1/18 Scale P-51B 3D Print Build

[JayW]

6 hours ago, Neo said:

im curious on the skinning part you mentioned "annealed aluminum" could you share more detail about what you use and what the process looks like ? i do allot of foiling myself so im really interested in this

 

I have a roll of .005 inch thick soft aluminum sheet, perhaps a 1xxx series aluminum (which is basically pure aluminum).  It is "annealed" meaning it has undergone a heating process at the foundry that softens it and makes it easy to form, even allowing it to take on compound curvature as long as it isn't too much.  I also have .005 inch thick heat treated alum alloy sheet (not pure aluminum) which is much stronger and more resistant to forming.  This is my preferred skinning material because it doesn't take on as much surface imperfections like little dents.  But that stuff can only be used on flat surfaces or surfaces with "single" curvature where stretching is not required.  For the P-51 engine cowlings on the bottom and top, which have a good bit of compound curvature, the soft annealed material must be used, and then burnished into shape.  For the side panels, they are much more flat and I will be able to use the heat treated stuff.  

[JayW]

Today was a day that I have been waiting for, and it had me on edge.  Today was the day where I finally would 3D print my first transparency for the P-51 - the Malcolm hood.  Recall the test part in grey resin turned out OK, and I learned a bit from it:

 

 

So I incorporated what I had learned, and I thought I was ready a couple days ago, but then OBG informed me that I might have the forward edge configured wrongly - it isn't supposed to butt up against the windshield frame as I have it; rather it slips into a slot on that frame.  What???  This picture gives a clue:

 

 

The clue is that the aft frame of the windshield looks wider than normal.   Look at the drawing:

 

 

 

So, it appears that part of the Malcolm hood modification includes a widened retainer strip over the aft frame, like this:

 

 

 

That is a cross-section through the windshield aft frame.  The red is the extension of the retainer strip.  It and the existing aft pointing flange on the extruded section that is the aft frame creates a slot for the Malcolm hood's front lip to slide into when closed.  The blue is the hood lip. 

 

I am sorry if I lost some of you with my less than excellent description, but suffice it to say it was back to the drawing board with the Malcolm Hood.  I deleted the heavy bead on the forward edge, and replaced it with a thinner extension that fits into the slot as shown above.  Here:

 

    

 

A close-up:

 

 

Actually there is a bulb seal that is crammed in there as well, but I am not going to go that far.  What you see there, I am pretty certain, is pretty much how it really is.  You can see that I have had to resort to a good bit of educated guesswork to produce a Malcolm hood.  Glad I have LSP friends who supplied so many great photos!  And thanks OBG for noticing that error.

 

And with that change accomplished, it was time to see if I could print up a hood detail in clear resin.  Results after nearly 6 hours (exposure time for the clear resin is more than for the grey resin):

 

 

I did two - one right side up, one upside down.  The one on the left turned out a bit better, but both are pretty rough.  Not real "transparent".  However, the shape is good.  I used the one on the right as a test part, post curing it and then sanding the devil out of it, and applying a car headlight glass restorer kit to it to try to get it transparent.  After a fair amount of work, I got this:

 

 

Before/after:

 

 

 

That is after a dip in Future.  You can see that it still needs a bit of work on the texture.  But folks - this appears to be a major victory.  Shape is good.  Almost no cloudiness.  No discoloration.  So now I get to really do a first class sanding and buffing job on the other (better) part.  And hopefully have a clearer more smooth end product.  If I am disappointed with it, I think I will tweak a couple of dials on the Elegoo, redo it, and see if it doesn't improve the print.  I would much rather 3D print my transparencies than vac form them, if I can get good quality.  I hope you all agree; tell me if you do not.

 

Now I have some confidence that I can create 3D printed transparencies for every window in the cockpit, and other parts too (like the landing light). 

 

SH!! 

 

Stay tuned for more coming soon.             

Edited November 7, 2023 by JayW

[MikeMaben]

I agree Jay. Are you sanding and buffing by hand or are you using power tools ?

[geedubelyer]

Great stuff Jay. The hood appears to have real potential.

 

I'm interested to see how the finished item looks after you've removed all of the surface texture to give a nice, smooth finish. 

What intrigues me is whether any layer lines will be evident through the clear parts. I wonder if there will be some kind of polarizing effect from certain angles? 

I certainly hope not but the process does lay one layer of resin on top of an already cured layer. Hopefully the transition between layers blends seamlessly. 

 

How delicate are these clear parts and how thin can you get them before they are too fragile to work on?

 

Cheers.

[Woody V]

Here's a trick you might try. Spray a light coat of black on the part. The black will act as a guide coat showing you where you have sanded. Sand until all the black is gone. Then use successively finer grades of sandpaper to remove all the scratches made by the previous grit of sandpaper until it has a just slightly frosted sheen. Finish by using progressively finer grades of polish like the Novus system or simply dip in Future or Aqua Gloss.

This is how we were taught to polish clear acrylic in USAF Tech School but the theory holds true for polishing any plastic.

 

Edited November 7, 2023 by Woody V

[JayW]

9 hours ago, MikeMaben said:

Are you sanding and buffing by hand or are you using power tools ?

 

By hand.  I have a dremmel so if you think there is an attachment that will get me a better finish, let me know.  

 

7 hours ago, geedubelyer said:

I wonder if there will be some kind of polarizing effect from certain angles? 

I certainly hope not but the process does lay one layer of resin on top of an already cured layer. Hopefully the transition between layers blends seamlessly. 

 

Doesn't seem so Guy.  Perhaps like laminated glass, the individual layers are not evident.  If I can get a significant improvement on the second part just doing what I did but more thoroughly, I think everyone including me will be happy with it.  

 

7 hours ago, geedubelyer said:

How delicate are these clear parts and how thin can you get them before they are too fragile to work on?

 

Good question.  My hood is about .025 inch thick at the boundaries, gradually transitioning to .03 thick in the middle.  That is about as thin as I dare for a fairly large part like this.  The real windshield side glass is 3/8 inch thick or .02 inch at 1/18 scale.  The canopy glass is 3/16 inch or .01 inch at 1/18.  

 

2 hours ago, Woody V said:

Here's a trick you might try. Spray a light coat of black on the part. The black will act as a guide coat showing you where you have sanded. Sand until all the black is gone.

 

Well now - I think I will try that.  Thanks Woody.  The rest as you describe - that is kinda how i have been doing it.    

Edited November 7, 2023 by JayW

[airscale]

astonishing progress Jay - really enjoying this come together and you pushing the boundaries

 

As you did ask, I will give my humble opinion... personally, I don't think it will be possible to get the optical clarity as high as it should be. I know you will give it your best shot and i do hope I am proven wrong, but I just can't see it being possible given the materials at work and the inherent distortion in creation by layers

 

I think you have fab master, and get the God of vacforming (Tigger) to pull you a couple - he does amazing work and has just done my P39 which has come out better than I could have hoped for

 

As I say, I hope I am wrong

 

Peter

[MikeMaben]

15 hours ago, JayW said:

     By hand.  I have a dremmel so if you think there is an attachment that will get me a better finish, let me know.    

 

You might use an electric toothbrush for intial sanding and buffing wheels in your dremel for polishing.

None of my Dremels can rev slow enuff so I bought a David 300 , but good luck finding one these days.

They rev down to about 300 rpm. Pete's suggestion to vac form sounds practical, Good luck.

[Oldbaldguy]

Is clear resin really clear?  Your example seems to have a dingy cast to it but that could be a by product of the photo. Looks like it has been sitting out in the sun and weather for decades.  Seems to me that if your machine could poop out a canopy of the right shape that was more a constant pour and less a layer cake, you might be able to make it work.  While the surface seems smooth enough, I’m not convinced you will ever be able to sand and polish your way past the internal structure of the part.  Vac may be your only option if you want a part that is acceptably clear for your scale.

[checksix]

Awhile ago I had a canopy SLA printed at Shapeways using something called "Accura 60". After sanding out the layer lines and dipping in Future, the canopy was crystal clear. Here's some info:

 

https://www.shapeways.com/materials/sla-accura-60

 

Not sure if this will help you, but thought you might be interested.

 

 

 

--Derek

 

 

Edited November 8, 2023 by checksix

[Woody V]

3 hours ago, checksix said:

After sanding out the layer lines and dipping in Future, the canopy was crystal clear.

 

When you understand the theory you come up with simple solutions, like this. 

[JayW]

5 hours ago, checksix said:

Not sure if this will help you, but thought you might be interested.

 

Oh it helps Derek - alot.  That canopy of yours looks like it can stand up to any other option for a transparency.  And also better than my first try.  I am using a liquid resin called Nova3D "High Transparency" , upon the recommendation of a fellow on a 3D printing FB page.  Also it has gotten good reviews on the web.   Who knows if it is better or worse than any other resin....   

 

I am going to hold the vac-form option in reserve for now.  And continue on with the 3D print option.  I had expected to be printing up several parts, tweaking all the while.  It is temperamental stuff.  So I will indeed be printing more parts, including the windshield parts.  And I guess I have the option of getting Shapeways to do it - they provided Derek with a most beautiful canopy.

 

Stay tuned!     

[JayW]

7 hours ago, Oldbaldguy said:

Is clear resin really clear?  Your example seems to have a dingy cast to it but that could be a by product of the photo. Looks like it has been sitting out in the sun and weather for decades.  Seems to me that if your machine could poop out a canopy of the right shape that was more a constant pour and less a layer cake, you might be able to make it work.  

 

I think the hood is more clear than the picture indicates.  I am surprised how clear it is actually.  It's biggest problem is something that I experienced on a -D model canopy months ago - which is a "layer cake" effect.  Perhaps it can be seen.  Not so much a visualization of individual layers, but a squashing effect that gives it a wavy look.  I was unable to fully buff that out on the test part.  I don't know what caused it, but I have some ideas.  It could be inadequate exposure time for each layer.  I am at 8 seconds (the grey is 3.5 seconds).  Nova3D recommends the 6 - 7 second range.  And I have it on fairly high authority though that closer to 11 seconds might be better.  I have already done a slew of industry test parts to get the right settings, with confusing results. 

 

Anyway, the part came out rather sticky and soft, which reinforces my hypothesis.  If the part, as it is being laid down, has insufficiently cured layers, then I would expect some deformation of some kind.  So my first tweak is to increase exposure time by a couple seconds per layer (which will significantly increase print time, BTW).  I am also going to tweak the "lift speed".  After the machine lays down a layer, it lifts up the part from the bottom of the tub to allow liquid resin to pour into the gap.  Then it comes back down to lay down the next layer.  That lift speed can affect the quality of the part - too much speed and it pulls harder on the part as it is lifting, possibly causing deformation. 

 

OK enough.  I will report out soon.      

[TankBuster]

Hi, Dont know if this will help with the polishing or not but I use a cotton bud in my battery operated Dremel to polish canopy's, not the cheap ones but buds that are pointy on one end and flat on the other (cheap one's scratch the canopy) which I buy from chemist. I cut flat end off and put in Dremel on lowest speed with Novus polish and they work great. Cheers.

[JayW]

So it's been two steps forward and one step back.  Or even one step forward and two steps back.  Nothing is coming easy.

 

First - to home in on that blue-nose-bastards-of-bodney early blue.  Tamiya says to mix X-14 sky blue with XF-8 flat blue at 3/1:

 

 

That got me this on the mule:

 

 

Yikes!  Not sure what y'all think, but I just have to look away.  Too blue.  To tone it down some, I mixed in some of the US Navy intermediate blue I used on my Corsair.  And promptly clogged up my airbrush!!  Those paints are incompatible. 

 

I think other modelers have struggled to find the right blue color too.  So I went to the local hobby store and talked with the owner who paints alot of models.  He says he likes the vallejo acrylics, and they have alot of blue colors.  We settled on a few color combos and I am going to fiddle around with these:

 

 

Field blue, pastel blue, and ultramarine.  Let's see how it goes - I will report out soon.  Anybody got any good ideas in the meantime, now that I shelled out some money for blue paint? 

 

On another front, I am continuing my adventures with clear resin for my transparencies.  I did a few innocent tweaks to the print file - increased exposure time by two seconds, and slowed down the lift speed.  I also added some supports to the Malcolm hood where the bulge begins and ends.  And then waited many hours for the result.  I got this:

 

 

Horrible parts.  Unusable all of them.  The extra supports on the hood did practically nothing good at all.  What I really wanted is good windshield side glass parts, and was denied that also.  For some reason they are the most pesky of all.  A surprise. 

 

OK - I told myself at the beginning that I will fail many times.  Stay tuned - I have reason to be hopeful.  And if I cannot succeed with my current approach, I might have Shapeways make the ones I am failing at.

 

 

Edited November 11, 2023 by JayW