Measurement tools - Page 1
Forum section: electronics / general

author: alamwte
author_rank: Regular Contributor
timestamp: April 17, 2022, 04:58:38 am
content: Hi,I have a little PCB board with about 12*27 mm width that I want to design a box for it. I need to measure its width and the diameter of its holes and the accurate location of these holes.I have used a digital Calipers but It is not easy to masure hole location and it is not acuarate enough for width measuring too.Which tool do you recommand to me ?I attached some similar board photos below.Thanks.

author: pqass
author_rank: Super Contributor
timestamp: April 17, 2022, 06:28:13 am
content: It doesn't look too thick. Try to make a photocopy (cover with a white paper sheet if you can't use the lid).Then markup and measure the photocopy with digital calipers like these:https://makezine.com/2015/11/13/how-to-use-your-digital-calipers-7-tips/Derive w/h scale factors (likely very close to 1/1) by measuring width/height of actual PCB vs the photocopy width/height.

author: eugene
author_rank: Frequent Contributor
timestamp: April 17, 2022, 08:15:52 am
content: I don't understand why/how digital calipers can't do what you need. Certainly outside dimensions of the PCB are trivial to measure with calipers. The inside diameter of a hole is also simple using the side of the caliper meant for inside measurements. To determine the location of a hole relative to an edge, measure the distance to both sides of the hole - side nearest to the edge and side farthest from the edge and average the two to find the center.I could probably perform a web search to find caliper tutorials online, but you can do that just as well.

author: Ian.M
author_rank: Super Contributor
timestamp: April 17, 2022, 08:46:51 am
content: Digital calipers tend to do a really crappy job measuring the diameter of small holes due to the offset between their inside jaws so they can slide past each other. While you *should* have a set of precision adjustable hole gauges for transferring inside diameter measurements for readout with a micrometer, few of us who aren't trained machinists have them.One quick & dirty approach is to compare the hole to the shank end of a selection of plain drill bits (i.e. ones where the diameter at the cutting edge is the same as the shank). This is typically good enough for fixing holes. A more accurate measurement can be made with the aid of an appropriately sized taper pin. Insert the pin in the hole till it just stops, without forcing it, and use a fine tip Sharpie or similar to mark round the pin at the board surface. Check the pin in the hole inserted from the other side in case the hole is tapered, then remove it and use the calipers to measure the pin diameter at the edge of the mark where the board surface was.N.B. if the hole is significantly bell-mouthed or chamfered this will over-estimate its diameter.If you can see a visible gap between the mark you made and the circle of contact, try to compensate for it when measuring the pin diameter.The same pin inserted a bit more firmly in the hole can be used as a stop to allow measurement of distance from the board edge to the hole, using the caliper's depth probe. Don't forget to add half the diameter to get the distance from the edge to the hole center.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: April 17, 2022, 05:34:19 pm
content: When doing stuff like this, I take a photo of it with a ruler in frame. Then I import the image into Solidworks (or whatever you'll be designing the enclosure in) and use the ruler for calibration (Solidworks has a dedicated tool for this).

author: jpanhalt
author_rank: Super Contributor
timestamp: April 17, 2022, 06:44:52 pm
content: Measuring on FR4 is inaccurate because of the FR4 and probably not because of your calipers. Unless you don't know how to use the calipers.Hole diameter: (outside dim. - inside dim.) /2 = hole diameter. Because FR4 is so inaccurate (relative to measurements on machined surfaces), I just use a drill to estimate hole diameters. With Imperial, I have a set of number, inch, and letter drills. A similar set for metric should work as well. Since most are probably drilled with metric drills, a good set of metric should get you close.EDIT: Be sure to use the drill shank as the plug gauge, not the cutting end. Measure the shank to be sure it is close enough to the labeled diameter of the drill.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 17, 2022, 06:55:05 pm
content: If you don't have a flatbed scanner, take a few closeup photos near a marked ruler, then measure by counting the pixels (coordinates) at high zoom on a PC.

author: Ian.M
author_rank: Super Contributor
timestamp: April 17, 2022, 07:24:17 pm
content: The board must be coplanar with the ruler and its long edge as near parallel as possible. You then have to compensate for various sorts of lens distortion (a sheet of squared or graph paper as a background helps) and to avoid parallax distortion and minimize lens distortions you need the center of the lens to be near-exactly over the center of the PCB at as great a height as you can reasonably accommodate, e.g. by inverting the head of a full-size tripod so the camera can look straight down.

author: nctnico
author_rank: Super Contributor
timestamp: April 18, 2022, 12:07:55 am
content: Quote from: Ian.M on April 17, 2022, 07:24:17 pmIOW: Take the picture from a distance and use the optical zoom of the camera to get a close-up.

author: bson
author_rank: Unknown
timestamp: April 18, 2022, 04:34:34 am
content: Fusion360 (and I would presume most other CAD tools) have a feature where you put an image (canvas) behind a sketch. You calibrate the scale by including e.g. a ruler in the image and then telling the software that "this is 50mm between these points". You can then draw a sketch based on the canvas, which you can extrude into a 3D shape like normal. I've used this for random PCBs, to 3D print enclosures and custom brackets, and it works well enough. Just make sure the camera is level to avoid keystoning.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 18, 2022, 05:13:24 am
content: There is art to using any of the techniques mentioned above. With proper technique the digital calipers can do the job. You can read tutorials but all of the methods will require practice and thought to get good results. Each has pitfalls that can result in large errors.

author: rteodor
author_rank: Frequent Contributor
timestamp: April 18, 2022, 05:47:13 am
content: Quote from: alamwteMilimetric paper, a stand and a lamp or a flashlight at a far enough distance (1,5 ... 2 meters).

author: eugene
author_rank: Frequent Contributor
timestamp: April 18, 2022, 04:23:49 pm
content: The OP wants to make a box to put the little PCB into. Not much precision or accuracy is required.The outside dimensions only need to be accurate enough that the box not be made too small.The diameter of the mounting holes need to be accurate enough to decide what size screws to use.The locations of the mounting holes needs to be accurate enough that the screws do not bind. If there is uncertainty, then choose a smaller mounting screw to provide clearance.This is not a demanding task and can be completed with calipers in less time than it took me to write this post.OP: post several clear photos of the board flat on a table with a millimeter or inches scale along side. Someone here (maybe me) will determine all of the needed dimensions from the photo.Also, please state the manufacturer and model of the device. It's not uncommon for the manufacturer to provide detailed drawings of things like this.

author: alamwte
author_rank: Regular Contributor
timestamp: April 19, 2022, 09:00:42 am
content: @pqass @evb149 @eugene @rteodor @CatalinaWOW @bson @nctnico @Ian.M @RoGeorge @jpanhalt @Domagoj T @eugeneThank you all to giude me.(I had this problem for a long time.)