SURFACE FINISH Q: How to get the best surface finish in casted part?

I’d like to find a way to reduce the prominence of the layer lines in the castable resin.

What is the optimum way to get good surface finish on a finished, casted part?

Are you preparing a printed piece in Castable before casting? I.e. polishing the Castable Resin?

I saw this image from page 4 of the “Recommended-Burnout-Process.pdf”

It seems Golden Century (the casting house whose process is shown in the PDF) is buffing the castable part.
What buffing attachment is this? What are they using?

How are you getting good surface finish on your finish/casted parts? Are you doing it on the metal or on the castable resin?

My concern is I’m casting some intricate AND thin parts so sometimes I run into the problems:
a) I could not adequately reach the surface with a tool
b) the part is so thin I fear breaking it were I to work on the castable resin part
c) manually polishing is too labor intensive

Is there a good machine you can use for automating this process? Rock tumbler w rouge, etc?

Curious how you all are doing it!

The fact that it’s a Dremel pictured makes me slightly twitchy - I don’t regard them as suitable for anything outside hobbyist work (but then my focus with rotary tools leans heavily towards stonesetting). No idea what they’re using; looks like it could be a felt, perhaps with a plastic compound - but I wonder how they are cleaning it afterwards. Ultrasonic?

Granted, cleaning up castings is more difficult than waxes - I use ceramic rods for more intricate castings but it’s time consuming. I’ve been looking at tumble finishing as a possible -
More kit, more space…


This is precisely the sort of solution I’d buy. I simply need to know which grits/what supplies to buy. All I want to do is smooth out the surface finish. There must be someone who’s accomplished this in an automated process.

How would an ultrasonic be used (heck, what sort of ultrasonic)?
Great looking book! Thanks for the link! Have you read/looked at that book? What are her suggestions?

I use a heated Elma ultrasonic cleaner (2.5l? Can’t remember) for most stuff - its primary use is cleaning polish from jewellery. Cleaning solution (expensive soapy water :slight_smile: ) heated up helps shift most residues, but it’s not the only way to do it. Warm soapy water and careful use of a toothbrush works on jewellery too - especially if there are stones that shouldn’t go in an ultrasonic (amber, turquoise, coral, pearl… Amongst many others).

I’ve got the book; broadly the recommendation is to use a sequence of abrasive media for casting cleanup with a vibratory polisher. AIUI the reloaders polishers aren’t really up to dealing with the media - needs to be more heavy duty.

Ah, yes, I’m familiar with the ultrasonic cleaner :slight_smile:

What are your thoughts on tumbling for layer lines after reading that book? Any ideas on solving the surface finish issue?

Bearing in mind this is more of a mass finishing solution… If you leave pieces in there long enough you’ll start to lose detail that you want to keep. Layer lines @ 25u aren’t going to stay for long.

I agree: you gotta be careful with how long you leave parts in the tumbler.

What grits/materials would you suggest for reducing the layer lines in a tumbler? And vibratory/rotary?

It’s all in the book - I’ve not made the jump as yet.

Most of my work is one-off or very small volume, so there’s margin for handwork to finish them.

If the surface area is easy to reach then Dremel can work. There’s some sanding sticks that can help and stuff like micro mesh cloth which can get things very smooth. For things that are high detail and fragile and hard to reach areas I use a fine grit sanding file, it takes hours to do though but there’s no other option if you want to maintain detail and not break the piece.

All good ideas.

I think the solution is really in machine polishing/tumbling. There are always hard to reach areas and the prints are inherently delicate.

Who’s got a process for reducing layer lines with minimal human input?

I’ve thought about this a lot, if the print is fragile then tumbling won’t work because it’ll break. I’ve wondered if sandblasting will work or if that would remove too much material on something high detail.

I have tried many different products to achieve a smoother surface.
I have just found that Scotch Bright works very well.
It leaves a satin like finish on the resin and after casting and tumbling it should be smooth.

It may be difficult to see the images but,
you get picture.

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Glued the Scotch Brite on a disk and put it on a flex shaft

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I do all my clean up in metal. I fill any holes with wax that I may have caused removing supports, Other than that I don’t do anything till it is cast. But I’m not making mass produced jewelry. I just tried the green Scotch Brite and it could not dent the cured resin. 3M radial bristle discs also do little to the surface of resin . 600 grit sand paper kind of cuts it but your creating a lot of dust and possible damage to the print . I think your best bet may be casting, then the 3m brushes and then magnetic pin tumbler for final.

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I have been using 4x steel wool after using files and sandpaper to take off any bumps from supports. It is really soft and easy on the part. I do recommend putting a business card magnet below or something similar to catch the fine wool at it wears. I have used the same grade to buff out cold cast parts as well as antique pewter.

No real need for gloves with it because it is too soft to get into your fingers.

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I don’t see it discussed much these days but an additional stage to all the mechanical steps we know and hate is electro-stripping after the file, emery paper and tripoli stages. Basically the opposite of plating. Most polishers do it for a few seconds. Makes them a lot of money.
If you skip down to figure 9 towards the end:

Prior to this step there is usually no escape from manual work albeit with motors and emery cloth, tripoli etc. Tiny grooves have to be filed and sanded in the direction of the grooves. Tumbling with magnetised steel or emery impregnated plastic will just glaze the high spots on a bad surface.

Another method is bombing.
My workshop did electroforming in the 70’s so we had enough cyanide - gold potassium cyanade to knock off the whole of Hatton Garden. You are required to have amyl nitrate in the workshop if you have cyanide.
We also hand finished, polished and plated master patterns. Non conductive materials can be made conductive by spraying with silver salts and a chemical - after that they can be Rhodium plated. But that was for making smoother master patterns, then rubbers and waxes. However it saved hours and hours of hand cleaning castings. The modern equivalent for 3D printed masters is spray painting them with a glossy finish. It is also said to form a protective barrier between the part and the investment.
We would do the best we could in the workshop and send parts to Sinclairs in Hatton Garden with instructions, strip, polish plate. They are still there.

GWM est 1973


I had posted about the air eraser from Paasche:

I have used mine on printed parts and it works really well. I would suggest a mask and some sort of box to capture the overspray because they can get messy. It works nice on tiny details you wouldn’t want to try to sand by hand and they take very little material off at a time so they are easy to control and forgiving.

Cool - mini sandblaster! :slight_smile:
Is this essentially just an airbrush with a carbide nozzle and needle, or is there more to it? also, what material/grits do you spray?

That sounds like a great tool to have. I found one on AliExpress for $44 with free shipping from the US. Claims to have the tungsten carbide tip. Will let you know how it works.

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You will probably find it invaluable on the tiny hard to sand areas. Larger areas your better off with good old sand paper or what I use is the 0000 steel wool (finest grade available I could get)