Enclosure advice please - glueing metal

[Tim Shoppa]

You are right I reckon - I did consider torx screws a while back, but can't
remember exactly why I dismissed them now... In a perfect world I'd still
prefer a totally "clean" front panel though, especially on such a small
front panel as this one.

Look in particular for "button head" cap screws. If you're in the US,
and don't have a nearby well-stocked hardware store,
I can highly recommend buying this sort of stuff from MSC...
http://www.mscdirect.com/

I think they're available in Torx but IMHO the Allen socket head or
one of the tamper-resistant two-hole designs is better for a front panel.

You don't say what else is on your front panel but if there's any switches,
pots etc. with threaded shafts, D-sub connectors, etc., these can be used for
both standing off *and* mounting. If you look at the catalogs you'll see
a couple of semi-standards for mounting depth.

Tim.

 

[Rich Grise]

As you say, epoxy is no alternative to proper mechanical fastening, but I'm
hoping it is sufficient in my case. So I wonder whether sticking nylon
spacers to the aluminum is going to produce a tougher bond than using
nickel-plated brass ones? And also what is the best type of adhesive to use
in either case?

There are things that are designed for sticking to aluminum panels - I'd
think there'd adhesive standoffs of some kind available, with some stickum
that works better on aluminum than epoxy. Kinda like double-sticky tape.
Can you use flathead thru studs, that you put in before you silkscreen it?
..06 is a little thin for Pem studs, after all.

Good Luck!
Rich

 

[budgie]

Or use a second aluminum panel, and 'press' studs.

A method I have used in the past - especially with thin decorative aluminium
panels - is the "second sheet". All the holes/fixings are to the "back" sheet,
which is often the original enclosure. The cosmetic skin with all the nice
artwork is then affixed with aything you like - contact adhesive for instance -
as it isn't under any real load. Often the shaft screws of pots or switches tie
the two layers together.

Philips (and Pye in the U.K.) used a similar technique on some rack-mount base
station radio equipment, and even pot shaft and switch nuts were clamping the
rear panel only. The front panel in those cases (no pun intended) was quite
thick and attached to the unit with only four screws into "D" handles.

 

[Alan]

http://www.speff.com

Thanks Alan and Spehro. It does sound very good, both in terms of robustness
and tidiness. I'm getting the panels made outside (FrontPanelExpress) so I
guess I could get them to do inner panels at the same time. Just need to
make sure I line them up accurately when it comes to glueing the two panels
together - the inner panel will have to be smaller than the outer one due to
the requirements of the enclosure. I could make some kind of jig I guess.

Dave

An alternate idea is to use the metal front panel with fasteners
installed and then put a self-adhesive label over the front made out
of polyester or polycarbonate or even brushed alimin(i)um if that is
what you want.

I've used polyester and polycarbonate labels on some of my equipment
and they are hard wearing and colourful plus you can have a "window"
for an LED/LCD display. Also you can cover the pushbuttons with the
flexible material and have effectively a sealed front where you can
still press the buttons - mark the outline of the button and label
(have a look at http://jenal.com/?p=4 for an idea)

Alan


++++++++++++++++++++++++++++++++++++++++++
Jenal Communications
Manufacturers and Suppliers of HF Selcall
P O Box 1108, Morley, WA, 6943
Tel: +61 8 9370 5533 Fax +61 8 9467 6146
Web Site: http://www.jenal.com
e-mail: http://www.jenal.com/?p=1
++++++++++++++++++++++++++++++++++++++++++

 

[SioL]

I've used polyester and polycarbonate labels on some of my equipment
and they are hard wearing and colourful plus you can have a "window"
for an LED/LCD display. Also you can cover the pushbuttons with the
flexible material and have effectively a sealed front where you can
still press the buttons - mark the outline of the button and label
(have a look at http://jenal.com/?p=4 for an idea)

Alan

Now this looks interesting. Where do you get these labels, how do you print on
them and how much do they cost?

SioL

 

[Dave Marsh]

There are things that are designed for sticking to aluminum panels - I'd
think there'd adhesive standoffs of some kind available, with some stickum
that works better on aluminum than epoxy. Kinda like double-sticky tape.
Can you use flathead thru studs, that you put in before you silkscreen it?
.06 is a little thin for Pem studs, after all.

Good Luck!
Rich

Thanks Rich. I've had a look at the self-adhesive standoffs. They would be
ideal but unfortunately the bases are too big (0.5" square) for this unit,
due to the holes for LEDs and buttons). I'd have to cut so much off the
bases that they might not have enough sticking power left. The studs idea is
a good one. Unfortunately this panel isn't having silkscreen - it is being
engraved and dyed instead. I'm going to try out some of the ideas in this
thread, such as the inner panel, and see how it goes.

Dave

 

[Dave Marsh]

Look in particular for "button head" cap screws. If you're in the US,
and don't have a nearby well-stocked hardware store,
I can highly recommend buying this sort of stuff from MSC...
http://www.mscdirect.com/

I think they're available in Torx but IMHO the Allen socket head or
one of the tamper-resistant two-hole designs is better for a front panel.

You don't say what else is on your front panel but if there's any switches,
pots etc. with threaded shafts, D-sub connectors, etc., these can be used for
both standing off *and* mounting. If you look at the catalogs you'll see
a couple of semi-standards for mounting depth.

Tim.

Thanks for the help Tim. I'll take a look at those screws.

In fact there's nothing touching the front panel, just 3 x 6mm tactile
switches, 3 x 7-seg LEDs and a couple of discreet LEDs. There is also a
tinted acryllic filter over the cutout for the 7-segs - this has a self
adhesive shelf that sticks around its cutout on the front panel.

BTW, I've already used your idea of mounting via a connector on the rear
panel, lol (even at one stage considered a totally non-functional "service
port" D-connector for this purpose, since it was easier and cheaper than
getting hold of the right size 90deg brackets!). In the end I found some
phono sockets that mount to both PCB and panel and used a couple for the
purpose - plus they are functional as well

Dave

 

[Alan]

Now this looks interesting. Where do you get these labels, how do you print on
them and how much do they cost?

SioL

Unfortunately you have to go to a label maker. My local PCB maker
will make them or there are a few local companies here that make them
specifically for electronic equipment or hardwearing labels for other
uses. I'm sure there is someone in you locality that should be able
to help.

There are also companies that will make a self-adhesive label with
built in switches and tracks that can be fastened onto the front of a
box as a keypad, etc (as shown in http://jenal.com/?p=5 ).

So I guess the answer you didn't want to hear is that you can't just
buy a blank label and stick it in a printer! You could start with a
clear sheet of poly(whatever) and silkscreen onto it (the back of it
for hardwearing) and then when finished cover the whole back with 3M
double-sided sticky stuff. Hey presto - a label!

If you want a cheap one-off label I've used normal office type sticky
labels, printed on then and the covered them with the clear sticky
plastic that is used for protecting books. Cheap and resonably
effective - but not really production quality.

Alan


++++++++++++++++++++++++++++++++++++++++++
Jenal Communications
Manufacturers and Suppliers of HF Selcall
P O Box 1108, Morley, WA, 6943
Tel: +61 8 9370 5533 Fax +61 8 9467 6146
Web Site: http://www.jenal.com
e-mail: http://www.jenal.com/?p=1
++++++++++++++++++++++++++++++++++++++++++

 

[Dave Marsh]

There is not very much adhesion area on a standard, e.g. hex, spacer, so
what glue strength you get from it isn't much. But *really* going
against you here is the fact that the shear strength of epoxy is pretty
weak, and your applied forces - both on the flats of the spacer and on
its face (spacer/glue/panel interface) - from simply tightening screws
are shear forces. Epoxies can have very high *tensile* strength but
your application cannot take advantage of them.

That makes a lot of sense and agrees with exactly what I'm seeing in my
testing so far.

So if we accept epoxy's relatively weak shear strength, how about
maximizing the glue surface area and getting a threadable material at
the same time by putting a metal or plastic panel between your board and
the nice front panel? Assuming all your board mounting holes are along
the outter edge of the board, you might then get away with a plastic or
metal panel that has its center cut away ; drill and tap at appropriate
points on the resulting "border".

I'm going to try this, and I think it is the same as what many others have
suggested too.

Or mount metal brackets inside your enclosure (it's OK to drill, e.g.
the bottom of the case, right?) and attach the PC board to those.

I think I'd rather leave the bottom of the case alone TBH, but it is a
sensible idea.

Many thanks for your suggestions Michael.

Dave

 

[Dave Marsh]

A method I have used in the past - especially with thin decorative aluminium
panels - is the "second sheet". All the holes/fixings are to the "back" sheet,
which is often the original enclosure. The cosmetic skin with all the nice
artwork is then affixed with aything you like - contact adhesive for instance -
as it isn't under any real load. Often the shaft screws of pots or switches tie
the two layers together.

Philips (and Pye in the U.K.) used a similar technique on some rack-mount base
station radio equipment, and even pot shaft and switch nuts were clamping the
rear panel only. The front panel in those cases (no pun intended) was quite
thick and attached to the unit with only four screws into "D" handles.

Hi Budige. Thanks for the insight. That definitely sounds a good way to go
for the *next* design! I'm going to apply the idea of the second/inner
panel idea as well as I can to this first design. Fingers crossed...

Dave

 

[Spehro Pefhany]

Unfortunately you have to go to a label maker. My local PCB maker
will make them or there are a few local companies here that make them
specifically for electronic equipment or hardwearing labels for other
uses. I'm sure there is someone in you locality that should be able
to help.

We make small quantities and specials up, it's possible to do it
in-house if you buy the equipment and supplies (in the thousands of
dollars or more depending on whether you go to a UV or solvent-based
process). It's an extremely messy, smelly and labor-intensive
process requiring skill, but you end up with a very rugged
professional-quality polycarbonate or polyester back-printed overlay
with transparent colored windows for LEDs etc., if you do everything
right (if you don't, well the ink might separate or the adhesive might
attack the ink, or the registration might be off, or the cutting die
might not be registered with the printing properly). IOW, it's real
manufacturing, and thus not so easy.

Best regards,
Spehro Pefhany

 

[Keith Wootten]

In message <[email protected]>, Dave Marsh

I'm going to apply the idea of the second/inner
panel idea as well as I can to this first design. Fingers crossed...

You could use a 1/4" thick inner panel/spacer made of rigid foam - maybe
the stuff sometimes used for mounting pictures. Make it the same size
as the PCB and cut oversize holes for the LEDs etc. Lots of area for
adhesive - For securing the PCB you could use countersink screws with
the heads on the front panel side of the rigid foam and the threads
projecting backwards through the PCB.

Cheers

 

[John Fields]

There are things that are designed for sticking to aluminum panels - I'd
think there'd adhesive standoffs of some kind available, with some stickum
that works better on aluminum than epoxy. Kinda like double-sticky tape.
Can you use flathead thru studs, that you put in before you silkscreen it?
.06 is a little thin for Pem studs, after all.

 

[Spehro Pefhany]

I like the SO series, which is okay down to 0.040 or 0.050".

Best regards,
Spehro Pefhany

 

[Dave Marsh]

I like the SO series, which is okay down to 0.040 or 0.050".

Best regards,
Spehro Pefhany

http://www.speff.com

A couple of question re the Pem fasteners - Do they *really* not show on the
other side, even for a panel thickness of 0.06" (say using the SO series,
for instance)? And do I need to buy a "Pemserter" press, as recommended by
them, or can I get the same result with a standard miniature vice?

Thanks,

Dave

 

[Dave Marsh]

In message <[email protected]>, Dave Marsh


You could use a 1/4" thick inner panel/spacer made of rigid foam - maybe
the stuff sometimes used for mounting pictures. Make it the same size
as the PCB and cut oversize holes for the LEDs etc. Lots of area for
adhesive - For securing the PCB you could use countersink screws with
the heads on the front panel side of the rigid foam and the threads
projecting backwards through the PCB.

Cheers

Thanks for the suggestion. That could well be easier & cheaper than a metal
inner panel. I am keen on the idea of coutersink screws pointing into the
unit too.

My only concern with using an inner panel is the alignment of the
countersink holes with the holes in the PCB. As an alternative, I'm
wondering about maybe having small discrete plates (metal/foam) made for
each screw. Each would have a single countersink hole so the screw could be
mounted pointing inwards as you say. A hex spacer and maybe a shakeproof
washer would be tightened against the plate so the screw was tight (as was
suggested earlier). Then I can bolt the spacers to the PCB for alignment
before glueing the plates to the front panel.

I know I lose a lot of the contact surface area this way, compared to a
single complete inner panel, but the area is still much greater than that of
a hex spacer or a screw head by itself. Also, these plates become very low
precision items that I can get made easily and cheaply somewhere (just a
square of metal with a countersink hole in the middle).

Dave

 

[Spehro Pefhany]

A couple of question re the Pem fasteners - Do they *really* not show on the
other side, even for a panel thickness of 0.06" (say using the SO series,
for instance)? And do I need to buy a "Pemserter" press, as recommended by
them, or can I get the same result with a standard miniature vice?

The SO series goes right through, so obviously it does show on the
other side, however it's pretty much flush. The type without a through
hole might be acceptable visible in some applications (the head is a
hex shape).

The Pemserter presses are rather large and expensive- even used they
are thousands of dollars and take up significant floor area. For
modest quantities (from 1 piece up into the many thousands), with the
fasteners we've used, a 3-ton arbor press with an anvil machined from
tough 4140 oil hardening chrome alloy steel works just fine.

I've not used the blind type- they require relatively expensive
milling operations on the panel, compared to simple punching. A
typical minimum depth of hole is 0.043 inch, which would leave 0.017"
thickness. Whether it is visible or not would depend a lot on the
details of material, finish and how the milling and crimping was done.
Despite the increased shipping costs etc., I'd be inclined to pay the
front panel supplier to do this operation (and check samples out
first) as it would be pretty easy to ruin a bunch of expensive
otherwise finished panels.

Best regards,
Spehro Pefhany

 

[John Fields]

I like the SO series, which is okay down to 0.040 or 0.050".

 

[John Fields]

A couple of question re the Pem fasteners - Do they *really* not show on the
other side, even for a panel thickness of 0.06" (say using the SO series,
for instance)? And do I need to buy a "Pemserter" press, as recommended by
them, or can I get the same result with a standard miniature vice?

The SO series require the panel to be pierced and the standoffs to
extend through the panel, so unless you have the panel covered with an
overlay of some kind or painted after the standoffs are installed,
they'll show.

The CHA's OTOH, are pressed into a blind cavity end-milled into the
rear of the panel, so they won't show if, after they're pressed in,
the front surface of the panel is properly prepped prior to anodizing.
Also, you need to make sure that the surface of the the thing doing
the pressing (the punch, PEM calls it) isn't marred to the extent that
it'll press markings into the panel which won't be removed with normal
prepping.

All you need to press them in is a flat-faced anvil with a hole of the
proper diameter drilled in it and and a way to exert enough force on
the sheet to force the aluminum surrounding the insert to flow into
the serrations and recesses in the insert. An arbor press is a good
way to do it, but you need to be careful not to exert _too much_
force, or you'll squeeze the panel out of shape. (I got that T-shirt
once...) Just follow PEM's guidelines on the data sheet and you
should be fine.

 

[Zak]

Nylon is almost impossible to attach to anything with glue of any kind
I have ever tried.

I'm told resorcinol glue should work - it is an old two pot waterproof
system for wood - very dark in color.

I wonder if the wood viariety is suitable:
http://www.sky-craft.co.uk/aerodux_data.htm

Thomas