[tutorial] Test fitting Footprints


#1

Hi everybody,

not a question, but I just want to share how I test fit footprints.
It’s a combination of a few things to make it work perfectly.

The first step is to print a PCB mirrored on a piece of Paper:
PcbNew -> File -> Print -> Options Mirror -> Print.

2nd step: Take a needle and pre-punch all the mounting holes into the paper.
(For the large holes I used a hole punch).

3rd step: Carefully put the connector into the sheet of paper.

4th step: Take a picture or scan the whole contraption with a flatbed scanner.
This makes it easier to see small deviations than with the naked eye.
If you also put a ruler into the picture you can use that (or the known distance between 2 pins) to calculate corrections for the next iteration.

The trick is to print the mirror image. This will ensure that you can take a picture of the connector pins and the PCB layout in the same picture. See below.


#2

It’s a good tip, we use it at work. Although now we rely more on MCAD, and can also 3d print board and components, for space models.

I wonder if anyone has tried 3D printing a board for the purposes of test fitting? (Not for actual use).

I wonder why I haven’t tried it… I should :slight_smile:


#3

Seems like a bit of overkill. Just get a piece of material, such as blank FR4, and drill holes in it.


#4

Seems like a bit of overkill. Just export to STL, and print it.


#5

Save the standard drill file and drill it, done in about 60 seconds for 10 holes including a tool change. :wink:


#9

Please be a bit polite to each other.
This little tip obviously was not ment for the guru’s with an in house fab but more for the hobbyist who is anxious to get his first pcb outsourced and has to wait a month for shipping because he’s not willing to pay the fee for same day delivery.

@bobc:
If you ever get around printing a pcb for test fitting connectors I’d like to see a picture of that here. Maybe even add a little tutorial of how you get the data from KiCad to your 3d printer?
I don’t have a 3d printer, but I’m betting on getting a mini CNC milling machine going within a few months


#10

I think the main problem would be that it’s difficult to get the resolution for small holes, so those would probably need some clean up. I have code to convert VRML to STL, so I might adapt that.

It is not necessary to have a 3d printer, there are 3d printing services, but obviously not as convenient as in-house. I have also got a small CNC, but don’t have a good place to use it, so it gathers dust.

For cutting flat sheets, a laser cutter might be better, that’s a whole other thing…


#11

Kicad Stepup (freecad extension) should do the trick. (or direct idf export.)
Maybe reduce the board thickness settings in kicad. You don’t need 1.6mm material thickness for this application. 0.5mm should be enough. (Kicad stepup uses this setting to define how thick the board body will be.)

From freecad you can then export a stl file which should be usable by 3d printers. (As i remember 3d printer slicers use stl files as input. If they could use step, that would be even better.)


#12

The printed image has to come out at a fairly accurate 1:1 scale. Between the rendering to a *.pdf document, then printing a hard-copy on a home or office printer, accurate scaling is not guaranteed . You may have to play with printer settings to get accurate 1:1 scaling.

Dale


#13

I did not intend to be impolite and hope I didn’t come across as such, but I also don’t smoke! :slight_smile:


#14

Please stop sniping at each other.

I thought that 3D printing had a small shrinkage problem, so no better than most paper printers


#15

Yes, I think a well calibrated laser printer would outperform a 3D printer, certainly the cheaper FDM ones. SLS or resin might be better, but those are expensive. At work we use an SLS printer for creating space models of enclosures and assembled PCBs.


#16

Thanks to @paulvdh, this was a nice topic actually.

Please keep things constructive around here, folks.


#17

Moots should be cooler now… :wink:


#18

I usually test-fit footprints with my own 3D models in the 3D viewer.
Naturally, if I make the same mistake twice I’m screwed :grin:


#19

3D printing is not that expensive today.

A defense contractor would actually cut and glue wood pieces to 3D model assemblies.

Not to long ago, that DC had a very similar part 3D printed.

I think it was done as a “sanity check”; so that a something simple mistake did NOT create a massive production failure later on.


#20

Hi @paulvdh
if you need to check a new footprint versus a connector, you can have a good feed back following this method:

  1. get the 3D STEP model from the connector manufacturer (this is generally available from good manufacturers)
  2. open the STEP model in FreeCAD
  3. in FreeCAD launch the StepUp Macro and load the kicad footprint you want to check using the macro
  4. align the model to footprint using the StepUp buttons and/or FreeCAD Assembly2 workbench ()
  5. check pins and anchors in a mechanical environment where you can check measurements and eventually collisions (an other StepUp function)

here an example of what can be done with FreeCAD to create a mate+ing footprint to a connector


#21

What would be useful would be to “print” the 3D modelled assembled board


#22

That is what I meant; the board and all components assembled on the board.


#23

It is a very nice way to test footprints. I always make a print and test it this way before production. Works also very well with smd parts. Especially with smd parts you can quickly mess up if you selected the wrong footprint for it. (especially the wide vs narrow footprint versions are killing).
With through hole pay attention to the drill / hole size as well!
Set the print settings to ‘Real drill’ in kicad:

Would be a shame when the holes are too small for the part :wink: