--- In
Homebrew_PCBs@yahoogroups.com, "designer_craig" <cs6061@...> wrote:
>
> John,
> I wouldn't think the fixer would cause the emulsion to turn pink. Could it be just the color of the base stock, I have seen tinted base stock before but don't remember seeing any in pink, its usually just a little brown like sepia.
>
Well, I wouldn't call it "sepia", but somebody else might call it that. But, there is more redness than sepia.
I am REALLY sure it happens during the fixing step, as I can see the developed film is quite white, and then after just SECONDS in the fixer, I can see it turning darker.
I am not using the right chemistry at all, just using the same stuff I use with my Agfa HTR3 film. The developer appears to work perfectly, but could be setting up some kind of chemical reaction when the film goes into the fixer. These red-sensitive films have a dye in the front to make it red-sensitive, and an anti-haliation backing dye on the back to stop any light that makes it through the film. These are dissolved in the developer.
> In the past I have used Liford Ilfoline IN-5 for PC flim work but a few years back I attempted get more and couldn't find any. I did find that Freestyl Photo still has a fairly good selection of sheet films but the prices are bloody expensive these days. 25 8x10 Sheets of Ilford FP4+ is $102 about $4 per sheet. www.freestylephoto.biz
>
There's this outfit called Ultrafine that is apparently making films that other makers have discontinued. They have something that is supposed to be the same as the Kodak PRD for $83 for 12" x 100 feet!
I was afraid if I had to buy new film it would cost $1000 a box. I paid ~$350 for a box of 100 sheets of the Agfa film over a decade ago.
> Tell me more aobut you photo plotter. I always wanted to build one but never had the time. What did you use for the drum? How are you doing the pixel timing as the drum rotates? Are you using a rotary encoder or just timing from an index pulse. What RPM are you running?
>
OK, it has an ~ 6.5" diameter drum, spun by a DC motor with a PLL control at 10 RPS. An encoder picks up a clock and it is multiplied by 20 by a digital PLL to produce 20480 pixel clock pulses per rev. The emulsion of the film is at a diameter of 6.519" x Pi = 20.480"
So, that makes it 1000 pixels per inch. I have a stepper motor that moves the recording carriage at 1000 steps/inch for the other axis. So, it lays down 0.6" of raster per minute. A 6" wide plot takes 10 minutes, regardless of complexity.
I have been using this system since 1998. The software is now extremely obsolete. I originally made it plot directly from Gerber files to raster slice buffers and to the machine, as the raster files are REALLY large. (I was going to make it an 8-beam plotter, but never made that mod. So, it stores only one bit per byte. Each square inch is one megabyte.) A problem is that anything past Windows 95 needs a driver to deal with DMA transfers to an interface. In Win 95, you can do it all from user-mode. But, the memory environment in Win 95 is very cramped. What I do now is compose the raster files on a program in Win 2K, and then send the file over the net to the plotter computer, still running Win 95.
Eventually, the old computer will croak and I'll have to re-do it all under Linux.
> After I finish up my CNC mill project I want to build UV laser diode raster based direct PCB writer. Volkan Sahin has already done some testing with great results. This eliminate the film and photo plotting entirely.
>
I also use this setup to make master artwork for panel labels, and make many copies of those. So, at least for a while, I think I will stick with silver film.
Jon