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Messages - Zuph

1
General discussion / Re: One more PCB fab house - Cheap stencils
I just got back some 2-layer PCBs and a PS-303DM power supply:






The power supply appears to work well.  I tested it through its range with a multimeter, and put a couple of resistor loads on it, and it was as accurate as my crappy radioshack meter, at least.  It's a little on the light side compared to similar power supplies, but for under $50, I can't complain at all.  The switch on the back was set to 220V when I took it out of the box, so that's something to look out for.

The PCBs are fine quality.  They aren't anything special, since they're for a through-hole kit I'm thinking about selling on Tindie, but the drill hits and solder mask are at least as accurate as seeed studio, if not a little better.  I ordered 10 and received 12, but one of them had a pretty bad scuff-mark from shipping.  The bundle of PCBs was stuffed against the side of the box with just a thin layer of bubble-wrap.

For the price, I'm happy.  Shipping was a little on the pricey side ($40), but it arrived just 5 days after shipping, a week after I placed the order.  If I'd had a choice for cheaper shipping, I would have picked it, but with the heavy power supply, I wasn't able to choose slow shipping.
3
Project development, ideas, and suggestions / Re: A stencil8 PCB tooling block for doing solder paste sten
[quote author="bearmos"]That certainly sounds reasonable. So was the issue getting the bit centered when starting the hole (which the center drill should help greatly) or actually drilling it? Also, 10k at 5IPM will probably generates quite a bit of heat because of the super light chip load - (not so good for the HSS bit)?
[/quote]

Unfortunately, the mill was built for milling wood, so I don't have a reliable way to get the spindle speed below 10k RPM.  I did use cutting fluid.  On all the holes, the drill hit was sloppy, but as it drilled down, it approached the "true" diameter.  Unfortunately, the holes are shallow enough that this still allows some play in the dowel pins.  A bigger problem is that the drill hit would occasionally skip all over the face of the block, resulting in even higher thrust loads, resulting in skipped Z-axis steps.  This happened on 2 holes in the block shown.

The drill press idea is interesting.  I may give that a go if milling delrin goes down-hill.  I do have access to a fairly nice (if ancient) drill press.
4
Project development, ideas, and suggestions / Re: A stencil8 PCB tooling block for doing solder paste sten
In my (also very limited) experience, Delrin is quite a bit easier to cut than aluminum.  This is a homebrew mill setup, designed and built by someone with a lot more experience in machining than I'll ever have.  The bit I used for aluminum was a coated HSS, 2-flute end mill recommended for drilling operations.  Feed speed was 5 IPM, spindle speed was ~10k RPM.  I was using a peck drill cycle, going 1/32" at a time.

The biggest problem is that the mill has a bit of slop in the Z-carriage when placed under high thrust loads. The result is that bit would skip around on the surface when penetrating.  With the delrin, I ordered a bit which claims superiority in drilling plastic.  Hopefully the reduced hardness of delrin (compared to aluminum) will mitigate this problem.  If that doesn't work, I'll order some center-drills, and indent the surface before the drilling operation.
6
Tools of the trade / Re: Cheap Solder Paste
Shipping in the US is on the expensive side of reasonable, about $15 (I've never bought enough stuff at one time to bump the shipping above that).  Shipping internationally is pretty pricey.
10
Project development, ideas, and suggestions / Re: Simple programmable load
I'm working on a nearly identical, but more complicated programmable load. I intend to include voltage and current sensing, fed back into an AVR controlling the load. A teeny scripting engine on top will allow the user to program various loads and duty cycles.