Drilling a heap of 25mm / 1" holes in sheet metal

I've got a job coming up to drill around 300 x 25mm diameter holes in some powder coated steel electrical enclosures. The metal is <1mm thick, probably
30 - 35 thou. Punching is out, I need to do this using my drill press.
I've done a bunch of holes in the past using a step drill, and then spent almost as much time again deburring the holes. I'de very much like to avoid using coolant or Trefolex due to the cleanup involved with the enclosures.
I'd like to drill the holes in one go (ie not pilot then change & drill) any recommendations as to the best approach or tool that I should use?
thanks
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K Ludger wrote:

Drill press be damned.
Punch!
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Seconded.
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If you absolutely *insist* upon drilling, get yourself a bunch of 1" bi- metallic hole saws and the appropriate mandrel.
The mandrel has a drill bit that will let you precisely spot the hole, drill a pilot hole, and keep the saw centered.
Practice on some scrap 'till you get used to the amount of pressure you'll need to apply.
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Well, looks like you need to use a hole saw. Wonder if they make them with brazed in carbide teeth?
I'd drill for a green lee punch and punch. I'd also beg borrow or steal ;) a hydraulic model or have an air ratchet to drive a non-hydraulic punch.
Wes
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The ball thrust bearings make those bolted punches very easy to operate.
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WB
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On Sun, 21 Dec 2008 00:16:08 -0500, the infamous "Wild_Bill"
Unless you buy a truly cheaparse copy from HF, complete with mismatched threads http://tinyurl.com/7cvcdl . This is one of the few tools they got -entirely- wrong.
RUN AWAY! RUN AWAY!
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Yup, and the slugbuster profile on the newer ones seem to cut through easier too.
Wes
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wrote:

==========If drill you must, you might look at a hole saw.
I don't see a 25 m/m listed, but this will give you an idea. http://www.use-enco.com/CGI/INSRIT?PMAKA0-0761&PMPXNO008810&PARTPG=INLMK32 you will also need the driver http://www.use-enco.com/CGI/INPDFF?PMPAGE`6&PMCTLG
As the metal is pretty thin you might want to consider an adjustable hole cutter. These are dangerous. http://www.use-enco.com/CGI/INSRIT?PMAKA1-5497&PMPXNO905220&PARTPG=INLMK3
An other option if your drill chuck is big enough [3/4 inch] is to use a rotobroch. Good but spendy http://www.use-enco.com/CGI/INSRIT?PMAKAB2-1418&PMPXNOx96673&PARTPG=INLMK32
http://www.rotabroach.co.uk/en/products/accessories/default.aspx shows an exact 25m/m their sku SRC250. They also show a morse taper adapter to replace the chuck.
Most any good mill supply house should be able to order for you if they don't have in stock. Enco items are exmples.
Let us know what you decide on and how it works
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wrote:

Rotabroach. Rotabroach is a brand name, annular cutter is the generic description. Not cheap, but will make clean, accurate holes in thin material without damaging the finish. Make sure your drill press will turn slowly enough, around 300RPM for mild steel. You may need an adapter, as they usually have a 3/4" shank for mounting in a mag drill. I use them on control panels for installing oiltight switches when I want something more accurate than a Greenlee punch.
http://www.imatech.com.au/images/products/28.jpg
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Ned Simmons

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You don't say what size or HP your drill press is. As you probably already know, the correct time to make the holes would be before the finish coating is applied.
How will you be locating the location of the center of the hole? Center punch? That's about how long a punch would take to make the hole. Any drilling or hole saw method will take considerably longer than punching. Some odd/uncommon/custom carbide-tipped spade bit with a center pilot drill may be faster if you could find, or make such a cutter.
You will most likely spend a considerable amount of time deburring the holes, regardless of the method you use to make the holes. Step drills will deburr the entry side of the hole if you just kiss the next step on the hole. If the hole is located in the back of a box (not the sides), the deburring time could be quite a bit faster, by flipping the part over to deburr.
I would hate to attempt to make that number of the holes without any cutting lubricant, maybe not liquid, but at least beeswax or even bar soap (not highly effective, but not extremely messy).
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    And -- before the metal is bent to make the box.

    Assuming a proper punch (e.g. a turret punch), though it is nice to have a center punch mark to feel for with the pip on the center of the punch.

    Agreed -- unless it is a case of:
1)    Drill a pilot hole.
2)    Assemble a Greenlee chassis punch.
3)    Spend quite a bit of time cranking on the drive screw.
    (this can be made easier by using a hydraulic drive for the     punch, but not as nice as a lever operated turret punch, or     even a floor standing single station punch of similar size.)

    And firmly clamp down the sheet metal to keep it from spinning and slicing open your wrists.

    Yep -- except for perhaps a CNC water jet.

    Except that I think that the largest step drill size is 1", which is his target dimension -- so there *is* no next step to use for the deburr operation.

    Or if it is done before the box is folded.

    Agreed. The only lubricant free method which I see as practical is the above-mentioned CNC water jet -- which could probably cut several stacked up at once.
    Didn't he say that he was going to be cutting in Stainless? That will make it more difficult for all methods except the waterjet.
    Good Luck,         DoN.
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Step drills for making 3/4" and 1" trade size electrical knockouts are available. The last steps on these are 1-1/8" and 1-3/8" so they should still deburr a 1" hole on the front side at least. A second operation with a cordless drill from the backside should be fairly quick.
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wrote:

If the enclosures are built, I don't have any advice, although personally I'd punch them. If they are not built, design your enclosures carefully, locating all holes, square round, large small, doesn't matter. Send the drawing (I use email) to an enclosure fabricator near you, and they'll plasma cut the holes in the flat sheet, bend up, weld, and powder coat the boxes. Saves a lot of money and hassle, plus hole edges are powder coated. That's about the only way I'll do enclosures of any complexity any more. I've also done it in 4X.
Pete Keillor
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The ideal thing for sheet metal is something that can remove a disk, rather than having to chew out all or the material. I've never used a RotaBroach, but if you can afford one, that may be your best bet. I'm not sure how bad they are for burrs. If you don't like deburring, a hole saw will probably be worse than a step drill. A trepanning tool might also work if you can hold & support it well.
Actually, I'm surprised you have a problem with burrs with the step drill. A good quality one (not a Chinese knock-off) has always cut a pretty clean hole for me, and if you move up towards the next step, you can deburr the top side in the same operation. For the backside, I use soemthing like a Noga or a Royal with the "?" shaped blade to get the far side of the hole.
With any approach, having a good hard backing surface will help with burrs and safety. If the metal can flex, it can grab, expecially if you you a single point adjustable cutter. A trepanning tool tends to scrape more than dig in, so it's a bit safer.
Doug White
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Annular cutter.
Jancy and Hougen are a couple of brands.
You will quickly get a feel for the pressure required, and leave very little burr.
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K Ludger wrote:

I would drill each hole location with a drill the same size as the pilot drill of a good carbide tipped hole saw. I would remove the pilot drill of the hole saw and in stead use a solid mandrel. A hole punch is a pain for more than a couple of holes. A cheap hole saw will make a mess after it starts to get a little dull.
John
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Wow so many replies - thanks to all!
I'm leaning toward drilling a single hole then using a Green Lee or Bramley punch (wrench driven unfortunately).
My drill press while substantial has been retrofitted with a 1/2 hp single phase 240V motor and with the current chuck (not morse taper) would not handle a rotabroach. The enclosures are an off the shelf prefabbed item my customer uses regularly. They are around 1'x1'x1' and are difficult to clamp/locate on the drill press. The hole location is not critical within 0.1" will be ok, its for a cable gland to be fitted into.
On the topic of chassis punches, will a 1/2 drive air wrench similar to the one at the link below drive a Green Lee or Bramley 1" punch?
http://www.toolstation.com/images/library/stock/webbig/45203.jpg
Would using soap / beeswax aid the punching operation?
Many thanks for all of the advice.
Seasons greetings to all.
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Sure should. At the very minimum it will reduce a lot of the manual wrenching

Never tried it.
I would take care to keep the screw threads lubed.
Wes

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That tool is commonly referred to as an air ratchet. They spin fasteners until the fastener gets snug, then the operator starts turning it as thae would a normal ratchet.
I never liked using them, or even being around them being used. They're loud and irritating. In close quarters, they can trap your hand or injure your fingers.
I prefer to use an air impact wrench, and for small/medium fasteners, the 3/8" drive was very satisfying to use. I don't know that a 3/8" impact wrench would operate the punch very well though.
Do you realize how slow that type of punch will be for 300 holes? As you know, you'll need to drill all the locations first. Then you assemble the punch thru the hole (quickly if you can), then you need to crank it down fully to punch the 1" diameter and shear the slug free of the box.
Then you disassemble the punch and clear the slug. Sometimes the slug comes out easily, other times not so quickly.
This method is a lot of parts handling and it takes time. If you start dropping the punch parts it goes even slower.
There will still be a sharp edge where the male die/punch part passes thru the metal, and although the punches don't usually cause much distortion, the hole edge might be flat, so a step drill might not work as well for deburring the hole.
Since the metal isn't heavy gage, you might be able to use a drill motor with some serious torque.
You might want to also have a smaller, lighter drill motor to run the bolt into the die quickly, then change to the slower drill motor with high torque.
The only way that I could see the punching portion of the 300 piece job moving along quickly would be to have at least several punches and a helper.
The 1 cubic foot boxes will take up a lot of workbench space, so a helper might be able to assemble the punches in holes, and handle moving the boxes.
I'd most likely try to find a shop with some sort of punch press to make the 1" holes.
Hole saws generally aren't fast (or accurate) and they dull quickly if they're pushed hard. In thin metal, they are prone to snagging and pulling the workpiece out of whatever is holding it. They should always be run relatively slow and be used with a cutting lubricant on metal, which gets messy.
If your drill press would stall while attempting to use a step drill, rotabroach or hole saw up to 1", then you're probably faced with using a bolt-type punch.
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WB
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