What's new
What's new

Best way to cut round duct holes in machine enclosure?

david n

Diamond
Joined
Apr 13, 2007
Location
Pillager, MN
Squares and rectangles are easy with a reciprocating saw, but what about round holes in a machine enclosure? 6" or 8" Ø? I want a nice round hole and not something that looks like a complete hack used an axe. Idears?
 
Well, the obvious answer would be to buy a hole saw the size you need...
 
Squares and rectangles are easy with a reciprocating saw, but what about round holes in a machine enclosure? 6" or 8" Ø? I want a nice round hole and not something that looks like a complete hack used an axe. Idears?

The obvious answer is a plasma cutter and a template. An air-nibbler and a template would do the job if the sheeting is thin enough.

Another method is to make a circle cutter, in-place:

Drill a hole at the center-point and put a shoulder bolt in there with some nice big washers or pieces of plate for stability (to limit flex).
Pivoting on the shoulder bolt, attach a piece of flat bar wide enough to bolt it to your wood-router.

Drill a starting hole and buzz the circle out with your router. If it's on a vertical surface, leave a tab at the top about 1/2" wide.
Cut the final 1/2" tab by hand, then de-burr the hole.

If you start getting too much flex or chatter half way through, use some short fasteners with nuts and washers in the cut groove to support the cut area, or just leave about 3 tabs and cut them after the router work.

A 1/4" or 3/8" end-mill will work, but the helix angle causes chatter in the sheet-metal. You'll get less chatter with a straight flute cutter.
 
Last time I took a piece of 1/8 aluminum flat drilled and reamed a hole at one end. I then pressed a long 1/8 pin at one end so the pin was half way through the aluminum. Then 4" over (or what ever radius you need) I drilled another 1/8 hole. Drill a 1/8 hole centered where you want your hole and another 4 inch away. Put a 4 flute 1/8 stub end mill in your drill and use your alum flat as a guide.

Can't say it was "best" but it got done with shit I had on my table.
 
Last edited:
jigsaw, and then some bench work with a die grinder to smooth out the edges.
Assuming this is for a ventilation duct?
 
How many 8"Ø holes have you cut with a holesaw in a hand drill? This is in the side of a machine. Can't take the panel off....................
None, but it doesn't mean it can't be done. Go easy and worry your way through. How many do you have to do?
 
Of some importance..is the enclosure stuffed full of gear now or is this a new, empty item! Chewing on a enclosure full of switches, mags and DIN rain can raise hell unless one controls the chips 100+%.

Stuart
 
How many 8"Ø holes have you cut with a holesaw in a hand drill? This is in the side of a machine. Can't take the panel off....................

I haven't tried to cut such a large hole with a hand drill, but I do think that it can be done. The danger in just using the center drill point for guidance, is that it will likely catch and skate across the face of the enclosure. If you were to use the hole saw in a drill press, and cut out a hole in 3/4" plywood, and then have a way of clamping the plywood in place on the enclosure, this would give you so much more guidance than just the center drill.

Brian
 
^ You want to try it, first your going to have to find a hand drill that can turn it and not many will then you need to consider the speed or lack there of it has to be turned at and also finding one i have only ever seen em upto 6" dia.

Me i would use a plasma if i can safely position a catch tray the other side, its effortless, but the location and both sides have to be safe for hot work and deepening on the machine it may well not be!

That leaves jigsaw, which whilst slow will work just fine, good saw and good blades and the results as good as your skill level. Just don't forget the hearing protection!
 
Lots of torque to control, drilling by hand w/ an 8” hole saw.
Any chance of having surface area near the work area so as to mount a rented
“Kor-IT electric core drill w/ anchor and vacuum base”
If there is enough smooth surface area for the vacuum to get a grip, that would hold.
 
Steel? How thick? I'd use a variable speed sawzall or sabre saw with a fine tooth narrow blade(or several blades)with CLEAR markings on the panel and then a 2" dia sanding drum in a drill to clean it up. Or do what the carpentry/drywall guys do and cover the cut up with trim plates afterward.
 
The obvious tool to use is an 8" hole saw.

Until you consider that such a cutter is simultaneously dragging over two FEET of teeth over sheet steel powered by a hand drill ready to tear itself out of your hands.

I'd probably go with the Sawzall and a narrow blade and then clean it up with a half round file.
 
For smaller holes (up to 2") in steel panels I am using Greenlee Punch Kits. For larger a hole saw. For 8" hole I would use an electric (or maybe air) jig saw with a fine teeth blade. Can be used freehand or with a circle cutting attachment after drilling a pilot hole.
 
The obvious tool to use is an 8" hole saw.

Until you consider that such a cutter is simultaneously dragging over two FEET of teeth over sheet steel powered by a hand drill ready to tear itself out of your hands.
Lol. I was actually thinking about the 6" when I wrote that, Lenox makes carbide tipped hole saws that size for stainless.

I made some pretty big holes with them when I was building my boat.

I didn't think of plasma cutting the hole, mainly because I don't have a plasma cutter. I'd probably go after it with a hacksaw blade on a sabre saw and smooth it out with a sanding drum.

Surely there is some kind of finishing on the hole- a grommet if nothing else. I assumed some kind of flashing on each side that the ductwork connects to.
 








 
Back
Top