I’m not into knives, but a friend asked me if my Repstrap could print a prototype knife handle. Seeing it as a learning opportunity,. I accepted the challenge.
I leveled the bed to .00mm in X and Y. I then printed the part twice, sliced at .1 and .2 layer heights using Slic3r.
Overall the handles printed well. The .1 layer height is so thing that I can practically push my finger through it which is to be expected.
I am most interested in learning if there is a way to make the slopes print any smoother. I assumed it was a function of layer height but both appear quite similar. Overall, I’m pleased with the results of these prints on my Repstrap. Are there other settings I should consider to further improve the quality of these prints?
230 seems a little on the hot side… 220-210 might give you better or sharper edges. With flat areas like that 3 to maybe even 5 solid layers top and bottom would give you a better surface along with 3 perimeters or shells and finally you might increase the sparse infill to somewhere around 30% plus or minus a bit.
More top/bottom solid layers, for sure. You want to increase those as your layers get thinner so that your top/bottom surfaces are at least .6mm thick, and .8-1mm is better. The bottom can be a bit less on the thin layers if you have your bottom layer set to your nozzle’s maximum layer height (which you should), but no matter how thick they get, never use less than three layers for top or bottom.
I disagree with @Brian_Evans about the temperature thing. I use 230C as a minimum for ABS on my machines (and go as high as 250C in some cases), though this will depend on the design of your hot end (both how accurately the thermistor’s temperature reflects that of the melt chamber and how efficiently it transfers heat from the heater to the plastic) and how fast you are printing. The 250C setting is for a short melt zone on an extruder that is really spitting plastic, and I would probably lower it if I wanted to print slower for some reason. Also, for others reading this, don’t go over ~240C unless you’re using an all-metal hot end.
Of course, the ideal temperature will also depend on plastic formulation. I settled on 230C in the old days when I was using a makerbot that printed slooooooooooowly (<40mm/s!) out of necessity with a pretty standard ABS formulation, but the stuff I prefer now (MABS and true-white translucent filaments like Afinia’s) tends to skew toward higher-temp formulas.
Even factory made knives handles break. I would put the maximum infill if it’s for a functional prototype, if it’s for an aspect prototype I would use PLA.
@Whosa_whatsis Fair enough… I typically print sloooowly on the machines I often use and hardly print ABS unless I have to. The OP is using a Repstrap so I assumed he would be printing slowly as well so I should have qualified my earlier statement.
About the infill… I seems to me that a medium density infill is actually stronger than a solid infill. Think cardboard.
@Brian_Evans I’ve been helping @Eric_Mack with his machine (he’s local, and comes to the monthly meetups at the shop), so I’ve seen exactly how fast it goes, which I would consider slow, but not as slow as my makerbot (at least not back in the day, before it had 3rd-party firmware with acceleration support).
1.75mm extruders also seem to need more heat despite all of the plastic being slightly closer to the heat source because it spends 1/3 as much time in the hot zone for the same rate of output.
@Whosa_whatsis Yeah my last cupcake I ran off a Sanguinololu and it worked fairly well but it was still in the mid 20s for speed if I remember correctly… that is until the hotend gave out and I didnt care enough to replace it.
I still dont feel the need to go much above 40 or 50 for print speeds though and have never ran ABS above 220.
Hey, thanks guys for your feedback. I’ll test out some of these ideas and see what difference it makes. I’m having a great deal of fun learning. I appreciate this community.
@Whosa_whatsis thanks for your help and encouragement. I have a new z axis and an E3D hot end. The Z axis is rack and pinion for now, which is a major improvement over my first z axis. Still working on a lead screw design for the next z. perhaps I will have something to show at the next Deezmaker open house in August.
I’m no expert but I would think going to an even thinner layerheight would come out smoother. You could make a small object to test it out with so you don’t commit to printing a new handel without being fairly sure it will be better.
I get better looking top layers by increasing the infill. Too less infill causes more bridging which makes it looking bad. Increasing the number of top solid layers might help as well, but slic3r does not always detect them correctly in case of slopes.
I read somewhere that Triffid Hunter recommends to use a line width of .5 mm regardless of nozzle diameter. Does that make sense and do you agree? At present I’m using a .4 mm nozzle with a .5 mm line width
@Eric_Mack PLA (good quality one) allows finer and more accurate details. If you printed a blade or if the handle had engravings, PLA would give better results.
@Eric_Mack Obviously that won’t work for a nozzle larger than .5mm, but I’ve been using .35 and .5mm nozzles both with a .5mm thread width with good results.
