Safe Insulating Materials?

[Steve Mavronis]

I was just about to post that I'm going to remove the foam in my old Dist+ and try thin cardboard or cardstock instead, since it's a good electrical insulator as long as it doesn't get wet.

Then I found this Formex page making me curious as an alternative. Where can you buy this stuff - do any local stores carry it?

Formex™ polypropylene electrical insulation
http://www.itwformex.com/Applications.html

- Electronic and Electrical insulation
- Barriers between PC boards and between PC boards and housings
- EMI/RFI shield

(Fish Paper and Aramid Paper Alternative)
http://www.itwformex.com/Fish-Paper-Aramid-Paper-Alternative.html

Polypropylene is a type of plastic. You can request free samples in various thicknesses and sizes - in black or natural which I guess is white. The only problem is probably getting sales calls afterwards from the company.

[PRR]

> Polypropylene is a type of plastic. You can request free samples

You got a pound of "free sample" in your recycling bin.  Yogurt containers, syrup bottles, ketchup bottles, caps, straws, medicine bottles. Look for this symbol:

[jasperoosthoek]

5 watts, push pull, all the way around?

[Steve Mavronis]

Thanks Paul for that plastic symbol info.

What I did last evening for my '80 MXR Distortion+ was use nice quality 'thin' brown corrogated shipping box cardboard, probably around 1mm (39mil) or less thick. I cut out a shape similar to the PCB (leaving room for the wires at the top edge) with 2 folded flaps for a snug fit on the sides next to the jacks under the PCB. For the MXR inner lid suface I carefully cut out a rectangle that would make a snug fit along the lip edges. Then I measured and used the circular X-acto cutting blade to 'punch cut' out the round corners precisely, by lining it up and hitting the blade top with a hammer. This gave me a perfect pressed fit to press the cardboard into with no gaps. The end result looks like it was made that way and no glue required.

X-acto Carving Router Blades

http://www.xacto.com/Product/X135

[KazooMan]

Cardboard just sounds like a problem waiting to happen down the road.  I use the material that Paul suggested.  I cut a piece the size of the board out of an old milk jug and then use a paper punch to put holes in it.  The plastic slips over the standoffs and insulates the board from the box.  My two cats help out in this cause by providing an endless supply of the heavier gauge plastic jugs that their litter comes in.  I can get a piece that is about 8" X 10" out of one of those.  If you don't use standoffs, heavy duty double sided carpet tape will hold the plastic in place.

[Steve Mavronis]

Cardboard just sounds like a problem waiting to happen down the road.

How so? Many manufacturers use cardboard as an electrical insulator. In dry state it is an excellent insulator. If cardboard gets wet it would conduct electricity. Maybe using it at the beach or where there is high humidity or If your pedal got soaked you'd have more to worry about then the cardboard shorting anything out.

But - It would be better to do the same thing with plastic (I'm fine with that) but just need thin flat sheets. I'm not going to use curved surfaces from other containers but I'll see what the wife has in our recycle bin!

Also, most container plastics are biodegradable being made from plants not oil (or with oil with biodegradable additives) so you aren't saving the environment by using them as PCB insulators, as long as they are disposed of properly.

http://en.wikipedia.org/wiki/Biodegradable_plastic

[KazooMan]

Well...... what if in the middle of some hot licks you accidently kick over your bottle of beer and douse your pedal board???     S**t happens!  It reminds me of the old Saturday Night Live skit called "The Pepsi Syndrome".

I just like the plastic.  It is thinner and probably mechanically stronger (more resistant to abrasion causing holes).  Even old eyelet board sometimes becomes conductive.

However........ now that I think of it there is probably another good reason for using cardboard.  We all know about the special Mojo that is found in paper capacitors.  Perhaps pedals made with cardboard just sound better.

[B Tremblay]

For floating circuit boards I've used a piece of plastic from a milk or detergent jug, cut to the same size as the circuit board, then use little zip-ties to secure the two pieces (through mounting holes). No potentially conductive material, rugged, yet easily removed if repair/modification is necessary.

[tasos]

i use transparency...it works fine for me!

[Steve Mavronis]

Well...... what if in the middle of some hot licks you accidently kick over your bottle of beer and douse your pedal board???    S**t happens!  It reminds me of the old Saturday Night Live skit called "The Pepsi Syndrome".

I guess you coat your plastic with Rain-X or something? If your pedalboard got washed down with beer you got more problems than whether or not your PCB insulation was plastic or cardboard.

How about let's see some pictures of everyone's PCB insulation techniques?

In the mean time I'm going to rummage around the house for usable plastic to test with. This is an interesting discussion because until this MXR repair it was a non-issue because I like PCB mounted pots to suspend my circuit board without any danger of shorting out against the case or other metallic parts. When I settle on a good floating PCB insulation scheme in both practicality and pro asthetics, I'll have the freedome of making solid pedals either way.

[PRR]

> most container plastics are biodegradable

At least around here, most container plastics are NOT bio-degradable. PE is the same stuff my uncle developed in the 1940s: lasts a decade or more in the sun, thousands of years if you throw dirt over it. PP is maybe tougher. Starch, PVA, and cellulose have real problems as retail packaging.

Cheap cardboard will turn to dust in 10-20 years. Like an old book's pages.

Lasts a lot longer than duct-tape, or the glue on electrical tape.

Beer is a problem.

That may be ample for your purposes.

> Many manufacturers use cardboard

There are better grades of "cardboard", rarely found in your recycle bin.

> an old milk jug

Technically polyethylene, not polyprop; but for this purpose, no real difference. (In a high-temp tube amp, PE may soften and make a wax stink before PP.)

If you are real meticulous: many of these recycled bottles/tubs are curved, you want flat. Put a small test piece in your toaster oven. At some temperature the plastic relaxes and flattens. At a very slightly higher temp it emits noxious (and flammable) gas then shrinks back into its original hockey-puck shape, so watch carefully. If you are super-fussy, whack a shape out of pine or foam, take the limp plastic out and work it down over the form with leather gloves. Ah, but then you may as well build a vacuum-table to get better conformance. But a vacuum-table wants full-size sheets to seal the suction, so now you are back to buying plastics. (Vacuum-form supplies may be a source of convenient sizes of suitable sheets.)

This site shows good prices if you want several feet of general-purpose plastic sheet:
http://www.professionalplastics.com/ABSSHEETFORMINGGRADE

They have the classic fishpaper but won't cut less than $45 worth; some entrepreneur could buy a whole sheet and cut it smaller, say 8x10 for $5.
http://www.professionalplastics.com/FISHPAPER

> pictures of everyone's PCB insulation techniques?

NSFW. I tested PC motherboards on an old Playboy magazine; right size, no chance of punch-through, and when one got too tattered I could usually find another.

[Steve Mavronis]

I'm curious, as far as liquids if the jacks aren't unplugged how would the interior get wet? They also make rubber gaskets for Hammond boxes but that's going too far for guitar needs.

This cardboard in my refurbished Dist+ is just temporary because I hate foam more. That also gets nasty after a couple decades or more. Can cardboard be coated with something electrically non-conductive?

As far as product plastic (or other materials for recycling) are there any that are not safe to use? Some plastic based things have textures or are maybe not as good as others to work with. I do like the idea of thin clear plastic under the PCB so you can still see the rest of the guts through it. I'm a pedal voyeur!

[Steve Mavronis]

Hey sorry for bring this up again but I have some flat plastic packaging from a Logitech webcam labeled as PET 1 and PET 01 symbol like this:



Just want to make sure it would be safe for electrical insulation laying against a PCB? I think it's alright Googling the properties of Polyethylene Terephthalate. A few posts back PP5 was mentioned instead.

[petemoore]

  I'm with Mr. Coffee and would add: using a small proportion of the rediculous amounts of plastic-package-fuel normally given to recycle or landfill provides a lifetimes supply of valueable electronic insulation material.
   Though it can be shaped and seamed using heat, bic and needlenose demonstrated ability. With a hard to custom make, teflon tipped/crimp-heater-sealing tool it could become an alternative to heat shrink tubing. I had positive result when wrapping a strip around a wire, then tightening the wrap with needlenose-twist, using a teflon tape tipped soldering iron or butane lighter to create the seam.
  Seems like it could be cut into strips the width of the length of shrink-insulation needed, shaped into U-end to wrap around the wire, then sealed by a fairly crimp-heater [similar to wire-de-insulator with heatable teflon jawtips...making shrink insulation that is easy to place and then even easier to heat-seal than it is to evenly heat heat shrink in a box.
 

[peterv999]

A black paper called 'fish paper' is what's used and complies fully with European safety standards for higher voltages as it withstand 500 volt using a metal testfinger.. It's about .5 mm thick and can be folded the way you like it. The paper is rather hard and impregnated with a substance.

Piet

[PRR]

> PET ... safe for electrical insulation laying against a PCB?

Yes, assuming no HIGH voltage (1000V, 500V with sharp points) and no high temperature (inside a tube-amp, direct contact with a power semiconductor), no large pressure or intense vibration which may eventually wear-through the plastic (over-stuffed Jeep radio).

Assuming you can tolerate teeny-teensy leakage, over a GigaOhm. Anything around a stompbox won't notice PET's leakage. if you were making a condenser mike head-capsule, you'd need to test your particular sample- some PET will be great, some maybe not, depending who sneezed in the vat.

For a 9V-48V stomp-pedal it's way over-spec, but the price is right.