Printed circuit board jig

Carvey
1

I’m designing a jig for milling PCBs. I’ve seen a number of PCB jigs already but I’ve decided I’m going to:

  • start off with a 1/2" thick 8"x12" sheet of acrylic
  • mill it flat so its surface is flat and level with the carving bit
    (CHEP posted video where he milled a piece of wood flat for this and I thought it was a good idea (CNC Prototype Printed Circuit Board Milling on $399 Sienci Mill One - YouTube))
  • mill out rectangular indentations for a 2"x3" and a 4"x6" copper PCB blank
  • mill out offset holes in each corner, making them slightly deeper than the PCB blanks (just a gap so a finger can get in and lift the PCB up)

Here are some images:

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I’m also going to 3D print some clamps to help keep the PCBs in place (I don’t want to use double-sided tape). The holes are for 8-32 thumbscrews.

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Here’s my dilemma: I haven’t decided yet on how I’m going to tighten the thumbscrews.
So far, I’ve come up with the following options:

  1. Flip the sheet of acrylic over and mill out hexagonal-shaped holes on the bottom face and use 8-32 hex nuts. These are pretty small, and requires a lot of accuracy (both front and top will need to match, and it seems like a tight tolerance)
  2. Flip the sheet of acrylic over and mill out holes slightly bigger than the 8-32 hex nuts, and then use epoxy to keep the nuts in place and keep form turning as the thumb screws turn through the threads.
  3. Forget nuts altogether, and tap the holes in the acrylic for 8-32 threads. I’ve only worked with acrylic a little, and I’ve heard that it can easily crack, though if I do go this route I will be tapping the holes manually by hand, and will be going slowly.

That’s what I’ve come up with so far, and I was wondering if anyone here has a better suggestion for what to use to tighten the screws.

Thanks,

Jeff

3

Be aware that no matter how flat you make your spoilboard, those pcb blanks usually have some warp in them. If you plan to use a V bit, that matters.

4

What about a heat set threaded insert? They’re pretty easy to use with acrylic.
If you’re open to it, I’d consider using HDPE for the jig.

Like @xfredericox mentioned, plan on some sort of autoleveling if you’re doing stuff with a really fine pitch.

@AngusMcleod Can you expand on your magnet suggestion? Embedded magnets?

6

Ok. That makes sense. I thought you were responding to the “how to tighten the screws”.

7

I use M3 T-nuts on my small jigs in MDF, would work on 1/2" acrylic if you removed the spikes.

8

Even simpler. Just tap the acrylic to the needed size. I’ve done it on projects. On a nice and thick piece of plexi it will take a thread nicely.

9

Looks like a good candidate for vacuum hold-down aswell :slight_smile:

10

Thanks Angus! I normally don’t work with magnets so it didn’t occur to me, but that’s a great suggestion. I think I’m going to try the tab and screw approach first, but if doesn’t work out I’ll go with “plan B” and use some rare earth magnets.

11

plan on some sort of autoleveling if you’re doing stuff with a really fine pitch.

I don’t plan on doing anything with QFP or anything that’s super fine - SOIC is probably the smallest I’d ever go. I plan on planing the top of the jig, so everything will be autoleveled.

Thanks,

Jeff

12

Even simpler. Just tap the acrylic to the needed size. I’ve done it on projects. On a nice and thick piece of plexi it will take a thread nicely.

Thanks Phantom, I decided I’m going to try this approach first. I was mostly concerned with the brittleness of acrylic, and thought tapping holes might be too much. Glad to hear you’ve done it before & it’s a viable option.

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14

If it’s cast acrylic then it’s a lot more forgiving than extruded acrylic especially with threading in my experience.

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