Finishing rough castings for painting or polishing

[Helder22]

So I just about to finish running my 1/2 scale Breisch Olds Hit Miss engine for the first time and need some advice.
Now that I know that everything is mechanically working, I want to take it apart and paint the parts that need to be painted, as well as polish the parts that need to be polished etc.
How do you guys generally smooth those castings up? Some of the parts are really rough, like the connecting rod and some parts of the frame. Do you file it? sand by hand? Use a Dremel?
The frame/body and flywheels might be a bit easier because since its going to be painted anyway I figure I can sand it a little, prime it, sand it again, until its relatively smooth, but some of the brass/bronze parts look like they may be a pain in the neck to work on.
Any tips?

 

[Philipintexas]

I've finished a number of engines from castings, in most cases I like to leave the slightly rough texture alone as it looks more authentic. I have gone so far as using bondo to finish some areas smooth for painting. This is an example, I left some areas textured and finished some smooth. I also found that saving money on paint isn't worth it. After hundreds of hours of work don't cheap out on paint. I buy small quantities of good automotive paint and clear-coat. It's not hard to pay $100 for a small amount, but it will last a life time.

 

[Jasonb]

Like Phil I prefer toi leave some texture, these parts were cast or drop forged they were never polished on the originals, you can get away with bare rims if teh engine does not have a separate pully.

It does also depend on teh individual engine, as an example the 1/3rd galloway i'm just completing uses 3 castings to represent what would have been one on the original so there are joints to hide and one part had beed over fettled at teh foundry

So after files, grinders and sanding it was given a good coat of bondo

Then rubbed down

High build primer, rubdown, refill if needed more primer

Things like the carb that lost its texture where holes were plugged or cast lines removed

Can be brought back to an even texture with an engraving tool

J

 

[Helder22]

Great looking engines! Thanks for the tips guys. I should have thought of bondo, duh. I was thinking about using automotive paint. I think Ill go with that.

 

[portlandron]

There is a product used in auto body work called surfacing or glazzing putty. It will fill small imperfections and tooling marks. It's like a very thick paint and does not require any mixing. The part needs to be primed first then apply the putty. It is easy to sand a feathers out good.

 

[Tin Falcon]

In my home shop I have not worried about making castings look perfect and personally do not like covering nice bronze or wood with paint.

I do have a lot of experience with perfecting surfaces.
Surfaces should be fared that is rounds should be round flats flat and curves gentle and graceful with no bellies kinks or flat spots.

for a model I would use a High talc filler polyester filler.
like http://www.evercoat.com/productDetail.aspx?pID=29
this is an old product so you may want to choose something newer in the product line.
and I second a high build primer for filling small holes and fair
small imperfections.
A two or three part urethane paint can help as well. Remember the faster the paint cures the less time for dust bugs and other crud to stick to your paint job.
But do be carfull sprayed paint leaves smooth surfaces but is nasty to the lungs so use the propper respirator for the job. Isociates are nasty.
Tin