Cutting D-Shaped Holes in Metal Project Boxes? - Page 1
Forum section: electronics / beginners

author: gigavolt
author_rank: Contributor
timestamp: July 12, 2020, 04:07:51 am
content: How do you guys do it?I'm sick of BNC connectors and the likes twisting around when I try to hook up a cable. The only solution I've found with google are expensive punch and die sets. We own one at work, but even that only has two or three "nice" fractional sizes. My BNC connectors won't work with it (0.378 in). Is there any solution for hobbyists like us?

author: tkamiya
author_rank: Super Contributor
timestamp: July 12, 2020, 04:25:36 am
content: My answer to D sub 9 pin is this:https://www.adorama.com/swehdb9mf.htmlput a big round hole and that'll take care of it. BNC connectors don't slip much if you torque it down. I have a sacrificial male connector and socket wrench to do this. Since I mostly deal with RF, and thus use feed through type, they have a built-in gasket to prevent turning, too. Even if you do the "chopped off circle" shape for BNC, it will turn. The thread part start cutting into the metal casing as you tighten it.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: July 12, 2020, 05:25:32 am
content: For an occasional hole, the most versatile method is to drill multiple small holes around the perimeter of the desired hole. Use a 1-2 mm drill bit and position the holes so that you end up with only about 1 mm or less of material between holes. Don't overlap holes, though. Then break the webbing and use a file to clean up and bring the hole to final dimension.It's slower than punches, but with this method you can make a hole of any shape and size, in virtually any material you're likely to encounter, using cheap tools.

author: rstofer
author_rank: Super Contributor
timestamp: July 13, 2020, 03:42:49 pm
content: The punch and die sets won't cost near as much as my solution: Build up a CNC milling machine.I had a project with 60 banana jacks in a grid pattern that wanted to be perfectly spaced. There were some switches and 10 turn pots with anti-rotation devices, a large panel meter and some LEDs. I just couldn't see doing some kind of 'step and repeat' drilling for the jacks and getting the tab hole locations right for the anti-rotation gadgets didn't seem feasible if I had to do it by hand.Interesting project! I learned a lot about CAD, CamBam and Mach 3.Now that the CNC mill exists, similar projects are easy!

author: dcbrown73
author_rank: Regular Contributor
timestamp: July 13, 2020, 04:43:38 pm
content: Quote from: rstofer on July 13, 2020, 03:42:49 pmI thought about picking up a milling CNC, but it only solves some box issues. The project image below; since it's a clamshell type box and no structural support for the sides / front & rear unless the box is assembled. I seriously doubt I could mill this box for this reason. (maybe a multi-axis CNC mill? I still have support issues though)FYI, it it's not clear. It's a AC current limiter with a bypass and volt / current meter.I just used a dremil with a cutting blade. The good is that the LCD volt / current meter cover and switches up the rough edges.This is what it looks like now, except the light sockets are actually attached to the top.

author: rstofer
author_rank: Super Contributor
timestamp: July 13, 2020, 04:59:04 pm
content: Jigs and fixtures...I would build some kind of offset bracket to provide support to the underside of the front panel. This might be as simple as a couple of pieces of wood. I would screw the box to the wood with screws more or less where the switch holes will be drilled (or milled). After the meter cutout was complete, I would rig a clamp piece through the cutout and drill/mill the switch holes. Since I would already have screw holes through the switch holes and it is unlikely they are perfectly centered, I would plan to mill the hole rather than have a drill bit walk away from the center point.Figuring out how to jig these things is the hard part. It has to hold the part firmly against the feed from the mill.Maybe a simple L bracket screwed to the top of the box where the lamp sockets go. This would be a more traditional mounting.When I cut that front panel, I was cutting two sheets of 1/8" Acrylic and I backed them up with a piece of MDF. I don't recall where I put the wood screws but it worked out somehow. I suspect they were outside of the final panel when I did the drilling and then I reclamped the part when I cut the perimeter.

author: Benta
author_rank: Super Contributor
timestamp: July 13, 2020, 05:59:56 pm
content: For connectors made for D-shaped holes (like BNC) there are special washers available to lock the connector.The washer has a D-hole fitting the connector, and a bent tab for locking.The idea is that you drill a round hole for the connector, and next to it a small hole for the tab. This will prevent the connector from twisting.No idea what they're called, but BNC suppliers offer them as accessories.

author: wizard69
author_rank: Super Contributor
timestamp: July 13, 2020, 06:15:01 pm
content: Even at work we often run into not having the right punch. There are many ways to deal with this manually.Drill then file to shape. To do this well you need a good vise, support boards and the layout skills of a tool and die maker. Using files can be very precise but it is a skill that take time to get right. One big trick here is support boards to support thing sheet metal or plastics.Drill then use a nibbler. Nibblers can actually be very handy in sheet metal work as long as you remain within their thickness capability.Dremel or small die grinders. Good but also a quick way to foul something up. You use cut off wheels and drilling for gross material removal and stones and burrs to finish off a hole.Acid and resist method. This is actually a commercial process like:https://www.photofabrication.com/that strives to fabricate parts in a way extremely similar to fabricating PCB. You do need to be willing to work with strong acids.The CNC router approach. Lots of money to do it right but maybe cheaper than buying dozens of punches. due to the round cutters you may still have cleanup work in the corners.CNC laser. Possibly the best approach if you can afford one with enough powerCNC plasma torch. Again not cheap and there is clean up required after the parts are cut. Great for stainless steel and other hard to machine materials.There are various presses and iron workers you can buy that can punch metal like nobodies business. Jigsaws and various forms of reciprocating saws, are often an ideal way to do heavier panels. Mounting a jigsaw under a table can often improve the results substantially, especially for lighter panels. You can actually use the blades to nibble away at the outline.Quote from: gigavolt on July 12, 2020, 04:07:51 amDo it like a PRO!All kidding aside there is no right way. Further the best way often depends upon what you are working on.QuoteIn a case like this punch with the closest you have and file to fit. Not ideal but it is the cheapest. One other possibility is to find out how much the right punches would cost you for the press at work and see if you can afford to buy your own set to work with the press. In a couple of occasions I've purchased personal tooling to work with the machines at work to get projects done.there are many manufactures out there that have taken various approach on the problem of standard ports in adverse situations. for example a high vacuum USB port:https://www.lesker.com/newweb/feedthroughs/instrument_feedthroughs_usb.cfm?pgid=0.Along the lines of more affordable Switchcraft has a whole series of connectors alluded earlier:https://www.mouser.com/datasheet/2/393/EHRCABNC_X_SERIES_CD-1144695.pdfand here:http://www.switchcraft.com/ProductSummary.aspx?Parent=1122.Pasternack has a whole bunch of flange mounted solutions such as:https://www.pasternack.com/bnc-female-standard-turret-terminal-connector-pe4011-p.aspx.Unfortunate none of the flange mounted solutions follow a common foot print. This means having to stay with one manufactures outline. For example the Switchcraft solution linked to is built on an XLR connector foot print. In any event there are numerous solutions to solving the problem of the "D" shaped cutout these are just quick finds I'm familiar with.

author: TimFox
author_rank: Super Contributor
timestamp: July 13, 2020, 10:47:15 pm
content: My simple suggestion for BNCs that only get reasonable "unscrewing" torque in use: Drill the normal round 3/8" hole. Then take a center punch and punch near the hole circumference to get a radial dent that will tend to hold the flat in place. Not as good as a proper D-punch, but much cheaper.

author: eloso
author_rank: Regular Contributor
timestamp: December 21, 2021, 01:10:20 pm
content: Very late to this party - but just in case anyone is interested after having found the page by means of a search, let me add a comment.I have found that it is much better to get the BNCs that have a double flat. I just did a little box with three of them and drilled 8mm holes. I used a file to elongate the holes - no measuring, no prep and when it comes to mechanical things - well lets just say its not my scene. Nevertheless, it really wasn't that hard - a couple of minutes each one. Didn't even use a vice. A small round file. The holes don't look pretty, but there is loads of leeway for error and at the end of the day the BNCs fit perfectly and don't rotate. The flanges cover all the little imperfections. The double flats mean less filing and less accuracy needed over the single flat types. I reckon you can spend more time fretting about these things than actually getting on with it. I know I did !CheersElosoEdited to fix a typo

author: Nusa
author_rank: Super Contributor
timestamp: December 21, 2021, 01:20:12 pm
content: If the metal happens to be material you're capable of welding, one can drill the hole and add some metal back to one side of the hole. You'll have to flatten the new edge with a file and grind it flush on both sides.

author: jonpaul
author_rank: Super Contributor
timestamp: December 21, 2021, 02:27:05 pm
content: Greenlee Chassis puncheshttps://www.greenlee.com/us/en/knockoutsCostly but last a lifetime.Jon

author: mag_therm
author_rank: Frequent Contributor
timestamp: December 21, 2021, 03:07:42 pm
content: There are BNC panel jacks with a square flange and 4 holes for M3 screws.Flange can go on either side of panel.