Enclosure advice please - glueing metal

[Dave Marsh]

Hi,

I have a small front panel made of anodized aluminum (0.06 inches thick). I
need to space off the PCB (buttons, LEDs etc.) behind it by approx 0.25
inches.

The PCB has 4 drilled holes for M3 machine screws. My problem is that I
can't put holes through the front panel. My idea at the moment is to glue 4
hex spacers to the back of the front panel and then bolt the PCB to it.

So far, I've tried nickel-plated brass spacers attached with epoxy ("plastic
steel" by Draper) on to the sanded aluminum. This came apart after some
pretty gentle leverage testing.

Just wondering (a) if I'd be better using nylon spacers - would these glue
better to the aluminum? And (b) what type of glue should I use for metal
spacers (or nylon spacers) on to anodized aluminum?

Many thanks,

Dave

 

[Activ8]

Hi,

I have a small front panel made of anodized aluminum (0.06 inches thick). I
need to space off the PCB (buttons, LEDs etc.) behind it by approx 0.25
inches.

The PCB has 4 drilled holes for M3 machine screws. My problem is that I
can't put holes through the front panel. My idea at the moment is to glue 4
hex spacers to the back of the front panel and then bolt the PCB to it.

So far, I've tried nickel-plated brass spacers attached with epoxy ("plastic
steel" by Draper) on to the sanded aluminum. This came apart after some
pretty gentle leverage testing.

Just wondering (a) if I'd be better using nylon spacers - would these glue
better to the aluminum? And (b) what type of glue should I use for metal
spacers (or nylon spacers) on to anodized aluminum?

Many thanks,

Dave

Epoxies are great, but I'd like to see that guy hanging from his
hard hat forever. Even if you drilled a hole and used epoxy like a
rivet, it could break - it's just a polymer.

If the panel had a printed overlay, that would hide the screws.

You should have something welded to the back of it with threaded
holes or whatever lends itself to mechanical fasteners.

Your panel is kinda thin to have holes bored, not drilled, in the
back but that might work. You'd need a screw with a real short
thread engagement. Then you could fasten some kind of mounting
fixture.

Another option is a two piece bezel around the panel which provides
for securing the panel and the board.

Sounds like you screwed yourself in the initial design phase unless
you just had this panel dropped in your lap or you salvaged it.

If you ever design an enclosure in the future, it would behoove you
to disect as much junk equipment as you can find and see how things
are normally done.

 

[Dave Marsh]

Epoxies are great, but I'd like to see that guy hanging from his
hard hat forever. Even if you drilled a hole and used epoxy like a
rivet, it could break - it's just a polymer.

If the panel had a printed overlay, that would hide the screws.

You should have something welded to the back of it with threaded
holes or whatever lends itself to mechanical fasteners.

Your panel is kinda thin to have holes bored, not drilled, in the
back but that might work. You'd need a screw with a real short
thread engagement. Then you could fasten some kind of mounting
fixture.

Another option is a two piece bezel around the panel which provides
for securing the panel and the board.

Sounds like you screwed yourself in the initial design phase unless
you just had this panel dropped in your lap or you salvaged it.

If you ever design an enclosure in the future, it would behoove you
to disect as much junk equipment as you can find and see how things
are normally done.

Thanks for your sensible advice Mike. You are pretty much right that I
screwed myself with this design somewhat! It's my first one and am learning
the hard way.

The panel is just 4" x 1" and made by FrontPanelExpress.com (I can heartily
recommend them btw). The "printing" is actually done by them as dyed
engraving and it looks great on the brushed aluminum, so I really don't want
to go to a sticky plastic overlay (it's a niche product for consumer audio
so needs to look pretty decent alongside people's amps etc.)

The screw thread idea sounds good, but the lack of thickness of the panel
may well be a problem as you say.

On the up side, there are just three 4.5mm diameter tactile buttons that the
user *should* press, and I think the strength of the adhesive is pretty good
in this direction, i.e. parallel with the panel. My leverage test was trying
to simulate a worst case and it succeeded!

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?

Thanks,

Dave

 

[Leon Heller]

Thanks for your sensible advice Mike. You are pretty much right that I
screwed myself with this design somewhat! It's my first one and am learning
the hard way.

The panel is just 4" x 1" and made by FrontPanelExpress.com (I can heartily
recommend them btw). The "printing" is actually done by them as dyed
engraving and it looks great on the brushed aluminum, so I really don't want
to go to a sticky plastic overlay (it's a niche product for consumer audio
so needs to look pretty decent alongside people's amps etc.)

The screw thread idea sounds good, but the lack of thickness of the panel
may well be a problem as you say.

On the up side, there are just three 4.5mm diameter tactile buttons that the
user *should* press, and I think the strength of the adhesive is pretty good
in this direction, i.e. parallel with the panel. My leverage test was trying
to simulate a worst case and it succeeded!

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?

Try rec.crafts.metalworking. There are lots of people there who are into
fixing things together in strange ways.

Leon

 

[John Popelish]

Hi,

I have a small front panel made of anodized aluminum (0.06 inches thick). I
need to space off the PCB (buttons, LEDs etc.) behind it by approx 0.25
inches.

The PCB has 4 drilled holes for M3 machine screws. My problem is that I
can't put holes through the front panel. My idea at the moment is to glue 4
hex spacers to the back of the front panel and then bolt the PCB to it.

So far, I've tried nickel-plated brass spacers attached with epoxy ("plastic
steel" by Draper) on to the sanded aluminum. This came apart after some
pretty gentle leverage testing.

Just wondering (a) if I'd be better using nylon spacers - would these glue
better to the aluminum? And (b) what type of glue should I use for metal
spacers (or nylon spacers) on to anodized aluminum?

Many thanks,

Dave

Nylon is almost impossible to attach to anything with glue of any kind
I have ever tried. Epoxy has exceptional adhesion to anodized
aluminum, better than to plated or unplated brass, I think. It also
has good stick to thermally oxidized aluminum. You can make good
clean thermal oxide by baking aluminum parts in a 450 degree oven for
an hour or so. But any clean aluminum has a thin film of oxide on it.

Most epoxies don't develop their full strength for a long time, or
until after they are thermally post cured. Can your control panel
tolerate a bake at 120 to 150 degrees F?

Another rule of thumb is that the slower the cure , the higher the
strength, so quick cure epoxies are useless for high strength
applications.

Filled epoxy is no stronger in adhesion that plain epoxy. That said,
some of the highest strength epoxies I have used (especially if
properly post cured) are Hysol filled epoxies like 9430 (white) or
9460 gray). These both contain silica, so they cannot be machined by
steel tools, but this doesn't sound like it would be a problem in your
application.

 

[Keith Wootten]

In message <[email protected]>, Dave Marsh

Hi,

My problem is that I
can't put holes through the front panel. My idea at the moment is to glue 4
hex spacers to the back of the front panel and then bolt the PCB to it.

Self adhesive nylon PCB mounting whatsits work well, eg Farnell 147-164.

Cheers

 

[Dave Marsh]

Try rec.crafts.metalworking. There are lots of people there who are into
fixing things together in strange ways.

Leon

Thank Leon. I'll give it a try.

Dave

 

[Dave Marsh]

In message <[email protected]>, Dave Marsh




Self adhesive nylon PCB mounting whatsits work well, eg Farnell 147-164.

Cheers

Hi Keith. They would have been ideal - problem is that the base of those are
20mm square and there is not enough room due to holes for LEDs etc. on this
small front panel.

Dave

 

[Dave Marsh]

Nylon is almost impossible to attach to anything with glue of any kind
I have ever tried. Epoxy has exceptional adhesion to anodized
aluminum, better than to plated or unplated brass, I think. It also
has good stick to thermally oxidized aluminum. You can make good
clean thermal oxide by baking aluminum parts in a 450 degree oven for
an hour or so. But any clean aluminum has a thin film of oxide on it.

Most epoxies don't develop their full strength for a long time, or
until after they are thermally post cured. Can your control panel
tolerate a bake at 120 to 150 degrees F?

Another rule of thumb is that the slower the cure , the higher the
strength, so quick cure epoxies are useless for high strength
applications.

Filled epoxy is no stronger in adhesion that plain epoxy. That said,
some of the highest strength epoxies I have used (especially if
properly post cured) are Hysol filled epoxies like 9430 (white) or
9460 gray). These both contain silica, so they cannot be machined by
steel tools, but this doesn't sound like it would be a problem in your
application.

Many thanks John for passing on your experiences. Yes, the front panel could
tolerate a bake of 150degF AFAIK. The two epoxises you mention sound very
good and I'll try to give them a go.

Dave

 

[Alan]

You could try and make a second panel out of alumin(i)um or plastic to
glue behind the first. That way you can put whatever fasteners you
want into the second panel. It will also give you extra strength in
the front panel

Alan


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[Paul Burke]

We had this problem many years ago, and found a screw with a knurled
head which could be interference- fitted into a blind recess in the
panel. Worked very well, but the guy who did it left years ago so I
don't know what they were called, and we avoid problems like that now.
We also had the luxury of a 3mm thick panel.

Paul Burke

 

[Spehro Pefhany]

You could try and make a second panel out of alumin(i)um or plastic to
glue behind the first. That way you can put whatever fasteners you
want into the second panel. It will also give you extra strength in
the front panel

Alan

That's a decent solution. You can press flush fasteners *through* the
inner panel to make an almost indestructable assembly. You do have to
machine or punch both panels similarly, though.

Best regards,
Spehro Pefhany

 

[JeffM]

I can't put holes through the front panel.

...glue 4 hex spacers to...the front panel...then bolt the PCB to it.
Dave Marsh

I'm with Activ8. Weld 'em.

[glue nylon spacers to the aluminum?]

Have you ever tried to glue nylon to anything? It's not easy.

 

[John Larkin]

Hi,

I have a small front panel made of anodized aluminum (0.06 inches thick). I
need to space off the PCB (buttons, LEDs etc.) behind it by approx 0.25
inches.

The PCB has 4 drilled holes for M3 machine screws. My problem is that I
can't put holes through the front panel. My idea at the moment is to glue 4
hex spacers to the back of the front panel and then bolt the PCB to it.

So far, I've tried nickel-plated brass spacers attached with epoxy ("plastic
steel" by Draper) on to the sanded aluminum. This came apart after some
pretty gentle leverage testing.

Just wondering (a) if I'd be better using nylon spacers - would these glue
better to the aluminum? And (b) what type of glue should I use for metal
spacers (or nylon spacers) on to anodized aluminum?

Many thanks,

Dave

If this is a production thing, you can have Pem blind spacers pressed
into the back of the panel. They are very strong and won't show on the
other side.

If it's a one-off, attach the PCB to the back of the panel with
Velcro.

John

 

[Frank Bemelman]

Hi,

I have a small front panel made of anodized aluminum (0.06 inches thick). I
need to space off the PCB (buttons, LEDs etc.) behind it by approx 0.25
inches.

The PCB has 4 drilled holes for M3 machine screws. My problem is that I
can't put holes through the front panel. My idea at the moment is to glue 4
hex spacers to the back of the front panel and then bolt the PCB to it.

Can you use selfadhesive spacers? If the board is the same size as the
panel, you may have problems to get them inside the corners of the panel.

http://www.itw-fastex.com/catalog/051.php

These are adjustable, but you also have fixed snap-type ones, from Thomas
and Betts if I'm not mistaken.

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

 

[Dave Marsh]

We had this problem many years ago, and found a screw with a knurled
head which could be interference- fitted into a blind recess in the
panel. Worked very well, but the guy who did it left years ago so I
don't know what they were called, and we avoid problems like that now.
We also had the luxury of a 3mm thick panel.

Paul Burke

That would be great, and in fact Front Panel Express offer this kind of
service with threaded spacers hammered into blind recesses in the rear of a
panel. The problem is the 1.5mm thickness, as you might have guessed - they
say the impression will be visible on the outside.

Dave

 

[SioL]

If this is a production thing, you can have Pem blind spacers pressed
into the back of the panel. They are very strong and won't show on the
other side.

If it's a one-off, attach the PCB to the back of the panel with
Velcro.

John

I've used double-sided adhesive tape (the 1mm thick foamy type).
It is extremely strong, taking it off if you make a mistake is a real pain in the butt.

It also provides a very small but usefull bit of flexibility (any hard glue will crack,
epoxy will crack when glueing metal to metal - its not shock proof).

The front panel side is easy to glue this way, you need a convenient matching flat surface
on the PCB, edges of the LCD display (5mm or so on each side) are more than enough
for a small PCB.

In fact I prefer this solution to screws for mounting LCD boards.

SioL

 

[Dave Marsh]

If this is a production thing, you can have Pem blind spacers pressed
into the back of the panel. They are very strong and won't show on the
other side.

If it's a one-off, attach the PCB to the back of the panel with
Velcro.

John

Hi John. It's a preproduction run of 100 units to test customer feedback.
From the trouble this has caused, we may well change the way the front panel
is made! I will look into the Pem blind spacers - FrontPanelExpress who are
probably going to make our panels offer a similar kind of service but say
the impressions will be visible with only a 1.5mm panel.

The velcro idea is not bad at all, even for 100 units, as long as the
backing adhesive lasts a few years. Then I guess it would match the
longevity of the self-adhesive PCB spacers that have also been mentioned in
this thread.

Many thanks,

Dave

 

[Spehro Pefhany]

I've used double-sided adhesive tape (the 1mm thick foamy type).
It is extremely strong, taking it off if you make a mistake is a real pain in the butt.

It also provides a very small but usefull bit of flexibility (any hard glue will crack,
epoxy will crack when glueing metal to metal - its not shock proof).

The front panel side is easy to glue this way, you need a convenient matching flat surface
on the PCB, edges of the LCD display (5mm or so on each side) are more than enough
for a small PCB.

In fact I prefer this solution to screws for mounting LCD boards.

SioL

If the PCB has mains voltage on it, you may wish to wrap the entire
board with several layers of black electrical tape.

Best regards,
Spehro Pefhany

 

[Dave Marsh]

thick). glue

Can you use selfadhesive spacers? If the board is the same size as the
panel, you may have problems to get them inside the corners of the panel.

http://www.itw-fastex.com/catalog/051.php

These are adjustable, but you also have fixed snap-type ones, from Thomas
and Betts if I'm not mistaken.

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

Those self-adhesive spacers look very good. Unfortunately the 0.5" square
base won't fit on our panel due to holes for LEDs etc. The second aluminum
panel does look a strong candidate now - thanks for the advice Frank.

Dave