Suggestions for making cutouts in plastic enclosures?

[reagle]

I am working on a new project using off the shelf enclosures. All is well, except I need one connector to poke through the side. Normally for project at work I'd ask the case vendor to do that, but in this case being a hobby project with small volumes, that's out of my budget. Soo,  I've been wondering- what can you guys suggest for a do at home type of cutting a rectangular slot in a plastic case? The key is making it clean and repeatable, so if I need to make 10 of these they'd all looks the same and fit

 I am thinking a router bit in a drill press or a Dremel with some type of a router attachment/stand?
Or do I need to build me a CNC box?

[Rerouter]

being how its only low quantity, i would probably just mark your shape, drill out the rough shape leaving 0.5-1mm at the edges then file flat, most of the hobby files will have one with a smooth edge, thats the one you use for corners, as it will not cut into the other face,

its a little tedious but considering its needs square corners (rectange) its the fastest way to get them done without first sourcing other tools,

[MikeO]

Reagle,

Do you happen to know a carpenter?  Recently one loaned me a multimaster/oscillating tool, and I bought one the next day.  These days, most of them own one, and may make a loan to you.  I favored a battery powered one, as it better suited my needs.  Since then, I've used a few, and learned that the tool matters less than the blades.  Here is a woodworking forum discussing them:

http://www.woodworkingtalk.com/f12/dremel-multi-max-vs-fein-multimaster-vs-rockwell-sonic-crafter-10557/

The perfect tool is a square punch, but they can be pricey, given their limited utility.  Google "greenlee square punch"

For ten units, I'd make a marking template.  You may find one already for you in the manufacturer's datasheet.  You can glue it to some cardboard from the back of a notepad to stiffen it.

If you can't mark well with pen or pencil, mark carefully with a sharp knife.  If it's ABS, maybe just mark with masking tape.

Barring all the above, I think Rerouter is advising you well.  Some plastics melt quickly with power tools, making a mess of your workpiece, and Rerouter's approach works best.  If the plastic is soft (e.g. PVC), you can make a template of scrap metal, affix with care, and use a very sharp utility knife.  Don't saw with the blade, push in and down, pull blade back without cutting, and then again, in and down.  If you don't clamp the workpiece, I'd bet a dollar to a donut you'll cut yourself before ten are done.

Regards,
Mike O'

[Rerouter]

the issue with using a blade is that it tends to push out the edges into a hard to clean up hump about 0.5mm higher than the surface, so while they are fine for marking i have taken to the drill and file approach so to avoid it,

[reagle]

Unfortunately I am surrounded by engineers
The cases are ABS 94HB, about 3-4 mm thick

[onlooker]

Possible steps:
1). Make a plywood stencil. If the surface to be cut is curved, then use a material that can follow the shape.
2). Clamp it to the right location of the box.
3). Use a hot knife at the right temperature (~200C) to do the cut. Or you can try your solder iron with a sharp tip.
You may need to experiment on the temperature and the cutting angle, and may need cut it in multiple passes. 

[MikeO]

Rerouter is absolutely right about that hump from the knife, but I don't think you'll be cutting ABS with a cold knife.  Regardless, you've been warned when it does come up.

My first hot knife was a cheap soldering iron modified to accept an x-acto blade.  The second version had a variac to control the temperature.  My current one came in a box that says "hot knife."  I'm not sure it's an improvement.

ABS is a tough material to work.  I've made many a proto out of it, and never once by choice.

Be prepared to have the filings statically clinging to you, the workpiece, your tools,... a shop vac helps.

ABS will reflow and close the cut if the curf is too narrow and temperature is too high, regardless of your cutting technique.  If you use a power tool that cuts in one direction (e.g. rotary rather than reciprocating) the waste will form a melted edge.  Send it to the inside, and crack it off with your fingers or a scraper.

Regards,
Mike O'

[reagle]

Sounds like fun either way! I think I'll try hot tool method- seem to recall doing that many many years ago, though the results typically sucked

[notsob]

For a few prototypes, drill out undersize holes, then file to shape, don't use normal metal drills on plastic (ABS) etc, use step drills

example of step drill set http://www.ebay.com.au/itm/28-Sizes-3-pcs-Smoother-Cutting-Titanium-Step-Drill-Bits-Set-Step-Bit-Tool-New-/140827210998?pt=AU_HardwareParts&hash=item20c9f4b4f6

use square profile files to file hole to size

Cheers

Peter   [ I'm still waiting to hear of someone trying a mortice drill set on ABS, used in woodworking, it's an assembly with a drill fixed inside a square cut chisel]

[MikeO]

[ I'm still waiting to hear of someone trying a mortice drill set on ABS, used in woodworking, it's an assembly with a drill fixed inside a square cut chisel]

If you don't back up the cut, the ABS will just break.  If you do back it up, I think you'll just bend the handle on the drill press.  Then again, it might work awesome.

Now, if we add a little inductive heating loop around the mortise tool...

I'm waiting for a video of someone's boss catching them fashioning an inductively heated mortising tool to make ten holes.  I used to have these four techs working for me that spent more than half of their time doing repetitive testing.  They were all ex-military, various branches, various nations, very bright, very creative, very bored.  Show up late one day, and this is exactly the kind of project the whole crew would be working on.

Regards,
Mike O'

[nctnico]

Make two cuts at both sides of the hole, use a knife to carve the bottom of the hole and use pliers to break the remaining piece of plastic. Another option is to get a rectangular punch. These are pretty cheap on Ebay but you'll need some kind of press and alignment mechanism.

[vk6zgo]

There is another thread about a similar problem in this forum under the title "Punching Holes in Jiffy Boxes".

[reagle]

Thanks- found it https://www.eevblog.com/forum/general-chat/punching-holes-in-jiffy-boxes

[G7PSK]

Cut the shape you require in a piece of tin plate or aluminium sheet such the you can fold up one side and one end to form a jig, then buy a pyrography  kit or tip for your soldering iron and use the hot knife to cut the hole in the plastic.


http://www.ebay.co.uk/itm/Weller-30w-Pyrography-15-pce-Hobby-Kit-Wood-Leather-/140387094581?pt=UK_Crafts_Other_Crafts_EH&hash=item20afb91035&_uhb=1

[Gall]

I do it in three ways.

1. Try to design the device so that only round holes are required. Small holes are just drilled, larer holes are drilled and reamed. It is wise to make small center hole first before drilling larger hole.

2. Cut by hand with a coping saw. By using proper technique one can make surprisingly complex things from wood or plastic. http://ahsapelyapimi.com/resimler/kutular/15.png

3. Mill them.

[Skibane]

Nibbling tool?

[Richardchris]

Well Abs will reflow and near the cut if the curf is too filter, and heat range is too high, regardless of your reducing strategy.  If you use a power that reduces in one route, for example turning rather than reciprocating the waste will type a dissolved advantage. 

[Alex Eisenhut]

Nibbling tool?

Exactly this. Very useful tool.