jetpack

My Feedback: (1)

I started an aspect of RC not many people steer into, and thats taking apart motors and smoothing the case castings with files and such, to remove all the casting defects. Now I would like to put the finish back onto them with grit blasting or shot peening.

The type of finish I am interested in is a coarse finish that I would like "smooth" meaning not like sandpaper, and would like to see the finish bright as possible.

If I went with a coarse silica grit and then steel shot blasted it, would that take all the sharpness out of it?

I guess what I am looking for is something that is textured but has a "gloss" finish. I might even want to send the castings out for anodizing if they turn out bright enough to where everything doesnt turn out "dark".

I guess I am hoping someone has experience that can help explain the differences and how to achieve them.

The picture on the left shows one I've been working on. I would like to surface finish the cooling jacket head and have it anodized with color, and the case left natural. It's to help all the small file marks left in it to even out the finish, plus the "extra cooling" it provides. The picture on the right is a factory picture of what finish they put on their castings. Its a rough finish but easily damaged, and if your not careful can act as sandpaper against other parts. A finish that looks this rough would be nice if it didn't snag a rag.

parrthd

from my experiences you will need a VERY low agressive aggregate, something like glass beads. we use this all the time at my plant on aluminum precision parts to just "clean" the parts without changing any of the dimensions. works pretty well. if you use something too coarse it will actually eat away at the aluminum.

now on to the finish of the peices, from the looks of the one on the left, i would say that's been through a polishing machine and come out looking like that. for practical purposes, i wouldn't go that route. there's plenty of companies out there that do that cheap enough. just send them the parts you want polished and they come back ready for assembly. however if you want to go that route yourself, they sell numerous "polishing" compounds, rubs, etc that you could try. (i do advise to "test" a peice of scrap first) most any body shop supply house has any rubbing compound you might need, you might also try a google search for "lapping compounds" (this is what mechanics use to "lap" vavle seats so they get a good seal. you might also try a normal dremel with the polishing felts on it with "jeweler's rouge" (i think that's right) they make a coarse and fine. stop by most any jewelry store and ask them about polishing compounds....

hope this is enough to get started.

jetpack

My Feedback: (1)

The one on the left is the one I just finished with polishing stones and brass brush, cleaned and scrubbed in "Barkeeper's Friend" sink cleaner. I was more looking towards putting a grit blast back on it to hide scratch marks and even out the color. However, grit blasting leaves a finish I am not too fond of, being too "sharp" for my liking and easily marked up. Thats why I was wondering if shot blasting it after would help this, or if it would just cancel the effect of the grit finish back to smooth.

All machining would be masked off, so nothing dimensionally would be changed.

Does cast aluminum anodize ok if its polished or grit blasted?

Stickbuilder

You will just have to try different media until you achieve the finish that you want. Walnut shells will often give you a soft patina on some aluminum alloys. This might be what you are after. As Parrthd said, you don't want to use such an aggressive media that you erode the parts. The final finish that you achieve depends on the alloy, the media, the pressure, the operator of the blasting machine. If you use a buff, with a compound, you will end up with a highly polished surface that will not be impervious to scuffing. I think that what you are looking for is somewhat like what Honda uses on the Motorcycle engine cases. This is an Epoxy finish that is heat cured. It ends up exceptionally smooth, doesn't scratch easily, and is very easy to clean. You might wish to experiment with something like that.

Bill, AMA 4720
WACO Brotherhood #1