Acetone smoothed ABS parts cracking

[Qtrain23]

i have some abs parts I've printed that have been acetone smoothed. I just noticed about 3 months later they're all cracking. Any idea what is causing it?

[Qtrain23]

[Jetguy]

layer bonding stress now exposing itself as the part has heated and cooled over time.

[Ryan Carlyle]

A couple thoughts in addition to what Jetguy said:
1) If you used WAY too much acetone (like a full dunk), the inside of the part can store residual acetone for a long time. I don't think this would cause it though.
2) If the outer surface is 100% smooth and has no cracks or voids, the air inside the part can put pressure on the surface as it heats and cools.

[Qtrain23]

That's what I've figured. I wonder if I shouldn't just use pla. I'm not sure how well it would hold up, and I like the having the ability to smooth it.

[Ryan Carlyle]

If it's residual warping stress, running your build chamber hotter will help a lot. (You do have an enclosure, right?)

[JF Kansas]

And more shells, like 3 if you are going to smooth with acetone...

[Qtrain23]

Printing on a 2x yea. I should lower the layer height to 0.2 instead of 0.3. These need to take a bit of an impact. Would pla be a better choice?

[Ryan Carlyle]

PLA is brittle, it'll crack and delaminates under impacts. Nylon is actually best for that but there's no good way to smooth it.

[Qtrain23]

Right. And I don't really have a printer set up for that. No aluminum carriage on the 2x Does taulman make something easier to print?

[Ryan Carlyle]

Any PET variant will also take impact well. Taulman t-glase or any other brand of PET.

[Qtrain23]

I have some pet+ that I got from make solid, but could never get good layer bonding strength. I think I was running 240 C and 60 mm/s. Maybe I just need to print it slower

[Ryan Carlyle]

240C seems low for PET+. 

[Jetguy]

I specifically printed the parts of my mini-Kossel in MadeSolid PET+ on a original Replicator dual at 230C and didn't have bonding issues.

Nothing trick about it and I didn't print slowly or anything. Bog standard 0.2mm layer height.

[Jetguy]

Sorry, I know that's not helpful saying I did it fine and for whatever reason you cannot.

 

The question is, was the problem printer a PTFE lined extruder? AKA MK10?

Mine was not, it was a genuine all metal Replicator Dual parts.

 

One theory behind that question is I have a much longer direct contact melt zone with the filament. So outside of just basic process temps, thermally, the filament polymer chains are being heated differently and that might be a factor. Because my zone is longer and more direct, the extruded layer would be much closer in theory to the set temp and therefore retain more heat and melt and bond to the previous layer without requiring higher and more excessive (IMO) temps to get layer bonds.

[Qtrain23]

just a standard rep2x

[Qtrain23]

I tried again last night. Got fairly good bonding strength this time printing at 40mm/s. I think I'm going to redesign these parts to make them easier to print

On Saturday, July 18, 2015 at 12:06:37 PM UTC-5, Qtrain23 wrote:

[Qtrain23]

I've been messing with printing this stuff the last few days. I've tried temps from 230-245 and various speeds, and it prints fairly well, but I'm having a problem with retraction now. When ever it retracts, it will leave a hole when it starts the next print segment. What are you using for your retraction settings?

[Ryan Carlyle]

I usually do around 1.3-1.4mm at 25mm/s for Replicator style direct drive printers. Make sure Extruder Hold is on (via LCD settings). 

[TobyCWood]

IMO you just discovered your problem. 

[Qtrain23]

And what would that be?

On Saturday, July 18, 2015 at 12:06:37 PM UTC-5, Qtrain23 wrote:

[TobyCWood]

.3mm layer height.

Try .2mm. 

[Qtrain23]

oh yea. Def part of the problem. My petg will be here today. I redesigned the parts to be 2 parts. going to try and see if the g works any better than the +. 

[Qtrain23]

Well I got some Esun PETG and it works great in my wanhao, but seems to instantly jam in my Rep 2X at the same speed/temp settings. Any idea what would cause that?

On Saturday, July 18, 2015 at 12:06:37 PM UTC-5, Qtrain23 wrote:

[Jetguy]

2X has an all metal thermal barrier and well lie to ourselves and say it was optimized for ABS- truth be told- not optimized for anything- they just screwed up and the team had no clue how an extruder even works.

 

The Wanhao (and nearly every other Chinese Replicator based design) is using a highly modified variant of the 2X thermal barrier mounting system with the bad thermal design- but they make the thermal barrier and nozzle hollow and cheat by using a PTFE 1mm thick wall liner tube inside to mask the filament from that bad thermal design.

 

So it works- the PTFE hack job effectively makes a working hotend- VS the 2X which has limited success with anything but ABS.

Obvious tricks to try are the oiling filament method to prevent cold end jams during retraction- the likely cause of all of your trouble.

[Qtrain23]

I was hoping you wouldn't say that lol. I should just switch out everything on the 2X to carls stuff and get it over with. It's super annoying to not be able to use anything but ABS in it. 

On Saturday, July 18, 2015 at 12:06:37 PM UTC-5, Qtrain23 wrote:

[Scott Booker]

I print PET+ on my R2X on a regular basis.  Jetguy's comments regarding the thermal barrier have merit.  They completely screwed up the interface between the thermal barrier and the cooling block.  Some thermal compound (Arctic SIlver, etc.) at that interface does help.

I get my best results with PET+ when I leave the front door open (and/or remove the top cover).  You don't really need the heated chamber for PET+ and the reduced environmental temps lower the cooling bar temp and improve the thermal barrier performance.  And although it's absolutely a band-aid, a filament lubricator helps to "get over the hump".  Personally I use vegetable glycerin liquid (e-cig base juice) with PET+ (nothing is required for ABS).... and have successfully pulled of some 15+ hour prints with a lot of retraction.

Carl's parts are certainly a better all-around solution.