Parts printing with outward draft at base

Hopefully someone has had a similar issue and can point me in the right direction. ABS prints on FF creator pro, 230/110 nozzle/bed temp. Every print I run ends up with an outward draft from the base for the first 2.5-3mm. The fist layer appears to get laid down just fine but ends up being undersized in both directions. Subsequent layers get wider and wider until I finally get to the intended width of the part. This has been going on since the first part I printed (calibration cube) but most of what I've done so far hasn't had much in the way of vertical sides so it hasn't been all that noticeable. Are the first few layers shrinking more than what comes after them for some reason? Is it a problem with the feeds/speeds I'm using? It doesn't seem to matter what software I use to send the build, both replicatorG and makerware have resulted in the same thing.

The more I think about it though, it does seem to happen only when printing over USB. I've run two parts with vertical sides off the SD card and both came out nice and square. Is it a usb communications issue? I don't have time today to run another print from the SD card and see what happens so I'll do that tomorrow morning and report back but any suggestions would be appreciated. This has occurred at .1 and .2mm vertical steps and with different shell counts and infill percentages.

are the layers lifting off the bed - or just the wrong size ?

Just the wrong size, I'm not getting any lifting or warping, just a steady increase from undersized to correct size as the part builds. For the parts I'm building right now the total height is small enough that the whole part has the draft. For taller parts though, once the intended dimension is reached it stays consistent.

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Originally Posted by soofle616

Hopefully someone has had a similar issue and can point me in the right direction. ABS prints on FF creator pro, 230/110 nozzle/bed temp. Every print I run ends up with an outward draft from the base for the first 2.5-3mm. The fist layer appears to get laid down just fine but ends up being undersized in both directions. Subsequent layers get wider and wider until I finally get to the intended width of the part. This has been going on since the first part I printed (calibration cube) but most of what I've done so far hasn't had much in the way of vertical sides so it hasn't been all that noticeable. Are the first few layers shrinking more than what comes after them for some reason? Is it a problem with the feeds/speeds I'm using? It doesn't seem to matter what software I use to send the build, both replicatorG and makerware have resulted in the same thing.

The more I think about it though, it does seem to happen only when printing over USB. I've run two parts with vertical sides off the SD card and both came out nice and square. Is it a usb communications issue? I don't have time today to run another print from the SD card and see what happens so I'll do that tomorrow morning and report back but any suggestions would be appreciated. This has occurred at .1 and .2mm vertical steps and with different shell counts and infill percentages.

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Would help to know what machine, software and firmware you are running. Some programs like pronterface require you to give them threads to process the job, and if you don't have enough threads assigned and are printing over USB, and do and do something CPU intenstive it can interrupt the print job, but that doesn't sound like your issue really... But not knowing what machine you have it's very hard to even give you any advice.

Update, I ran another set of parts for my current project off the SD card and they too have the draft. So now there is no apparent difference between parts with and parts without draft which is making me doubt if I ever got any parts without draft. Unfortunately the ones I think were straight were quick test pieces that have since been lost to the garbage can. I will have to run those parts again and see what happens when the current job finishes. I was thinking it might be a difference in section thickness (maximum width across a single layer) but I have parts that are both thin and thick that show the same draft.

Geoff, I'm working on a flashforge creator pro, using makerware 2.4.1.24 (though I also had the issue using the latest version of replicatorG) firmware is sailfish 7.7 (pre-installed)

Ok, ran some more parts and this time realized that makerware defaults to 90/150 for speeds. Dropped that down to 60/80 which is where I was running things with replicatorG and the batch that came out this time is sans draft. However there is now a bit of a bulge at the bottom, still for about the same 2-2.5mm. The edge quality is also pretty lousy until past that bulge. The rest of the part looks great it's just the first 2mm or so. Any overhangs print fine so it seems there's only a problem with that bottom section of the print. Is it possible to fully support my parts so they don't start until say 3-4mm above the build plate? That should clear the crappy print area and leave me with good parts.

Another update. Ran some parts this morning at the same 60/80 speeds. Everything I've been printing lately is pieces of the triceratops skeleton puzzle from thingiverse so while each print is technically different pieces, the pieces themselves are not much different from print to print. I started printing these things at .1mm layer height. Upped that to .15mm with no appreciable difference in quality/drafting/bulging. Dropped speeds down to 60/80 at the same .15mm height and the draft was replaced with the bulge. Ran some parts this morning at .2mm and 60/80, behold the return of the draft but only in some areas this time. Even on the same piece some edges are angled and others are not. Also, the edge finish and top layer smoothness was hugely improved over the .1 and .15 prints. Just finishing a print now at .2 60/80 with NO RAFT (every other print up to now I have used a raft). No draft, no bulge, great edge finish, and while it's not quite done yet, the top layer finish looks to be coming out quite nicely.

At this point I have two theories about what's happening.

1) The code being generated for the rafts is in some way corrupt. Either the code is being generated with errors or the profile settings are wrong (I don't yet know enough to start screwing with a custom profile)

2) The raft is shrinking while the first few layers are being printed which is drawing those layers in, causing them to be smaller than subsequent layers. Once the print reaches the 2-2.5mm height the shrinkage is either done, or the part has gotten strong enough to withstand the forces being applied to it.

I'm less inclined to believe that the issue is from raft shrinkage because it would seem that larger prints should be less prone to this effect since there is more time between layers for things to cool but the drafting (until this morning anyway) has been consistent in height and angle (at least by eye) regardless of the size of the part.

Sounds like a flow issue. Many slicers alter flow/speed/height of the first few layers so they stick better to the bed.

You need to get a calibration cube working first, before doing other stuff.