Making Transfers.

Materials - what to use and where to get it.

Tools - a bare bones set of tools.

Modifying the fork-ends with stainless faces.

Modifying the bottom bracket shell to work with my mix of angles.

Mitering the tubes.

Soldering the main triangle.

Soldering the rear triangle.

Cleaning up the lugs. Complete with lots of pictures of the naked unpainted frame.

Making transfers.

Painting.

Addendum.

Incidentally, whilst researching how to do this, I came across a couple of companies that specialise in smallish runs of transfers for frame builders. These are:

• Screen Specialty Shop A US company that makes transfers and stickers for many boutique US brands. They won't talk to you unless you want hundreds though.

• Victory Circle Graphics Another US mob that does smaller runs, starting at about ten or twenty sets.

Pros of silk-screened water slide decals:

• You can make the design pretty much as complex as you like, with lots of colours.

• The decal is very thin, so will disappear under the clear coat.

• Lots of mucking about needed, making a screen for each colour.

• Adhesive isn't as good as with vinyl, so the decal may bubble if it's hit by a stone or similar.

Creating the artwork

Before I started doing anything, I thought for a while about what I wanted to say on the bike. I'm a troublemaker by nature, so wanted something a little silly, and a bit offbeat. I thought about just bunging my name on the downtube, perhaps in a ripoff of the Colnago font or something, but discounted that idea pretty quickly.

Inspiration came while riding my old fixie to work one morning. I'd been teasing our tropical fish before I left, and was thinking about them a little, thinking that something to do with fish would be neat. I thought that it would be cool to call the bike "Little Fish", and to have a cartoon of a little fish about to be gobbled up by a big fish on the downtube. However my sketches all looked pretty lame, resembling a Jesus fish more than anything else. Then I thought that rather than draw it side-on, I'd try from the front. One of our fish is a tart, and can usually be seen staring at you, up against the glass, with big eyes. I drew an oval for a body, stuck some fins on, drew an enormous pair of eyes, and a surprised mouth, and voila. I reckon it looked pretty cool, and it had just the sort of humorous slant that I was looking for.

So next I drew it properly on the computer, using a vector drawing package called Corel Draw. Vector drawing is good because you can scale the result as much as you like and your lines stay smooth, with no pixels. I arranged a set of decals to fit on a page. Two for the downtube, two for the seat tube, a head badge, a more complex head badge, and some other bits and pieces. The result is shown below:

The screen printing process

Before I go further, I should probably talk a little about the process of screen printing. It's fairly simple, but the devil is in the details. One starts with a screen. The screen is simply a wooden or metal frame, that has a fine polyester mesh stretched over one side. Most people use screen printing to print on t-shirts, so use a coarse mesh, like 43T (43 threads per centimetre), so they can get lots of ink through. For finer detail work, a finer mesh is necessary. I used 77T, as I was able to get a bunch of used 77T screens quite cheaply. The problem with finer screens, however, is that they clog more easily, so some trade-off must be made between definition and ease of use.

Next, the screen is coated with emulsion. Emulsion is a photo-sensitive chemical coating. It acts to block up the mesh in the areas where you don't want ink on your decal. Once the emulsion has dried on the screen, it's still water soluble, so can be easily washed off. However, if you expose it to UV, it hardens, and becomes somewhat waterproof. By selectively exposing the emulsion using a positive of our artwork, we can create a screen with emulsion where we don't want ink and open mesh where we do.

Finally, the screen is laid over the top of the decal, ink is put on top of the screen, and a squeegee is drawn across the screen, pushing ink into the open areas of mesh, and transferring the artwork onto the decal. Too easy! Except of course that it isn't nearly as easy as all that.

Making the positives

As each colour in the decal (including white) needs a separate screen, so too each colour needs a separate positive. The positive must be black where we want ink to pass through, and clear otherwise. I used transparency film in a laser printer to make my positives.

Corel draw is able to create "colour separations", where it prints each colour on a separate page, in black. To do this, all colours used in the drawing must be defined as "spot colour" rather than CMYK or RGB combinations.

Coating the screens with emulsion

This is probably the messiest single step. The bare screen must be coated with a uniform layer of emulsion. One can buy a special tool to do the job, but I never found one at any of the screen printing supply places I went to. Bear in mind that this must be done without UV or daylight present, and in between coating and exposing, the screens must be kept in the dark. I fit a 15W orange bulb to the light socket in my garage, and worked at night so that I wouldn't have a problem with sunlight coming in (not that this matters much, as our garage has no windows). There's no need to keep the light down as much as one would in a photographic darkroom, but just try not to expose the emulsion too much.

The emulsion I chose was Ulano LX660. This is a diazo-polymer dual cure emulsion, which simply means that it's sensitized with a separate chemical (mixed in before you start) and is relatively waterproof after curing. After mixing in the sensitizer, I heaped some emulsion on a squeegee and coated the screen, first on the outside face, then the inside face. On the first few screens, I tried to coat the whole screen. This doesn't work very well, as the thickness of emulsion varies too much. It works much better when you just coat the center of the screen where you'll be putting the artwork, in one go.

After coating, I left the screens in a box for a day so that they could dry. I had some trouble with the first few, as the emulsion was too thick in places and wouldn't dry. I ended up redoing a couple.

Exposing the screens

In order to expose the screens, you need some sort of light source to expose them with. I simply used a "daylight" fluorescent tube, held about 30cm above the screen. Daylight tubes emit a lot of UV, which is what does the work. I stacked a couple of pieces of MDF, then a sheet of glass, then the screen (facing side up) then the artwork (upside down) then another sheet of glass. By sandwiching the screen and artwork between pieces of glass, it ensures they are in intimate contact. Putting the positive upside down on the print side of the screen ensures the most crisp result, as the actual toner is in direct contact with the emulsion.

I first did a test exposure, as I had no idea how long I should expose the emulsion for. This involved covering up parts of the positive progressively, such that 1/4 of the artwork is exposed for 10 minutes, 1/4 for 20 minutes, 1/4 for 40 minutes, and 1/4 for 80 minutes. I did this with the lamp about 60cm from the screen.

When I washed the test screen out, Only the 80 minute exposure worked, and then only marginally. All the rest simply washed out. I decided to reduce the distance to the light by half, to 30cm, which would increase the intensity on the screen by a factor of four, and expose the proper screens for 30 minutes each.

Above is a photo of my workbench with a bare uncoated screen ready for exposure. I didn't take any photos after I'd put the emulsion on the screens, as I didn't want the flash to cause any grief with the emulsion.

Finally here's some pictures showing the exposed screens, ready to print with. Note the excess emulsion, especially on the one on the top-left.

A jig to hold screens and decals in proper alignment

As I have four colours to print, I need to come up with some means to keep everything accurately aligned during printing. When preparing the positives, I put four simple registration marks on each one, in exactly the same place, so that I had something to index off from one print to the next. For my first couple of tries (which were a complete disaster - see below) I simply taped the decal paper to my workbench, and clamped a screen on top with a couple of paddle-pop sticks as spacers. For the proper print runs, however, I needed something a little more sophisticated. Tape was useless for holding the decal paper down, as the decal paper separated when the tape was removed, and aligning the screen between prints was very awkward.

I solved the first problem by building a vacuum table. I took a sheet of perforated aluminium a little larger than the decal sheets, and mounted it so that it was flush to the top of a piece of board. I used my router for this. I also cut channels so that air could flow from all the holes under the decal sheet to the back of the board. Finally, I constructed a simple airtight box under the board, and put a piece of 1.25" tube in the side. When I put a vacuum cleaner on this port, it sucks air through the perforated sheet. Any decal in contact with the sheet is held down nice and flat.

The issue of keeping the screen in alignment was solved by making a large hinge. On one side of the hinge, I constructed clamps to hold the screen frame, and on the other side, I simply drilled holes. Carriage bolts pass from the bottom of the top board, through a plate, then an oversize hole in the top board, then through the fixed part of the hinge. By putting wing-nuts on the top, they are easy to undo and do up, and the screen can be positioned anywhere within a 40mm diameter area.

Again, a couple of photos tell more than I could in pages of text:

On the left is a photo of the jig with a screen mounted. The vacuum hose can be seen coming out of the box on the right. The right side photo shows the vacuum plate, with the screen lifted up. When printing, there are pieces of masking tape on the vacuum plate surrounding the print, so that it can be accurately positioned.

An important lesson

When I started, I had no idea of what sort of ink I should use. I went to the local artists supply shop, and returned with some "artists acrylics" and some printing gel. The printing gel is mixed with the artists acrylic paints to make them flow more easily, and to retard their drying time so they don't clog the screen. The whole lot is water soluble.

So once I'd made the screens, I thought I'd do a test print. I took my most complex screen, taped some decal paper to the bench, mixed up some acrylic and gel, and printed on the decal paper. The result was pretty disappointing. The ink wasn't adhering terribly well to the decal, and was beading up.

I gave it another try, and disaster struck. This time the decal adhered itself to the emulsion on the bottom of the screen. When I tried to remove it, I separated both the decal from it's backing and areas of the emulsion from the screen. A post-mortem revealed that the water in the acrylic softened the emulsion, and also softened the glue in the decal paper. These then stuck together quite well. Matters weren't helped by the super high humidity we'd had in Sydney for the proceeding week.

So now I knew artists acrylics, whilst probably fine for screen-printing on t-shirts, are absolutely hopeless for water-slide decals. Finding this out cost me two screens.

After a google search, I found a company here in Sydney, Australian Specialty Inks, that manufactures ink. Even better than that, they manufacture ink specifically for printing on water-slide decals. A phone call gave me pricing. Unfortunately the smallest quantity they sell is 1kg. Most of their inks are around $45 to $50 per kg. I swallowed my pride, and ordered the inks I needed, along with retarder, thinner, and screen-wash (used to clean any excess ink off the screens). My screen printing exercise is now turning into the most expensive part of the whole process.

Getting it all together

Once the ink arrived, I tried again. After a brief false start caused by a screen that wasn't quite as clear as I thought it was, I managed to get some prints that worked quite well. One of the anticipated problems was maintaining alignment between the white pass (on white backed decal film) and the orange pass. I solved that (sort-of) by leaving the screen for the white parts in the press, cleaning it, and then printing a black version, and using that to align subsequent screens.

I wasn't 100% happy with the alignment between colours though, which varied fairly randomly by up to 0.5mm or so, enough that it was obvious about 50-60% of the time. I managed to get five good prints (which satisfies my requirements for now), but the rest weren't good enough to use.

Next time I do decals, I'll redesign my hinge arrangement, as there was a little play in the hinges. Also, the wooden screen frames were a little flexible. A workmate suggested putting alignment dowels at the front, which would lock that nicely... Further, I used masking tape to provide an edge for the decal paper to line up on. This wasn't as definite as it could have been. Next time I'll tape thin steel rules to the table to align the decal film.

A close up of one of the decals, scanned at 150dpi, is shown below. If you look carefully, you can see that the blue isn't quite aligned with the rest of the colours. You can also see parts where the black didn't quite print through: