This topic contains 16 replies, has 8 voices, and was last updated by Richie 8 months, 3 weeks ago.
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From that pic it’s hard to tell but it looks like you’re over-extruding in that print. Could be a number of things, but first thing to ask is have you run the full calibration routine? (all 3 steps?) It takes 20min or so and you only need to do it first time you use the printer. But doing that will properly align the print heads, and calibrate the distance for the first print. It can make a big difference. Getting it just right in the beginning is important as from that point on parts will adhere well to the bed, without severe over-extruding.
Second thing is when you say “melting the first few layers without raft” do you mean the first couple layers appear “bulged” like it’s a brick of jell-o, which has settled and is just a little wider at the first couple layers? This is sometimes called elephant foot, and is common with heated beds, it’s hard to avoid without designing your part to compensate, such as a slight chamfer on the bottom 1mm or so of the part (or significantly dropping the temp of the heated bed, which unfortunately affects adhesion). Using a raft might get past that problem somewhat, but unfortunately most slicers default raft algorithms these days aren’t too great. Once it’s dialed in though you can get that “velcro like” raft removal. But because 99% of prints people are doing with Robox are without raft, to echo the others above you tend not to see a lot of experience with it.
So my advice is:
First off:
Make sure to run all the calibration routines, and make sure you have particularly the nozzle open/close and bed height routine done correctly. read the instructions carefully, when it says a piece of paper should slide easily without touching, it means without touching… Or you can use lightweight cardstock, and calibrate with that, but instead adjust until “it just moves freely without too much friction”.Following this activity bed leveling is done 100% automatically, but this initial calibration will adjust for manufacturing differences, or settling during shipping and so on.
This will ensure that the head is calibrated for the perfect distance from the bed. And as such it will minimize “Elephant Foot” of your prints (but not eliminate it totally) on raftless prints. It will also ensure you get good adhesion to the bed on your prints.
In addition as I pointed out above, it looked like there was some over-extrusion. This doesn’t mean that the profile is off, it likely means the head is too close to the bed, and that first layer is very “Squished out”. Then the following layers end up with the after-effects of that, impacting quality of the print.
It’s surprising how much of a difference simple mechanical calibration can make on print quality.
Secondly to answer your question specifically about rafts:
As I said above, the default raft behaviour of most slicers I’ve used from many other printers, all suck… That said with enough tuning/tweaking they can be made to work very well.
First thing is that rafts work best with materials which see a large shift in layer adhesion with temperature variance. For example PLA is very “sticky” at a fairly wide temperature band. So if you lower temperature to reduce layer adhesion, you can’t lower it far enough to really make a difference without causing other problems (inability to extrude fast enough and so on). But ABS layer adhesion can be affected with a fairly small shift in temperature, without severely impacting printability. Makes ABS an ideal material for printing on rafts.
The idea is when you do your raft, you want your base layer (the layer touching the bed) slightly over-extruded, so it’s squished down into the bed nice and good, and printed slightly hotter than usual, with a higher bed temperature. Then after that layer you can drop your print temperature to normal, and bed temperature to normal. The next couple layers are usually just structure of the raft, to ensure a nice even surface. Then you get to “Interface Layer”. The interface is the most important part, because you want this to be slightly weaker, and easy to break the part off, while still leaving a good finish on the part.
This also means the bed temperature can be reduced slightly, and the part is being printed slightly higher off the bed, resulting in no “elephant foot” effect.
The way this “break away” interface layer is usually achieved is:
- Lower temperature enough that layer adhesion is quite poor
- Look for “round extrusion”. In other words:
- Slightly under-extrude
- Extrude at a faster feed rate, reducing time for clean adhesion
- Increase the Z spacing slightly so that the layer isn’t “pressed together”.
- Alternate direction of extrusion for interface layers, so that the “Raft Side” of the interface goes one way, and the “Part Side” goes 90degrees to it.
- All of this results in a point of contact between the part side, and the raft side that is minimized, with 2 “round extrusion” layers, at 90 degrees from one another, the contact is minimal (only at where the 2 peaks touch at each line of extrusion) and with the cooler temperature the plastic doesn’t “stick” as well at that interface.
Unfortunately the mechanics of this (the layout of the extrusion and direction) isn’t really in your control, you’re at the mercy of the slicer. However usually you can control the temperature of the interface, speed, and flow usually. As well as bed temperatures possibly.
So basically to make your raft removable, you will need to create your own profile (likely in advanced mode) and experiment with values in speeds, temperatures, and bed temps to get that optimal “break away” capability at the interface layer.
Conclusion:
All the above said, the “Elephant foot” effect of printing raftless really shouldn’t be a big deal on 99% of your prints. If your printer is calibrated well, and you’re using default profiles, it should be quite minimal, and can usually be cleaned up easily when you don’t have control of the part design. And where it’s your own part, a minor chamfer can actually completely offset the “elephant foot” resulting in a nice square perfectly dimensioned part bottom.
Speaking as someone who has many years of experience 3D printing, on many different printers. I can say the PEI build surface on the Robox is like some kind of Miracle. It works brilliantly, and wherever possible I avoid rafts like the plague, they are just a giant pain in the ass (and the hand, as I have a few scars to prove it, as you’ve also learned recently).
So hopefully the above info both helps in answering your specific question about rafts, and maybe gives you some pointers if you feel the need to go that route, and also helps you perfect printing raftless so you don’t have to deal with those aweful things any more 😉
Good luck and happy printing!
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This reply was modified 9 months ago by
Glasswalker.
With ABS in particular, I found that any adhesion problems are solved by always giving the bed a wipe with a paper towel and a tiny bit of isopropyl alcohol before printing with it, as this removed finger prints which turned out to be the biggest single cause of prints lifting and peeling.
Since doing this as standard I haven’t needed to mess with brims or rafts at all when printing with ABS, even though my bed is still un-sanded (I’m hoping when it eventually gets its upgrade + service they will sort this for me as I’m not keen on trying it myself!)
in brief:
Raft Layer Air Gap. Setting under the support tab.
Make it bigger 🙂 will change depending on material.
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