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Full Spectrum Engineering 40W Hobby Laser

At Modern Device, we construct a lot of surface-mount printed circuit boards. The process involves putting paste solder on PCBs, and for that, you need stencils.

We were using the Epilog Mini 24″ laser at (Providence’s) AS220 Fab Lab, but it wasn’t convenient to go to the lab every time we needed a stencil, and it was more than inconvenient when the stencil was flawed in some way.

So we took what we knew would be something of gamble and purchased a 40W FSE hobby laser for about $2500 from Full Spectrum Engineering about a year ago.

We excitedly unboxed it, filled a bucket with water to cool the tube, hooked up the air compressor for air assist, aligned the head, fired it up, and… pushed the pulse button and got a large splat.

You can see from the odd teardrop shape that it looks like an optical system that is meeting its screen obliquely.

You can see from the concentric circles on the lens holder this photo how far off axis the inside lens holder was milled. It amounted to about .030″ – so some really sloppy machining. Full Spectrum Laser was entirely sanguine about the sloppy machining – assuring us that this couldn’t be the problem with the poor performance.

We milled the lens holder by hand with a dremel tool and a reamer. The optical path is still eccentric by about .006 but it seemed about as close as we were going to get by hand. Also since the lens holder was milled slightly larger, we assumed that the lens would self align with the mirror shaft above it as the lens holder was tightened. We also replaced the lens with a meniscus lens from Laser Optics & Mechanisms, about $100, rejecting the Full Spectrum $250 price for what was no doubt a much cheaper Chinese lens. Searching on Alibaba we found several firms offering to sell us Laser Cutter Lenses for as little as $12 each. The “shelf” in the lens holder needed to be enlarged just a bit to fit in the .750″ lenses on offer at Laser Optics. Our efforts paid off and the “splat” went away, as we saw our first clean dot since firing up the laser.

It’s definitely not an Epilog. The z axis isn’t motorized, so you have to twist a little nut to raise and lower it, which can be difficult (though FSE provides a file to laser-cut a plastic knob !?! ), and the bed is rather small (around 11 x 14  paper), but for 1/4th the price, it’s actually a reasonable deal.

The controller uses an XMOS chip and an FTDI chip for USB to serial, it’s running some proprietary firmware that will only interface with FSE’s RetinaEngrave software (Windows-only, based on dot net), and for almost a  year we had to stretch the y axis by .46% to get dimensionally accurate cuts. To Full Spectrum Laser’s credit they have improved the software and finally killed this bug. Our guess is that they also implemented microstepping on the stepper motors, which also has improved the minimum resolution.

The support from FSL has been a bit spotty — the bootloader on our controller died and we had to pay $100 for a new one.

Their forums at FSL are censored, so you may be better off discussing issues on the CNC Zone forum.

Their laser tubes are cheap though ($300) and we have yet to need a replacement (as of june 2012), here’s a pic of the tube:

Here’s an example of a Mylar stencil we cut with the laser:

We’ve made stencils with pads as small as .3mm pitch lead holes in them, but they don’t last forever due to the flimsiness of Mylar. We wet sand the stencils after cutting, with something like 600 grit wet-dry, to take the burs off the aperture edges. So far the laser cutter is doing about what we bought it for, so if it stays in good health for a year or two, I would say our bet will have paid off.

Some resources that we have found useful and interesting:

We’ll start a discussion group on our forum for people who might want to ask us questions about the laser. It might be easier than scrolling through lists of comments on WordPress.