Drilling large hole in thin plastic enclosure - Page 1
Forum section: electronics / general

author: Jeroen3
author_rank: Super Contributor
timestamp: March 13, 2025, 09:21:45 am
content: I want to make four 12mm holes in the top of this housing. I have drilled a lot of enclosures with large twist drills, and they typically grab the plastic a bit. Which is normally not a problem when can clamp it down.This box is different....https://www.phoenixcontact.com/en-gb/products/component-housing-upper-part-me-225-ot-1mstbo-kmgy-2914877I can 3D-print an insert for locating the holes from the inside. But holding this flimsy unit is tricky.Any recommendations?

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: March 13, 2025, 09:47:48 am
content: Hi,try something like:https://www.reichelt.de/de/de/shop/produkt/stufenbohrer_tin_4_0_-_20_0_mm-132165Good luck

author: jpanhalt
author_rank: Super Contributor
timestamp: March 13, 2025, 10:25:24 am
content: I second a step drill bit. They don't tend to pull in, so clamping is probably not necessary. Amazon sells a set of 3 for $7 USD.https://www.amazon.com/HSS-Step-Drill-Bit-Set/dp/B0BG43YQ4K/ref=asc_df_B0BG43YQ4K?

author: Berni
author_rank: Super Contributor
timestamp: March 13, 2025, 10:35:43 am
content: Yep i used step drills a lot with plastic and they work well.You do have to feed the drill in very gently or it can still grab if it tried to bite off too much at once, but it certainly does not have the problem with twist drills that like to make an oval hole and then "thread themselves in" rather than finishing the hole into a circle.

author: Kean
author_rank: Unknown
timestamp: March 13, 2025, 11:44:53 am
content: I would- 3D print a jig for centre punching the 4 holes- Use a small pilot drill - say 3mm- Use a long step drill 3-12mm in 1mm incrementsIf you are going to do a lot of these, then maybe talk to a toolmaker about getting a 4-gang punch made.Edit: Probably a punch and die with the die doubling duty as the holder/alignment jig, maybe with the part held facing down (although that may then need deburring of the holes).

author: Jeroen3
author_rank: Super Contributor
timestamp: March 13, 2025, 11:55:08 am
content: Yes, I have a step drill.... it requires drilling outside-in where I can't hold the thing...So, I need to create something for that first...

author: JohnG
author_rank: Frequent Contributor
timestamp: March 13, 2025, 12:49:19 pm
content: There are special twist drill bits available specifically for plastics. They usually have a smaller angle and probably some other features. I don't have personal experience with them, but it might be worth looking into. An example:https://www.fine-tools.com/kunststoffbohrer.htmlI also have a set of step drill bits, one of which has a largest step of 0.5". So, perhaps there is a step drill that has a max OD of 12 or 12.5 mm that you can use from the inside of your box, since you can fit a regular 12 mm bit.John

author: Jeroen3
author_rank: Super Contributor
timestamp: March 13, 2025, 01:17:27 pm
content: Well no, not a lot. But dozens.Phoenix did not get back to me for customizations. (Nobody does stuff in Europe anymore)I was thinking about forstner, I have used that for large 22mm holes before.Maybe if I make a larger 3d print insert or get a piece of wood I can hold it in the vice when drilling out the pilots.It's 2 euro per, so I can afford to screw some up.

author: themadhippy
author_rank: Super Contributor
timestamp: March 13, 2025, 01:29:21 pm
content: 12mm holesaw would be my first choice,or maybe a punch but they can crack certain plastics.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 13, 2025, 01:59:59 pm
content: You can make your own drill for plastic by "dubbing" of the edge. That is, grind the sharp point off each cutting edge. You'll see the same thing done for brass that also tends to hog in (pull itself into the work).

author: David Hess
author_rank: Super Contributor
timestamp: March 13, 2025, 10:10:15 pm
content: Quote from: themadhippy on March 13, 2025, 01:29:21 pmA common high speed steel holesaw would be my first choice unless a punch could be used, but they are not normally that small.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 13, 2025, 11:29:30 pm
content: Quote from: David Hess on March 13, 2025, 10:10:15 pmBack in the day, screw operated hole punches in around that size were commonly used to cut holes in aluminium to fit 7 pin miniature tube sockets.Somebody may have a few lying around.

author: coppercone2
author_rank: Super Contributor
timestamp: March 14, 2025, 12:48:05 am
content: Quote from: JohnG on March 13, 2025, 12:49:19 pmI own a kit of these drills. They are narrow and sharp like a spear tip. The big difference is if you drill thick material, it does not pull. If you drill a block of lexan on a drill press, using a conventional vise (i.e. not a vector vise), you will see it wants to pull up into a normal twist drill for metal, and you can get the work piece to get pulled out of the vise easily, in a situation where you would not expect this to happen if drilling say steel.The plastic form drill reduces this by ALOT. I think it also leaves a better surface finish on the bore if you look sideways. But it still pulls a bit. And for manual drilling, getting rid of the 'pull' makes it ALOT easier to control the drillingI don't know if its suitable for thin sheets, I would assume the step drill is better, but I suspect the step drill is not optimized for drilling plastic, and you could probobly make a 'plastic only' step drill that does a better job. I think the rake angle would need to be substantially steeper if it follows the form of a regular plastic drill. But this does not change the fact that for drilling a thin object, the 'plastic twist drill' might have bad performance to a step drill, which has good performance, so long its sharp.But if you do drill thick plastic, I think the plastic drills are invaluable, it makes it into a normal operation instead of a savage one where the tools are basically controlling you. I kind of feel like if you drill with the wrong rake, your "machinist skill' basically turns into "GO sea biscuit!@! go!!!" or trying to push a moose through a door (conversely).

author: shabaz
author_rank: Frequent Contributor
timestamp: March 14, 2025, 02:17:06 am
content: You can get 12 mm punches, and they're pretty low cost (google Q-max punch). (12.7 mm might be more popular, you may want to consider using that instead).If I had to do a few dozen of these, personally this is what I'd consider:(1) Create a PCB design for the front panel, it could be 1 mm thick or whatever, or it could even be aluminium-core PCB, with the 12 mm hole cut-outs where you want them, and any legends as desired(2) Glue the front panels onto the plastic piece(3) Drill the pilot hole for the punch, and this can be crudely done since there's no need for any accuracy, so you'll save time not having to mark up each workpiece, nor having to create a jig(4) Use the punch, and precisely align it into the circular cut-outs in the PCB design.(5) Done.

author: David Hess
author_rank: Super Contributor
timestamp: March 14, 2025, 06:17:11 am
content: Quote from: vk6zgo on March 13, 2025, 11:29:30 pmI have some Greenlee screw punches but I do not know that they would work on thinner plastic, or that they are made that small. The material problem can be solved by placing thin aluminum on each side before punching. I used to do this to punch discs out of silicon rubber sheet.

author: Poroit
author_rank: Frequent Contributor
timestamp: March 15, 2025, 09:28:08 am
content: If you own a router or jigsaw, you could make a support jig out of plywood and then cut the holes with a Step drill like other members have already suggested.Holes saws and twist drills don’t make nice clean holes in plastic compared to Step drills.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 15, 2025, 11:39:18 am
content: You can also get cheap diamond-dust hole saws from your favourite crapvendor to do the job, but I'd be nervous about drilling something like this unless you have a drill press and a means of clamping the workpiece so the hole saw doesn't wander. The previous posters suggestions of step drills seems to be the best option since it's self-aligning.To drill from the inside as the OP seems to be suggesting, what about using a right-angle adapter on a standard drill?

author: 5U4GB
author_rank: Super Contributor
timestamp: March 15, 2025, 11:40:41 am
content: Quote from: Berni on March 13, 2025, 10:35:43 amYou also have to be very careful to stop at the correct step, once you've got plastic swarf winding all around the drill bit it's easy to misjudge which step you're on.

author: 5U4GB
author_rank: Super Contributor
timestamp: March 15, 2025, 11:52:11 am
content: Quote from: coppercone2 on March 14, 2025, 12:48:05 amStep drills are ideal for drilling plastic, you just have to apply the comments made by previous posters about using them. One other thing I haven't seen mentioned is that they're problematic when drilling thick plastic, i.e. where the plastic is thicker than the step depth. For that you need to carefully drill to the edge of the next step and then use something like a deburring tool to cut the remaining previous-step plastic lip away to match the current step.Another thing with thick plastic, typically found in outdoors-rated cases, is that the plastic is often thick enough that you can't fit a PG9 cable gland onto it because the plastic is too thick to allow the locknut to be tightened onto it. In that case you need to cut a thread into the hole in the case and screw the PG9 into the case.

author: coppercone2
author_rank: Super Contributor
timestamp: March 15, 2025, 11:53:08 am
content: I never said their bad but it might be possible to optimize it for plastic. they are good on basically anything. I never saw one thoughI guess it would be very long with big steps? I don't think a 'plastic only' step dril exists.

author: jonovid
author_rank: Super Contributor
timestamp: March 15, 2025, 12:47:33 pm
content: for plastic enclosures starting with a pilot hole.drill it through ever so slowly slowly. I use step drills with a back plate behind were the hole will be drilledso no gaps between thin plastic & back plate.

author: Bud
author_rank: Super Contributor
timestamp: March 15, 2025, 02:20:07 pm
content: I use this reamer tool, works for both metal and plastic and hole diameters are not step limited. But obviously this method is not mass scalable, just for a few holes at a time.

author: TimFox
author_rank: Super Contributor
timestamp: March 15, 2025, 02:35:25 pm
content: When step drills are usable:They should be used in a drill press, where you clamp down the object, and guard against going one step too far by using the press’ depth limiter.They are available with different numbers of cutting flutes: I have had best luck with single-flute bits (Irwin “unibit”).They are available in inch and metric (usually 2 mm steps).

author: Langdon
author_rank: Frequent Contributor
timestamp: March 15, 2025, 07:37:37 pm
content: A good step bit:https://laoa.com/products/laoa-pagoda-drill-bit-3-13mm-4-22mm-4-32mm-hss-co-m35-hex-triangle-handle-power-tool-spiral-grooved-metal-steel-step-drill-bitLAOA makes good stuff.

author: TimFox
author_rank: Super Contributor
timestamp: March 15, 2025, 08:29:38 pm
content: Back in my university days, we used diluted "tincture of green soap USP" from the medical stockroom as a lubricant for drilling plastic.Cleans up afterwards in running water.(Intended for use in cleaning dirt and debris from wounds.)

author: coppercone2
author_rank: Super Contributor
timestamp: March 15, 2025, 09:38:16 pm
content: This is true, if you take the little cup you put laundry detergent in, fill it with water to make a soap solution, and dip fostner bits in it before you drill wood, it drills much much betterDip before each hole, this is how I made my wooden trays for coaxial connectors of various kinds with more speed, less heat and no smokeBut you do need to wash it off and oil it when you are done. It might be the same for plastic and I bet it even might work on metal instead of oil. The main problem is that its too runny for metal. I wonder if you put some thickener in there if it would beat out oil, because its thermal conductivity and capactiy is much greater, and it might be just as slick

author: 5U4GB
author_rank: Super Contributor
timestamp: March 16, 2025, 11:03:17 am
content: Quote from: TimFox on March 15, 2025, 02:35:25 pmYou can also find them in odd step sizes if you need that although they're a lot less common than the usual 4, 6, 8, 10... steppings.

author: themadhippy
author_rank: Super Contributor
timestamp: March 16, 2025, 12:26:04 pm
content: Quoteor get a conecutter, although you need to pay attention with them.

author: Jeroen3
author_rank: Super Contributor
timestamp: March 24, 2025, 07:09:06 am
content: A small 4mm drill guide on the inside for the pilot hole.Then with the step drill (that starts at 4mm) drill the remaining.

author: Poroit
author_rank: Frequent Contributor
timestamp: March 25, 2025, 02:19:48 am
content: It looks very professional....nice job

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 07, 2025, 01:56:45 pm
content: If you have a drill press, you can make a punch yourself.1. take a piece of square or rectangular tubing.2. Drill a 12 mm hole in it.3. Take the 12mm drill, and grind it a bit "hollow" on the solid end.4. Put the drill upside down in the drill press.4a. Likely, the chuck does not hold the drill straight, so position the square tube so it's hole is below the end of the drill.5. Put your plastic in between the square tube and the drill, and push the back of the drill though it (no rotation!)I sometimes use this method, but it does not work in all materials. It does not work well in brittle plastic for example.

author: EC8010
author_rank: Frequent Contributor
timestamp: August 25, 2025, 09:49:25 pm
content: Chassis punch is the way to go. Greenlee in the US, Q-Max in the UK. Yes, step drills can be surprisingly good, but plastic has a nasty habit of behaving oddly when heated by the friction of a drill.

author: themadhippy
author_rank: Super Contributor
timestamp: August 26, 2025, 10:32:52 am
content: QuoteIts horses for courses , some plastics shatters into 1000 bits or splits when you try and use a q punch