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PCB UV exposure box

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AdeV:
So... thinking about this scientifically  :lol: - on the underexposed one, the overexposed white blobs are about 7.4mm diameter. The tops of the LEDs are about 4.8mm diameter, and the lens sits approximately 7.5mm above the PCB which is 1.6mm thick. The light board slot is 16.2mm below the glass guide slot, giving a total lens-to-glass clearance of (drumroll) [wait, I need the calculator for this....] 7.1mm. Ish.

So... cranking that all around the ole' grey matter (with a piece of paper and this post as a reference guide!), we can arrive at the conclusion  :scratch: that the light has spread from the top of the LED by 2.3mm in total, i.e. 1.15mm on each side (if a circle had sides). So now it's a simple  :palm: geometry job to find the angle of spread to find the minimum height difference needed to give full coverage & no dark spots - although without a frosted lens, it'll still be a bit brighter in a grid pattern, unfortunately, unless I mount the LEDs in the other room....

So, the angle of the dangle times the mass of the ass equals the heat of the meat - as they say, but actually we need a bit of Pythagoras here, so we'll go with that instead. In this case, TOA: Tan = Opposite over Adjacent, or 1.15/7.1 = 0.162ish; arctan of that is 9.2 degrees. Since that's only half the angle, double it and add 2(ish) to get about 18 degrees. Which is actually slightly better than the 15 degrees I vaguely remember the data sheet said; but that could be measurement error.

Last but not least, we need to cover the whole area with light - and now, my maths basically runs out, so it's google o'clock to find out what the minimum gap I need between lens & workpiece to get full coverage. Then, once I've fixed the blasted spindle brake, I'll make some new slots in the box, machine up an acrylic top to replace the shonky glass, and try again!

For a laugh, see the attached calculation sheet...

AdeV:

--- Quote from: seadog on January 02, 2019, 01:32:32 PM ---..."mix up some Cupric Chloride acid to etch the copper"

Don't you mean ferric chloride?

--- End quote ---

Nope - I haven't got any ferric chloride; and given my production rate, I'd need to buy more every time I wanted to etch a PCB. Cupric Chloride is a mixture of HCL + Copper (and a little peroxide to get things going initially), has an unlimited shelf life, and just occasionally needs a top-up of acid to keep it going. It's a bit slower than ferric, but a shedload less messy, and better still I've got all the components on the shelf to make a batch  :thumbup:

Brass_Machine:
Hi Ade!

Nice looking solution so far.

I have been away slightly because I have been working on shiney stuff... IE Jewelry. I just made a UV bath for curing UV Epoxy. Not sure how it would work for you. It does have set timers... 120 seconds, 180 seconds and 30 minutes.

I took 2 inexpensive UV nail cure machines that are used for curing finger nails. They are U shaped. Connected them together to form a 360 degree UV bath.

Eric

AdeV:
Hey Eric,

Looks interesting! I presume you drop a glass/plastic container holding your cleaning solution + dirty things in there to be nuked/teleported?  :lol:


Anyway, I did some back-of-the-envelope Googling/maths, and arrived at the conclusion that I need ~ 38.5mm between the top of the glass and the LEDs to get 100% definite coverage. This is fine in the bottom of the box, where I have nearly 70mm height to play with; my current design has the lid section only 40mm deep. So... I need to revise that slightly & split the difference between the lid & the base. But for now, I'll just try to get it working with the one side. Hopefully.... this weekend coming, as I'm back to work tomorrow.

tom osselton:
Just thinking could you not oscillate the led rack to manage the uv coverage?

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