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Curtiss Mohawk In RAF service

Started by Carl Smoot · 120 ≡ · ↻ 2 weeks ago

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Carl Smoot said 4 weeks ago:

I've started reading the instructions for the etching kit. One of the things it mentions is that very fine lines smaller than .007 inch will be difficult to etch successfully. This means that my art work as currently drawn is too fine and will need adjustments since most of the black lines are approximately .003 inch (about .1mm).

Where this concerns me most is the louvers because the area is very small and in order to have adequate brass material for the number of louvers that are supposed to be present (10), the lines were reduced to .1mm thick. I am going to spend some time with the artwork and see what I can accomplish with .2mm line thicknesses (.008 inch). I may have to reduce the number of louvers created from 10 to 6 or 7. We'll see.

The other thing I saw in the instructions is something I thought about but for some reason felt I didn't need to do (for the wrong reason). These are the small bits of brass that remain to hold the parts to the brass sheet (the sprue connectors). I was thinking that it wouldn't be a problem if they etched through and away from the brass sheet, but it is a problem because of the amount of handling required and the necessity for maintaining registration and proper etching times on both sides of the metal. The parts need to remain in position throughout the etching process.

Anyway, the bottom line is that I am going to spend the necessary amount of time to get all of this setup so it goes as smoothly as possible. Since there is limited amount of supplies in the kit I want to have a successful etch on the first try.
George R Blair Jr said 4 weeks ago:

Hi, Carl (@clipper): In my mind, a new technique is always easier than it turns out to be in reality. I am sure you will get this figured out. Remember the old PE that used to have a plastic backing that you had to peel off the pieces? Is this the same?
Spiros Pendedekas said 4 weeks ago:

Looking forward to see how you will tackle this, my friend @clipper. I am sure you 'll sort it out.
John vd Biggelaar said 3 weeks, 6 days ago:

Love to see the outcome of the etching, Carl @clipper
All sounds promising.
Carl Smoot said 3 weeks, 6 days ago:

I thought I was going to have to completely redraw my artwork this morning because I watched a video yesterday evening which had the artwork as a negative of the artwork I had drawn up. IN other words in my art, the black areas will be etched. In this video, because of the technique that person was using, the white areas are etched and this caused me some confusion at first. But I verified this morning, that at least with the kit I have, the black areas are etched.

So a word to the wise, be careful if you decide to use photo etching because apparently depending upon the technique used, the art must one way of the other.

Today I am going to focus on getting the artwork completely ready by adding the art for the sprue connectors to hold the pieces to the rest of the brass (after etching) and to see what I can do about the line widths in my louvers (I mentioned this in my previous post). Sorry there are no pictures yet, but I promise to include them when I start doing something that can actually be photographed.
Carl Smoot said 3 weeks, 6 days ago:
Here is the corrected artwork for my photoetch experiment. It has increased line widths and sprue gates added. Also added are registration marks because I need to align the art work on both sides of the brass. This image is blown up some to make it visible so the lines look pixelated. All line widths are .2mm. The black areas are the areas that will be etched and the spaces between parts is double the line width. You'll have to zoom in a bit to see the sprue gates.
1. Louvers

2. Tubular Bomb Fins

3. Upper Landing Gear Cover

4. Lower gear Doors (upper and lower pieces)
George R Blair Jr said 3 weeks, 6 days ago:

I am really looking forward to seeing how these work out, Carl (@clipper). I have some popcorn ready for the big show. :o)
Spiros Pendedekas said 3 weeks, 6 days ago:

Your artwork looks excellent, my friend @clipper! Looking forward to the PE outcome!
John vd Biggelaar said 3 weeks, 5 days ago:

Great drawings, Carl @clipper
Looking forward to how this will turn out.
Carl Smoot said 3 weeks, 5 days ago:
One more revision to the artwork. I saw this when I was reviewing the instructions. The revision consists of making the second part of the image a flipped horizontal version, rather than a duplicate version. This is because the clear material being printed on can only be printed on one side and this side needs to face the brass (I believe, or faces away from the brass). So it must be a mirror image.

The second part of the revision is that the sprue gates need to only be on one of the two images. This is because each image is responsible for etching one of the two surfaces of the brass. By eliminating the sprue gates on one of the images, the etching will only etch half way through the metal, leaving enough material to hold it in place, but being thinner and making it easier to cut out the parts later.

I am going to attempt to do this today, but taking my time going through the steps first to make sure I get it correct.
1. Notice the mirror image and the little white sprue gates missing from the second image
John vd Biggelaar said 3 weeks, 5 days ago:

That's a nice idea to etch half way through to enable cutting, Carl @clipper
I'm eager to see how this turns out.
Carl Smoot said 3 weeks, 5 days ago:

The first attempt was a failure. I believe the main reason this happened was because I misread the instructions. The metal is laminated between two sheets of blue photoresist film. These sheets have a protective clear film on both sides of them. The instructions say to remove the film from the dull side and place the metal between them (dull side towards the metal on each side of the metal). Then this entire sandwich gets laminated between two sheets of laminated carrier film using the provided laminator.

The laminated sheet is then placed between the two artwork images printed on a clear inkjet printer film and held in place between two sheets of acrylic using clamps.

At that point, you're supposed to expose the combined sandwich to incandescent light (or sunlight) for specific amounts of time. Then afterwards the artwork is removed from the acrylic sheets and the metal is removed from the artwork. Then , and only then, you're supposed to remove the second photoresist clear protective film that remained on the outside of each photoresist sheet.

It's this last step that I screwed up. I knew I had to remove the clear protective film, but I was thinking I had to remove it before doing the lamination process earlier. So I removed it then and then proceeded with laminating and everything else afterwards. The clear protective film, I believe is supposed to allow you to pull the artwork away from the metal without pulling the photoresist with it. Since I had removed this clear film earlier, the artwork was somewhat stuck to the metal.

When I pulled the artwork away, some of the photoresist came off with it. See the picture below.

So I've stripped the photoresist off of the brass and I will have to redo the process again. At this point, I've only lost a small amount of stripper, two small pieces of photoresist, and two small pieces of the clear laminating film, as well as the couple of hours I was doing this.

What is encouraging is that it looks like the thin lines transferred to the metal properly.

Back to trying again.
John vd Biggelaar said 3 weeks, 5 days ago:

Such a pity this happened, Carl @clipper
A positive note is that indeed the thin lines seem to work nicely.
Carl Smoot said 3 weeks, 5 days ago:

I guess it's not in the cards for today. I got all the stuff put together correctly this time and placed it under the lamp to expose the photoresist and of course my just purchased , brand new, incandescent light bulb, the only one I bought, decided to burn out before I could even start. I guess quality doesn't exist anymore.
Spiros Pendedekas said 3 weeks, 5 days ago:

Looks like the photoetched gods fight you a lot, my friend @clipper! Good thing is that the thin lines seem to work, so, once you get a new lamp, the results will be great.

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Curtiss Mohawk In RAF service