Perfect Casting prep / Iron Castings

[pirmin]

Hy Guys ,

When working with Castings i found that many People do Not Prepare their Castings corect before Painting or Machining.

Of course a Cast Part should still Look Like it was Cast,that IS the Whole meaning of Castings beside their functionality .

But!, to many People underestimate that Rough Cast Model Engine Parts Like for Example Steam and Gasoline Engines do Not Look Realistic If u dont Alter the Surface. It would Just Look Not in Scale !

Of course it depends a Lot how the Castings came Out of the Foundry.

I saw Pristine Cast Stuart turner Castings with slick smooth surfaces,but i also saw pretty Rough and Brittle Castings in the Past.

Same goes for the PM. Research Modells.

A exception Here are the Castings i Received from the Engineers Emporium,they where Well Dome,very smooth and the surface Texture is nice and even,and only a very think black coat of slag/ residue is left.


However, every Casting needs Präparation.


Some dont do it at all,some People only use coarse Handfiles or Rough Sand Paper.

My prefered Methode ist to use 240 G sandpaper to Clean the Sand residues, the next step involves precise filing and finishing Off fillets and edges with Needle Files in all different shapes depending on the Angle and Form that wants to bw achieved.

To Finish after that i use sandimg sponges with a very fine Grit (600-1000G)

Then i apply 2 Components Car filler in Edges and cavitys,and maybe also where i want to have a altered shape,as Shown in one of the Pictures i added a bigger fillets on my Deutz Castings from the Engineers Emporium.

After that step sanding wet is necessary to fill all cavitys and Form the surface even .

Next would be several Coats of Spray Filler ,sanding, repeat untill statisfied and the Last step befire Painting would require 1200 G sanding sponges for Automotive Paint.

After those steps the surface of a small Casting is even and does Not appears unrealistic as IT would do with the Grain pattern in the Surface If untreated.

The Key is to minimite those Grains to a.minimum or even remove them completley,so that If the Casting is looked at,No Grain is visible.

I add a few Pictures to visualize what i Just wrote:

[Jasonb]

A lot will depend on the scale of the model. I have made quite a few that are 1/2 or 1/3rd scale so the texture on those would be coarser than a model that is 1/10th or 1/12th scale where a smoother finish would be more appropriate.

I've even made replicas of engines at 1:1 scale so they don't need any scaling allowance.

You also need to think about what you are modeling. A mass produced engine that came straight out of the factory is unliley to have been fettled as much as one that has had a build up of paint layers over many years or have been over restored by a keen collector.

Typical example of how I treat a casting set here https://www.modelenginemaker.com/index.php/topic,4863.msg97803.html#msg97803

Then again there are those hardly touch the castings as they get their enjoyment from designing and getting a never before model up and running.

[Jasonb]

Here is an actual full size image of that engine model I linked to.

You can easily see that the mould split lines still show on the spokes and inside of the rim, the crankshafr shows the same lines and the rectangle where the gate was when it was cast is quite visible.  They certainly did not have a mirror finish, I don't go much below 120grit.

So know your subject and prep the castings to suit.

[pirmin]

yes jason thats right !

i also do not go after a mirror finsih, it would be to much, but the size of the Otto D2 , it would just not look right for example and while i was working on the castings today i thought hey, i make a short posting about this subject .

[Michael S.]

Hello pirmin,
In the past, it was common practice in machine factories to make the castings nice and smooth after processing with a filler. Since the castings had a lot of dents and rough edges from the sand mold when they were made 100 years ago, a lot of filling and sanding was done. Today most castings are flawless.
When I restored my locomotives years ago there were many holes and dents that I had to smooth out.

Michael

[Vixen]

Hello pirmin,

Beauty is in the eye of the beholder. Not everyone seeks perfection in their casting finish.

Look at the light alloy castings on this Honda RC115 racing engine. It was one of the fastest 50cc racing engines ever built. The castings are covered with blemishes and imperfections. Honda concentrated their precision on the machined parts that matter, rather than the cosmetics of the castings. Super smooth casting would look out of place and would not capture the raw spirit of this engine.



Mike

[Admiral_dk]

Mike - Honda also gained a bit extra Cooling because of that surface and I know of others that specify a rough surface for the same reasons on their castings ....

But I agree that it is a individual preference ....

Per