Painting fittings

Hi Chaps

Quick straw poll for the cognoscenti. Generally when fitting angle brackets etc to larger parts such as frames permanently by riveting do people paint before hand at least in primer so as to avoid bare metal under the fitting or not bother and do the lot afterwards?

Just fitted the spring brackets to the bogie frames of my King (without paint) so the question is a little academic as far as they are concerned but I'm sure there are other areas where it would apply.

regards Martin

Depends how you are riveting. Hot or cold. If hot riveting the paint will burn. I primed and painted the spokes and rims of my traction engine wheels prior to assembly to prevent rusting. Assembly was done at a later date. The setting of rivets on the spokes where done cold. (5/16" dia rivets were set with 3 different shaped snaps, requireing a maximum press force of 15 tons). The assembled wheels then grit blasted prior to final painting.

Paul

I have no idea what the standard practice is but I would have thought a layer of paint would be undesirable as once riveted it could lead to a loosening of the fitting if the paint layer was compromised by heat and cleaning or lubricating fluids. This might be unlikely but possible in my mind. Probably talking through my fundamental orifice but I would go no paint.

Mike

mmm, so far the definitive answer is maybe or maybe-not then.

Martin

Metal to metal contact must be better than metal to paint contact so I would say no to painting. I build complete and then strip down to paint rather than paint as I go, reason is that I don’t seem to get any rust in the workshop, probably has something to do with a dehumidifier running constantly!

For riveted assemblies on my traction engines such as strakes to rear wheel and spokes to wheels I spray the mating areas with grey primer before assembly. My guess would be that the joint would be sufficiently tight (all rivets closed cold) that the thickness of paint is immaterial. The rivet expands to fill the hole, so it's a pretty tight fit. Try getting one out when forming the head has gone pear-shaped!

Andrew

You could encourage a bit of flash rust then apply phosphoric acid to get a hint of phosphate protection prior to assembly. The meniscus of paint at the joint should seal the joint but if you have insufficient paint or an unpainted side of the joint then it might leave a way in for moisture.

Back in the 60's at the aircraft factory, we painted all al alloy panels in an undercoat before riveting . For military aircraft, we painted, and then all external seams had a jointing compound (can't remember the name , it was yellow and it washed off with soap). If panels had to be "fettled", the bare surfaces were etched with a brown 'acid' called Alachrome? and washed before riveting to the adjoining structure.

Duralac?

Andrew

Edited By Andrew Johnston on 04/02/2020 19:33:00

Well there doesn't seem to be anyone shouting about major issues either way. Sort of take you pick really. As I've already done the side frames for the bogie 'sans paint' I shall not change anything now. The brackets were not degreased so I'm not particularly fussed about corrosion. The thought that did occur to me after riveting up was would I encounter painting issues because of small amounts of oil trapped under the brackets and difficulty degreasing prior to painting. I think I'm probably overthinking things again by the responses.

cheers Martin