ruffrecords

PCB mounting holes
« on: February 21, 2018, 05:05:46 AM »
How much meat do you need to leave around a PCB mounting hole to ensure it is strong enough?  I know it depends on the application but this is for static pro audio; not touring gear so vibration is not an issue. I have looked on the net but there seems to be no hard and fast rules. One rule I have seen is to leave one hole diameter between the edge of the PCB and and the edge of the hole. This means a 3mm holes would need to have its centre at least 4.5mm from the edge of the board. I have looked at several PCB design guidelines but none of them mentions this.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


shabtek

Re: PCB mounting holes
« Reply #1 on: February 21, 2018, 07:12:43 AM »
Number of mounting points, thickness and mass of pcb need to be considered--with the iron we might use we may deviate from some rules
"really fine players do not use stomp boxes or master volume, they match the amp to the room and turn it up to 11.  Stevie Ray, BB King, Albert King, Duane Allman, Dicky Betts, Louis Armstrong"
   -CJ

JohnRoberts

Re: PCB mounting holes
« Reply #2 on: February 21, 2018, 11:55:58 AM »
That really depends...

Massive components (like transformers) need their own attachment to survive typical shipping stresses. Jacks and connectors need their own attachment hardware to reduce stressing solder joints.  With PCB the material is also a factor in mechanical strength.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

ruffrecords

Re: PCB mounting holes
« Reply #3 on: February 21, 2018, 12:14:02 PM »
Number of mounting points, thickness and mass of pcb need to be considered--with the iron we might use we may deviate from some rules

In my particular cases there is either:

1. Lightweight iron (mic input transformer) but also card guides supporting the PCB. The mounting holes concerned are used to attach the PCB to the front panel via a right angle bracket.

2.  No iron and no card guides.

To put this into context, the DIN standard system for the Eurocards I use has an M2.5 screw to attach the front panel to the PCB via a small die casting that acts as the right angle bracket. The hole in the PCB is almost 4mm from the edge of the board leaving 2.75mm of meat. I have a new low cost scheme I want to use. If I implement this so it is compatible with the DIN standard then the PCB will be fixed by an M3 screw a mere 3.16mm from the one edge of the PCB which will leave only 1.66mm of meat. Not enough I think. If I disregard the DIN standard (which means changing the PCBs), my new low cost home-brew scheme will use an M3 screw with the hole 5mm from the edge of the PCB which will leave 3.5mm of meat, which is plenty.

All these different hole sizes and positions is what prompted me to ask if there any rules of thumb for this sort of thing beacuse I am pretty certain this is going to come up again.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: PCB mounting holes
« Reply #4 on: February 22, 2018, 06:35:53 AM »
Hello

I'll say leave at least the room for washer (and spacer) not showing outside pcb edge, even if you don't use some, just as a gauge.
M3 washer is about 7mm, putting hole at 3.5 from edge, which is 1.9mm meat from edge (for 3.2mm hole)
For M2.5, washer is 6mm, hole at 3, meat 1.7 for 2.6mm hole

Here, 2.5 holes is 2.84 from the 100mm edge and 5.64 from the 160mm edge
http://www.roth-elektronik.com/fr/produkte/detail/artnr/RE317-LF/category/Cartes+d%27+Exp%C3%A9rimentation+Dual+Inline?grid=2%2C54
Constrained by DIN41612 connector

Best
Zam

ruffrecords

Re: PCB mounting holes
« Reply #5 on: February 22, 2018, 07:39:49 AM »
HI Zam,

My Eurocard boards are just like that. The holes on the left for the DIN connector are very close to the 100mm edge but, once the 32 or more connections to the connector have been soldered, the screws have very little work to do. Also, the board is supported along its top and bottom edges by card guides.

It is the two holes on the right that are the ones that matter. They are used to connect the front panel to the board. They are 5.64 from the 160mm edge but they have been moved in further than the connector holes from the 100mm edge. They are 3.556mm from the 100mm edge rather than the 2.84mm of the DIN connector. This gives them 2.26mm of meat which is not far off the one diameter rule.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: PCB mounting holes
« Reply #6 on: February 22, 2018, 08:27:10 AM »
It is the two holes on the right that are the ones that matter. They are used to connect the front panel to the board. They are 5.64 from the 160mm edge but they have been moved in further than the connector holes from the 100mm edge. They are 3.556mm from the 100mm edge rather than the 2.84mm of the DIN connector. This gives them 2.26mm of meat which is not far off the one diameter rule.

I think originally front hole pattern copy back connector pattern so you can also have DIN41612 connector at front for service.
The math you just give is for M2.5 too at front side, don't you want M3 ? or I miss something ?
Anyway with M3 you should be fine too ?
3.56 centre will give you 1.96mm for 3.2mm(M3) hole

Best
Zam

ruffrecords

Re: PCB mounting holes
« Reply #7 on: February 23, 2018, 12:49:03 PM »
I think originally front hole pattern copy back connector pattern so you can also have DIN41612 connector at front for service.
The math you just give is for M2.5 too at front side, don't you want M3 ? or I miss something ?
Anyway with M3 you should be fine too ?
3.56 centre will give you 1.96mm for 3.2mm(M3) hole

Best
Zam

I don't know if originally the front was the same as the back but here is the current spec taken from the Vero catalogue:



The holes are the same distance from the 160mm edge as the connector holes but they are further in at the front. Hole diameter is2.7mm so it is definitely not a 3mm screw (all the front panel mounting hardware you can buy is designed for M2.5 screws).

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

buildafriend

Re: PCB mounting holes
« Reply #8 on: March 04, 2018, 12:30:52 AM »
I tend to make my holes for a 6-32 screw and I plan their positions around the heaviest parts (xfrmrs) or near headers that might get tugged on. the width of my standoff pads are usually the same as the hole size unless it's getting squeezed. I also like mostly nylon stand offs and then sending the ground home on one metal standoff

abbey road d enfer

Re: PCB mounting holes
« Reply #9 on: March 16, 2018, 02:27:43 AM »
How much meat do you need to leave around a PCB mounting hole to ensure it is strong enough?  I know it depends on the application but this is for static pro audio; not touring gear so vibration is not an issue. I have looked on the net but there seems to be no hard and fast rules. One rule I have seen is to leave one hole diameter between the edge of the PCB and and the edge of the hole. This means a 3mm holes would need to have its centre at least 4.5mm from the edge of the board. I have looked at several PCB design guidelines but none of them mentions this.

Cheers

Ian
There's no hard rule. In terms of mechanical constraints you need to build it and see if it withstand the efforts you impose. Very often, different factors will decide. At Soundcraft, the distance was 5.08mm, because that's what the auto-place machnines wanted for the positioning holes.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.