Casting Preperation

I am just starting on some castings I have for a universal pillar tool, and wonder at what stage most model engineers clean the castings up?

I have decided to go all over them with a file and emry on the non machined faces before machining as I am concerned, that I will slip and damage a face if done after machining. How do you do it?

When doing things like traction engines and stationary engines do you clean the castings up all over? I find the finish very coarse on some castings but superb on others even though all sand castings.

Steve Larner

It's the first thing I do. I go over the whole casting with a wire brush to get rid of casting sand, grit and the like. Then I go over all surfaces that will be unmachined with files to remove flash and any casting imperfections. I don't bother with emery. On surfaces that will be machined I only remove flash and suchlike if needed to ensure that the casting will seat properly during machining.

Regards,

Andrew

Per Andrew, except I then give the not-to-be-machined regions a coat of paint. Makes then nicer to handle and easier to clean.

regards

Geoff

(currently in Germany for a rail impact test)

With the castings for my UPT, I gave them a scrub up on a brass wire wheel on the bench grinder, then a couple of coats of hammerite before machining.

The quality of the castings is pretty good so they didn't need a lot of cleaning up

CB

Are you painting directly over the filed surface of adding stopper / filler on your traction engine?

Steve

Is the paint red-oxide type primer?

Does it take topcoat ok after the cutting oil/ tapping fluid etc that gets on it ?

Like the others I fettle the castings first, removing the part lines also gives an indication of a chilled casting as the thin bits are the first to go hard. On smaller items I run a die grinder with a grinding bit over the surface to knock off the high spots.

Mostly I don't paint before machining, you should not really need coolant on CI and I tap/drill it dry

Unless there is a major problem with the casting I won't fill it on a live steamer like a traction engine but on some of the stationary engines then its out with the U-pol. As an example I filled this last weekend as the model used three castings where the original was one piece so there are joint lines to hide and the large amount of filler down the side is where they trimmed too much off at the foundry.

Thanks for the detail, Nice illustration, much appreciated.

Is U-pol a filler from the car paint factors?

Steve

Steve: I haven't actually painted anything yet on my traction engines. I'm not planning to go mad with filler before painting. For castings that are not seen, like the differential centre, they'll just get painted. For more visible castings I might use a bit of filler if there are visually intrusive defects, but I'm not intending to smother the castings in filler and then sand most of it off in order to get a smooth finish. Life is too short!

Regards,

Andrew

Halfords do U-pol, I find it sands better than P-38

I have to agree with Andrew. I spend effort making fabrications look like castings, and I want my castings to look cast!

Neil

PS> it's nothing to do with being able to blame surface finish on casting rather than painting technique (or lack of it).

Hi Steve

The Pillar tool is a good choice of project. I built one 30+ years ago and I use it often - with another current thread in mind it might almost be my favourite tool! You will see from my picture though that I didn't take too much trouble with "prettying up" the castings but then it was never intended to be an exhibition subject. I'm not likely to make the sensitive drill attachment either but I do have some dials to stamp for an "in progress" Stent project someday so the punch holder is in the offing.

Norman

On softer castings I use an old Wolf engraver to reinstate the texture if its required, this Lukenheimer carb is a good example, you can see the smooth areas where its been fettled and plugs silver soldered in to fill fuel passages.

And the same thing after 5mins with the Wolf

This is the side of that engine I posted above showing where it was ground away by the foundry and where the lower casting has had to be milled away as one mating part was 3/16" smaller diameter than the other. This engine also suffered from the nasty habit of using Dymo lables to identify the patterns which are reproduced on the castings, by the time they have been ground off you loose all the sand texture