Fed up with this constant battle re enclosures - need a solution

[boylesg]

I have this constant battle of figuring out a way to attach PCB's and Arduinos to the bottom of project boxes using the little nylon hex standoffs.

I have tried the following and it is a losing battle:

1) Just gluing the bottom of the PCB (solder and all) with silicone to the bottom of the box, with the obvious problem of if you want to remove the PCB and make modifications
2) Gluing the bottom of the stand offs to the bottom of the box with silicone with the obvious problem that there is just not enough surface area for the silcone to bond effectively.
3) Drilling holes and screwing the stand offs into the bottom of the box or a piece of MDF that I then silcone to the bottom of the box. But it is near impossible to get the precision required with a hand drill and the resulting holes never quite line up and cause me no end of trouble.


Basically I need to expand the bottom of the stand offs into a small disk that can be successfully glued, independent of each other to the bottom of the box.

The problem is I cannot come up with a quick, simple and cheap method of producing small enough MDF disks or coming up with any other source of small 3mm or so thick disks of plastic or MDF that I can use.

Are there any solutions out there that don't require CNC drilling that others have come up with????

Even now I used a Uno to position the holes in a piece of MDF. But by the time I drilled the holes big enough to push the hex stand offs into, the damn holes did not line up exactly and I couldn't do it!
It is a bloody pain in the ar$e.

I have though of metallic or plastic washers, but the chances of getting some with a large enough surface area, small enough hole and thick enough metal is negligible.

Holding and arduino uno on the bottom of the box and drilling the holes through the PCB holes in the bottom of the box doesn't work either because the uno inevitably moves a bit while drilling and moving to the next hole and again the problem is that the holes do not end up precisely lining up. It just can't be done without the precision of a CNC milling machine due to the tight PCB tolerances.

 

[Kajunbee]

What I usually do if I have several holes to drill is drop a screw or pin to hold the boards position. Each time you drill hole s drop a pin or screw to hold it in position.

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I usually drill the first two holes that are furthest apart from each other on the board.

 

[boylesg]

What I usually do if I have several holes to drill is drop a screw or pin to hold the boards position. Each time you drill hole s drop a pin or screw to hold it in position.

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I usually drill the first two holes that are furthest apart from each other on the board.

Yeah I have tried that sort of thing as well but I also find this unreliable because the damn board can still move on you between holes. And you only have to be a 1-2mm out and it still makes it difficult to get the stand offs to line up with the holes in the PCB. And there is VERY little margin for error.

Some one out there must have conceived of a method that does not involve drilling holes that are tightly dependent on each other. Surely!

 

[SLK001]

3) Drilling holes and screwing the stand offs into the bottom of the box or a piece of MDF that I then silcone to the bottom of the box. But it is near impossible to get the precision required with a hand drill and the resulting holes never quite line up and cause me no end of trouble.

There's your problem. You need to develop the skill to drill a precision hole with a hand drill. Start with an accurate layout. Use a pair of dividers to locate holes if you have to. CENTER PUNCH the locations for holes - this is key as it prevents the drill from wandering from your desired location. Center punches are relatively cheap - less than $5US. Start drilling with a small drill - around 0.063" (or use a proper center drill) and step up to the final value you need. The material of your box will determine how big a step you can take.

Once you have drilled your proper hole locations, taking a PCB in and out is a breeze.

 

[KlausST]

Hi,

if you work precisely you should be able to be within 0.5mm with Kajunbee`s method.

To further avoid movement you may use double faced adhesive tape.

If you have multiple identical devices to produce, you could spend a PCB as a stencil.


Klaus

 

[andre_luis]

You could also consider fastening the PCB by rails, as for example the 90 degrees card guides made in plastic, but you should ensure that there is nothing with tall profile at the bottom side of the board, or close to the edges.

 

[Kajunbee]

Yeah I have tried that sort of thing as well but I also find this unreliable because the damn board can still move on you between holes. And you only have to be a 1-2mm out and it still makes it difficult to get the stand offs to line up with the holes in the PCB. And there is VERY little margin for error.

Some one out there must have conceived of a method that does not involve drilling holes that are tightly dependent on each other. Surely!

Yes, it's not foolproof and it's highly dependent on how tight the pins fit in the holes among other things. Another option is to drill oversized holes in the mdf and use something like jb weld to anchor the standoffs bolt threads. The oversized holes would give some room to play with if hole placement is not exact. Then just mount all your standoffs to the board and press it into the jb weld filled holes.

 

[d123]

Hi,

Happens to all of us, more than we'd admit probably. In all honesty, I'm no Olympian with a drill, pretty bad sometimes (only broken 2 0.9mm drill bits in the past 2 years), but a lot of it is practice, like removing the sheath from a cable without cutting into/through the actual wire is an acquired skill with each cable-stripper or knife. And for a drill, using gravity to your favour where possible (i.e. drill downwards to make reliable contact with the spot to drill). I also screw a PCB I am drilling and cutting tracks into onto a 4 cm thick, 40x40 cm martyr board as soon as the first and then the perpendicularly opposite holes are drilled. I mark/gouge the centres of drill holes as best I can with a small Philips screwdriver I filed to a delightful point - it's a really useful tool in several ways (Is that what an awl is, a spike on a handle?). It guides the drill bit during that first worst, slippery moment which is really important for me, drilling or skating on shiny copper...

I'd go with the cardholder style supports, too. I use standoffs a lot though. Sometimes metal and nylon standoffs mean unsightly metal or nylon screw heads or bolts visible on one external side of the box - it looks a bit you know what and Frankensteiny for my liking.

I don't find that putting the drill through drilled pcb holes is so detrimental if you're quick, so maybe just using the pcb as the template for the enclosure and as a guide for the drill bit, as suggested above too, is the simplest and quickest way of precision drilling.

Have a look in a dollar shop for those rubber feet/circles/dome shapes to stick under stereos and everything else electrical you have. They come in all shapes and sizes, are so cheap, and could with good glue be a suitable solution (and they're so easy to drill and you needn't be so accurate as they are usually rubbery and give a lot of play room). You could even get ~1 cm diameter ones and scoop/drill out a seat/platform for the standoffs, for a snug fit with friction pressure to hold them in place and take in and out without screws or glue on the pcb itself.

 

[boylesg]

Hi,

Happens to all of us, more than we'd admit probably. In all honesty, I'm no Olympian with a drill, pretty bad sometimes (only broken 2 0.9mm drill bits in the past 2 years), but a lot of it is practice, like removing the sheath from a cable without cutting into/through the actual wire is an acquired skill with each cable-stripper or knife. And for a drill, using gravity to your favour where possible (i.e. drill downwards to make reliable contact with the spot to drill). I also screw a PCB I am drilling and cutting tracks into onto a 4 cm thick, 40x40 cm martyr board as soon as the first and then the perpendicularly opposite holes are drilled. I mark/gouge the centres of drill holes as best I can with a small Philips screwdriver I filed to a delightful point - it's a really useful tool in several ways (Is that what an awl is, a spike on a handle?). It guides the drill bit during that first worst, slippery moment which is really important for me, drilling or skating on shiny copper...

I'd go with the cardholder style supports, too. I use standoffs a lot though. Sometimes metal and nylon standoffs mean unsightly metal or nylon screw heads or bolts visible on one external side of the box - it looks a bit you know what and Frankensteiny for my liking.

I don't find that putting the drill through drilled pcb holes is so detrimental if you're quick, so maybe just using the pcb as the template for the enclosure and as a guide for the drill bit, as suggested above too, is the simplest and quickest way of precision drilling.

Have a look in a dollar shop for those rubber feet/circles/dome shapes to stick under stereos and everything else electrical you have. They come in all shapes and sizes, are so cheap, and could with good glue be a suitable solution (and they're so easy to drill and you needn't be so accurate as they are usually rubbery and give a lot of play room). You could even get ~1 cm diameter ones and scoop/drill out a seat/platform for the standoffs, for a snug fit with friction pressure to hold them in place and take in and out without screws or glue on the pcb itself.

Yeah done all that sort of thing. It is even impossible to retain the tight tolerances by drilling the holes with a pedestal drill! Impossible - there is ALWAYS enough movement in the piece to throw the holes out enough so as they do not fit board!

It is bloody infuriating.

The only viable solution that I can think of is to make those stand offs with a 5mm or so diameter flange that can be glued to the bottom of the box - simple and quick.

But no such stand-offs exist apart from the type used for PC motherboards sometimes with the through hole spreaders. Some of them come with flat flanges.
But you can never get the spreaders small enough to fit through the small Arduino board holes!

Please someone manufacture a convenient and inexpensive solution for Arduino!

 

[Kajunbee]

Have you ever tried those adhesive type standoffs. I don't know durable they are but I can't see a much easier solution. If the hole of your arduino is 3.2 mm you can find them on eBay.

 

[d123]

Hi,

It's just practice and patience until you drill more accurately.

If the mountain won't come..., as they say: Make the pcb drill holes 1 - 2 mm wider to give room to move and fit the headers - and to preempt you, don't tell me you've tried that and it doesn't work because it's standard practice for drilling and lining up tiny and huge things.

An Arduino is not a PCB so there you can only depend on improving your drilling skills to fit the tolerances you'll have to play with.

You'll just have to practice drilling accurately on spare pieces of PCB instead of getting in a state about it. What can't be cured must be endured.

 

[boylesg]

Hi,

It's just practice and patience until you drill more accurately.

If the mountain won't come..., as they say: Make the pcb drill holes 1 - 2 mm wider to give room to move and fit the headers - and to preempt you, don't tell me you've tried that and it doesn't work because it's standard practice for drilling and lining up tiny and huge things.

An Arduino is not a PCB so there you can only depend on improving your drilling skills to fit the tolerances you'll have to play with.

You'll just have to practice drilling accurately on spare pieces of PCB instead of getting in a state about it. What can't be cured must be endured.

If you could get unpopulated arduino PCB's with the holes it would make it a lot easier.

You could then tape the PCB flush on to what ever you are drilling the holes into and there would be much less room for error even if the drill is not held perfectly vertical.

Suppose I could try that - load one of the arduino boards into diptrace, delete everything except the holes and send the design off to Seed Studio or whatever.

But it would seem to be a very simple matter for the stand off manufacturers to simply make screw in flanges for their standoffs!

Thought of another idea at Bunnings today - rare earth magnets and steel washers. Easy to tape or silcone in place and easy to remove the board if needed.

As long as you are not using a Hall sensor.

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It is not that I don't have enough practice using a hand drill or pedestal drill.
The problem is that the tolerances with PCBs are extremely tight and it is VERY hard to get the required precision to line the holes up.
Even punching the holes first with a highly sharpened nail punch....there is no guarantee that the point of the nail punch makes a dent that is not a fraction of a mm out that then gets a bit further out of alignment when you apply the drill to the dent.
You might get 2 holes to line up nicely and if you are really careful you might get 3 holes to line up correctly. But I have never managed to get 4 holes to line up exactly.

Another problem is that epoxy resins do not adhere well to plastic that project boxes are made with.
Silicone works fairly well, but you need a reasonable surface area for it to adhere strongly.....unless you embed the standoff in a glob of silicone which is messy.
Does anyone know of any glues that WILL adhere to ABS plastic etc over the small surface area of a nylon standoff?

 

[Kajunbee]

There are two types of plumbers glue that I know of. One is for pvc and the other is for abs plastic pipe fittings. You might experiment with the abs glue. Not sure how well it would work on your enclosures because the grade might be different than abs pipe fittings. Then there's the issue of whether it will bond nicely to the nylon. Unless someone else knows only experimenting will tell.

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In my opinion it probably wouldn't be much better than hot gluing besides being messy. I believe your on the right track with blank boards. If you can guarantee they don't move I don't see how you can go wrong.

 

[d123]

Hi,

Is there somewhere in Arduino world a spec of the board, just the board, with the length, width and hole positions and diameter? That would be great: it's perfectly right. If you could get hold of that, any old bit opf flat thickish metal and then in a schematic capture or similar input that info. or to a CNC machine or whatever if you have those tools, you could use a piece of 2 to 3mm thick metal as a template that would last "forever".

I've found a hobby glue in a pound shop that's very good for what it is. I used it to make separators for the battery compartment in a box with clear plastic and a cardreader style shelf for the pcb. I did it quickly and sloppily (prototype) and overdid the glue maybe a bit. I carry this around sometimes and bash it about and the separators are still in place, unbelievably. Maybe hobby glue, Metacry-something-whatever I'll bet it is, that transparent stuff that is liquidish and is so hard to get off fingers really might be all you need. The hole in the standoff can absorb some glue and add rigidity maybe.

 

[Kajunbee]

Try searching " arduino hole dimensions - adafruit industries.

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I was thinking along the same lines as d123. The plus side of using a thicker piece of metal as a template is that it will help you keep your drill straighter. Provided you drill the holes straight when you make the pattern.

 

[betwixt]

I usually print a copy of the PCB layout (with holes) and tape it flat to the bottom of the enclosure so there is no 'parallax' error then drill through the paper. It's as accurate as he original PCB artwork.

Remember you can mirror (reverse) the image and use it to drill through the outside of the enclosure as well if it's easier.

Brian.

 

[Kajunbee]

Great piece of info, would never have thought of printing mirror image.