Knockout Punches on 1/8” aluminum plate

Steve White

New member
Jul 6, 2018
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Fort Worth, Texas
I am making up some speaker cabinet IO panels from 1/8” aluminum plate for a pal on a turd polishing quest for some old subs he has. Need to punch some 31mm and 41mm holes for Neutrik Speakon connectors.

Seems like my Greenlee and Enerpac KO sets are rated to 12ga steel. I know back in my electrician days, I punched out some pretty thick steel power panels up to 2 1/2" using the Enerpac set.

Anybody try these type of punches on 1/8” aluminum plate? I suppose I could just offer one up to the test gods and try it out.
 
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Oct 25, 2018
80
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Bideford, Devon. UK
No empirical knowledge, but it sounds like a breaker to me!
Average aluminium would have around 200MPa shear strength, mild steel perhaps 300MPa - you're asking to shear 2.5 times the thickness. Worth trying as a potential sacrifice, but stand well back...
 

Steve White

New member
Jul 6, 2018
22
4
3
Fort Worth, Texas
No empirical knowledge, but it sounds like a breaker to me!
Average aluminium would have around 200MPa shear strength, mild steel perhaps 300MPa - you're asking to shear 2.5 times the thickness. Worth trying as a potential sacrifice, but stand well back...
Thanks Carl, exactly what I was seeking.

EDIT: Brainfade event - it’s 1/8” 0.125” thick plate. Yeah, 1/4” would probably be explosive.

This took me here: Aluminun and Steel Engineering Properties

I'm going to test this afternoon with a die that I have a couple of. Will use some moly-grease on the threads and face shield and gloves. Looks like T6 may be a problem, but softer tempers may be ok. The stock I have is 6061 T4, so it's probably at the upper end of something that may work. Probably order some softer stuff and figure it will work, it not I'll have to use hole saws and well that's way more time consuming - maybe stack up multiple plates or just use a fly cutter in the mill.

In the end, a process faster than single plates and hole saw going one at a time will be found. :)

I'll post up the results.
 
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Steve White

New member
Jul 6, 2018
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Fort Worth, Texas
Well it works, with a few caveats. Can't get too close to the edges. No problem there, punch holes first then trim panel if necessary to final size.

I'll try out drilling as large a hole as possible with the Unibit (stepped drill) next time. This time I just did the standard sheet metal method and drilled the holes large enough for the stud on the KO punch to go through.

I wouldn't try it with anything thicker than the 1/8". It pulled through ok using the cordless impact gun rated at 200' lbs max. Didn't seem to load up anymore than with sheet steel in the range it's designed for (max 12ga as I recall) or rack panels I use them on.

Drilling out close to final size with the unibit should make it a breeze to punch holes for Neutrik's in aluminum speaker panels.

I'll come back and post an update when I make the first panels to show the layout. That's done with Visio, printed full scale and spray glued to the panel. Makes layout a breeze, just dimple all the holes with a punch and get it done. Cut to size if necessary using the template guidelines. Took about 40 years of fabrication to finally figure this out - it's getting easier. :)
 

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Oct 25, 2018
80
10
8
59
Bideford, Devon. UK
That's looking really good.
Lower strength grades of aluminium can be very 'sticky' to cut compared with steel, sometimes making them appear harder/tougher than they actually are when machining - try some drilling oil on the cut.
 

Geoff Doane

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Nov 19, 2011
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Halifax, NS
I've probably punched hundreds of 15/16" holes in 1/8" aluminum and lived to tell the tale. Clamp the plate securely in a vise (horizontally) and don't try to go too fast, seems to be the secret. If you use a big wrench, it's easier, but also possible to get the punch extremely hot. I think that may be what trashes the threads. When I have broken punches, it's always the bolt that breaks, and that was from cutting an uneven holes and the bolt bent before it snapped.

Unfortunately, I don't know what grade of aluminum I was using. I've just gone to my local sheet metal shop and asked them to cut the sizes I need. It takes seconds on their big shears.

If you don't need smooth edges (the connector will hide the cut edge), a hole saw is much quicker. A drill press is a good idea, and hearing protection is mandatory.

GTD
 

Steve White

New member
Jul 6, 2018
22
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Fort Worth, Texas
^^^ I gave up on wrenches with knockout cutters some time ago. The first evolution from wrenches was to a 1" socket in a 1/2" drive ratchet. That works pretty good on electrical panels out in the field - I was an electrician back then. Socket/ratchet is always ready to go in toolbox - no batteries to keep charged. For my home shop, I don't put a wrench of them anymore, do them all with a cordless impact gun as pictured above. Keep the threads on the stud lubed and 0 heat. The moly grease is working great.

What the punches offer are a much cleaner hole and using a step drill for the pilot, followed up with the KO set & cordless impact gun is for me, is orders of magnitude faster than a hole saw and is a more accurate hole. Using a wrench & KO cutter or hole saw and drill press requires a vise or firm clamping to drill press table of the work piece. Using impact gun, the work piece can be held with a gloved hand and not much effort is needed. Setup time is much better as well.

With a small plate, as opposed to a power panel, using a wrench with the torque needed has a tendency to warp and bend panels when they are locked in a vise or clamped down - not so much an issue using the impact gun, as the mass of the KO cutter absorbs the torsional force of the impact gun and most times I just hold the work piece by hand.

Thanks for sharing sir.
 
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