Prusa XL 3D Printer

[GreenTwin]

There are some assumptions that have to be made with making castings.

One has to assume an approximate factor to scale up the 3D print with, to allow for shrinkage in the metal.

Generally the scale factor is not too critical, but for parts like cylinders, where you have to drill a ring of holes around the perimeter of the cylinder, if your scale factor/shrinkage factor is off, they your hole pattern will also be off.

It is a bit of an art to pick the correct shrinkage factor so that the dimensions on the drawings will fall within an acceptable range with the castings.

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[GreenTwin]

93%.
Getting close.

For the 2nd pattern half on this flywheel, I will use the 0.25 mm accuracy, and see how the two halves compare.

I will have to fill the pattern either way, since it still has lines in it.

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[GreenTwin]

The first print half is complete.

The surface finish is a little bit more coarse than I had hoped for, but not bad all things considered, and better than many 3D prints that I often see.

The bed adhesion was perfect, and I had to pull pretty hard to remove the print from the bed.
This bed is a satin bed, and my previous Prusa had a smooth bed, so perhaps the satin bed gives more surface area for adhesion.

3D prints generally have to be smoothed no matter what, and so hopefully the smoothing process for this pattern half will be relatively easy with the automotive skim coat.

The pattern by JasonB is a really nice unit, and not something I have been able to achieve in 3D modeling.
Hats off to fantastic modeling work by Jason, and especially the willingness to share such a fine pattern.

Now we will try the second pattern half.

If this pattern where symmetrical, I could print one pattern half, and use it to cast two permanent patterns in aluminum.
Since this pattern is asymetrical, then I have to print two reverse-face pattern halves.

The excellent bed adhesion is a BIG deal on the XL.
Lets hope that continues to work as well as it is working now.

Edit:
The Prusa MK3 mentioned cleaning the bed with 90% alcohol, and sometimes with acetone.

This Prusa XL sheet has explicit instructions to clean cold with 90% alcohol, and NEVER with acetone, and it says the acetone will ruin the bed finish, so a word to the wise.

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[GreenTwin]

Starting the left side pattern print.

I changed the quality setting from 0.15 mm to 0.25 mm, and the print time decreased from 17.5 hours to just over 7 hours.

We will see what the 0.25 mm setting looks like.

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[GreenTwin]

Maybe I am confused about the non-symmetrical left side, right side prints.

The left side print appears to be the same as the right side.

Scratching my head now.

Edit:
Nope, looks are deceiving.
The left side is indeed a mirror image of the right.

The right side spokes initially curve counterclockwise from the hub.
The left side spokes initially curve clockwise from the hub.

At a glance, both prints look the same.
LOL, I have been looking at flywheel patterns too long.
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[lee webster]

You got me worried there for a moment. Luckily I have a small flywheel to hand that has curved spokes, so I could check it. The spokes do curve differently. And just to correct a glaring error in your staement, you can never look at flywheel patterns for too long. Never.

 

[GreenTwin]

I am looking at the print quality settings in the Prusa Slicer.

The first JasonB flywheel half was printed with a "0.15 mm DETAIL", which is 17.5 hour print.

The second JasonB flywheel half that I am printing now uses "0.25 mm QUALITY", with a 7 hour print.

The current print surface does not appear to be appreciably more rough than the 0.15 mm setting, and it is progressing much faster.

The standard nozzle that comes with a Prusa XL is 0.6 (mm ?), which I think is larger than an MK3, in order to get a more acceptable print time with large prints.

So I think the larger nozzle will give a more coarse surface finish.

The surface finish is ok so far on the Prusa XL.
Not perfect, but usable I think with some fill material such as skim coat.

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[GreenTwin]

You got me worried there for a moment. Luckily I have a small flywheel to hand that has curved spokes, so I could check it. The spokes do curve differently. And just to correct a glaring error in your staement, you can never look at flywheel patterns for too long. Never.

I like your attitude !

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[GreenTwin]

I am going to try the "Skim Coat" product (see post #100), which is a flowable polyester 2-part auto body glaze.

I think the skim coat is for horizontal surfaces, and there is a risk of it sagging.

I also purchased a similar product from the same company for vertical surfaces, but I am going to try the flowable horizontal material first.

I have not used body glaze before, and so there will be a learning curve with this product.

I figure that a sag can be sanded out, and it is more important for me that the filler flow and fill all the lines in the 3D print, to give a smooth surface.

They generally apply body glaze with a plastic spreader, but I am not sure this will work for my flywheel 3D prints.
I may try a paint brush, but the success will depend on how fluid the filler is.

I also purchases a product called "Seal Skin".

The seal skin is actually the one for horizontal surfaces, and the skim coat is for vertical surfaces.

I guess I will start with the Seal Skin product.

As mentioned previously, these products require a commercial-chemical-rated respirator to be used safely.

Here is a video about these products.

 

[Jasonb]

Generally the scale factor is not too critical, but for parts like cylinders, where you have to drill a ring of holes around the perimeter of the cylinder, if your scale factor/shrinkage factor is off, they your hole pattern will also be off.

I would say something like a cylinder the hole pattern will not be off, just slightly closer or further from the edge. Where is does become more critical is with a long part that has bosses at each end, say something like the beam of a beam engine. If the casting shrinks more or less than expected then the boss ctr distance will be off and your holes if positioned to plan will no longer sit in the middle of the boss.

This is why if offering kits commercially a test casting or two may bee needed to prove the pattern and then any changes made.

You can certainly spend too much time looking at patterns which could be better spent looking at the resultant castings and machining them

 

[GreenTwin]

You can certainly spend too much time looking at patterns which could be better spent looking at the resultant castings and machining them

My workload is keeping me out of the shop, and so all I have time for is an occasional pattern.

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[ajoeiam]

I am looking at the print quality settings in the Prusa Slicer.

The first JasonB flywheel half was printed with a "0.15 mm DETAIL", which is 17.5 hour print.

The second JasonB flywheel half that I am printing now uses "0.25 mm QUALITY", with a 7 hour print.

The current print surface does not appear to be appreciably more rough than the 0.15 mm setting, and it is progressing much faster.

The standard nozzle that comes with a Prusa XL is 0.6 (mm ?), which I think is larger than an MK3, in order to get a more acceptable print time with large prints.

So I think the larger nozzle will give a more coarse surface finish.

The surface finish is ok so far on the Prusa XL.
Not perfect, but usable I think with some fill material such as skim coat.

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View attachment 147841

Looking at that print settings list and given your comment that you would still need to be 'smoothing' the resulting pattern (from the even 0.15 mm print quality setting) I would suggest that you need to find some pattern to print at the 0.32 and 0.40 mm print quality levels.

That could dramatically reduce your print time on large items, save input product and if it doesn't introduce any other 'challenges' besides some smoothing - - - - might just be worth considering for any larger patterns.

(I could see you doing a diy 3d printer so that you could print say a 18" cube or perhaps even a 24" by 12 or 16" tall version at some point in the future - - - grin!)

 

[Jasonb]

It's a pity you can't set duel heights for example if it could go round the external surfaces twice at 0.2mm and then on alternate layers do a 0.4 for the remaining surface thickness and any infill. Similar to what I do on the CNC with a coarse roughing cut to remove the majority of the waste and then a fine surface finish path

As Pat has found you can only usefully print as big as you can cast particularly on the more bulky shapes that need a lot of iron for the pour, not so bad if it is just long slender parts.

 

[lohring]

You can set variable heights in PrusaSlicer.

Lohring Miller

 

[GreenTwin]

As Pat has found you can only usefully print as big as you can cast particularly on the more bulky shapes that need a lot of iron for the pour, not so bad if it is just long slender parts.

One option that can be used if the mass of a part gets excessive with gray iron is to substitute 356 aluminum, which is what I am going to have to do on the engine that will go with this flywheel.

I am not too keen on 356 aluminum, but it does allow casting of larger parts without having an overall engine that weighs more than 100 lbs.

If 356 aluminum is tempered to an approximate T6 temper, it gets rid of most of the tool loading problems, and gives a harder and stronger casting.

The mass ratio between gray iron and 356 aluminum is about 3:1, so a 66 lb frame in gray iron becomes a very manageable 22 lbs in aluminum.

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[GreenTwin]

The left flywheel pattern half 3D print is complete.

Again, perfect bed adhesion in a very drafty room, and this is a significant improvement over my MK3S.

The surface finish is not what I would wish it would be, but the print size is impressive.

There is no chance of using any spray paint to fill this print; the grooves are too deep.

The pattern will have to be filled with some sort of filler, so lets hope the auto body filler I purchased works without too much trouble.

I have not used the auto body filler yet, and I am not sure if I want to experiment with this nice 3D print, so I need to find an old 3D print and experiment with the filler on that.

Thanks again JasonB for a really nice pattern. Most impressive 3D modeling work for sure.

I will try to experiment with the filler a bit this afternoon.

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[Jasonb]

Pat I thought it was crucible size that was getting to be the problem eg volume not just the weight?

It is an attractive flywheel, I was tempted to use a smaller version for the engine I have just finished but in the end stuck with a 99mm dia one with six straight spokes to retain the shape shown in the 1905 engraving. I'll just have to find something else to use one on, maybe a small No6 would be fun to do.

 

[Jasonb]

Also Pat how are you arriving at the weights of the castings.

Alibre gives that flywheel of mine at 20lbs for the rough casting when done at 12" yet you have a machined one at 33lbs? If the same applies to the frame then your figures ar 50% high? so the frame might only be 40-45lbs in iron not 66

 

[GreenTwin]

The engine JasonB is referring to is a scaled up Cretors No.06, as shown in the attached screencaps.

The mass numbers are from Solidworks, with the flywheel mass based on a flywheel similar to the JasonB unit, but with more crude spokes.

Bill of Material (12 inch flywheel):

1. Base/frame.
Weight in gray iron = 66 (lbs) (machined)
Overall height = 14.8 inches to crankshaft centerline
Diameter of round base = 12 inches

2. Cylinder.
Bore = 2.0 inches
Weight in gray iron = 5.6 lbs. machined

3. Flywheel

No.02 Style:
Diameter = 12 inches
Weight in gray iron = 21 lbs. machined (26 lbs pre-machined)

No.06 Style:
Diameter = 12 inches
Weight in gray iron = 33 lbs. machined

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[GreenTwin]

This is the No.06 original flywheel, and the spokes and rim have considerably more mass to them than a No.02 or No.01 style Cretors flywheel.

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