Cast finish.

[Bo’sunParticipant @bosun58570]

Good afternoon,

I'm building a small Traction Engine that uses several aluminium castings.

Clearly they needed to be fettled, which I've done.

Is there a way to restore the cast surface finish where the fettling has taken place.

I don't have, or even access to a blast cabinet.

Thanks.

[Bo’sunParticipant @bosun58570]

How to restore it?

[pgk pgkParticipant @pgkpgk17461]

I’ve not tried it but you can get cheapish sandblasting attachments for a compressor and knock up some sort of box to try and recycle some of the grit?

[lee websterParticipant @leewebster72680]

Hi Bo'sun,

I've not tried this myself but I wondered if some coarse tough emery cloth glued to a hammer head and then tap the surface to speckle it. It would, of course, only work on surfaces you can get a hammer to.

[ChrisLHParticipant @chrislh]

Professor Chaddock made his carved from solid engine crankcase look like a casting by grit blasting with home made kit. You do however need a compressed air supply to make it work. Relevant ME articles p. 456 05/05/ 67 and p. 515 19/05/67. If you don't have access, PM me and I will provide scans by email.

[JasonBModerator @jasonb]

If you scaled down a full size grain of sand to suit your small traction engine then you really don't want any noticible texture.

If you must then the old Wolf engraving tools can be quite good at adding back texture in the larger scales or even holding a dot punch in your fingers and doing similar manually has worked for me. On fabricated work that I want to look like it was cast I tend to file off the external corners and then just run the side of a Dremel grinding point over the flat surfaces more to make them a little uneven than to add texture. I also do this to castings to reduce the texture left by the sand.

I've not found blasting to add texture to smooth areas, at least not enough to replicate a coarse cast one. Grit or bead blasting on aluminium tends to give more a die cast finish than sand cast, I use it to give a uniform finish after tooling marks have been removed with emery which leaves directional marks.

[JasonBModerator @jasonb]

This is a grit blasted steel cylinder fabrication, done to clean up after soldering more to texture but it only leaves a fine surface texture more like 180g abrasive than sand would leave on a casting and once painted won't show. Iron would come up with the same sort of finish

This is bead blasted aluminium, just a nice satin finish that is quite uniform again if you painted it you would not know it had been done.

This post of mine shows the effect of the Dremel and that is on a 1/2 scale model not a small one.

[Trevor Drabble 1Participant @trevordrabble1]

Maybe try gentle pecking using fine carbide or diamond tools in a Dremel type tool ? Chronos do good ranges of both. I got my diamond ones from them and the carbide ones from JB Tooling , who l believe will be at the Midlands Show in October .

[Ramon WilsonParticipant @ramonwilson3]

I used a mounted stone point at slow speed to achieve the effect on this aluminium crankcase

 

It could be painted over I guess but I chose to bead blast it to achieve the kind of impression of the original I was hoping for. This was not a casting but machined from solid but the effect would be similar.

 

I have also used an engraver to dimple the surface of bronze to give a cast impression

The tool needs to be blunt, not a sharp point for the best effect. Here's another example on a home made valve body.

 

Hope that's of use – Tug

Edited By Ramon Wilson on 13/08/2022 22:54:12

[JasonBModerator @jasonb]

Interesting to compare the "cast" valve with the painted casting behind in Ramon's last photo. Can't quite remember the scale of his diagonal engine maybe 1/12th but once painted it's effectively smooth and I would assume you want to paint the traction engine model.

Is it a Wells?

[Neil LickfoldParticipant @neillickfold44316]

I have used emery tape and the leather side of a copper rawhide hammer. It did match quite well to the casting surface around the fettled area.

[Bo’sunParticipant @bosun58570]

Thanks all,

Plenty to be experimenting with. The surfaces will eventually be painted, so there is some tolerance, but I'm mindful not try and disguise the fettling by the over zealous application of paint.

[Jon LawesParticipant @jonlawes51698]

I wonder how the model tank boys achieve the Zimmerit look?

[JasonBModerator @jasonb]

Thin layer of putty and then poke it with a flat bladed tool in vertical rows. They also use the slow Dremel for texturing flate armor plate

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