Machining acrylic/polycarbonate for PCB case - Page 1
Forum section: electronics / projects

author: radian
author_rank: Contributor
timestamp: July 25, 2013, 04:25:22 am
content: Hi all. So I found a site that sells cut to size clear acrylic and polycarbonate for a reasonable price. I'm thinking of using 6 pieces to create an enclosure for a power supply PCB I'm designing. I think this would be much more flexible than buying a pre-made case.Now I don't want to glue the pieces together, instead I'd rather use screws. The tricky part is attaching the pieces at 90 degrees. At some point I will need to drill and tap an edge (or use 90 degree brackets). Anyone have any experience with these materials? Which is better to use and what sort of thickness should I aim for? I was thinking 3/8 inch with small screws, but not sure how much clearance I will need when drilling into an edge.Thanks

author: poorchava
author_rank: Super Contributor
timestamp: July 25, 2013, 05:40:45 am
content: Generally to have an aesthetically pleasing enclosure I'd aim at 3-5mm thickness. Tapping that will be pain in the ass. Acryllic tends to crack and deform, especially the cheap extruded one.I'd rather glue it

author: baoshi
author_rank: Regular Contributor
timestamp: July 25, 2013, 06:39:07 am
content: Quote from: radian on July 25, 2013, 04:25:22 amI have seen clear acrylic cubes with embedded screw holes at 3 faces, size about 1.5x1.5cm. You only need to install these things at the 8 corners and drill the panel for screw to go through.

author: Corporate666
author_rank: Unknown
timestamp: July 25, 2013, 07:23:16 am
content: We machine (literally) tons of acrylic each year.Tapping a hole on the end of a sheet will be tricky unless you have some way to accurately hold it and drill the hole. There are all sorts of specialized profiles for drills to drill it effectively, but honestly, if you go slow, you will be fine. Same with tapping... shoot for a 60% thread for a bottoming tap and drill 4-5 threads deeper than you will actually tap and it will be no problem. If your fasteners are small, you should be OK if you leave 1/16" wall thickness between hole and edge.But actually, I recommend gluing it. MEK partially dissolves the acrylic and as it evaporates, the acrylic actually melts together giving a crystal clear and very strong joint. Only problem is the MEK does not fill gaps, the pieces must fit together perfectly before gluing.

author: fcb
author_rank: Super Contributor
timestamp: July 25, 2013, 06:43:43 pm
content: +1 for MEKYou can make a sort of filler if you dissolve some of your CLEAN acrylic in MEK, it's quite tricky though.I've seen some big acrylic structures that are tapped M4 AND glued.

author: XynxNet
author_rank: Regular Contributor
timestamp: July 25, 2013, 08:01:47 pm
content: You can machine polycarbonate and acrylic with woodworking tools. Just drill it slowly and use a drill press and a machine vice, when drilling the edges.Cutting a thread in both materials works very well, so you can use machine screws.I personally prefere polycarbonate because it is stronger and bends instead of fracturing when stressed. It's much more expensive though.Be aware that both are thermoplastics. It is easy to heat parts of the sheets (for example with a constantan wire) and bend them. That might be an attractive alternative to screwing parts of your case together. On second thought bending might not be a good idear if your powersupply can get really hot, because the sheets might unbend themselves then.Both materials should be maschined with their protective sheets. Removing them should be your last step, exept if you heat them, then you should remove the protective sheets before heating because otherwise they burn into your acrylic or polycarbonat.If you want perfectly transparent edges use first a scraper, than sand with 280 grade grit-paper or directly wet with 600 grade grit-paper. Depends on the quality of your scraping (Does this word exist??).

author: edavid
author_rank: Super Contributor
timestamp: July 25, 2013, 08:05:40 pm
content: Quote from: radian on July 25, 2013, 04:25:22 amHow about telling us the site?

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: July 25, 2013, 08:22:50 pm
content: Joints using t-slots, nuts and bolts can be used if laser cutting.check out the details here.One caution learned the hard way. Laser-cutting results in high edge stress. If you wipe the freshly cut piece with alcohol to remove residue, you may have hundreds of stress cracks instantly! It looks kind of cool...sort ofMachining by other methods may also have this problem.

author: Corporate666
author_rank: Unknown
timestamp: July 25, 2013, 09:34:23 pm
content: Quote from: XynxNet on July 25, 2013, 08:01:47 pmFor bending, acrylic is easily bent with a hot wire setup - gives nice crisp straight bends and will not unbend with heat (you have to hit the melting point of the acrylic, but if it gets that hot, you have other problems)As for clear edges, two even easier solutions are1) blow torch. Hotter is better - MAPP works well, but regular blowtorch for plumbing works nicely too. Just take a few scraps and get a speed and distance worked out and it's easy to do. This is how the pros do it.2) MEK. The MEK dissolves the acrylic, so some MEK on a rag wiped over the edge will instantly melt the edge and make it clear.The big problem with polycarbonate (besides price) is that it gets destroyed by UV light. It goes yellow and brittle over time, whereas it's not really much of a problem with acrylic.If getting pieces laser cut, it is easy to have interlocking tabs put in the pieces (sort of like a dovetail joint from woodworking). MEK is usually applied with a syringe and capillary action draws the MEK into the bond line. Squeeze the syringe until a drop starts to form and then touch it to the bond line, and it will get sucked in... hold for several seconds and you have a welded together piece that will be extremely strong.

author: radian
author_rank: Contributor
timestamp: July 26, 2013, 12:55:44 am
content: Thanks everyone, some great suggestions.So what I'm thinking is to get 4 pieces of acrylic square rod and mount it in each of the 4 vertical corners of the box. Then I can drill from each box face into the rod. This will allow me to purchase thinner acrylic (maybe 1/8") plus won't require as careful drilling. I'm thinking of getting myself a tabletop CNC mill to drill the holes (Sherline Mill, CNC ready for around $1400 before tax - no steppers or controls at this price however). Overkill? Well, yes, but I've always wanted to try machining, and this may just be the excuse I'm looking for.Here's the site I found for cut to size plastics:http://www.tapplastics.com/product/plastics/cut_to_size_plasticFor example, for 10 pieces of 5"x5" 1/8" cut clear acrylic, cost is $10 total ($1 per piece, can't beat that). Shipping is pricey at $20 however (to Canada) and with UPS as the courier, I'm afraid of the brokerage fees I would be facing. Instead I found a local plastics company near me, so I think I'll go with them to begin with. Cost is higher locally at about $4 a piece, so probably looking at around $30 for the enclosure in the end. More than buying one off the shelf, but hey, it's more fun this way.

author: MacAttak
author_rank: Unknown
timestamp: July 26, 2013, 01:15:52 am
content: Beware if you are using high-speed drills or saws. As noted, these are thermoplastics. They begin to flow when heated and are very viscous and sticky. It will easily bind a bit or blade. If you're lucky that will just cause it to look crappy. If you're not lucky you could be dealing with an injury depending on your workholding setup and/or use of protective gear.So you probably want to use the lowest speed setting and only work the material a little bit at a time. Let the material (and the tools) cool down.You can even get decent cutting results with a jigsaw or tablesaw as long as you go very slowly and minimize friction heat. I used to make panels for car audio subwoofer enclosures using 3/4" Lexan (can make some beautiful cabinets using lexan as a light pipe and decorative etching on the interior surface). We used a hand-held jigsaw for all cuts, fine-toothed blade, and only cut an inch or two at a time before letting it cool. Also it helps to leave the protective paper on the surface while cutting to prevent any damage to the surface.

author: Spunky
author_rank: Regular Contributor
timestamp: July 26, 2013, 03:33:03 am
content: I would use PETG instead or acrylic. Acrylic is too brittle to make anything durable, it's only advantage is that it's the clearest of the transparent materials, but it cracks with very little encouragement. PETG is almost impossible to shatter, easy to form with heat, drillable, solvent weldable, jigsaw-able, etc. It scratches a bit more easily but it's tough. It's the same stuff drinks bottles are made of, but when it's 4mm thick it's perfectly clear and looks great. You can buy it in sheets from RS.

author: Spunky
author_rank: Regular Contributor
timestamp: July 26, 2013, 03:33:58 am
content: Also sold as Captrad and Spectar (brand names)

author: poorchava
author_rank: Super Contributor
timestamp: July 26, 2013, 07:59:49 am
content: There are actually 2 different types of acryllic: extruded and cast. Extruded acryllic is much cheaper than cast one, but it is a total bitch to machine in any possible way.Extruded acryllic when milled, sawed, drilled will likely melt and wrap around your tool bit. A partial solution is to use lubrication/cooling such as WD40 or non-aggresive cutting fluids. In general the way I have found to machine extruded acryllic semi-reliably is to combine very fast feed, slow rpm, very shallow cuts (or pecks in case or drilling) and lubricant. Whenever you can glue it - do it

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 26, 2013, 01:37:42 pm
content: you may also consider aluminium angle bar and rivets for fixed assembly. screws only at the back or front for circuits and components assembly and later maintenance. YMMV.

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2013, 08:46:18 pm
content: With acrylic there are 2 methods to solvent join, one uses a MEK and acrylic solution and the other a MEK and acrylic monomer and then you add a catalyst that then cures the monomer to make it into acrylic. This has some gap filling properties and as well is a lot more UV stable when used outdoors.With any joint the problem is getting a good cut, either you use a water cooled saw blade with fine teeth to get a clean cut or you will spend time with a sanding block and 80 grit paper then 120 grit afterwards to get a smooth edge. If you use a square block inside as a fillet then you can make it very strong, just use a square extrusion about the same thickness as the material, and weld it along the entire length after fitting up and sanding. Air bubbles are a problem though, just work from one end to the other and you get good results.