ABS printing issue  

RE:

The part on the left looks like you are over extruding, with the raised areas of the infill and the extras on the brim.  Have you calibrated for this filament ?  You know as in actually measured the average diameter with callipers and plugged that number into the filaments diameter in the slicer filaments profile and then printed a single perimeter test cube and measured the wall thickness to make sure it matches the extrusion width so you can then accurise the extrusion multiplier ?

RE: ABS printing issue

Thanks for the reply. I'm a relative noob. I've never done the procedure that you are recommending. It sounds a sensible thing to do though. I'm retrying the same models in PLA and the same plucking is occuring to a lesser extent. When i've got this job out of the way i'll do a calibration print and report back in a couple of days. Thanks again.

RE: ABS printing issue

Most people when they calibrate for a filament forget about the diameter.  They go straight to printing a single wall cube and measuring the wall thickness and then adjusting the extrusion multiplier.  They seem to forget that every calculation the slicer makes is based on the filament diameter.  So if your filament is in reality 1.76mm then its going to push a bit extra plastic through for each millimetre extruded.  And if its 1.72mm (which is a common diameter for some filaments) then its going to under extrude and they adjust the extrusion multiplier instead of measuring the filament and changing the default 1.75 to match the reality of the filament.  

I've found that if I put the actual value in the filament that I very rarely have to touch the extrusion multiplier on my setup.

RE: ABS printing issue

I measured the filament with my digital calipers and it is exactly 1.75mm. It's a good point though. I'll make a point of measuring each new roll of filament as I use it and make the appropriate adjustment.

RE:

I've done quite a bit of ABS printing, usually with good luck, but I've found that there are some prints that are difficult for ABS to do on the Prusa.

In general, ABS is more tricky to print, and more susceptible to various calibration parameters than is PLA or PETg.

If the above were my print, the first thing I would do is double-check the Z calibration, first using the internal 'zig zag and flag' method, and then one of those 3x3 single-layer calibration prints.  This will show any issues of left/right (and front/rear) bed leveling and will allow an input of 'fudge factors' to correct any of them.

Again, if this were mine, I would let the print go a few more layers before concluding an issue.  I've found that some 'globbing' on the first layer(s) resolves as additional layers are laid down.

As far as general ABS printing on the Prusa, I would offer a few hints, which cumulatively help to assure better ABS prints.

1. If you don't have an enclosure, use the 'draft shield', which is available in both PS and Cura.  Likewise, don't print ABS in a cool or drafty room.

2. Before launching an ABS print, preheat the machine to ABS temperature and let it sit at least 15 minutes or so to come up to temperature and stabilize.

3. Use a release agent! Always with ABS! The PEI coating on the build plate cannot take a joke with a stuck ABS print.  I've learned the hard way on this.  I personally use Layerneer, but glue stick also works.

4. When the print finishes, allow the print and the build plate to cool to almost room temperature before attempting to remove it.  Again, learned the hard way.

Some prints just do and do not work well with ABS on the Prusa and similar printers.  I've had good luck with things such as small project boxes, detailed pieces such as fire escapes for model railroad buildings, etc.  However, thinner prints with large surface areas tend to warp and curl up at the corners.

I've been trying out ASA, as an alternative to ABS, on both the Prusa and Ultimaker printers, but have not reached a conclusion yet.  ASA seems to be less susceptible to warping, but the jury is still out and I just don't have enough experience with ASA yet to say anything authoritative about it.

RE: ABS printing issue

Thank you for taking the time to type up that detailed reply. I have to confess that for now, we've done the job in PLA in the hope that the customer won't be able to tell the difference. This hopefully gives me the time to learn how to use ABS. I was experimenting  with PLA on my Prusa Mini at home last night. I created a test cube with a single filament wall. I found that I had to set an Extrusion Multiplier of 0.92 in order to get the wall thickness and overall dimension correct. When I go into the office i'll calibrate the  Mk3S with ABS.

RE: ABS printing issue

Some users seem to diss PLA, but in actuality, it's very good when used within its limitations.

The limitations that come to mind immediately are temperature/humidity tolerance and ability to use chemical smoothing.

PLA cannot take a joke in direct sunlight or in a hot car.  It will deform and/or decompose.  It does poorly indoors in warm/humid environments, think boiler rooms or greenhouses.

It also will not smooth/polish using acetone (or similar solvent) fumes.  I have heard that dichloromethane (methylene chloride) will chemically smooth it, but I have never tried it myself.

Other than that, it prints very easily, shows detail very well, and is reasonably strong.

One test case I have is a flush valve actuator which sits inside a toilet tank (very humid) and it has two small-tooth gears which have been going strong with several actuations per day for over two years.  It's held up reasonably well.  It's had a few issues (such as corrosion on sensor leads) but nothing to do with the gearing.

RE: ABS printing issue

Posted by: @jsw

Some users seem to diss PLA, but in actuality, it's very good when used within its limitations.

The limitations that come to mind immediately are temperature/humidity tolerance and ability to use chemical smoothing.

PLA cannot take a joke in direct sunlight or in a hot car.  It will deform and/or decompose.  It does poorly indoors in warm/humid environments, think boiler rooms or greenhouses.

It also will not smooth/polish using acetone (or similar solvent) fumes.  I have heard that dichloromethane (methylene chloride) will chemically smooth it, but I have never tried it myself.

Other than that, it prints very easily, shows detail very well, and is reasonably strong.

One test case I have is a flush valve actuator which sits inside a toilet tank (very humid) and it has two small-tooth gears which have been going strong with several actuations per day for over two years.  It's held up reasonably well.  It's had a few issues (such as corrosion on sensor leads) but nothing to do with the gearing.

An additional limitation of PLA is its higher tendency to creep, especially when used at slightly elevated temperatures (30 or 40°C) where it theoretically should still function properly. It is also getting brittle from UV exposure (not the only material type that is not well suited for longer UV exposure though, ABS doesn't fare that well there either)

Other than that and your points, PLA is actually a pretty good material. For many of the week points, the fairly easily printable PETG is a good alternative. 

If you do need the heat stability of ABS but need something easy to print with almost no warping whatsoever, have a look at TitanX or 3Djake nice ABS (supposedly made from the same material). They are a kind of ABS+ and very easy to print.