What to do when component drawings are incomplete or wrong - Page 1
Forum section: electronics / projects

author: admiralk
author_rank: Regular Contributor
timestamp: November 20, 2022, 05:08:50 pm
content: For my project I am using several PCB mount cable connectors and started to make the footprints. The first one is for this TRS socket:https://www.neutrik.com/en/product/nj3fd-vStart with the R and S pads, no problem. Place the T pad and the only x offsets I can see are for the 2 holes. OK place those and am all set except for where they go in x. They provide a cad drawing, so I should be able to use that, but that is completely wrong.I really need a center mark for this as well since I do need to line up a hole in the case also. I was assuming the cross in the drawing is the center, but at this point am not sure. Maybe I could get a better drawing from a different brand, but really want to use Neutrik. So, how can I get these dimensions without actually buying the parts first and hoping I can get accurate enough measurements from them?

author: jmelson
author_rank: Super Contributor
timestamp: November 20, 2022, 05:48:34 pm
content: This drawing is just palin WRONG! The top 2 dimensions are totally in conflict, one of them must be the missing link between some of the other floating dimensions.Jon

author: wraper
author_rank: Unknown
timestamp: November 20, 2022, 06:10:31 pm
content: Their drawing misses a single dimension. For some stupid reason component drawings often lack a dimension between something located in center and pads/holes symmetrical against it, and then you need to guess.

author: admiralk
author_rank: Regular Contributor
timestamp: November 20, 2022, 06:21:22 pm
content: Sorry, the top one I put in, in autocad that is why I said the dimensions are wrong in the first place. If it matched the one provided, I could easily go off the cad drawing alone. I assume the dimensions they provide are correct, so the drawing is not to scale, which kind of defeats the purpose of providing a cad drawing in the first place. I suppose I could try and figure out a scale factor from the given dimensions, but I have a feeling they will not all match.Wrapper, I get 8.8876 or something close to that for that dimension. 5.08 sounds about right, and I see where you got that from. That might be a good enough guess so that I can bend the pins a little if I have to and maybe make the holes a little bit bigger.Yes, I think you are right. I get the same dimension from the center line to both the R and S pads.

author: tooki
author_rank: Super Contributor
timestamp: November 21, 2022, 09:27:27 am
content: Quote from: admiralk on November 20, 2022, 06:21:22 pmHuh? I don’t see what’s confusing, other than them forgetting the 5.08mm wraper drew in for you.The Neutrik drawing is clear about the scale: 3:1 for everything except the footprint, which is at 5:1.Regardless, this is why I am now fastidious about placing the 3D models into my PCB designs*: if a component doesn’t fit onto its footprint, it’s very obvious, especially for THT parts. So it adds a layer of certainty. (And yes, before you ask: I have indeed run into a manufacturer publishing the wrong model for a part. But whenever you encounter a discrepancy, you’ll want to carefully review everything.)*more precisely, into the component footprints, so that they are already ready for any future projects where I might use the same part

author: ajb
author_rank: Super Contributor
timestamp: November 21, 2022, 11:07:11 pm
content: The drawing really ought to have a proper centerline to make it explicit that the T pin is centered and the S/R pins are symmetrical about it. If you look very closely at the PDF you can actually see that right about where wraper drew in the 5.08mm dimension there's a join between the extension line from the existing 3.18mm dimension and what is actually the vertical line of a center mark. Looking at the other views in the PDF confirms that the center cross in the footprint view is the same center as shown in the mechanical and panel cutout views--or more pedantically, that all of those center marks are on the longitudinal center axis of the part.Quote from: admiralk on November 20, 2022, 06:21:22 pmYou have to be careful adding dimensions to DXF/DWGs from other people. Often these are exported from a 3D CAD package and the resulting dimensions can have scale factors applied in multiple different places depending on how the source drawing was structured, the whims of the designer, and the vagaries of the DXF/DWG exporter. If you want to be able to work with the CAD objects in modelspace--whether to take dimensions, or to create additional drawings from it, you should first double check if the dimensions are true to the drawing scale or not. A simple DIST between extension lines of any given dim will do. If not, I would recommend scaling the whole drawing to 1:1 first. Fortunately this is super easy in AutoCAD: select all, SCALE, set the basepoint, hit R for Reference, select the endpoints of a dimension as your reference length, then type in the actual indicated dimension. This will make all of the existing dimensions wrong, but that's okay, they weren't to be trusted anyway, so you can delate them and then take whatever new dims you need.To answer the more general question, comparing to available 3D models helps, or you could contact the manufacturer and ask for clarification, or honestly, if it's a part you can get one of off the shelf right now (as opposed to something special order or with a massive MOQ), sometimes that's the most reliable option.

author: admiralk
author_rank: Regular Contributor
timestamp: November 22, 2022, 12:48:29 am
content: Thanks for the autocad tip. I did not notice any scale references in the drawing, but did not look for any in it either. What little I learned about working in autocad is to draw to actual dimensions and scale in the plot. wrapper got me squared away. I really need more sleep and new glasses.

author: DBecker
author_rank: Frequent Contributor
timestamp: November 22, 2022, 07:05:43 pm
content: The drawing does appear to be wrong, but keep in mind a production drawing for a machinist will have a different emphasis than what you care about for a PCB layout.The production drawing will typically care about a reference plane/axis/centerline. The jack assembly needs to be symmetrical along the insertion axis, and so the dimensions will be specified from that axis to avoid stacking. It's more important that the contacts are symmetrical around the centerline than matching a specific value.That comes through in the drawings for the pinout, with some modifications. For the ring and sleeve pins, the drawing indicates that the forming operation for those pins sets the spacing at 0.400". The underlying structure results in them being about 0.2" from the centerline, but that's only controlled by the overall tolerance spec. Of course for the PCB layout we only care about the tolerance from the reference pin -- we need both pins to be about 0.20" from the centerline. It isn't useful to know that if one is 0.198" that other will be spaced 0.202"