Cutting foam inner for case

[Bob Eager]

I've just purchased a small clamshell type case for storing a portable disk drive, etc. Nothing fancy, just a plastic casing with a thick wodge of foam shaped to fit each half.

I've always had limited success cutting the foam in the past, but this is a bit former and looks to be OK if I use a nice sharp knife.

However, there is one thick piece of foam in each half, rather than the two thinner ones I'm used to. So, how do I cut a neat rectangular hole in the foam, limiting it to (say) half the depth of the foam? (i.e. how do I do the horizontal cut?)

I thought of slicing the foam in half horizontally, then cutting the hole in one half. But even doing that horizontal cut neatly is a puzzle.

I have no sophisticated tools; is there some easy way that I've missed?

Thanks

[EricP]

The guy in the local foam shop cuts it with a newish large wood saw. The sort with the wide blade you cut planks with or a tenon saw for smaller cuts.

You can apparently use a hot wire like used on polystyrene, but I have never seen it used on foam personally.

For a large horizontal cut through the centre it would be worth making a guide of some sort up like a jig.

[fred]

In article , Bob Eager writes

I'm so glad you're doing this one first, I've got a couple to do and was just mulling over the cases on CPC to find the best one. Where are you getting yours from?

When I was working with military stuff the transport case inserts were made of pre-cut layers of Plastizote foam of an inch or so bonded together to avoid this sort of difficulty. There is a foam supplier round the corner from my office so I may buy layers to stack up and solve the problem, do you have any near you?

Assuming you have to cut, hot wire is definitely good for polystyrene and more rigid foams but I imagine the insert is the soft stuff so may not take this too well (dep practice on scrap). Google has many tips for hot wire and wooden guides.

Cutting with a new scalpel is usually easy but impossible to do neatly for a long and wide cut. Would it be possible to use a razor sharp sabatier type knife to make the horizontal cut?

[Andy Hall]

For a future reference, in case you have need again...

I use several Peli cases for equipment of this size and larger

suppliers and price variation.

These are stout polypropylene and very tough - suitable for handling by the monkies employed by the airlines.

There are normally several layers of foam insert - some full sheet and others vertical square fingers of foam joined at a few places. You can pop out the fingers to the shape of the object and also cut them easily to length with scissors. I glue pieces together with spray mount adhesive. If I need to make a change of equipment I just alter the foam. it's possible to buy spare sheets as well.

[Bob Eager]

Sounds like a possible solution.

Thanks.

[Bob Eager]

CPC...! This one is SG32411 (03)

I don't know of any. In this particular application a small, cheap case was all I wanted, so I don't want to go to great lengths.

This is actually surprisingly rigid.

Good idea. May have something there.

[Bob Eager]

I considered Peli, and would use them for something more demanding. Not cost effective for this situation, though.

[Roly]

I've had to do this sort of job for a number of items of equipment and haven't yet found the ideal solution for me.

The solution to avoid at all costs is the pre-cut diced foam, where you tear out bits to leave a hole. You end up tearing out additional bits every time somebody puts the item into or out of the case.

I made a couple of hot wire cutters out of guitar strings ( steel - not nylon ! ) and an old 12v lighting transformer fed by a dimmer. It's possible to set the current to an appropriate amount so that it cuts freely without burning.

Guiding such a cutter is quite a challenge. The best I've found was 3mm mdf cutouts, but the results weren't as perfect as I had hoped.

I also made a hot wire cutter that had a horizontal wire to trim down the waste material to a different thickness so that it can be put into the bottom of the hole that you've just cut out.

Being in the audio business, I've still got some single-edged razor blades. They make neat cuts in thin foam. A scalpel will do the same.

Thick foam that's moderately rigid can be cut neatly with a serrated bread knife - I use one with a finely scalloped edge and it works well.

Some tool shops also sell a scalloped jig saw blade and mention their suitability for foam. I've never used one, but it looks like it might work.

[Dave Plowman (News)]

I'm told the best microphone foam windgags are made by freezing the foam before machining. Dunno to what temperature, though. But you could try putting the bit in the freezer first?

Other way is a hot knife to melt rather than cut.

[Andy Hall]

Nonsense

No you don't if you stick the pieces together. A suitable heavy duty spray mount adhesive does this perfectly, and the pieces don't pop out unless you go out of your way to yank them out fairly hard.

[Dave Plowman (News)]

Saw them in Lidl the other day, strangely. I've still got a few boxes so didn't buy them.

[Bob Eager]

Can't do any harm. I'll try that.

[Bob Eager]

Following another suggestion, I'm going to try that.

Difficult for a large horizontal cut, though.

[Andy Hall]

Bit of moisture first.?

So they're called windgags. I've always wanted to know the proper industry name for them.

Why are there sometimes foam ones and other times those grey fluffy ones?

I'd have expected them to attentuate the high frequencies more than they seem to do....

[Dave Plowman (News)]

It's one name. Other one is pop shield. The last being more appropriate to a close vocal mic - although it's doing the same job, preventing wind, ie breath, getting to the diaphragm.

The 'animal' is for extreme conditions. It fits over what is known as a basket which is a windgag for less severe conditions. It also waterproofs the combination. If you dismantle one you'll often find the mic inside has a foam gag too. Bad practice as any gag effects the top response but quicker in a situation where the basket has to be removed often - ie drama where you'd not want it inside. If the mic isn't moved and indoors you can get away without any windgag at all. But swinging it around in a boom will produce wind noise.

If you want the neatest looking mic 'in shot' so no windgag you use an omni-directional where the diaphragm is only 'open' on one side - these are far less sensitive to wind noise. Cardiod or indeed any directional types route sound to the back of the diaphragm and use cancellation to give the directivity pattern, and anywhere sound can go, so can wind...

The fluffy or animal comes with a hair brush, and giving it a good working over helps reduce top loss, as does a good wash every so often. But every windgag does to some extent. The least worse are the gauze screens you'll see used in a recording studio for close micing vocals.

[Andy Hall]

Thanks. That's one more item for my curiosity list.

[John Rumm]

The ali attaché case I use for my smaller Router is filled like this - works very well. I seem to recall that was a fairly cheap case from CPC (promoted as a video equipment case - but in reality works well for lots of things)

[fred]

Thought it might have been ;-)

I have them on my list, your size 1 would be perfect for mine on its own but I want to put the ac adaptor and leads in there too so it will have to be size

2 which is a bit more of a handful.

I wasn't meaning anything special, this shop just sells replacement stuff for sofas and most big towns seem to have one squirreled away somewhere. Might be handy if you mess up the supplied stuff.

I'll def try Dave Ps freezing trick on mine and the dimmed lighting transformer/guitar string technique of Roly's sounds like a a winner if I ever need to use hot wire for anything.

[Richard Perkin]

"Dave Plowman (News)" wrote in news: [e-mail]:

See eBay item 160100677164 and larger quantities in the seller's 'shop'. I'm going to buy a few but haven't got a round tuit...

[Bob Eager]

Thanks to everyone who suggested things. It's done.

I put it in the freezer for a few hours; no appreciable chage (guess if I'd wet it first...).

I stood it on end, gently nipped into the Workmate jaws. Sliced down, freehand, using a long Kitchen Devil knife. This was fine serrations on one edge, big scallops on the other; I used the fine serrations. It cut with no trouble at all. I could have made a jig to get it "Andy Hall" perfect, but of course any slight irregularity is only visible if that surface is visble overall. Since the two cut sides go back together after I've cut holes in the top slice, it's fine for me.

Only problem was that the knife was barely long enough.