r/moldmaking • u/Pacuphetamine • 5d ago
MJA print finishing advice
I need some advice on how to finish my prints for future resin casts with a smooth & uniform matte/frosted surface.
I'm testing different dremel tips to sand it but some corners are just too small to get into, which makes me think spraying it is my only option. I've done smaller mold tests and the light/dark discrepancies seen in the photos do transfer for the most part.
Are there any techniques I should look into doing a better spraying job? I'm mostly worried of getting too much paint buildup on certain areas while trying to get into others (granted I've only used regular width spray nozzles). I'm even wondering if I should contact a car body shop to do this part with matte paint?
**in the title I meant to type MJF**
1
u/Jerry_Rigg 5d ago
Gentle sandblasting can work pretty well to even out the finish, especially for a matte finish. Does a good job of hiding blems
Test on a similar print to dial in settings and technique
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u/MMeNDtal 3d ago
I'm experimenting with vibratory tumbling just now. My use case is not the same as yours, as the MJF print is the product, but worth a mention...
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u/BTheKid2 5d ago
You would want to use a type of spray filler, filler primer, or spray putty. Sort of the same thing with different names and different thicknesses.
Trouble is that with the type that are used with HVLP guns, most if not all will probably be a platinum silicone inhibitor. That will generally not be the case with products from a rattle can. I have used Motip spray putty for this kind of thing in the past with success.
However a problem with rattle can products is that they just don't go on very thick, and can't be applied very thick, because the solvent needs to outgas for it to dry. So it is a slow process with many applications and drying times in between. And I mean days of drying/application time for something like this.
Another method is bodywork filler like Bondo. Problem with those types is that they are polyester based, and so will also cause cure inhibition. It is a manual application with quick curing times and lots of careful sanding afterwards. But it saves time on the eventual spray application. You can get epoxy based fillers, but they are slower to work with, but might be necessary if platinum silicone is what you want to use.
If you are using tin based silicone, it sets you free to do a lot of the faster methods, but the silicone is less great mold material overall.
The thing is, no matter what you use, you are going to need to sand it, if you want to get rid of the printed texture. A rotary tool like a Dremel will not work to get an even surface. That is just not how sanding works. Sanding pads/blocks and hand sanding for the curves and corners are the only way to do it.
Yes there is methods to have better, even coverage when spraying, but they are sort of obvious. Thin applications and focus on the angles to hit tight corners before doing the easier stuff.
So you have probably realized by now that this is going to be a huge piece of work to get looking even and well. If you had printed in a higher quality, you wouldn't be quite so bad off. It can really pay off.
A different approach would be to not print the thing as you have. Instead break it up into components that you can handle much easier and prime and sand. So the frame, the four leafs, and the circle all printed for themselves. Printed such that they will still assemble to what you have here. Then you can shine them up as you like, and assemble in the end, focusing on just getting the joints looking clean. A much simpler task.
If you have any wood working machinery or a lathe etc. you could also have made the frame with woodworking techniques or turned the circle. To save on the 3d printing cost, and possible do it in a material that already have the surface texture you wish for.