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View Full Version : Riveting pcb holes - engineering type input sought!



HankMcSpank
15-04-2015, 04:34 PM
Long time no post how you all doin'?!!! :-)

I need your input!!

I've a little widget that I used to make ...basically a pcb with 2 x m3 holes tapped into it ....it's looking like that I'm going to have to dust it down & start selling again (sigh).

Problem: Tapping M3 holes directly into 1.6mm thick pcb is not strong enough (especially since I use paper based FR2 board vs. fibre glass based FR4...this is because FR2 is a whole lot cheaper & presents a far nicer grade of dust for inhaling when I mill it!) .....at the moment I tap the m3 holes, & put nuts onto the screw behind to reinforce the hole - not ideal). So I need a more robust way of reinforcing the holes in the pcb.

These self broaching nuts initially seemed a good option....http://www.rapidonline.com/mechanical-fastenings-fixings/affix-self-clinching-nuts-m3-type-2-pack-of-50-33-3802 .. except the hole has to be 4.2mm to receive those nuts ....and they have to be a couple of millimetres away from the board edge (not sure I understand their "Min. radius thickness from sheet edge" ...is that to the edge of the nut or the centre of the nut?) ...this last bit is the deal breaker (I can't move the holes, and with a 4.2mm hole to receive those nut, it'd be too close to the edge of the pcb...it'll probably crack when inserting the nut under pressure).

ok, second option, re-inforce the hole with a rivet, so I was looking at these copper rivets...

http://www.aliexpress.com/store/product/500pcs-lot-High-Quality-M2-5-d-2-5-L-mm-2-5mm-Brand-New-Copper/1255111_32271034053.html

their hole is 2.5mm diameter ...bearing in mind I need an M3 tap, that seems in the ballpark, but I then worry how much of the rivet would even left after the M3 thread was tapped inside it??

My main problem though is how do you even crimp something like that? (it'd need a die /punch of some kind or other, but I can't even begin to work out where I'd source one from?!!)

Cheers in advance!

Jonathan
15-04-2015, 08:57 PM
Slightly off off topic, but have you considered getting the PCB manufactured? It's pretty cheap in China.

You can get riveting tools to use as a method for making vias in PCBs, but they're too small. Maybe something to imitate.

Instead of riveting, perhaps you could use a lathe to machine your own insert from brass and solder it to the board on both sides, or would that not be strong enough?

HankMcSpank
15-04-2015, 09:05 PM
Hi Jonathan...thanks (as ever) for the input.

Truth be told, I don't trust Chinese fab houses.

This is fairly low run....I'm probably talking 40pcs maximum per annum .....it only takes me about 15 minutes to mill 10 nested copies of my pcb layout, therefore just over an hour to mill one years supply of the pcbs needed!

Actually, I think I've found the tool I need....

http://www.mouser.com/ProductDetail/Keystone-Electronics/1714/?qs=pkhVRPZ8ecAI7P8SqT5kVQ%3D%3D

which crimps these eyelets.....

http://www.mouser.com/Search/ProductDetail.aspx?qs=g5fiFmky%2fl452QtP4fbZOg%3d% 3d (1/8" ....they'd probably do for M3)

The rivet press for riveting thru hole rivets for PCBs costs about 500!

Re using a lathe...I don't have one, & that sounds time intensive (& I'm trying to get the time down to build one of my widgets....it already takes me about 1.5hrs (I'd rather use something already available & cheap as chips...hence looking at brass/copper rivets/eyelets) ....also I suck with a lathe

(Incidentally, I've found a cheapskates method for PCB stencils....from drinks cans! https://www.youtube.com/watch?v=JWUJtmgh55M .....except he's etching, that could readily be milled)

cropwell
16-04-2015, 10:07 AM
I read your requirements about position of the hole and I thought maybe a steel M3 riv-nut could be soldered into the PCB. The one I have are 4.7mm OD and 8.7mm long. I have the mandrel for the setting tool, but they are fragile and hard to come by, but it sounds as though setting them in the PCB would not be an option anyway.

mekanik
16-04-2015, 02:58 PM
Looks like the best option is going to be soldering to the board, i would get some 2 or 3mm brass plate cut off a strip drill and tap several holes and the cut it to a length that dives you a reasonable surface area, then solder it to the board.
You could do the drilling on your cnc and knock off a bath in a reasonable amount of time.
Regards
Mike

Boyan Silyavski
17-04-2015, 01:20 AM
Any leather eyelet pliers will do the job and if they don't reach, then refabricate something similar with longer reach from them . If it was me i would simply instant glue each side a washer. If the glue is good it would stick forever.

Plus, nobody could convince me that the PCB eyelet which they sell for 10cents is not in fact leather eyelet.
http://www.mycncuk.com/attachment.php?attachmentid=15153&stc=1

http://www.mycncuk.com/attachment.php?attachmentid=15154&stc=1

i2i
18-04-2015, 01:40 AM
Long time no post how you all doin'?!!! :-)

I need your input!!

I've a little widget that I used to make ...basically a pcb with 2 x m3 holes tapped into it ....it's looking like that I'm going to have to dust it down & start selling again (sigh).

Problem: Tapping M3 holes directly into 1.6mm thick pcb is not strong enough (especially since I use paper based FR2 board vs. fibre glass based FR4...this is because FR2 is a whole lot cheaper & presents a far nicer grade of dust for inhaling when I mill it!) .....at the moment I tap the m3 holes, & put nuts onto the screw behind to reinforce the hole - not ideal). So I need a more robust way of reinforcing the holes in the pcb.

These self broaching nuts initially seemed a good option....http://www.rapidonline.com/mechanical-fastenings-fixings/affix-self-clinching-nuts-m3-type-2-pack-of-50-33-3802 .. except the hole has to be 4.2mm to receive those nuts ....and they have to be a couple of millimetres away from the board edge (not sure I understand their "Min. radius thickness from sheet edge" ...is that to the edge of the nut or the centre of the nut?) ...this last bit is the deal breaker (I can't move the holes, and with a 4.2mm hole to receive those nut, it'd be too close to the edge of the pcb...it'll probably crack when inserting the nut under pressure).

ok, second option, re-inforce the hole with a rivet, so I was looking at these copper rivets...

http://www.aliexpress.com/store/product/500pcs-lot-High-Quality-M2-5-d-2-5-L-mm-2-5mm-Brand-New-Copper/1255111_32271034053.html

their hole is 2.5mm diameter ...bearing in mind I need an M3 tap, that seems in the ballpark, but I then worry how much of the rivet would even left after the M3 thread was tapped inside it??

My main problem though is how do you even crimp something like that? (it'd need a die /punch of some kind or other, but I can't even begin to work out where I'd source one from?!!)

Cheers in advance!How about soldering 3mm brass nuts to the top or bottom of the board.

HankMcSpank
18-04-2015, 02:38 PM
Thanks guys....great input. I can't solder brass nuts, because it a single sided board ....and the solder side is on the wrong side for the nut to go on :-(

silyavski ...I'd forgot that I've actually got one of those tools lying around somehwre (probably in my loft), I'll dig it out & give it a go!

mekanik
19-04-2015, 10:47 AM
Although the link to the intended rivets gives a reference (h) for the wall thickness the seller does not specify a size. Thread depth for 3mm thread is 0.3mm so it is going to have to be about 0.5mm wall thickness to give you a bit of lee way.
Can to send a quick sketch on how you need to use the holes for fixing and why you cant solder a nut/plate to the board.
Regards
Mike

HankMcSpank
20-04-2015, 07:42 PM
Can to send a quick sketch on how you need to use the holes for fixing and why you cant solder a nut/plate to the board.


For now, I'd rather not post my drawings, but I can't solder a nut becuase like I say it's single sided pcb ....and on the copper side of the pcb, the enclosure will be butting up against the pcb surface.....if I soldered a nut on that particular side, then there's be a gap equal to the height of the nut that was soldered onto the pcb (which would look awful)

mekanik
20-04-2015, 08:24 PM
Sorry can't see your logic there, even if you use the hollow rivet method i think you will find that they protrude from the board also, and forgive me if i am wrong but all the pcb assemblies i have seen the wires from the components also protrude through the board with a solder fillet.
But i am only a klanky so what do i know.
Good luck on whatever you decide.
Regards
Mike

HankMcSpank
20-04-2015, 08:29 PM
Whilst not the same project at all, this guy has the same challenge & you can therefore get a flavour...

http://www.cycfi.com/2014/08/neo-base-boards/

...mine will be a similar shaped pcb to that - and one of these covers goes atop ..... http://www.themusiczoo.com/product/1729/Fender-Stratocaster-Pickup-Covers-White/ )

The logic of using the rivet is that it probably sits proud less than 1mm on the top surface (ok, so I said in my former post that the enclosure butts up against the pcb.....indeed it does, but at the perimeter only, there's probably about 1mm of 'head' clearance where the holes are)

mekanik
20-04-2015, 08:49 PM
I know you don't have a lathe so this is probably not going to help but i think the best solution would be a top hat type of insert drilled and taped 3mm the flange could be 0.5mm thick so minimal protrusion, clearance hole in the board to locate it while soldering top hat in place.
Regards
Mike

mekanik
20-04-2015, 10:09 PM
http://www.theinsertcompany.com/brass_multi_micro_inserts_for_plastic.php

HankMcSpank
20-04-2015, 11:12 PM
http://www.theinsertcompany.com/brass_multi_micro_inserts_for_plastic.php

thanks but they looks broadly similar to the nuts I referred to in my opening post...

http://www.rapidonline.com/mechanical-fastenings-fixings/affix-self-clinching-nuts-m3-type-2-pack-of-50-33-3802?utm_source=AffWin&utm_medium=Affiliate&awc=1799_1429564225_1a44f76f3ddfe70b314658e0d0b4ee 75

(actually the ones at Rapid Online have smaller hole 4.2mm vs 4.6mm for M3)

like I say, the spec for those things suggest my pcb holes are going to be too close to the edge of the board.

magicniner
21-04-2015, 10:14 AM
Have you considered M3 RivNuts?
I've set M6 Riv-Nuts in Polycarbonate, Fibreglass and ABS by using a washer on the back and crimping tight enough to hold but not tight enough to damage, the hole in the base material is drilled clearance and it's the tension of the Riv-Nut between head and washer that holds by friction on the surfaces.

I used washers cut from Polyurethane sheet on both sides of the Polycarbonate and Fibreglass to prevent wear with vibration, rain and road dirt but I suspect you won't have those issues ;-)
Regards,
Nick

mekanik
21-04-2015, 11:09 AM
thanks but they looks broadly similar to the nuts I referred to in my opening post..

Was just looking for the makings really, it's a simple job to chuck these on a mandrel in the lathe,remove the serations and even skim the flange OD if that's too large.
Regards
Mike

magicniner
21-04-2015, 11:54 AM
Was just looking for the makings really, it's a simple job to chuck these on a mandrel in the lathe,remove the serations and even skim the flange OD if that's too large.

You don't need to skim the serrations, you need to adjust the drilled hole size to suit the material you're using to avoid splitting, you'll still have significant resistance to turning from the mechanical fit, add a 2-part adhesive for adequate retention and you're sorted.


thanks but they looks broadly similar to the nuts I referred to in my opening post..


If you use a backing washer, as I stated, the hollow section spreads and partially collapses outside the washer and doesn't spread in the substrate, no stress on the hole, just compression of the board, so no splitting.
I guess that's similar ;-)

magicniner
21-04-2015, 12:05 PM
I have the mandrel for the setting tool.

Whilst you can buy and use a Riv-Nut setting tool all you need is a flat steel bar with a hole through it and roughed up a bit on the side presented to the Riv-Nut head, preventing slipping when setting.
Use a bolt or bit of threaded bar through the flat bar and fully engaged with the Riv-Nut threads.
With lubed washers & well lubed nut on top, tighten nut whilst ensuring the bolt doesn't turn and set the Riv-Nut to the tension or height of your choice.
I use 60% Moly paste for the lube as it gives the best possible friction reduction and thus translates as much torque as possible into tension.

- Nick

mekanik
21-04-2015, 01:05 PM
My idea was to solder the insert, removing the serations means you can have a smaller hole in the board so the board is stronger. the inserts could be machined to practically any size you want.
Regards
Mike

magicniner
21-04-2015, 02:06 PM
Brass bar stock is cheap enough, I suspect you could knock out a few dozen in an hour once you have the tooling and a procedure set for your lathe.

The topic title does lead one to think down a riveting specific mechanical route ;-)

mekanik
21-04-2015, 06:44 PM
Brass bar stock is cheap enough, I suspect you could knock out a few dozen in an hour once you have the tooling and a procedure set for your lathe.

The topic title does lead one to think down a riveting specific mechanical route ;-)
You are correct the OP was looking for an off the shelf solution and your method is proven so it looks like the best choice in that regard, have my doubts about the rivet method only because of the wall thickness of the hollow rivet, the method i offered puts no strain @ all on the PCB. if OP sends me some of the inserts i pointed too i will gladly machine them to the size required.
regards
Mike