Thread: Drilling holes in steel ... small then big?

I need to drill some 8mm holes in approximately 3mm steel. Is it better to drill a smaller hole and then the 8mm or just go in boots and all with the 8mm. I will need to use a hand drill on a ladder if that makes any difference.

Thanks

Stinky.

Use a center punch - simple, easy and accurate.

Hi

Centre punch the hole, then predrill with a bit no more than 1/2 the size of the finished hole (4mm) and then drill the 8mm hole. Will stop any jamming and can leave a cleaner hole.

cheers

dazzler

8mm doesn't really need a pilot hole

If your up a ladder and the drill is sharpened properly ie new .... Go with the 8mm , don't press too hard let the drill do the work , use the centre punch & watch as you break through, drills can bite and throw you off balance, and being up a ladder can mean a fall

As others have said.
Also apply a squirt of oil to the bit before drilling........this helps as a lubricant.

Originally Posted by Sir Stinkalot

I need to drill some 8mm holes in approximately 3mm steel. Is it better to drill a smaller hole and then the 8mm or just go in boots and all with the 8mm. I will need to use a hand drill on a ladder if that makes any difference.

Thanks

Stinky.

Stinky

I find the best way to drill larger holes in thin metal is to first punch them with a pressure centre punch as shown in the first pic. I find these ideal especially up a ladder because you only need one hand to centre punch.

I then use a Step Drill (See second pic.) the reason being is that it starts off with a 4mm hole and then work up to the hole size required. The beauty with step drills is that they drill very neat holes in thin metal without tear out and when they break through they do not grab, which can be a bit hairy when you are up a ladder hanging on with one hand

Baz,

You blokes never cease to amaze me, draggin out stuff I've never seen before!

So could you please explain how a pressure centre punch works (one handed!)

... and where do I get a Step bit???

Cheers,

P

Midge,
when I was at school it was called a prick punch (don't know if the auto censor will let that thru) also known as a pop punch. Don't know how it works exactly, it just does. I know there's a spring in there. Any good hardware or engineering supplies place will sell you both. Step drills are great for drilling through purlins etc. Don't buy a cheapie it won't last more that about 50 holes (DAMHIK )

Mick

Originally Posted by bitingmidge

Baz,

You blokes never cease to amaze me, draggin out stuff I've never seen before!

So could you please explain how a pressure centre punch works (one handed!)

... and where do I get a Step bit???

Cheers,

P

Biting

I've had my punch for about 30 years and it was made by Eclipse and has a number on it No. 171. I have seen these punches in Bunnings. As Mick says I think they are called a prick punch. You turn the little knob on the top and it adjusts the spring pressure and you just put the point where you want to drill the hole and push down on the punch and it goes click and then you have your centre mark. If you want it abit more defined you just push 3 or 4 times to make the mark a bit heavier.
See here http://www.blackwoods.com.au/product...5&black_found=

The step drill that I have is a Bordo made in Germany I purchased from a Australian Industrial Supplies distributor of which there is 13 of them in Qld and they have the step drills on special in their current catalouge on page twenty. They make them in both imperial and metric and various sizes and steps and range from $69 to $79

Go here http://www.aisnational.com.au/almar/index.html

Biting, this is a rough drawing of how the punch works,well at least the one I own, which is a cheap chinese version, the tip pushes a pin which is held of center by a small spring and in turn the pin pushes a hammer?mechanism with a stronger spring, when the pin gets centered by the countersunk part of the hole it goes through, it releases the hammer bit, thingymijig and it strikes the pin and in turn the punch, then, blah,blah,blah,blah!!

Drilling off a ladder ? Not for me I hate hospital food. It is a real BIG NO NO with Work. Health & Safety.Yes its a tad harder to sort out the proper stands and what not, but !!!
Without a pilot hole and in that particular position, the chances of the drill walking are greater.This will change the distance between hole centres.

The correct infomation on the various pops shown or talked abou is :

The spring loaded jobbies are known in the trades as
AUTOMATIC centerpops.

A PRICK punch has a sharp fine point for locating the scribe lines that centre the drill hole location. - the point ,say ground at 30 degrees.It is fine for small hole centres and witness marking.

The CENTER pop is larger diameter and a blunter point angle... used to enlarge a small pop point to accomodate a bigger diameter drill to prevent it climmbing out of the smaller pop hole..Commonly where hole centre dimensions are not critical.

Rather than use a step drill which is a fine tool for gauge sheet metal, I would re grind my clearance angle on my twist drill to minimise break through grabbing on the 3mm sheet.The grind angle needs to be very shallow- less than 3 mm of drill height,.
please do not hurt yourself
Cheers
Grahame

If you are after a cheapie, I got my spring-loaded centre punch from SuperCheap Auto for $5.95.

It's served me for about 2 years so far, mainly making a hole for lathe centres to sit in.

Cheers,
Andrew

Speaking of drill bits, Ive used a set of the cutters on the link below, they are great and can be used in a normal drill, well worth a look.

http://www.drillmate.com.au/cutters.html

Weeeeeeeelll it's like this you see. (aside from distractions and rambling)

The fine art of metal cutting, is just that - a fine art.

Then there is what you have on hand and then there is what is practical under the circumstances.

The fine art part.

Drilling - is metal deformation and cutting - simple.

There are lots and lots and lots of tried and tested forms of genius on this topic, from metalurgy of the drills, metal removal rates on all sorts of metals, and the blending of drill life, and drill performance.

There is precision drilling, precision drilling and reaming, and then there is precision drilling, reaming and honing... (microhoning etc., etc., etc.)

Then there are production tolerances, clearance holes and then there is crap drilling - albiet subdivided into well done crap drilling and awful crap drilling.

Punches fall into several varieties. The Prick Punch serves two purposes, the first of which is to mark out hard to see lines or location point on metal surfaces - for oxy cutting, shearing lines or as a marking point for FINE drills (up to a few mm in Dia), or as a marker for the drill punch.

The prick punch has a very narrow angle of (something or other) and it's more akin to a needle, as it's prurpose it to drive a small hole INTO the surface.

The drill or heavy punch, (center punch) has a tip angle approximating that of a drills (something or other) angle.

This is the secondary punch that OUGHT to be (usually) used after a prick punch.

Now back to the question of drilling a fine hole before a big hole.


The fine or pilot hole - is usually only used on accurate holes above 10 - 12mm +.

It's called a pilot hole. It's main purpose is to guide the big drill into the work, to minimise tip wandering and to aid in location and accuracy.

The Center punch (to center the drill), well when a big drill is started off on a small indentation, can and if not almost always, unless the center punch mark is very deep, the work and drilling head are fixed and very rigid, and the drill short, can wander off mark and can drill a hole in the wrong location, that is slightly out of round and if the hole is deep enough, it can be noticeably off to one side - which can seriously disrupt the alignment of parts.

A pilot hole ought to be no bigger than 25% of the following drill size.

And because the tip of the bigger drill - interacts with the cutting edges and rake of the drill, to regulate the cutting speed at a uniform pressure on the drill, the drill feed rate, and to create swarf in a peculiar fashing, without the tip bearing on solid metal - will begin to increase it's cutting speed.

So the ideal big hole will be marked out with a prick punch, followed by a center punch - the pilot hole is drilled and then the main (big) drill is fed through at a mechanically set feed rate, for the metal being drilled (with and without lubricant) and the drill diameter.

However one can drill a small hole, say perhaps at 5 or 6mm and then one can oversize the hole with a 8mm drill.

BUT as there is NO metal under the tip of the drill, to offset the cutting rate of the drill, one must use a manually restricted feed rate, to stop the drill pulling it self through the hole in a "screwing" fashion.

If you want to do very nice and accurate holes, it's probably worth doing pilot holes on an 8mm hole, but by the sounds of things, I dunno, I guess it's up to you to suck it and see...

I recall some one saying something up on a ladder, well from my experinece, I have a neato 900W hand drill - with LOADS of wrist twisting torque, especially with 13mm holes - and it's a real hazard, especially with the bastard trigger locks - when the drills grab coming out of a hole, up on a ladder in thick steel.

So If I was in that position, I'd be using a small and light drill machine, and perhaps a 6 or 7mm drill for a pilot hole...

Dunno,

Try it both or several ways, and then do a mental calcutation of all the work and time and effort doing it either one way or the other, vs. the quality of workmanship needed, offset by is it really necessary and will anyone either notice or care...

(bonus points for continuity and distractions and incoming calls)