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-   -   Joining polycarbonate /Perspex panels to make a case? (https://www.vintage-radio.net/forum/showthread.php?t=141696)

astral highway 26th Nov 2017 4:58 pm

Joining polycarbonate /Perspex panels to make a case?
 
Hello, one of the chief considerations and challenges for me in the design of my project is a far lighter case and chassis than during the last trial. It was simply too heavy to be practical.

I am intrigued by the possibility of joining together Perspex pieces to make a case that could enclose a copper sheet chassis. Is Perspex/ polycarbonate tappable to take a screw or could I use self-tapping screws? Please treat me as knowing very little about the tools and terminology and tools related to assembly with screws, etc; I won’t be offended!

Ideally the structure should be capable of taking a reasonable load - perhaps 3-4 kg. I will separate the EHT power supply and encase that separately.

Thank you !

paulsherwin 26th Nov 2017 5:06 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
You can cut a thread in drilled holes but it won't be very strong. Have you considered Superglue or other adhesives?

Scimitar 26th Nov 2017 5:10 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
I think Acetone is the solvent to use, I have done it about 35 years ago, but the memory grows dim! If you get your perspex or Acrylic from a professional supplier, they should be able to confirm the best option.

GrimJosef 26th Nov 2017 5:41 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
Don't try acetone on acrylic (Perspex). It will craze the surface. Tensol https://www.amazon.co.uk/12-Acrylic-.../dp/B01MF90AFS is the stuff developed by ICI to do the job. After enough practice it's possible get an invisible join. Much easier to use is the Simplex Rapid I mentioned in the other thread. But it leaves a bead along the join and is unlikely to look pretty.

Cheers,

GJ

G6Tanuki 26th Nov 2017 5:47 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
2 Attachment(s)
Yes ypu can make decent threaded fastenings into Perspex/Lexan: you drill a hole and then fit a brass bush.

The ones I used [though for the life of me I can't recall the name of them] were a tubular Brass threaded insert - the first third of the insert being solid, the remaining 2/3 having four slots cut in the sides. The entire thing was knurled on the outside.

You drifted them into a hole drilled into the Lexan, then when you screwed the screw into the thing it splayed the four sides of the part that was in the bottom of the hole out so they grippped the plastic.

A few minutes with your favourite search-engine will show options like those in the attached pics.

astral highway 26th Nov 2017 5:50 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
1 Attachment(s)
Hmm, iI’ve definitely seen commercial work in Perspex (clear) , housing electronics. There may well have been a mechanism to hold the screw, which had a hex head to be tightened or released with an Allen key.

It evoked in me a recollection of the typical IKEA method of securing load-bearing materials, but on closer analysis of this photo, for example, I see there is no similarity whatever.

Here we can see stanchions securing the PCB but then in the corners, threaded Perspex pieces to take long screws securing the multiple rounded corners in a sandwich ...

Aerodyne 26th Nov 2017 6:31 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
You might consider folding the acrylic sheet to save some mechanical construction work. A hot-air gun, with suitable shielding* of the parts you don't want heated, will allow you to make folds in the stuff.
* a couple of lengths of timber, set either side of the fold point, will prevent the heat getting where it shouldn't. The folds so created will naturally have a radius, dependent upon the thickness of the acrylic.

Tony

astral highway 26th Nov 2017 6:56 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
Tony, thank you, that’s an interesting tip.
What skill level is involved in folding a 5mm thick sheet, would you say ? It i expensive stuff for a trial !!

mark_in_manc 26th Nov 2017 7:53 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
Perspex (Acrylic) is less bendy in its normal state than lexan (polycarb), but easier to bend with heat. Lexan is possible - I've done a sidecar screen (sorry, for this forum, errrm, record player lid :) ) in 2 or 3mm lexan, and put two 50mm radius bends in it with two heat guns and a lot of careful bending round a former. It took ages, and was really tricky - too hot locally and it bubbles. In a factory they do it with a huge humid oven over a former, and apparently it just 'flops on' when you get it to the right temperature all over.

I've made tanks for water and sand at work in lexan, tapping threads just into the plastic itself. I think I used 24mm sheet, with M8 threads, and something thinner with M6. It works OK, so long as you do not over-tighten and strip it. We have some kind of super-runny glue too, but the joints have to be _perfect_ as it has no gap-filling properties at all.

It's quite nice to work with, on a big table saw with a sharp blade, but less forgiving than wood.

Another thought - I've made stuff which just slots together, no fasteners at all - a bit like '70s scandi-cool furniture from Habitat.

Argus25 26th Nov 2017 11:29 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
I would recommend using the correct acrylic glue. The companies that work with acrylic often leave the protective paper on the sheets, until after the gluing, that way any glue runs do not mark the surfaces. And it is possible, with practice, to get a near invisible join.

For tapping/threading and putting screws into it, I would recommend 4-40 or 6-32 UNC threads rather than fine metric. A good thread for 6mm to 8mm thick acrylic is 1/8" BSW which has a very similar thread pitch to 4-40 UNC.

Bending thick acrylic can be tricky without the right equipment.

With regards to brass inserts, the press fit ones can result in splitting of the acrylic over time. The screw in ones are better into a threaded hole, with a very small amount of adhesive. Though it is possible on the press fit ones and to have less of an interference fit and use a small amount of adhesive instead.

Boater Sam 27th Nov 2017 12:33 am

Re: Joining polycarbonate /Perspex panels to make a case?
 
If you want some scrap to practice on, find an old acrylic bath on the tip.

kellys_eye 27th Nov 2017 10:37 am

Re: Joining polycarbonate /Perspex panels to make a case?
 
Chez at Ultimatehandyman shows the construction of a 'line bending machine' to heat and fold perspex/lexan etc. The device is very simple and the results are more than acceptable for making cases.

https://www.youtube.com/watch?v=XveHMbzbyYQ

I'm currently using floorboards - specifically 'laminated' floorboards - of the type you can purchase by the pack full from the local DIY supermarket for £10 and upwards (depends on the finish you want!). There's enough material in one packet to keep the most ardent case-maker busy for a year.

These are 6-8mm thick, cut easily with a hand saw and, if you can use a table saw with a 45 degree cut angle, make terrific cases for the likes of hi-fi's etc. Team it up with some 6mm square stock (also available in said DIY places ) or aluminium angle - for making front panel brackets - and you have yourself a sturdy and appealing case for pennies.

Craig Sawyers 27th Nov 2017 10:53 am

Re: Joining polycarbonate /Perspex panels to make a case?
 
By the time you have bought polycarbonate or acrylic sheets, and scrapped some trying to perfect the technique, it might be actually cheaper to buy one. Google "Model Display Cases".

Craig

Skywave 27th Nov 2017 12:12 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
Quote:

Originally Posted by GrimJosef (Post 994617)
Don't try acetone on acrylic (Perspex). It will craze the surface.

I can confirm that. :thumbsup:

Quote:

Originally Posted by GrimJosef (Post 994617)
Tensol https://www.amazon.co.uk/12-Acrylic-.../dp/B01MF90AFS is the stuff developed by ICI to do the job. After enough practice it's possible get an invisible join.

I can confirm that, too. :thumbsup: It is very effective for making lasting, strong joints with Perspex. I discovered Tensol Cement way back in the mid-1960s when I made a case for an AMU (or ATU as such was then called). I still have that item today, despite it being transported around the country in packing cases bounced around in cars, vans and lorries during various house moves from those early days until now.

Al.

Aerodyne 27th Nov 2017 1:17 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
Bending 5mm acrylic (Perspex) sheet would indeed require practice before committing a large piece to the heat gun. The gun must be kept moving or blistering may occur. Not too close to the sheet or it will become damaged, i.e. slowly does it.

Thinner sheet is a lot easier to handle. As for tapping the stuff, a tapping made into 5mm would work but it would not be strong, regardless of thread pitch, though as suggested earlier, a coarser thread would be preferable.

I used Tensol cement for school projects - No. 10 is thick because it contains dissolved Perspex, so it is rather treacly in use and can be messy. Pure solvents can be applied using a syringe for accurate location and minimal overspill.

Again, at school I used a strip bender which was simply an electric fire element set a little way below the gap created by two metal surfaces. The sheet was held in place by hand until the sheet became pliable. Very easy to do, provided the element length wasn't exceeded.

Strip bender:

https://www.abbeon.com/Item--i-1257

Tony

kevinaston1 27th Nov 2017 2:46 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
I get a number "DJ Workstations" in for repair; the perspex front panel having been fractured.

Tensol 12 is nice and this, and with care, even a big crack becomes almost invisible after repair.

BE WARNED. This stuff really is bad for the respiratory system. You need to work in a well ventilated area, with a GOOD ventilator face mask.


Kevin

Skywave 28th Nov 2017 12:08 am

Re: Joining polycarbonate /Perspex panels to make a case?
 
1 Attachment(s)
Good advice, Kevin: Tensol cement contains three active chemicals, all 'not nice': 2-phenoxyethanol; methyl methacrylate; dichloromethane (a.k.a methylene chloride). The vapours of all, if breathed in, will do you no good whatsoever, with the last chemical probably the worst in that regard. Information received indicates that users who have a heart problem should stay well away from the vapours of dichloromethane.

If I recall correctly, wasn't dichloro' the active ingredient in the now not obtainable original Nitromors paint remover? And for some reason, the word 'anti-freeze' is now lurking somewhere in the back of my memory . . .

Tensol cement #12: the data safety sheet is attached. (It's a pdf download):

Al.

Boater Sam 28th Nov 2017 12:28 am

Re: Joining polycarbonate /Perspex panels to make a case?
 
We had some adhesive for repairing dishwasher racks by gluing plastic caps over rusty wire ends. Had dichloro and Methyl Meth in it, horrendous stuff, COSHE regs nightmare for workers.
They never came off though!

astral highway 28th Nov 2017 1:29 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
Hello everyone,

Thank you for all these very useful comments, too detailed to reply to each of you individually! I've certainly got a wealth of advice here.

I'm quite intrigued to be about to learn two new skills: working with polycarbonate and also threading for the first time. Quite a learning curve!

Thank you also for the advice on the correct adhesive. I will make a note and heed the COSHH advice!

Richard_FM 28th Nov 2017 2:41 pm

Re: Joining polycarbonate /Perspex panels to make a case?
 
I heard that chloroform was a good solvent for chemically welding perspex, though very hard to obtain & use!


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