Little retraction help please

[Motopreserve]

Hey folks. Been toiling away on the Rostock V2 for a little over a week. Total blast, I'm enjoying myself immensely. Still having a few issues that I'd like to resolve. I feel the mechanical alignments/tuning are sound. Z and end stops all level with a .002" feeler gauge. Bed is flat. Extruder is calibrated. Filament diameter measured and entered.

Done a ton of reading here and elsewhere, and I'm afraid my brain is getting a bit spun out. Need some help and clarification from the experts here on SeemeCNC...

I'm printing only ABS, matterslice, 225-230c, bed at 95 (great adhesion with glue), .2 or .25mm layer height and never faster than 35mm/sec.

I'm getting a few "blobs," "bumps" or pimples - you take your pick on the term. Not horrible, but it comes up mostly on the changes of direction. Sometimes in the middle of a layer. After researching I kept seeing retraction issues come up. So I decided to try my hand at the 'hollower pyramid' to chase down any retraction issues. I Printed 3 before I realized that the reprap page that suggests it does not offer any advice of what to look for, and what might fix it. Yikes! So then I found the thread http://forum.seemecnc.com/viewtopic.php ... &start=100 on the forum. Some great prints and settings (from a bunch of different slicers) but again, not really advice of what to look for and what to change in order to fix it.

I am including photos of the 3rd print of this pyramid. The towers look worse in the photo than in person - but they could use help. Also, more interesting to me is the consistent deformity of the inner plane of each tower. You can see it in the pic from the bottom.

Thanks for any and all advice.

[img]http://i1227.photobucket.com/albums/ee427/nortstudio/3D%20Printing/D3663400-1F21-49D3-B130-25495598C06A_zpsqcmqrx8d.jpg[/img]

[img]http://i1227.photobucket.com/albums/ee427/nortstudio/3D%20Printing/5785A525-6F6F-4934-BBB0-60F32510D2F2_zps0rafbd9z.jpg[/img]

[Jimustanguitar]

A retraction problem would look like hanging strings, blobs (a different kind) or little pocks on every layer. That's not what you have going on here.

This actually looks quite good for just getting started. What's going on is that the plastic is actually hot for too long. The overhanging edges of each layer are sagging before they cool, and that's why it looks much better on the top side than the bottom.

[Jimustanguitar]

So I would try lowering your speed to increase the time on each layer, lowering the temperature, or turning on a layer cooling fan.

[Motopreserve]

Thanks so much Jim. I have had some blobs in the middle of layers on other prints - which is one of the reasons I landed on this test for retraction issues. Just to see if I could check it off the list. Trying to be methodical, but it's just too fun to keep printing functional things I'm using - instead of waiting until I get everything nice and pretty

The funny thing is I did a 4th print after I posted this. Slowed the speed down to 20mm/sec and increased the temp from 225 to 230c (the most successful temp for my other prints). The outer area came out better, but the inner area was about the same.

I wasn't sure if the layer fan was appropriate for ABS. Are there settings that should be coded to enable it only after a certain layer, or only run at a percentage below 100%?

I'm also wondering whether I should mess with acceleration and jerk. Just started researching that because I have had some issues with small circles (3-6mm) laying down on the first layer. The adhesion is usually good - but the nozzle travels so damn fast for those little moves, regardless of how slow the first layer speed is (12mm/sec usually). At first I thought that might be retraction related - but it's more like the thing is moving away from the circle before it's even done.

Thanks again.

PS: is the mustang vintage or modern?

[Jimustanguitar]

There's an open debate on whether or not to use a cooling fan on ABS. It works very well for me, but it's a bad thing for others. Trial and error is the right answer.

Retraction issues will look more like this:
[img]http://www.jonshobbies.com/wp-content/u ... action.jpg[/img]


And a cooling fan will fix things like this:
[img]http://i.imgur.com/DptBx.jpg[/img]

[Motopreserve]

Thanks for the pics. I am definitely NOT having issues like that first pic. Thankfully, because that looks creepy!

I'll try the fan and see how she does. I printed the shroud right away, but haven't wired it up because I haven't gotten PLA yet. Do you have any suggestion for fan %, and whether it should be on the whole time? I can trial and error it - but a general rule of thumb for starting point would be awesome.

Appreciate all the help.

[Jimustanguitar]

Here's another look at when you're not retracting enough:

[img]http://static1.squarespace.com/static/5 ... action.jpg[/img]

[Jimustanguitar]

Another note... You could be over-extruding. Have you ever measured a length of filament and then extruded that amount to see how close you are?

[Motopreserve]

I did. I measured 3 times to make sure and it was only 1mm off when it was stock. I actually fixed it, figured it might as well be spot on.

I did try the extrusion multiplier down To .9 (from 1) for the last 2 prints and it seemed to tighten up the outside areas a bit.