1/87 3D printed details.

[Bernd]

3D printer equipment costs are now cheaper than buying pressure pots and vacuum chambers for bubble free production castings. For some more detailed casting, making 2 part and 3 part molds was quite tedious. Part warpage is always an issue too.

3D printing does have the mess of cleaning and sprue removal, but resin casting has flash problems as well.  Frankly I found it more messy than resin casting overall along with the panic pressure of getting the resin mixed, vacuumed, poured and into the pressure pot in time.

Edited to just casting subject.

I don't have a problem using Smooth-On products for resin casting or plaster. I don't use a pressure pot or vacuum chamber. I did use a pressure pot once and found that when you dropped the casting it was almost like a tiny explosion. If you think about it, where does the air go to under pressure? You compress all those bubbles into tiny little grenades.

Here's some pictures of a mold I made for a structure. Note all the bubbles in the mix.



Pour the rubber in from a height of about a foot.



Let the thin layer set for a minuet so that any bubbles have a chance to come to the surface. Then pour in the rest of the rubber. Let cure. No bubbles.





I agree with the shelf life of the product as you said. What's the shelf life of printing resin?

That's been my experience making molds.

B~

[Rail and Tie]

I don't have a problem using Smooth-On products for resin casting or plaster. I don't use a pressure pot or vacuum chamber. I did use a pressure pot once and found that when you dropped the casting it was almost like a tiny explosion. If you think about it, where does the air go to under pressure? You compress all those bubbles into tiny little grenades.

Actually, I have found through experience and testing that the vacuum degassing process pulls all the nasty bubbles out of the resin before pouring. The bubbles formed while pouring are nominal compared to the mixing process. Where the pressure pot process shines is with small cavities and thin details in the mold where you might get air trapped in thin and long cavities. In fact, compressing the tiny bubbles makes the whole part more homogenous and actually stronger, since all the bubbles are gone and the resin is forced together during curing. If you have exploding /brittle parts after demolding, it is likely due to the mixing process and curing with a bit too much catalyst. Also expired resin usually flashes hotter and much more brittle, at least with smooth-on products. 

If your resin is mixed with too much catalyst the part will cure on the outer surfaces of the casting first and create increased internal stresses when the core cures. With Smooth on products such as Smooth Cast 300 series products, if you get the mix perfect (even though it is quite forgiving on mix ratios) you can watch as the mixed resin turns from clear to white and see the core of the casting turn white first then heading to the outside surfaces. This creates a stress free casting with very little warpage.

As for 3d Printing resin shelf life,  it is usually over a year depending on where you order it from. I have some lesser used colors that are over 3 years old and seems to work just fine. It does take a bit more to mix prior to using as the pigment and UV starches settle to the bottom of the bottle. I am also finding the UV resins are not as picky when coming to storage temperature swings.

 

[Rail and Tie]

Sorry about the digression down the resin casting rabbit hole. This thread is about 3D printed details, which I can't get enough of! That is why our motto is "Detail Insanity". If it can be modeled in HO, than it should be modeled!

Regarding layer lines, here is a good example showing the difference in printing orientation to minimize the lines. (printed on my old dental printer) The photo on the left is printing with the wheel laying flat on the build platform. On the right it is standing up. You can see the supports still attached to the wheel on the right. Both these are printed at 25 micron X,Y and the same build layer thickness.

This is one of the potential disadvantages of 3D resin printing, you always have on face on the part that will not be as good of finish because of the little support nubs. Usually I make that surface on the bottom of the part or the gluing face of the part where it is not visible after assembly.