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Finishing a casting

What filler should I use?

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John Wood108/12/2009 15:53:58
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116 forum posts
Most castings seem to have a pretty decent external finish and only need a file and wire brush to get ready for painting however, the ones I am working on at the moment have part numbers cast into them which need filling in before painting. In the articles I have read about preparing castings I can't find any actual products referred to as being suitable so can anyone point me in the right direction please?  I have both cast iron and alloy castings to deal with.
 
Thanks
John 
MichaelR08/12/2009 16:08:59
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528 forum posts
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I have used car body filler, and plastic metal filler all work to good effect on cast iron and alloy. I have also used the plastic/chemical metal filler on blow holes on areas to be machined.
NJH08/12/2009 16:13:56
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2314 forum posts
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Hi John
A very good question and one I was about to ask. On past projects the castings have been pretty good but  I would like a really good finish on this one. I did contact our esteemed editor and he advised an automotive spray filler which I am yet to track down. However I guess that  this would not be suitable for filling casting holes ( nor yet small machining dig-ins whoops!)  I doubt that Pollyfilla would suit.  How does Anthony Mount achieve that finish on his models and how do good machine manufacturers get that "buy me" look ?
JasonB08/12/2009 16:29:40
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25215 forum posts
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Plastic Padding body filler or "chemical metal" can be used. If the part is likely to be subject to heat then something like "JB Weld" is better.
 
If you want a supersmoothe finish then a small die grinder or dremel tool with a small flapwheel and or emery cloth will remove all the high spots. Then a thick primer, rub down, prime then rubdown etc until you have the surface you require.
 
If My Warco is anything to go by the makers coat the whole casting with a layer of epoxy filler and then sand it back.
 
Jason
mgj08/12/2009 18:25:59
1017 forum posts
14 photos
Jason - you missed the elbow grease bit...
 
One alternative for machine tools rather than models is Hammerite. 
 
The model aircraft people have a very good product called microballons. These are actually tiny little glass balls, but to you and me it looks like a fine sand. Add to expoxy resin, and you get a nice sandable, but epoxy coat which is much better than car filler and much easier to sand and of course it sticks like ... to the proverbial. Acetone is the best solvent, paint thinners works but is second best. Layer thickness doesn't matter.
 
Increasig the ballons content  makes it very soft, more epoxy less ballons makes for a good solid surface.
 
Cheap, quick and  very easy to use, but its worth just wiping it over with acetone once when hard to stop the sandpaper pinning on the outer retarded air coat typical of most epoxies.
NJH09/12/2009 11:01:58
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2314 forum posts
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Well John I don't know if that helps you but it certainly helps me. So thanks Stick, Jason and Meyrick. If I can presume on you good folks further can you give any idea where I might best get these products ? Especially  JB weld ( one bit will get hot)  I ask because I live in the depths of rural Devon where bits for tractors etc are easy to find but they don't bother much about paint finishes!  " Thick primer" I guess an automotive parts supplier? Meyrick I can find an aeromodelling shop when next I go to Exeter but Acetone might be tricky?
Elbow grease - I know, I know but luckily this is a small engine!  ( and I do have a dremel)
Gordon W09/12/2009 11:38:35
2011 forum posts
Tractor places are usually the best places for such things, JB weld, acetone, good quality m/c paint etc.,usually cheaper too, -argue about discounts. Could also fill casting defects like we did back when I worked in a foundry-- good old putty.
DMB09/12/2009 12:52:11
1585 forum posts
1 photos
Hullo John,
I have used `LOY` sometime ago. I seem to remember that it came in squeezy tube, like toothpaste. Got it from carspares shop who were at that time next door to long-gone Blabers Foundry, in Brighton. They recommended the stuff, saying that was what Blabers bought to fill in blemishes in patterns. Try reading up the excellent  description of working on castings at the start of the QUORN articles.
John.
JasonB09/12/2009 17:01:41
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25215 forum posts
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Hemmingway's do JB weld but I got mine off e-bay from This seller
 
I just use several brushed coats or a red oxide type metal primer should be able to get something at the local DIY store by someone like International paints
 
Halfords or DIY store should have plastic padding or e-bay again
 
Acetone and reclaimed acetone brush cleaner can be had from from a fibreglass suppliers,  I usethis one, they also do the glass bubbles. Failing that nail varnish remover is similar just dont get the "acetone free" ones
 
Jason
NJH09/12/2009 19:17:38
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2314 forum posts
139 photos
Jason
Thank you very much indeed.  No excuses now then! I will get on, order the bits and finish the job.....then progress the other 5 projects I have on the go. Maybe, with my ability to put things off , it should be the clock first! 
GoCreate09/12/2009 21:04:09
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387 forum posts
119 photos
Hi
Halfords sell JB weld and high build primer. 2 or 3 coats of high build primer rubbed down with very fine wet and dry paper used wet gives a super smooth finish. I casting I did recently was like a morror after spraying with  pheonix enamel.
Nigel
John Wood112/12/2009 15:24:00
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116 forum posts
Well thanks again guys for all the info. I reckon there's enough choice now to be able to source something suitable locally. I have at least Halfords, Countrywide and a couple of independents to go at so thanks again.
 
Regards,  John

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