cutting panel knockouts in aluminum sheet

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zotdoc
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cutting panel knockouts in aluminum sheet

Post by zotdoc »

I have to cut out square holes in a sheet of 20 guage aluminum for 48 power connectors. Is anybody out there with experience in this that has some tips as to the easiest way to do this with hand tools?
dyarker
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Post by dyarker »

For two or three holes I'd suggest a nibbler. For 48 holes I suggest a Greenlee punch.
Dale Y
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jwax
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Post by jwax »

What size holes?
zotdoc
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Post by zotdoc »

The holes are for molex 12 wire power connectors, MLX series and are about 1.25 by 1.25 inches and have two little tab cutouts at each end. I'll look into the greenlee punch thing. Thanks to all.
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MrAl
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Post by MrAl »

Hi there,

I was going to mention the punch too but wasnt sure if they still made
them. I guess they do so that's cool :snuke:
LEDs vs Bulbs, LEDs are winning.
Robert Reed
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Post by Robert Reed »

Dyarkers Greenlee punch would certatinly be the easiest, howevever I don't knw now if y0u will find one to match that hole size. Nibbling 48 holes by hand is a real chore. A jig saw with the proper metal blade is the other option. All three methods will require careful layout annd 3/8" pilot holes for starters . The greenlee method will require these holes to be on dead center, the other methods wont. Once properly set upand supported the jig saw method is quick as you can make all vertical cuts at once . Then turn the panel 90 degrees to make all the horizontal cuts. The jig saw method will requirer a quick deburring and a good fine tooth blade.
The method comes down to how accurrate the holes have to be, some of these connectors require a maximum +/- 0.010" deviance from target dimensions. Your spec sheet should include that info.
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Lenp
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Post by Lenp »

Good luck on the Greenlee punches. Seems that round and a few 'DB'series connectors is what is available today.

Here's a trick I use for odd panel cutouts that may work.

First lay out all the cutouts with a CAD program, to full scale. Add a target for the exact center of each cutout then print it. Use a spray adhesive and mount the sheet to the panel to be cut. Use a hole saw and drill press to cut out as much of the center as you can without hitting the cutout boundary lines, using the opening's center target as a guide. Then use a nibbler to cut to the lines and touch up with a file as necessary. Rmove paper and glue with a solvent. This sure beats laying out each hole by hand directly on the panel!

I may be able to help with the CAD if you cannot do it.

Len
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jwax
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Post by jwax »

Wow! zotdoc- That sounds like one massive "Firing Panel"? Am I right? :grin:
You may save hours of cutting/hacking with a visit to a local sheet metal shop. A CNC punch would easily do that job in an hour, with minimal setup time and cost. Hint- find a small shop that's hungry!
Send us a pic when done!
Bear
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Post by Bear »

Zotdoc: If the hole is a 1.25"sq. why do you need the locating tab??
An 1.25"sq. Greenlee punch should not be too expensive as opposed to going to a sheet metal shop & paying for layout, setup & run time.
What I would do is: 1) buy the punch 2)buy a socket for square head bolts and 3) put the socket on a 1/2" impact wrench & then use it to turn the drive screw.
This method will work as we used this method to punch 1/8" aluminum. Since you are only going to be working with B&S 20ga.(.032") alum it will be a breeze. Don't forget to lubricate the punch as that is the thing that is going thru the metal not the die.
Theoretically it would take 4 tons to punch that hole, but I'm sure that the punch will have some shear on it so that the force req'd. will be much less.
You may also wish to consider some kind of stiffeners for this panel if the holes are going to be close to each other, otherwise you may end up with a "swayback" panel.

Good Luck

Bear
Dean Huster
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Post by Dean Huster »

http://www.greenlee.com

Greenlee used to have all the standard punches for the electronics industry such as octal, 9-pin and 7-pin tube socket holes, IF transformer square holes, etc. I don't think they cater to electronics as much as they do the electrical industry these days. I did buy a chassis punch for DB-25 connectors once, but it wasn't a Greenlee product, so you might have to venture outside that brand name to find the appropriate punch. Check with the manufacturer of the connector as they probably have a source for a matching chassis punch for that item. That's your most likely source right there.

Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.
Engineer1138
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Post by Engineer1138 »

Q: How much is your time worth?

A sheetmetal shop may do the job for about $100 setup cost if they are not busy/are hungry :-)

A punch for that size hole will be expensive. I'd expect a Greenlee punch to cost about $200+
Mouser has a few cheap (about $50) square punches up to 0.5x0.5", but I haven't had much luck with them. YMMV, I was trying to punch 0.1" cast AL. Now I use a milling machine!

For 20 gauge AL I'd try a cold chisel. About $5 at Home Depot, get a good file to sharpen it.

Google "nick carter square hole" and see what results. Nick Carter had some good tips on cutting square/rectangular holes in panels on his site.
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jwax
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Post by jwax »

Agreed Engineer. Not only is time a consideration, but how pro do you want the finished panel to appear? If you do happen upon the correct punch that is affordable, you'll get a nice job, and a great paperweight unless building more is in your plans.
Robert Reed
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Post by Robert Reed »

I have made chassis, subchasis,panels and enccosures for years. The first thing to bear in mind is how professional the finished appearance has to look? Will it be painted or natural? Material-Plasti, stainless, Aluminum or steel. For each material and finish a certain degree of caution must be used. Aluminum is by far the easiest to work with and my material of choice when possible. In any metal working of this type, two things are of paramount importance and that is material support and the angle that the material is worked with. I do not have access to a metal shop so improvisation becomes a common occurence in working these materials. Since you mentioned thin guage aluminum, we will concentrate on that material only. The required piece is doublesided taped to a piece of 1/4"birch plywood to give it ridgidity, Next a metal scribe is used to layout the hole cutouts using a good carpenters square. If these cutouts are symetrical and in line ,you can just scribe the lines from end to end and side to side without hesitation or interuption.
Then put an X with a felt tip marker where the actual cutouts will be made. The tools used will invaribly strart with a drill bit of the required size for the cutout at hand. This may be a 1/16" driill followed by a riffling file, or a larger hole followed by a larger file. Machinists call this procedure "hogging out" to remove the most unwanted material in the quickest way possible, then followed by minimum filing to the required size hole. In your case, install a pilot hole followed by a series of fine tooth saber saw cuts all in one direction and followed by all cuts in the opposite direction all of which are just inside the scribe lines would be the quickest and easiest way to accomplis this task. while still mounted to th backing board fiinsh the opening by flat filing just to the scribe line.Next step is a thorugh wet sanding wth #400 git wet paper followed by #1200 grit wet paperto rid the visible scribe lines. Then carefully remove the backing and do any minor deburring if neccessary. IF layout line and final filing have been done carefully you will have a satisfactory panel. I have made many panels and chassis with all sorts of size and shape holes. The results were very professional. As involved as it sounds, once the work peice is setup, the work goes surprisingly quickjly. Just take you time and work carefully. I have priced various projects like this in the past at jobber shops and the price was incredible for one off setups. This is what prompted me to go it on my own. Again, the secret to success is backing the work peice and supporting it at the proper working ergonomic angle. At the very least, you will need a good bench vice for starters and one which allows absolutely no movement while work is in progress!
PS- one oher method I have used on occasion is to make up a wooden template and use a carbide bit in my 1 HP router. the bit cuts aluminun like butter, but beware thre are very soft aluminums that gum up and require frequent cleaning of the bit- harder is better!.
zotdoc
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Post by zotdoc »

Thanks to everyone. I'm trying to make my own punch out of some tool steel I have. If it works I'll try to post a pic. Mr. Reed's idea about the router will be what I use if I can't make the punch. I'm using T51 6061 aluminum which is the hard kind, so this should work. Zotdoc
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Lenp
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Post by Lenp »

Greenlee does make square. D and other punches. They are available at 'msc industrial supply, a great industrial supplier
Here's the link for the punches
http://www1.mscdirect.com/CGI/GSDRVSM?P ... 0034302218

You better have some deep pocket$ though!

Len
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