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scottfsmith

Looking for absolute best reproduction quality

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I am printing mouthpieces for trumpet/cornet and any small glitch will change the acoustics.  So, I want to get as close as I possibly can to a 100% copy of the original measurements.  This is on a UMO+.

So far I have worked on shrinkage and found that I can usually use a constant of .15mm added to the radius measurements will give a copy generally measuring to within .1mm of the original.  Two places where some additional correction are needed are at the rim, where it shrinks a touch more, and in the narrowest part of the bore, where it shrinks more.  I also found as I decrease the layer height the error in the bore decreases.  I am finding even at 40 micron I get better quality than 60 micron so have settled on 40 micron layers.

I am only now starting to experiment with slower speeds, I was just using the default speeds in Cura's "ulti" mode but am starting to experiment with halving those speeds.

There are still two effects I am having, the shank of the mouthpiece has a wall that gets progressively thinner, but at some point there is a discontinuity where the wall jumps in more than it should have.  It looks like a layer or two was left out.  I assume this is related to how Cura is moving the head around, its changing some mode there.  Another issue is there is a small "wave" bump on the inside of the bowl on one side only.  I think this is a form of "ringing" according to this guide.  The discontinuity on the shank gets somewhat better at thinner layering but is still there.  The bowl wave gets a lot better at 40 microns, its one reason why I am preferring that setting.

What I want to know is if anyone else has strived for absolute reproduction and what Cura parameters you used.  I read on the 3dverkstan pages about how the acceleration can be reduced, but have not tried that yet.  Its not a Cura option I can find but seems to be in the Motion menu on the UMO+.  I am sticking to defaults for all but layer thickness and speed, but am also wondering if a somewhat cooler print head would be better for the smaller layers - less need for heat given slower filament feeding, and I should probably use as little as needed.  Oh, I am doing 4mm wall thickness to get a solid object with no fill.

Edit: here are pictures of my latest print.. on this one I used the front panel to reduce speed to 50%, otherwise it is ulti quality, 40 micron layers. I also reduced acceleration on the shank part of the print, to 1500. This print with reduced speed did come out better than earlier ones but you can still see banding on the shank end. The bowl defects are very minor, there is almost no "wave" with 40 microns and half speed. The exterior shank is also irrelevant as it can easily be filed down, but the interior of the end has similar glitches in it which I will need to sand down. Overall a fine print really, but I am looking for the MAX quality!

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Edited by Guest

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On the shank, it looks like you're either getting extrusion variability (maybe heat) or perhaps over extrusion. Since it is a thin wall, when you look at the layers in the slicer I think you'll see it isn't an evenly divided by your line thickness (probably nozzle width) so it has to estimate by injecting very thin gap fill. It's probably overdoing it a bit. You'll probably get better results if you can figure out either to have the line widths be a little wider (if your nozzle has a flat portion beyond the orifice, that can work) or change the wall thickness so that it is an even multiple of the line width so there is no gap fill error.

As it moves up, it looks like it is being over heated. My guess is that you're getting reflected heat from the nozzle onto the part that the cooling fan isn't keeping up with. One simple way to mitigate that effect is to print two of the part some distance apart (say 30mm or so) on the bed, so that it gives some more part cooling time before adding the next layer.

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The bumps covering most of the shank only happened at the slower speed. Maybe reduce the printer head heat given the slow extrusion rate? This print fed the filament through very slowly so the filament is getting much more time to melt (10x more than a normal quality print) so hopefully it would be OK at say 200C.

The rings on the shank end also happened only at the slower speed, I just had one big dropoff there when printing the same file at 100% speed. Unfortunately I sanded down all the higher speed prints already so don't have one to post. In some ways they were better; they looked like the way the bowl exterior looks on most of the shank. Looking at the slices at the shank end it is running into problems because its between lines and is having to do partial fills. I can't change the overall wall width as the exterior fits the cornet and the interior would change the sound.

One other odd thing happened on this slow print that has never happened before: the very end of the shank (top layer) completely under-extruded. You can see the jaggy stuff in the picture.

Anyway, I will probably try less nozzle heat and slightly faster than this previous one (but with 1500 acceleration max) for the next print.

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OK here is a print at 200C nozzle temp.  I used 20mm/s on outer line of shell and 60mm/s on inner ones.  I also had 1500 max acceleration.  On the above print I used 15 outside / 30 inside.

Clearly this is better.  It has the discontinuity of the earlier fast prints but not quite as bad.  The bowl has a very tiny "wave" in it but I don't feel it with my finger so it can't be too bad :)

So for the above print the temperature was clearly too high.  I don't know if there is any way to improve on the discontinuities when the printer shifts modes due to the thinning wall.  The mouthpieces have to be hand-finished anyway since the rim can't be printed properly, mouthpiece rims have subtle curves that have a significant impact on how they play.

One other improvement of 200C is the "dome" of the bowl, the part right before it becomes the most narrow, is where there is the most overhang from layer to layer; it has been printing too narrow here and it is probably due to the plastic drooping a bit. At 200C this is much better. It almost makes me want to try a slightly cooler temp...

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Edited by Guest
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OK here is a print at 200C nozzle temp.  I used 20mm/s on outer line of shell and 60mm/s on inner ones.  I also had 1500 max acceleration.  On the above print I used 15 outside / 30 inside.

Clearly this is better.  It has the discontinuity of the earlier fast prints but not quite as bad.  The bowl has a very tiny "wave" in it but I don't feel it with my finger so it can't be too bad :)

So for the above print the temperature was clearly too high.  I don't know if there is any way to improve on the discontinuities when the printer shifts modes due to the thinning wall.  The mouthpieces have to be hand-finished anyway since the rim can't be printed properly, mouthpiece rims have subtle curves that have a significant impact on how they play.  

One other improvement of 200C is the "dome" of the bowl, the part right before it becomes the most narrow, is where there is the most overhang from layer to layer; it has been printing too narrow here and it is probably due to the plastic drooping a bit.  At 200C this is much better.  It almost makes me want to try a slightly cooler temp...

 

If you print with thinner layers, It extrudes a lot slower as not as much plastic is required. This means the material is in the heat zone for longer and therefore expands more.

This also goes if you slow it down. so slowing it down and going for thinner layers means you can drop the temp heaps.

I can print at 30mm/s 0.1 layer and 190degees. So 20mm/s and 0.04 layers should be able to print cooler then 190degrees.

Another thing is if you have 20mm/s for outer shell and 60mm/s for the inner shells then If you optimize the temp for the inner shell the the outer one will be to hot. Or if you optimize the temp for the outer shell then the inner ones might under extrude.

So for best quality its best to keep them all the same so you can get the best temp.

If this now print to slow you may find going back to a higher layer height for example 0.06 and getting the right temp and speed will be better then your previous tries. or settle for a slightly higher speed but keep them all the same.

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I don't usual reply to topics as I'm a bit of a newby, but I would consider printing the other way around and possibly in two to get some of the height out. I assume the important bit is the internal shape printing the other way would make it more accurate, also I use simplify 3d which I personally think would handle that better. just my opinion.

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Bob, great minds think alike ;) I am in fact right now running a print upside-down since the overhang will then be on the outside. So far it looks a bit better on the shaft. I don't really care how the outside looks at all, in fact the design there is something I just made up in about 2 minutes. Its all about the shape of the inside.

@Labern, I will try an even lower temp to see how that does. I will bring the outer and inner closer; I want to optimize for outer and as long as its hot enough to feed the inner I will be OK but I will probably slow it down a bit. I should say I'm not sure I really need a lower temp though as the product is coming very near to spec. But its always worth a try; the goal is to find the absolute best spot for the kinds of prints I am doing.

@danilius, I use a range of sandpapers and then polishing compound so I can get a very nice finish with the PLA. In any case the goal isn't so much looks as how it plays.

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OK, the first upside-down print failed, I added a support base to the design since its standing on the narrow shank but did not make it thick enough and it wobbled.  So I redid it with a 2mm thick base and got a fantastic print - the bowl in particular has zero glitches inside.  All the glitches that were inside the bowl are now outside since that is where the overhang is.  I could see it is where the printer head is doing a 180 degree turn is where the "wave" is forming.  Most importantly there is no deformation at all in the bowl, I don't need to sand it out to fix it anymore.

Re: temp, since I had a print running when I posted the above I just dialed temp down to 190C and it still printed great.  This was without any change in speed.  So, I am sticking to same speeds and 190C temperature.  The shrinkage/deformation seems a little less at 190C and it might be worth trying to dial it down a touch more.  I tried 180C on a test print and the inner shell was not filling at 60mm/s, so indeed I would need to slow the inner shell speed down to print at 180C. So, sticking to 190C for now to keep overall print speed from getting more out of hand.

Here is the summary of whats working best for me now in Cura.  Other than these I am using default parameters inherited from the "Ulti" setting (not sure which ones it changes besides layer height).

Temp: 190C

Layer height: .04mm (from ulti)

Outer shell speed: 20mm/s

Inner shell speed: 60 mm/s

Shell thickness: 4mm (this is for me to get a solid object, 4mm is infinity here)

Front panel Motion menu: set accel to 1500

One added advantage of flipping the print is I can get a correct rim shape off the printer itself rather than sanding down the rim that was sitting on the print bed.  I am now tuning the rim inner lip shape, every .1mm there affects how the mouthpiece plays.

Edited by Guest

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Phew Labern yep that's defo a typo error I meant 65 and just been reducing it down to 60 printing a very fine taper which has to be accurate (Leure Taper) and the bed is holding to much heat. still using your fan shroud with Olson Block though.

scottfsmith

like the print but there is a bulge on the stem is that on purpose and is the length of that stem specific. I take it at the other end is a very thick adhesion layer. Reason I ask when I suggested print it other way around I was thinking of splitting that stem.

But you know exactly what your after and it looks very clean.

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Bob, the shank is a taper going right to left in the picture, it is for friction insertion in the instrument. Every dimension of it is constrained by either the instrument or the acoustics, there is no room for any variation until you get to about the middle when the outside is no longer in the instrument. The print of the shank is accurate, the only glitch is about 6cm from the left end when the wall gets to a certain thinness there is a little bump. Its almost not visible in the picture and easy to file out. And its on the outside which is not the critical bit.

I have done a couple more refinement prints and its getting hard to find a measurable difference with the original. :)

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