Wednesday, 13 July 2011

More on how not to clearcoat decals on carbon

"I am embarking on the same endeavor. Where did you get your decals made? Also, what kind of clearcoat did you use? Did it come in a can or did you need a compressor / sprayer setup?"

Made locally by “Signarama” in Surry Hills, Sydney. I don’t know the technical term but they are a 3 layer format; waxy backing paper (removed first), white vinyl lettering/images (the meat in the sandwich), and clear third layer for the purpose of positioning the graphics before being peeled back to leave the graphics in place.

A small air-filled gap of a few mm surrounds the edge of each graphics item (a result of the step at the layer junctions). It’s important when putting the 2-layer sticker on not to force contact to the frame at this junction as the gap allows the clear plastic outer to peel off without also lifting the image layer with it . Peel the clear layer off at the sharpest angle possible. The smaller the art detail the more likely it will lift with the clear outer – I found a sharp metal point was required to hold down the smaller art features. Expect intricate artwork to be more difficult.

The lettering and images (white on transparent backing) were designed in a .ppt doc on a big sheet (1m*1m), so that the images could be displayed in real size (largest images being ~30 cm long). I saved the page containing all the art as a .png file (any image format without serious compression would probably suffice), then cropped to the sticker size before saving each image individually (MS picture manager). Starting big means you won’t compromise resolution or show pixilation. Supplied to the printer on a USB stick, the files are then converted to some sort of vector format required for printing. Once the shop has done the conversion, I believe repeat orders are cheaper. I had stickers for three frames made at once, which came out at approx. $30 per set.

The bad news is that repeated sanding is a real pain. The good news is that if it all goes to hell it’s amazing what can be achieved with sandpaper. I predominantly used 2 grades – 800 grip to remove the original surface and do the heavy lifting on imperfections, and 1200 grit to attain a smoother surface before applying top coat. I’m told that 1500 or 2000 grit paper exists, although I couldn’t get my hands on any. Sanding is best done wet – just keep dipping the paper in water. This also prevents inhalation of particulates. Use finger pressure behind the paper so as not to produce flat-spots, as might happen with a block of cork or wood. Remove the resultant slurry with a cloth and inspect under good light. Imperfections will jump out as the surface dries, which happens very quickly.

Once the decals are in place, apply 3-4 very light layers of clearcoat. I used “Motospray Acrylic Top Coat Clear”. Practice on a sheet of newspaper first to convince yourself you are still just wetting the surface. Nozzle should be at 20-30 cm. Adjust your angles of attack for each pass to make sure you wet different sides of the tubing. Each "layer" for me is simply 2 gentle consecutive passes of the nozzle (left to right, right to left). Do two passes on the down tube, then the seat-tube etc, slightly adjusting angle of attack for each sweep till all surfaces are covered. For me this = 1 coat. Wait approx. 5 min between layers.  Although touch-dry after 5 min, there is still enough solvent to bond the next layer. The whole process only takes 15-20 min. Leave the frame to dry over a few days (required for traces of solvent to completely vanish – might be quicker in summer). Remember that less can be more! You simply want to seal the edges and provide a thin coat to protect from the elements. One session might indeed suffice.

In the case of my second frame I made the mistake of spraying late in the day as the sun was setting with the temperature dropping fast. I suspect that the last coat caught the dew to produce a matte finish (solvent evaporation is a cooling process). Hence, I sanded this one back lightly, then re-coating the following weekend in the middle of the day. No runs or cracks for either attempt.

Be warned that the finish achieved by this method is a little grainy (think orange-skin – only visible up close) compared to the original lacquer. I believe the process can be taken further if you are after that absolutely perfect finish. The next step involves something called “cutting compound” – an automotive cream containing some sort of abrasive – to polish and buff the surface to a mirror finish, although for the moment I’ve decided it’s not worth the effort and I just wanted to ride the thing.

I did my frames in winter. I’m guessing that the particles which come from the can might “lie flatter” on the surface in warmer conditions, and produce a finer finish. The vibe I get from petrol-head forums (USA) is that most people wait for the heat of summer to do their final sprays. Additionally, most use some sort of spray gun/air compressor set up, which probably yields finer droplets to give a smoother finish. Many also use a more industrial “2-pac” style paint, which requires the mixing of two components, one of which is extremely toxic, and requires special breathing equipment etc.

Given that bike frames tend to spend good chunks of time wearing grime sweat and tears rather than strutting show-room floors, I reckon that the finish achieved from a hand held aerosol will be more than adequate for most of us to have some fun with.

Hope this helps.

 Cracks in the lacquer that were subsequently sanded out
 That's better - note the slightly rough finish
And finally the build - 8 kg of wombat (7.5 with even vaquely schmicko wheels).  An amazing improvement over the cellnago.  Cost approx 2K.  3K once some nice wheels are factored into the equation.  You can't really beat the budget packages most shops now sell, especially once labour is factored in, but you will end up with something unique.

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