Drilling Accurate Holes in Thin Sheet Metal With Twist Drills

Drilling thin sheet metal with regular drill bits can be hazardous and even if you are able to get the drill bit to cut through, the hole will often be oversize, triangular or pentagonal in shape and there will be snaggy burrs all around the edge. The big danger is that the sheet metal will try to lift off the drill table and run up the flutes and when it reaches the chuck it can spin out of control and cut your hands to ribbons.
Now, you can use a step drill and they are specifically designed for sheet metal and thin stock but what do you do if you want a hole that is a specific and non standard size, like a letter drill or number drill size.
The trick is to trap a couple of folds of soft cloth like cotton, or some other non synthetic cloth (not nylon) between the workpiece and the tip of the drill. Then just drill through the stock as you would normally. The cloth will keep the stock pushed down against the drill table and as the cut progresses, the cloth will pack into the flutes of the drill bit and keep it centred as the cutting edges break through.
This is not my idea. I first read about it in the Model Engineer Magazine many years ago but it works and it's simple.
Regards,
Preso
Check out the video for some examples of how well it works.
https://www.youtube.com/watch?v=cAGiuXOKKi8

Very nice idea. I do like it. Thanks. Are you using a brad pointed drill ?

No, the beauty of this technique is that you can just use a regular twist drill. There is not need to modify the drill bits that you already have.
Regards,
Mark

Thank you for teaching this to us.(Me). I am 60 years old and could have used this technic 53 years ago when I started building things. It is a blessing to learn something new so helpful in the shop. Thank you! Doug

Here's hoping the wife doesn't find out what happened to her cardigan...

Thank you for sharing. This is a good technique if you're in a pinch, however, I would not do this on a regular basis. Using a sheet metal punch is much safer and no risk of a very sharp-edged piece spinning.

I picked up a used Pexto no. 5 punch for $25 (I think) earlier this year. It's from the late 1930s. Still work fantastic. A perfectly punched hole every time in sheet metal. New these punches are $80.

pexto 5 punch for sale | eBay
Pexto 5 Jr Hand Punch only – Batavia Machinery, Inc (machineryone.com)

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Originally Posted by jonlegrand1

Thank you for sharing. This is a good technique if you're in a pinch, however, I would not do this on a regular basis. Using a sheet metal punch is much safer and no risk of a very sharp-edged piece spinning.

I picked up a used Pexto no. 5 punch for $25 (I think) earlier this year. It's from the late 1930s. Still work fantastic. A perfectly punched hole every time in sheet metal. New these punches are $80.

pexto 5 punch for sale | eBay
Pexto 5 Jr Hand Punch only – Batavia Machinery, Inc (machineryone.com)

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I've got a couple of those punches, though one of mine is a Whitney-Roper, and the other a cheap copy, and if you only need holes near the edge of your sheet metal, they are very nice. Unfortunately, they're useless more than an inch or so from the edge of the metal. Great tools within their envelope, even the import, but not a replacement for the drill press. I was using them to put rivet holes in bits of metal that were going to be armour for medieval recreationists. Haven't done that in a few decades, but still have them. Also three different sizes of drill press. Hi! My name is Bill, and I'm a toolohaulic!

Congratulations Mark Presling - your tip for drilling accurate holes in sheet metal is the Tool Tip of the Month for August 2023!

This is a free and easy tip that anyone can use to make nice holes in sheet metal.

Some more nice tool tips from August:

Spreading U-Bolts by remidgett
Drilled Slot/Square/Rectangle Procedure by hemmjo
Flat/Square/Angular Parts on the Lathe by hemmjo
Makeshift Lap by Philip Davies
Protecting Bulk Coffee Beans by rgsparber
Extra Long Syringe Oilers by mklotz

Mark Presling - we've added your Tool Tip to our All Tool Tips of the Month winners post. And, you'll now notice the tool tip award in the awards showcase in your postbit, visible beneath your username:

https://www.homemadetools.net/forum/...fTheMonth1.pnghttps://www.homemadetools.net/forum/...MonthIcon1.png

And, you'll be receiving a $100 cash prize, in your choice of Amazon, PayPal, or bitcoin. Please PM me your current email address and prize choice and I'll get it sent over right away.

Congrats again :thumbsup:

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Originally Posted by Mark Presling

Drilling thin sheet metal with regular drill bits can be hazardous and even if you are able to get the drill bit to cut through, the hole will often be oversize, triangular or pentagonal in shape and there will be snaggy burrs all around the edge. The big danger is that the sheet metal will try to lift off the drill table and run up the flutes and when it reaches the chuck it can spin out of control and cut your hands to ribbons.
Now, you can use a step drill and they are specifically designed for sheet metal and thin stock but what do you do if you want a hole that is a specific and non standard size, like a letter drill or number drill size.
The trick is to trap a couple of folds of soft cloth like cotton, or some other non synthetic cloth (not nylon) between the workpiece and the tip of the drill. Then just drill through the stock as you would normally. The cloth will keep the stock pushed down against the drill table and as the cut progresses, the cloth will pack into the flutes of the drill bit and keep it centred as the cutting edges break through.
This is not my idea. I first read about it in the Model Engineer Magazine many years ago but it works and it's simple.
Regards,
Preso
Check out the video for some examples of how well it works.
https://www.youtube.com/watch?v=cAGiuXOKKi8

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Sorry, but I just can not understand for the life of me why I see so many people not take the extra time to secure the work piece to the table.

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Originally Posted by charles scozzari

Sorry, but I just can not understand for the life of me why I see so many people not take the extra time to secure the work piece to the table.

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I have to loudly agree. Freehand drilling in small parts is difficult and dangerous at best. Sheet metal is extra dangerous and difficult to hold securely in the average drill press vise. What's needed is a finger plate. The term is inherited from the British where the form has a single "finger" clamp to secure small parts. My version...

https://www.homemadetools.net/forum/...603#post189775

provides a table to which multiple clamps of differing types can be attached to secure almost any odd shape. Most important is the fact that the plate has projections on the bottom that allow it to be clamped securely in the drill press vise once the part has been secured to the top of the plate with suitable clamps.

Spotting drills are ideal for thin sheet metal.