So following up on materials suggestions made in response to the previous post on this stage monitor project, I’ve been playing with Delrin (acetal copolymer), a long-polymer-chain plastic.

It looks even more old-Star-Trek than the diagrammes I made. Seriously, I’m wondering if they made the bridge consoles out of this stuff. Cut a bunch of holes for buttons into it and you’re off.

Which is exactly what we’re about to do. But first, lj:tereshkova2001 asked if I would report back about how this plastic works as a material. Since that’s pretty hard-core geekery, I’m including that down at the bottom of this post, and talking about the panel assembly first.

So after I cut off my new panel backing from the rest of the sheet I’d bought, I decided the easiest and best way to place all these holes would be to adhere the printed scale diagramme to the plastic itself, and just drill through the paper at appropriate points.

Since movable spray fixative doesn’t seem to be a thing anymore, I came up with an alternative plan of two layers of tape – one single-sided, one double-sided. The single-sided layer is packing tape (of which I have lots), applied to the panel:

One of the reasons I didn’t just use double-sided tape in a single layer is that stuff is really hard to remove, so if I tape it to tape that’s easier to remove, I don’t have to fight that battle. Also, the packing tape is wider, meaning the holes cut in the tape don’t break any single entire length of tape, which means I always have a section of “handle” when pulling the tape up once we’re done.

Anyway, then the double-sided tape goes on the back of the cutting diagramme:

And that gets us to the third reason for two layers of tape: I had to position the diagramme on the panel so the hole guides are in the right place. You can’t really draw on Delrin, or on double-sided tape, but you can certainly use your pink glitter gel pen on ordinary packing tape just fine:

And now you know exactly where to position your cutting guide/diagramme on the panel.

BREEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE


EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE

As I was warned, this material really likes climbing the drill bit. That’s true for any plastic, and this isn’t worse, but it isn’t better, either. Fortunately, that wasn’t doing any actual damage. This is what one of the holes looked like:

Along with an insert test, which showed that yep, this seems to be working fine. I drilled out the rest of the holes, and peeled off all the tape. Having tried this before with double-sided tape only, adding the packing tape layer made this much easier.

Eventually I got most of the sockets and switches and such in place. A few of them needed separate bolts to hold them onto the board. Drilling those holes also involved tape for position control, but in a slightly different way. Again, you can just drill through the tape:

As of writing this, I have all the components integrated into the panel. I’m really pretty happy with it. There are a couple of little scratches which aren’t my favourite things in the world, but it’s not like anybody will notice them, ever.

As you can see, I have started wiring the thing. Green light means “plugged in,” red light means “power switch is ON.” Those are neon and I’m a little worried about noise from that – it’s not supposed to be an issue, but No Trust I, so I’m probably going to wrap the backs of those in copper shielding. If I have to, I can cut them out entirely and have no harm done.


And besides, it looks pretty cool.

I still need to drill attachment screw holes around the outer edge of the panel – which I kind of forgot about until just now, oops – but that won’t break anything. Then it’s wiring harness time!

I hope this keeps working out. See, what I’d really like to do is be able to move up to a modern iPad-driven sound system, but all of those use and expect self-powered speakers. If I can make these passive monitors into self-powered and it actually works? That’d let me actually move my gear into this century. Which would be really nice.

Anyway, that’s where the project stands right now. Hopefully I’ll get to work on it more tonight and have another update soon.

Now, as promised – NOTES ON HANDLING AND WORKING WITH DELRIN!

For the record, I’m using the basic Delrin formulation (no glass particles added as a hardener, etc), at 3/16th” thickness.

absynthe77’s comment that it works kind of like a very soft aluminium kind of stands up. It’s not exactly like that – you can melt this with a cutting wheel in ways you can’t melt aluminium, for example – but I see what they mean.

The aforementioned melting is minimal and not bothersome. It doesn’t clump up into a paste like acrylic plastics do, which is much nicer, and it doesn’t foul your tools, which is critical. You can cut it with an edge-grinding Dremel bit and it doesn’t get goopy and weird; it flakes off in manageable pieces, instead. But it’s still soft enough to cut with a basic Dremel cutting wheel and I haven’t accumulated much wear yet.

Here’s an edge cut made that way:


Note the circular-saw-like cut pattern; it didn’t melt the plastic away, it cut.

Unlike acrylic, Delrin does not score-and-snap. I gave it quite the depth of cut and got absolutely nowhere trying it. I even gave it another go after getting out a cutting wheel, just to see if I hadn’t scored enough, but no, it just wasn’t having any of it – not until I was almost entirely through the sheet. So while it has some flex, it’s very strong against snapping and cracking.

In some ways, working with it kind of reminds me of linoleum block print cutting, only a much harder material. With a Dremel cutting ball, for example, you can scoop bits of it out, almost exactly like linoleum block cutting. That’s pretty nice, and is how I made the square holes I needed – well, that and an xacto knife and file for finish work. Most of it was just scooping out plastic with the Dremel.

I haven’t worked with many plastics, and when I have, I generally haven’t enjoyed it, but this… this is fine. Fouling isn’t an issue, it doesn’t send sparks like metal so you don’t have to worry about shop-vac fires and can run the vacuum the entire time, I didn’t really seem to be able to overheat it in a meaningful way.

If there’s a downside, it’s that it does scratch like plastic, and more easily than aluminium. So you’ll need to take some care with that. It’s not look-at-it-funny-and-it-scratches soft, but a stray screwdriver would definitely leave a mark.

So, yeah. Definitely something I’m glad to be able to add to the toolkit. At least, so far.

eta: I’ve discovered the old speaker-level inputs used by both speaker and amp are an obsolete cable connection standard. I’m upgrading the speakers to self-powered, but I want to maintain the speaker-level-input functionality too. Do I re-implement the old standard? I mean I guess so, but. Ugh.

eta2: It was, for the record, a stupid standard.
 


This post is part of a series on restoring infamous vintage stage monitors. Spoiler: they made good, in the end.