View Full Version : Making rectangular slots

04-14-2007, 01:30 PM
I have to make a bunch of rectangular cutouts in 0.09" wall thickness cast aluminum electronic enclosures. I plan to get the HF mini-mill to do this (among other things) in a month or so, but until cash allows, I have to do it by hand and I'm looking for ideas.
Currently I layout the area to be removed, taking care not to damage the already powdercoated finish, drill two 11/16" holes close together and then file away the remaining material. It's time consuming (about 1/2 hour or so each) and I have to be very careful to mask the untouched area so I don't scratch it.

I'm going to need to do a bunch until I can afford the mill. If anyone can suggest a faster way of doing this with hand tools & a drill press, it would be appreciated. I have a nibbler, but the material is too thick for it.

04-14-2007, 01:55 PM
I'd be scouring the catalogs from Allied, Mouser, McMaster-Carr, etc. etc. looking for a neat little injection molded plastic snap-in insert that goes in a round hole, and which can more easily be modified to accept whatever goes in the rectangular hole.

I'd modify these plastic parts, then pierce the housings with a hole saw, and snap 'em in.

Otherwise, if this was in production quantities I'd have the boxes run at a CNC or sheetmetal shop, THEN powdercoated.

I had to do a very similar fix at my last job; an additional hole to hold an
RS485 jack needed to happen in a large folded panel of .080 steel which was assembled in an appliance and which couldn't be removed to do the retrofit. I made small aluminum plates into which the jack was snapped, and these had a couple screw holes. The large panel had a 1-1/4" hole sawed in and 2 screw holes drilled. The adaptor plate was screwed on.

This enabled the retrofit to be executed without moving or disconnecting the appliance.

04-14-2007, 02:03 PM
try one of these for assorted grommets plastic and otherwise.http://www.reidtool.com/
Reid tool has some intersesting thing in the shop area. Outwater is the fabricator's toy store for displays and furniture.
Surplus may have them cheap.
All electronic's also.
Lee Valley has all kinds of furniture and fab hardware no one else does, as they make it.

04-14-2007, 02:05 PM
Assuming MM's suggestion doesn't work for you, how about a Dremel/Die Grinder with cylindrical carbide bur?

Make one guide plate out of something suitable, say 1/4" hot roll. Drill your starter holes in you powder coated plate. Clamp the guide into place, maybe with some gasket material or the like between them to protect the finish. Then run the bur around to clean up to shape. Obviously the guide should be run against the shank, not the bur, with probably some wax lube on the shank as well. Guide plate is needed for semi-fast work as cutting neatly to a line using a bur is very tedious at best.

04-14-2007, 06:23 PM
A router in conjunction with a ball bearing equipped router bit and a guide bushing (machined to the size required) clamped to the work might be an option. Then file the corners square if required. 0.090" thick Al would be easy work for a router.


Frank Ford
04-14-2007, 06:36 PM
How about buying the mill with a credit card or on terms. You might well pay the extra interest in saved time on all those holes.


Frank Ford
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Nick Carter
04-14-2007, 06:53 PM
My favorite method is a jewelers saw, if you can fit it in. I wrote up a short article a while back with a few ideas. The router jig also would probably work well and be fast.

04-14-2007, 09:07 PM
Make yourself a cutout jig and use a router. With a 1/4" bit, there wouldn't be much to file out in the corners. (If the corners have to be squared.) A carbide bit will eat through that like butter. A speed controller might help to turn down the router speed a little bit. It'll take you longer to set up each box than the cut the holes. ;)

04-14-2007, 09:48 PM
I like the guide plate idea. I have a Dremel and can cannibalize some old lawnmower blades for the guide. I've never tried cutting metal this thick with the Dremel before, but I also have a 1/4hp laminate cutter if the dremel can't do it.

Normally I'd just order enclosures from someone who can provide cutouts, but my quantities aren't large enough to justify it in this case.

Your Old Dog
04-14-2007, 10:12 PM
Greenlee the folks who make punches for electricians and guys who need to punch chassis may have something in your size.

If either of the sides were long enough I'd make my first pass with a air cutoff tool and a worn down blade. Then finish with your drill bits and files.

look at page 62 on their PDF file of their products.


04-15-2007, 02:13 PM
A hand nibbler is another inexpensive tool that could be used to make almost any shaped hole.

It can be seen here in figure # 5.



04-15-2007, 09:43 PM
You could make up a punch and die to fit an arbor press and punch the hole. Sounds difficult if you've never done it before, but I've done lots of 'em, and it's no big deal.