Question about SQUARE cutouts - Page 1
Forum section: electronics / general

author: atwoz
author_rank: Regular Contributor
timestamp: June 27, 2012, 01:27:19 pm
content: Hello Forum. I am designing a new board that will have several square cutouts inside the board. The question is: Can a standard fab house do square cutouts?I believe they use a drill bit or something similar to cut out the square hole, however since its a round tool, the inside corners of the square wont end in a corner.Does anyone have some experience with square cutouts??Thanks!

author: free_electron
author_rank: Super Contributor
timestamp: June 27, 2012, 01:30:51 pm
content: If you have a phenolic board you can have those die-punched.for a fiberglass board punching works if the pcb is less than 20 mils thick.Otherwise it is routing.... And that leaves round corners. No escaping. You can ask a cleanup rout using a 1mm bit which gives the corner a .5 mm radius. But you will pay extra

author: _Sin
author_rank: Regular Contributor
timestamp: June 27, 2012, 01:41:02 pm
content: Unless you can convince the fabricator to use a reulaux triangular drill bit

author: atwoz
author_rank: Regular Contributor
timestamp: June 27, 2012, 01:43:36 pm
content: Thanks for the fast replies!I guess I will have to overshoot (don't know the right term) the cutout. Since I have to fit square connectors inside those holes I will just have the drill bit overshoot in the corners so the connector fitrs. I will end up with a square cutout with some circles in the corners, ugly but I guess I have no other choice.I will be using that board as a front panel.

author: digsys
author_rank: Unknown
timestamp: June 27, 2012, 01:57:05 pm
content: QuoteDon't be so hasty. With a 40/50 thou router, the corners are very small, and unless the connectors are made of metal, they fit beautifully snug inan exact square hole. I've done it many times. In a worst case, it's just a tiny "nick" with a small square file.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: June 27, 2012, 02:09:13 pm
content: You can add some drill holes in the corners to reduce the corner radius

author: bronson
author_rank: Regular Contributor
timestamp: May 02, 2014, 06:54:07 am
content: So how are these square bottom-mount LEDs handled? A square LED in a round hole would look terrible, and I can't imagine everyone ordering this LED is using a phenolic PCB with die cut holes.http://www.digikey.com/product-detail/en/APTR3216SGC/754-1171-1-ND/1747888What am I missing here?

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 02, 2014, 07:36:16 am
content: if the quantity is managable. you can pick cheaper service (round corner), dont care and whatever. and then buy a square file, or triangle if NA, file the corner yourself. using skill and dremel and cutting disc or diamond bit somesort will also do the trick, ymmv.

author: nihilism
author_rank: Regular Contributor
timestamp: May 02, 2014, 08:53:46 am
content: Quote from: bronson on May 02, 2014, 06:54:07 amallow enough clearance over the led size to compensate for the radius of the corners which could be as little as 0.5mm a side?

author: kizzap
author_rank: Unknown
timestamp: May 02, 2014, 10:26:00 am
content: common method to get around the issue in most designs is as follows:http://www.omwcorp.com/img/cutawaycornerspocket600x514.jpgBasically you run the router out a little bit 45° from the corner, which solves the square peg/round hole issue.

author: bronson
author_rank: Regular Contributor
timestamp: May 02, 2014, 04:56:38 pm
content: Great replies, but why are so many of these bottom-mount LEDs are square? If you can't see the overdrill anyway, why not just make 'em round and easy for everybody? There must be some application I'm not aware of.Hoping to manufacture these one day so, unless the PCB fab has a mortising machine, I'm probably only allowed router tricks. I'll have to buy some parts and play with kizzap's suggestion.

author: Niklas
author_rank: Frequent Contributor
timestamp: May 03, 2014, 01:24:22 pm
content: This week I had a look at a problematic smoke detector produced in Asia that had stamped cutouts in 1.6 mm thick FR4. The manufacturer could easily have gone for routing with a 2.4 mm drill bit for these smoke chamber snap in holes as this was inside a plastic box. Instead the board manufacturer used a stamping tool, probably to reduce cost for high volume production.The finish on the edges on the stamped FR4 is not that great. Uneven and a bit rough, similar to what you get with v-cut. Why not investigate what you can do with traditional routing and a bit of artistic creativity? Extend the milled rectangle to become an S-shaped trench? If you can't hide it, try to exploit it instead.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 03, 2014, 07:18:08 pm
content: Don't know why the datasheet drawing has a square "hole" outline, but the dimension is correct.The protruding body is listed as 1.4 x 1.6 mm.The diagonal is sqrt(1.4^2 + 1.6^2) ~= 2.1 mm.So a round hole >= 2.1mm will suffice. Probably 2.6 would be a good idea? If you want to route that for a little better straight-sidedness on the hole, you can, but you'll probably incur the cost of a route (...which probably isn't anything, and if your board outline is already non-rectangular, a rout process is required, regardless).Tim