Prusa XL 3D Printer

[Jasonb]

Although I do like dogs, I like this more Raw casting should be about 7.5lbs and will finish machine down to 8.5" dia

 

[GreenTwin]

That is a great looking flywheel.

The dog test print is basically a check of the moving parts, since it has quite a bit of vertical height to it.

Up next is the JasonB flywheel.

I will have to pick a scale.

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[krypto]

GreenTwin, is this Prusa XL your first 3D printer?

 

[GreenTwin]

I previously purchased a Prusa MK3S, and have had pretty good luck with it, with the exception of some bed lifting issues.
The MK3S print area is 9.84"×8.3"×8.3", and so I ended up printing parts of patterns, and then piecing the various pieces together, which is not ideal for pattern work since it can lead to misaligned sections.

When I got the MK3S, I was confused about setting the bed height, and getting that first layer the correct thickness is all important for bed adhesion.
I was able to get support from Prusa, and got the first layer adjustment thing figured out.

This Prusa XL is very nice in that it automatically sets the first layer height, and that is a nice value-added feature for sure.

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[GreenTwin]

JasonB was kind enough to send me an STL file for his niffty Cretors-like flywheel, and so I got it loaded into the latest Prusa slicer.

I changed from 0.25 mm quality to 0.15 mm.
That change stretches out the print time to 17 hours, but that would be well worth waiting for if the surface finish work is greatly reduced.

The highly anticipated JasonB flywheel XL print has begun.
The diameter will be 12 inches.
Go big or go home, as they say around these parts.

Fingers crossed.

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[Jasonb]

It will be interesting to see how the print measures when complete and how close to the CAD file it measures in all axis though it's a bit low for a good Z test. The dog may look OK but being such an irregular shape hard to tell if the print was accurate for size. Would it have been worth doing some tests on more easily measured shapes before spending time and filament only to find the callibration needs tweaking to get the part to come out the right size as nobody wants an oval flywheel.

I hope you stayed up through the night to take time lapse photos of the flywheel pattern

 

[GreenTwin]

Nobody in their right mind would stay up all night taking pictures of a 3D flywheel printing.

Here you go.

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[GreenTwin]

I printed a sample dog "Buddy" that was on the Prusa flash drive, to see how accurately a tall irregular object would print.

There was no bed lifting, and no problems with the print.

Its impressive to see a print like this with no supports required.

I will keep this as a benchmark print, and compare it with any changes I make to later print files.

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[lee webster]

I am looking forward to the finished flywheel, especially seeing how well four locating holes match up. When I printed my flywheel patterns, I used two holes. One circular hole in the middle, and one slot in the rim that lined up with the middle hole. The slot was the same width as the circular hole and 1mm longer. The pin would be a good fit one way, to ensure the spokes lined up, but gave a bit of wiggle room the other way. The slot was only in one half of the pattern, the other half had a normal circular hole.
I do love a nice flywheel!

 

[stanstocker]

I'm such a wimp, I would have settled for printing a calibration cube first... I like the dog. Maybe seal it with a polyurethane coating then spray paint with gold paint. Rig a strong magnetic base up and plop it on as a hood ornament. All the Mack truck wranglers will think you are mighty grand! Yes, I just listened again to Zappas's Moving to Montana, thought of the song when Tina Turner died, always got a kick out of the Ikettes vocals on it. The XL looks to be working out nicely, heck of a printer from what those who have them are saying.

 

[GreenTwin]

The XL looks to be working out nicely, heck of a printer from what those who have them are saying.

So far the comments from those on youtube who are using the XL seem to be very positive.

It is a bit of a risk to buy any new generation 3D printer, but I do have confidence in Prusa, and I also have confidence that Prusa will fix any problems that may arise.

I know others who have purchased Prusa in the past, and Prusa stands behind their products, and will fix any problems you may have.

The Prusa is about a quality printer, but also as much about supporting their product too; and I think a 3D printer user needs both.

The dog ate almost an entire roll of PLA, but I needed a good tall test print, and it proved the capabilities of this printer are not just hype.

This new design is interesting in that the bed moves vertically, but the print head only moves horizontally.
Seems like a good rigid design approach.

I think this printer has great potential as far as things I want to do with it (pattern making).

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[GreenTwin]

I selected the dog as a test print, as I mentioned because it is very tall, but also because it has a lot of irregular shapes, and no supports at all.

I am very impressed that the XL can print something like that without any supports.

I think the XL can also resume after a broken filament, and even resume after a power outage if I remember correctly.
It seems to be a very fault-tolerant 3D printer, which is a testament to the thought that went into the design.

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[GreenTwin]

Printing progresses.

A bit slow on the finest setting, but worth the wait I think.

Photos under the LED lights only give the filament a red color.

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[Jasonb]

Although the dog proves it can print a tall object it is not an easy thing to measure to see if it turned out 9 15/16" tall or 10 1/16" tall when it should have been 10" and with such an irregular surface you would never know if it were leaning slightly to one side or skewed.

Some cubes both solid and with holes through them and tall rectangular shapes would give a better idea of accuracy as you could measure the finished item and compare with the designed size

 

[GreenTwin]

While patterns can be made very accurately, the casting process is not so predictable.

Shrinkage rates vary according to alloy.

Basically you try to get a casting that falls into a range of usable sizes, based on an estimated shrinkage factor.

And many of the surfaces are machined (they have a machining allowance included for this), and so the accuracy is achieve after machining.

The best way to get an accurate casting is to use a 3D printed pattern, and to use bound sand.

No amount of accuracy in a pattern will compensate for how some rap on a pattern to remove it from greensand.

Flywheels that have 3D printed (or CNC'ed) patterns, and are cast using bound sand, turn true without wobble on the inside unmachined surfaces.

While accuracy in a pattern may be a good thing, there is more to making an accurate casting than pattern accuracy.

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[Jasonb]

But its a good starting point to have a round pattern, if the print or CNC cut pattern is oval you are not getting off to a good start

You mention a cold draught. it would be interesting to see it that has any effect on a tall slender part as one side cooling faster may make it contract and therefore you would get a bent in the part much like the cooling causes it to lift from the base

 

[GreenTwin]

You mention a cold draught. it would be interesting to see it that has any effect on a tall slender part as one side cooling faster may make it contract and therefore you would get a bent in the part much like the cooling causes it to lift from the base

My smaller Prusa MK3S seems to be very sensitive to any air drafts, and it appears to cause bed lifting, ruining the part.
That has been my biggest problem in the past.

With the dog print, I turned on the window AC unit, and it is blowing cold air across the room, and past the Prusa XL.
There was no bed lifting with the dog, and it was still fully adhered to the bed when the print was complete.

The Prusa XL bed does get quite hot, if that means anything.
I can't recall how hot the MK3S bed got.

Bed adhesion has a lot to do with getting the thickness of the first layer correct, and that was at least part of my problem with the MK3S.

The XL is self-adjusting on the first layer, and so no doubt that helps a lot with bed adhesion.

There is a lot of talk on the Prusa forum about installing an enclosure around XL units, to stop the draft, but so far my XL does not seem sensitive to draft at all, and if all continues like this, I would say there is no enclosure needed around an XL, at least in the room where I am using it, which is very drafty.

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[GreenTwin]

But its a good starting point to have a round pattern, if the print or CNC cut pattern is oval you are not getting off to a good start

Yes this is very true.

The most noticable place I see alignment/accuracy problems is on the inside of the flywheel rim, and some flywheel castings wobble noticeably, even though the outside of the rim is machined true.

Accurate patterns and castings helps with fit of the various mating parts, and prevents the casting from being too thin in places where you have to drill holes (all holes are centered on their bosses with an accurate casting).

The green twin was cast mostly with bound sand, and those parts only needed a light skim, since they were very close to final size, and the round parts were very round.
It saves material too when you only have to do a light skim to reach final dimensions, and it saves time too.

There is a term in the casting industry, which I think is "near-net" size castings.
This is when the casting is almost exactly the same size as the machined unit, and this is a very desirable trait in casting work.

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[GreenTwin]

We are at 82 percent.

I am not sure if I will use the 0.15 mm accuracy setting on future prints, since it really stretches out the print time, but I wanted one print to compare with the dog print, and see if changing from 0.25 mm to 0.15 mm made a significant difference in surface finish.

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[GreenTwin]

I am going to try this skim coat that I purchased last year.

It is suppose to flow out smooth and cover pinholes and such.

The downside to the product is that it requires a full commercial respirator.

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