Castings dull & prep for paint

[matt stevensParticipant @mattstevens90637]

[matt stevensParticipant @mattstevens90637]

Hi All,

I am new to model engineering and learning fast on my dads machines…unfortunately he cannot help me as he is badly disabled and hence why i am using his machines.

Anyway – i have started building a Stuart 10V steam engine, so far so good, but i have noticed that the machined castings dull very easily. The finish is good and smooth and the geometery is correct but they look dull. When i look at google images of this engine, the castings are shiny…..any advice?

For info i am using a diamond shaped carbide bit in the lathe tool.

Thanks

Matt

[matt stevensParticipant @mattstevens90637]

Another question…. Once i have machined all my parts for the steam engine ready to assemble, whats the best way to clean up the castings to ensure all dirt is off, swarf etc so they are ready for painting?

Thanks, Matt

Edited By JasonB on 22/03/2014 11:58:44

[JasonBModerator @jasonb]

Welcome Matt. I've moved your two postings into one thread as they are related.

The brightness of a finished part is a personal thing, some people get the buffing wheel out and "bling" up the parts others prefer a more subtle approach and just leave the parts with a machined finish which is generally what I prefer. There are times when say a flywheel or pully rim may want a bit more work especially if it is being hand finished to give a crown to the rim. In cases like these cover the lathe well with paper or a board, don't use rage for safety reasons and use some emery cloth backed with a piece of wood or MDF, you will find the sheen stays on these parts. For milled surfaces lay the emery on a piece of glass and rub the work over it.

I tend to wipe down parts with either acetone or Celulose thinner prior to painting.

Simon over on MEM did quite a detailed description of preping and painting his Stuart No 4 which would be worth a read

 

J

Edited By JasonB on 22/03/2014 12:10:17

[Clive HartlandParticipant @clivehartland94829]

Spokes and inner rims always look better when dressed over. It takes off the roughness, see an old machine and it is completely worked over and all bright parts polished. I often wonder at the amount of handwork done.

Clive

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by JasonB on 22/03/2014 12:06:07:

don't use rage for safety reasons

I find it's best to avoid rage altogether in the workshop

Russell.

[Steve WithnellParticipant @stevewithnell34426]

A few thoughts on painting a Stuart engine,

One thing I'd agree with is the need to dress and remove all the roughness from castings before priming. However, take care as the castings can be pretty soft and it's easy to remove too much metal (esp flywheel spokes). Be careful not to take the edges off machined corners, especially the flywheel, it can spoil the appearance. I use 25mm wide emery tape in 80 and 400 grade.

Also don't be too hasty in rubbing down paint coats, it can take quite some time for the paint to harden off. It's important to degrease the parts before spraying with primer (metths, thinners, isopropanol all work for me). The first coat of primer will reveal remaining defects in the finish. These can be filled with cellulose filler, be very sparing in its use and again let it harden off fully before rubbing down.

For paint, I use Halfords spray car paints – for my Stuart I used "Vauxhall Pine Green" which I think looks the part and a gloss black for the base plate. Some parts eg Cylinder cap, I've polished to an almost mirror finish (brasso and fine emery) and the finish is long lasting. Spray paints prefer warm dry conditions to cold damp ones.

Masking out is a key stage, the quality of the masking out will determine the quality of the final job. It needs a lot of patience on small models. In fact most this takes patience.

 

Steve

Edited By Steve Withnell on 22/03/2014 21:55:41

[julian atkinsParticipant @julianatkins58923]

i agree with jason, cellulose thinner everytime!

you ought to build a few miniature locos – some of the castings these days are atrocious! years ago Kennions and Bonds O' Euston Road specified nickel added to the iron casting. lovely castings! the last lot of wheel castings i had were very poor and soft and loads of black dust. i machined an old set at the the same time as tend to turn wheels in batches and the older castings were quite superb and lovely to machine. cast iron for flywheels etc on your Stuart engine will produce a very good finish if finished with fine grade wet and dry etc for the surfaces that will be unpainted

cheers,

julian

[matt stevensParticipant @mattstevens90637]

Thanks all for the comments….

I see no-one has used or recommended the actual stuart paints themselves! Is this because of cost or because people prefer to use their own colours i wonder?

With regards to preparing before painting – I noticed from Jasons link that the fella in question also used a dremel with a wire brush – seems like a good choice. But i wonder if taking so much of the roughness off the castings and making them all pretty smooth takes away the authenticity? Maybe its personal preference, but whilst the Stuart No.4 in the link looks absolutely superb, i can't help but thinking a bit rougher would have been better?!?

Thanks

Matt

P.S. I have a long way to go before being ready to paint anyway – just preparing!

[JasonBModerator @jasonb]

I think most people pop into the local Halfords and find a colour they like,nothing wrong with the Stuard ones though.

One thing to remember is that sand does not scale so the surface it gives on a 1/12th scale model is twelve times rougher than on a full size engine. Same goes for mould shift and thickness of flash at the parting line. Its not such an issue on say a 4" traction engine but can look a bit rough and unfinished on these little engines.

You can also find that the foundry has been a bit too heavy handed when grinding off the moulding gates or two parts don't line up due to distorted castings, both of which can be seen below

Which needs a good coat of body filler

Then rub it all down

And once its paited looks OK as it still has some texture and undulations that you expect on a casting

 

I also find a light run over the surface using a grinding bit or sanding drum in the Dremel works well.

This is the as cast surface

And after a light going over with the Dremel to take off teh worst but not go as far as a polished surface

Edited By JasonB on 23/03/2014 13:35:37

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Matt ,

Finish on full size steam engines varied from one thick coat of red lead to finely finished in everyway with beautiful and sometimes ornately lined multicoat paintwork .

Personal choice really but most workaday engines in full size wre somewhere in the middle – clean and neatly painted and finished but nothing special .

Full size and model engines painted the same way look different – simple optical effect .

Always worth dressing castings and giving them a slopcoat of any reasonable paint before starting machining .

Paint on castings in the rough keeps them and you much cleaner and prevents oil getting into the usually quite porous iron .

Regards ,

Michael Williams .

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