maersk

laser cut perspex rack enclosure?
« on: April 05, 2012, 10:31:29 AM »
so...i'm new here (hi everyone) and in the midst of building some diy audio gear (gssl, calrec eq, 808 kick)
but i'm on a tight budget and the rack enclosures i've found seem to be pretty pricey - nothing below £40.
i have access to a laser cutter at uni but it will only cut perspex and wood.
do you think a perspex rack enclosure would be strong enough?
...i found this http://www.groupdiy.com/index.php?topic=42483.0

the other option is to find some old/broken rack gear (perhaps a network switcher) and gut it.

i can't find any info and figured some of you guys might have an idea?

edit: just realised this might be better suited in the "machine shop"


sahib

Re: laser cut perspex rack enclosure?
« Reply #1 on: April 05, 2012, 06:06:23 PM »
Welcome.

You don't put pro-audio circuitry into a plastic housing.

A perspex front panel may  look good but it will be exposed to EMI.

I suggest to look up e-bay. You can pick-up rack equipment for parts or repair for  a few quids. Shipping will probably be more but still cheap. Plus you get lots of parts.

maersk

Re: laser cut perspex rack enclosure?
« Reply #2 on: April 06, 2012, 07:37:36 AM »
okay, i'm steering towards a rack shelf type thing but still thinking perspex faceplate.
would EMI be a massive problem?

Rob Flinn

Re: laser cut perspex rack enclosure?
« Reply #3 on: April 06, 2012, 10:57:44 AM »
okay, i'm steering towards a rack shelf type thing but still thinking perspex faceplate.
would EMI be a massive problem?

Ideally you want the electronics sheilded/screened.  Perspex wont do that for you, although it would probably look good.

If you are in the UK, I would look at the CPC site for cheap(ish) rack cases.  The links below are for the 1U & 2U cases both of which are £40 or under.  & the shipping is free over about £45
http://cpc.farnell.com/unbranded/r2100-1uk/19-rack-cabinet-1u/dp/EN55271?Ntt=en55271
http://cpc.farnell.com/unbranded/r2100-2uk/19-2u-rack-cabinet/dp/EN55272?Ntt=en55272
regards Rob

ej_whyte

Re: laser cut perspex rack enclosure?
« Reply #4 on: April 16, 2012, 07:33:08 AM »
That linked SSL was the first piece of DIY I built, and now having learnt more I will admit that using a perspex front panel is technically not a good thing. However, I will also say that I have not had any EMI problems, and have not felt the need to change the front panel to a metal one. I could imagine that in a large commercial facility there may be issues, but it has been fine for my uses.

Not to encourage bad build-practice, this is just my experience. YMMV.

Cheers

gemini86

Re: laser cut perspex rack enclosure?
« Reply #5 on: April 16, 2012, 06:06:18 PM »
The problem is, the more gear you build in perspex enclosures, the more emi that will be floating around your studio. You're going to create your own emi problem, eventually.
- Rodney

"...you better call Kenny Loggins, 'cause you're in the danger zone."

Gold

Re: laser cut perspex rack enclosure?
« Reply #6 on: April 19, 2012, 03:18:56 PM »
Does anyone have any basic tips for cutting and bonding acrylic sheet? What kind of cutting tools (bits)? What RPM range? How do you get really clean edge? I know there are chemical polishers and you usually bond with something that comes closer to melting the edge than an adhesive. Acrylic sheet 101.

sahib

Re: laser cut perspex rack enclosure?
« Reply #7 on: April 20, 2012, 12:10:29 PM »
In order to get a right angle cut you have to cut it on a table (circular) saw. If you cut it by hand or on a band saw then you have to straighten it with a router (or a milling machine if you have an access to one).

For smoothening the edge (or surface) you'll be using sand paper. For this make yourself some sanding blocks in various grits by sticking the sand paper onto a timber (or any other) block using a double sided tape.

Start with 100 grit to take the roughness. Then sand it down with 180 grit and then something like 120 and 240 grit. If you are going to bond the edges then you do not have to go any further as the glue will fill in and the whole thing will come up transparent.

Apart from anything there is a deliberate need for not polishing the edges which are going to be glued. If the surface is polished to total clear then if you do not bake it in the oven, as soon as you apply the glue the surface will crack hairline due to stress.

For gluing there are three main adhesives.

First one is Tensol which comes in two parts. There is also single part type but I never used it. You mask off the the areas that you do not want the excess glue to go onto. Apply the Tensol to the area and position the part to be bonded. Now the excess Tensol will spread over the masking tape. Do not touch it. Leave it to dry for an hour or so until the Tensol  chewy hard. Then carefully cut the excess along the edges using a surgical scalpel (I use Swann-Morton 10A, 25 and 26 blades). Remove the masking tape carefully and leave the whole thing to set for 24 hours. This is a permanent bonding.

The other two types of adhesives are Chloroform and Dichloromethane. I don't use Chloroform as I suffer from migrane terribly. Dichlo is lesss smelly. Both of these are in water consistency. All you need is an artsist's paint brush of an appropriate size. You hold the pieces together, dip the brush in dichlo and touch the edge. The dichlo will run straight in. Then repeat it all the way. In a minute  or two  it will be strong enough to hold itself. After half an hour all will be rock solid. But this is not as permanent as the above method, though as long as you don't force it  itwill stay for years. I stil have things that I glued twenty years ago.

For polishing the surface to totally transparent, after 240 grits you continue with 400 and 800 grits. then use 1000 and 1200 grits but this time you have to dip the sand paper into water and then apply it onto the acrylic gently. Once you are happy with the surface then take a bit of balsa wood or even thick cardboard, apply some T Cut (for polishing your car's paintwork) and rub the surface down to water clear.

There is also flame polishing  but it is not really a hobby application.

Also some people may advice using polishing mop on a drill. I do not reccommend that for polishing edges as it will take off the corners. For surfaces you also have to be careful. If you go too hard or stay on for too long you may wear out the surface and create a "crater". Getting rid of it means starting the sanding down procedure right from the beginning. Even then there is a risk that it never gets right.  If the piece to be polished is managably small then the best way is to have the balsa wood or the cardbaord taped up on a flat table surface, TCut applied and the piece rubbed on a circular motion.
« Last Edit: April 20, 2012, 12:14:34 PM by sahib »

Gold

Re: laser cut perspex rack enclosure?
« Reply #8 on: April 20, 2012, 02:26:39 PM »
Perfect! Thanks Sahib.

sahib

Re: laser cut perspex rack enclosure?
« Reply #9 on: April 20, 2012, 04:52:32 PM »
You are welcome.

Just realised that I forgot to mention.

Chloroform and Dichloromethane are not strictly adhesives. They actually melt the material on the surface and as a result two parts bond together. Also make sure that all that stuff is used in a well ventilated area.



 

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