gr5 2,095]

So I agree it is stringing. Possibly extreme stringing. Pretty easy to get rid of - read my post above.

I'm wondering about that retraction speed of 60 though. I don't think it's possible for the retraction motor to move that fast. Maybe try 20? Marlin changed the code that controls the extruder stepper and there was a bug and I have a version from last December (with the bug) and I assume you have a version with the bug fixed (actually maybe not - not sure if Daid has updated Marlin in Cura since December) so I can't really speak intelligently about the speed other than 60 seems too high. The bug made higher speeds slower so 40 might give you 20 and 60 might give you 10 or something bizarre like that - I really don't know the details. But a slow retraction speed would give the filament time to blob. I really recommend you do a test just like that stringing test print in my post above.

 

[gr5 2,095]

More details about extrusion speed bug:

http://umforum.ultimaker.com/index.php?/topic/1734-marlin-bug-the-myth-of-retraction-speed/

I use speed of 40mm/sec and have this bug so it's actually 20mm/sec I guess.

Note that this speed doesn't affect normal printing which is much slower, but mostly affects retraction.

 

[illuminarti 18]

There are a couple of things you could try to get this to work better. Firstly, lower your retraction speed. 60 is too high, and kinda meaningless given some bugs in the Marlin firmware. Better try a speed of around 40 if you're using the standard firmware, and 30 or so if you have built your own fixed firmware (see: my discussion of the problem here).

Secondly, increase your travel speed to at least 150mm/s. That will help break the bead of filament when moving, rather than dragging it across the gap.

Some people do adjust layer temps for first layers vs bridging etc. Some slicers allow you to set a different first layer temperature, but Cura currently doesn't. However, I've never felt the need to do that. Make sure your z=0 position has the head just touching the bed, use the widest blue tape that you can find, and wipe it with isopropyl alcohol before you start the print, and the bottom will stick just fine at most any temperature.