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Meccano restoration – Spraying

For the previous page on stripping and preparation, click here.

Part 2: Painting large quantities, with a spraygun

For information on an easier way to paint, using spray cans, click here.

Hanging parts for painting

I painted a large number of parts using the method described on the previous page, and they came out well.  But there were a number of problems.  I had decided to progress to a compressor and spraygun, which allowed me to use custom-matched colours for a lot less money.  Using paint from tins also allows a great deal more control over the brand and consistency of paint.  That meant that I could experiment more to get a better quality, thinner, and glossier finish.

Having gone that far, I decided to move to the next stage of hanging parts.  Here is an explanation of my reasoning.  The problems with the paint-can spraying method were:

• Inaccurate colours.  Custom colours are extremely expensive.
• A slightly lumpy finish, or at least difficulty in obtaining a thin flat coat.
• Waiting for the paint to dry before turning over for the other side.
• Transferring to the oven is a slow process, having to re-hang everything.

There are a number of solutions that have been proposed to fix these issues.  For the quality issue, many suggest using a primer coat.  But Meccano didn't do this, so I have difficulty seeing how this would make the parts nearer to the original finish.

In fact, why don't we go have a look at how Meccano did do it?  Here's a picture.  If we could copy this method, we should be able to get a closer match to the finish, surely? Apart from the total lack of face masks, of course!

The key is the hanging rack.  Making a good rack would solve the issue of hanging and waiting for the paint to dry, so long as the racks can go straight to the oven (as they would have in Binns Road).  Ideally, what we need is a set of racks that:

• Fit in the oven, preferably several at a time.
• Allow easy hanging of a range of different parts (adjustable to suit each part).
• Allow handling of the parts while the paint is wet.
• Can hold parts securely during painting (of both sides of the part).

Building the frames

The key limiter here is the oven, since I don't have a large conveyor oven as was used in Binns Road. Measuring the inside of the available space gave me an internal height of 15'', and depth (front to back of the oven) of 16''.  I built frames to fit this – exactly 15'' high and 15½'' wide, as shown in this picture.  There is a 2'' obstruction at the front of my oven, so the bottom 2½'' has to be two separate feet to sit over this.  Building the feet from strips (rather than angle girders) allows them to bend a little to fit the oven exactly.  In this way, the racks are 'jammed' into the oven and held in place by the flex of these feet.

The two main crossmembers are 15½'' long (I found a stack of reproduction 18½'' angle girders and chopped them down, but you could overlap angle girders instead).  The 'front' (right) is a 12½'' angle girder (this goes to the front of the oven), and the 'back' (left) is a 12½'' strip. The feet are 5½'' strips bolted to the verticals and sticking out by five holes.  You will need to modify these feet to fit your particular oven, probably.

Now, the left-hand vertical 12½'' strip has a series of hooks on it, formed by bending thin steel garden wire.  In addition, I made a number of other 12½'' strips with more hooks.  You can see the right-hand one set two holes in from the right-hand edge of the frame.  This strip allows 12½'' parts to be held horizontally in the frame, and the right-hand angle girder then becomes the 'handle' for carrying the entire frame.  For smaller parts, you can make a number of further perforated strips with hooks on both sides (as per the one in the middle of this picture), allowing you to hang double the number of smaller strips.

This is the key to the design.  Only the left-hand strip is fixed as part of the frame.  The right-hand and middle strips can be moved as required, bolting them to the top and bottom angle girders in whatever position is required.  Here is an example of another frame, set to take three colums of smaller parts, which have been hung on the frame ready for painting.

As far as spacing of the hooks is concerned, it depends on the parts you're painting.  I have found that I need two different green frames – one has three hooks per four holes (just bend the hooks up and down to even out the spacing), as the ones above have.  This frame holds strips, flat girders, double angle strips and so on.  The other frame has a hook every other hole, which is ideal for angle girders, curved strips and other parts that need a little more vertical room.

The red frame, shown to the right, has a different arrangement of hooks again.  Three hooks are needed per part in order to hold them firmly.  You can see that the left-hand and right-hand strips have hooks top and bottom (2½'' apart), and the central strip only has a single hook for each part.  This frame will take up to eight flexible plates, flat plates, or flanged plates. 

Thinner (5½''x1½'' and 2½''x1½'') plates can be held further down the strips, still using three hooks per part.  Braced girders can be held by tweaking the lower hook up a little to fit the part.

The picture to the left shows a 4½''x2½'' flexible plate hung, ready for spraying. Note that the hanging hooks go down and backwards from the strips, then bend back towards the front, followed by the 90° bend where the parts sit, and the end points back upwards.  This holds the parts flush with the strips, prevents them coming off the hooks easily during spraying, and keeps the wire hooks away from the parts.

This close-up of the part from behind shows the hook in more detail.  Now, remember that the objective was to enable us to paint both sides of the part without having to re-hang them.  By ensuring that the wire stays away from the edges of the part by the hole, we can spray them completely, provided we get the spray angle right. 

What happens if we don't?  Well, we would get a 'shadow' of unpainted (or badly painted) area behind this wire, coming away from the hole where the part was hung.  Lo and behold, if we check carefully some original Binns Road parts we can easily find examples where this has happened.  The imperfections on the original 1950's part (shown to the right) are exactly what we would expect using this type of hook.  If you look carefully, you will find up to three of these imperfections on many flexible plates, showing the holes where each part was hung. 

In my opinion, this finding shows that we must be on the right track to get a more accurate paint job.

Ready for spraying

It's not at all easy to get the spraying right.  Most of the experts you will find are connected to the motor industry.  They use multiple primers, two-pack enamels, several coats, and gloss lacquers to get the sort of finish they want.  We're trying to spray very small parts, with a single coat of old-fashioned enamel, to get a thin but glossy finish with as little effort as possible. 

You will need a compressor, a water trap (which often come with an inbuilt pressure regulator), and enough hose to go from the water trap to your spray gun.  It's important to get a gun you're happy with – a small lightweight one is easier to handle, and you need to get one with a gravity-fed cup.  Many times you'll be spraying in different directions (particularly up and down), which precludes most other types of paint feed.

Then, you'll need somewhere to hang the frames.  Here's a picture of my spray booth (which should really be a separate room with suitable airflow and extraction, otherwise you'll get dust on the parts and paint on everything else). You only need it about 8 x 4 feet; the smaller the room the easier it is to arrange sufficient airflow.  A simple wooden frame allows me to hang up to four frames at a time (only two are shown), and the whole lot can hang from a mount in the ceiling that allows it to be rotated easily to paint the back.

The paint I use is a simple old-fashioned one-part enamel.  If you ask for this at your local automotive trade supply store you should be ok.  You don't want modern cellulose-based or two-pack varieties.  We're trying to keep as close as possible to the original finish, remember?

You will certainly need to experiment.  A lot.  Get a load of 5½'' strips ready and be prepared to bin a good number of them. I was recommended to thin the paint by 10%, which turned out to be hopeless.  Far too much paint was coming out at a time.  I have now settled at a mixture of about 50:50.  If the paint is too thin it will run too easily (as you are applying more paint in order to get an opaque coat).  Too thick and the you'll end up with big lumpy bits of paint everywhere as you try to get in all the corners of parts, or a speckled finish if you try to correct this by spraying less paint.

Note that there are two different solvents available.  "Thinners" is used only for cleaning up the spray gun after painting, you don't add it to the paint.  "Reducer" is what you use for thinning the paint (confusingly), which is more expensive.  You will need lots of both – reducer for thinning the paint, and thinners for cleaning up afterwards.

Most spray guns and paint instructions tell you to stay well away from the parts, at least 6'' and sometimes as much as 12''.  I couldn't get the finish I wanted like this, until I found someone who suggested that I use much less paint from very close – about 2 inches away from the part.  It's possible that with enough paint flow you could work from the distance in the photograph at the top of this page, but you can see how much paint is being used up!

Spraying technique

The most important spraying technique is to avoid the paint getting too thick.  If you do, the solvents in the lower layers of paint will force their way out of the top coat while the paint is still drying.  This is called 'cratering' and shows itself by tiny craters in the final surface of the paint.  The way to avoid this is to spray the parts twice and wait for the first coat to dry off slightly before spraying the second one.

At first, I spray the parts a couple of times, concentrating on the undersides and edges.  It's not critical what the finish looks like, or whether you get paint evenly everywhere.  You're trying to get a general tone of colour over the majority of the part.  But not too thick.  I do one coat from low down (pointing upwards at 45°), then another coat from above to catch the bits I've missed.

Now turn the frames around, and do the other side the same.  You have a rough coat over most of the parts, but can still see the metal through the paint.  Go out of the room for a couple of minutes to let this coat dry.  If you don't, you'll get cratering.

Now, come back and do the next coat.  I spray a light mist from a few inches away over the whole frame to lay down some wet paint (and get into any missed areas), then come back for the final coat.  This is a slow even pass from left to right across each part, from close range (2 or 3 inches).  When I say 'slow' I mean about two or three seconds to move across a foot.  The speed will depend on the rate of spray you have set your gun to, but generally its best to have as low a pressure and flow as you can manage, while still fully atomising the paint.  Go the speed that you need to lay down a glossy coat on the part, in one hit.  If you go too fast the finish will be speckled, and if you go too slow the paint will run. 

Now flip the frames over and do the same thing to the other side.  All done! Hang up the spray gun, pick up the frames by their handles and put them in the oven at abour 130°C (270°F) for about 13 minutes.  The exact numbers may be different for your particular paint, and you will need to experiment.  The paint I'm using doesn't recommend baking at all, but you still need to do it.

Painting parts with bosses

Ok, let's get down to some of the tricky bits.  The first one you'll come across is painting parts with bosses – cranks, face plates, pulleys, sprocket wheels and so on.  My technique requires another Meccano construction, shown to the right.  It's a large flanged plate with an axle sticking out of the middle, and a collar mounted about half an inch from the top of the axle.

Once you've stripped and cleaned each part (see the page here for details on stripping and drying), you need to mask off the boss.  A good quality masking tape is required, and you'll need a small piece of it stuck over the boss and pressed down.  Place the part on the axle, put a sharp blade in between the boss and the part, and turn the part with the other hand.  Doing it like this lets you get a very neat circle, which is much harder to achieve if you don't keep the blade still.

So far so good.  Once you've put the top piece of tape on each part, turn them over and wrap a piece of masking tape over the bosses, as close as you can to the steel, and pinch the masking tape together to stop any paint entering the boss from behind.  You will be spraying right up to the masking tape from all angles, and need to make sure the boss stays paint-free.

A final hint for the trickest part – the large fork piece.  Use another bossed part such as a crank to make the circle, then carefully peel off the circular piece of tape and put it on the fork piece.  Otherwise it's near-impossible to get a perfect mask.

The masking tape will be perfectly safe during the baking, and once they're out of the oven you can remove the tape to reveal a perfectly painted part with a clean boss!  No more excuses for bits of paint all over the brass, one of the worst offences when repainting Meccano in my opinion.

I hope that this page is useful to you...  I'd love to hear any comments, either by email (click Contact Us at the top of the page), or if you have any suggestions for this page please leave them below.
For the previous page on using spray cans, click here.

Further information

Total number of messages on this page: 27.  This is page 5 of 5.   

DUNCAN SCRASE      (at 1:54pm, Thu 21st Feb, 08)

Hi I am looking for a match for Meccano Army Green 78 Reply: I would suggest, if you're using a spray gun, taking a part along to your local auto spray supplier and getting them to match from it. Preferably from a formula colour, so they can repeat it. The match should be near-perfect. I understand there is a slight difference between pre-78 army green and 78-79 army green, so taking a part is the best idea to get a good match.

Chris Mothershaw (Epsom UK)      (at 9:32am, Fri 7th Dec, 07)

Tried to leave a note about colour matching, but had it thrown out as suspected spam. What could I have said that was so offensive???!!! Chris M Reply: No idea! Sorry about that! Did you put a link in the message? I don't think it likes that...

Alan Keith      (at 3:39am, Fri 2nd Nov, 07)

I've found an easier and more secure way of masking off the riveted side of bosses: add a collar using a very short axle and tape over the collar, ensuring you're covering the rivet at the same time. For the large fork piece, mask the collar before you install it on the part to be painted, then drop and rotate the boss slightly into position. Reply: That's an interesting idea, but the trouble is that the riveted side of the boss varies in size quite significantly (and of course some bosses are non-circular, and some are half an inch diameter). It sounds like a lot of work if you have dozens or hundreds to do, but if you have enough collars... I know someone who used to use a bolt and washer, but with both these methods the seal isn't perfect or the right size, and the extra parts affect the painting of the flat area. There's no problem with 'security' with masking tape, it is even safe during powder coating.

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