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View Full Version : Drilling holes in steel ... small then big?



Sir Stinkalot
25th Jan 2006, 07:52 PM
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.

Groggy
25th Jan 2006, 07:57 PM
Use a center punch - simple, easy and accurate.

dazzler
25th Jan 2006, 09:42 PM
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

echnidna
25th Jan 2006, 09:48 PM
8mm doesn't really need a pilot hole

Ashore
25th Jan 2006, 09:50 PM
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

maglite
26th Jan 2006, 01:42 AM
As others have said.
Also apply a squirt of oil to the bit before drilling........this helps as a lubricant.

Barry_White
26th Jan 2006, 10:36 AM
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

bitingmidge
26th Jan 2006, 12:09 PM
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:cool: :cool:

journeyman Mick
26th Jan 2006, 12:24 PM
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 :o )

Mick

Barry_White
26th Jan 2006, 03:53 PM
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:cool: :cool:

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_details.asp?part_no=07277205&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

Dano48
26th Jan 2006, 11:22 PM
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!!:D

Grahame Collins
27th Jan 2006, 08:01 AM
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

arose62
27th Jan 2006, 09:14 AM
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

Dan_574
1st Feb 2006, 07:13 PM
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

2shane
3rd Feb 2006, 03:21 PM
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)

TassieKiwi
3rd Feb 2006, 04:46 PM
Sheesh. The bloke's just drilling a wee hole guys. Tie the ladder off at the top, have someone hold the base if you need to. Drill as close to the center of the ladder as you can - Take it nice and easy - if the drill bites, drop the bas1ard.:D

Den

TEEJAY
3rd Feb 2006, 05:38 PM
Sheesh. The bloke's just drilling a wee hole guys. Tie the ladder off at the top, have someone hold the base if you need to. Drill as close to the center of the ladder as you can - Take it nice and easy - if the drill bites, drop the bas1ard.:D

Den

Drop it onto the poor bugger holding the ladder :rolleyes:

One thing I have found invaluable with drilling steel is firstly start with a sharp drill bit and use the moly cutting lubricant stuff (what ever it is called properly) fantastic for keeping the bit sharp and quick ease of cutting. Also don't set the drill speed too high - it will just heat up the bit, take out the temper and make it blunt. The Moly stuff helps heaps I have found.

Cheers

Wood Butcher
3rd Feb 2006, 08:10 PM
I use Rocol RTD as a lubricant on drill bits. It makes a huge difference in the performance and the life of the cutting edge. Worth having a look at it.

DanP
4th Feb 2006, 10:41 AM
However one can drill a small hole, say perhaps at 5 or 6mm and then one can oversize the hole with a 8mm drill.

Your pilot hole should never be more than half the size of the inended drill size and is normally about 1/4 the size. Drilling a 5 mm pilot for an 8 mm drill when working up a ladder... You might as well just climb to the top of the ladder and jump off.

Dan

DanP
4th Feb 2006, 10:44 AM
BTW if you look at the centre of a drill bit tip, you will see a small flat bit in the centre of the tip, where the two cutting angles meet. Your pilot should be a clearance for that part.

Dan

Ashore
4th Feb 2006, 07:35 PM
One thing I have found invaluable with drilling steel is firstly start with a sharp drill bit and use the moly cutting lubricant stuff (what ever it is called properly) fantastic for keeping the bit sharp and quick ease of cutting. Also don't set the drill speed too high - it will just heat up the bit, take out the temper and make it blunt. The Moly stuff helps heaps I have found.

Cheers


We use to use stuff called " treferlex" I think is the spelling a green compound with a most distinctive odour a must for tapping steel espically with small taps but also for good for turning and drilling

LPeterStacey
3rd Mar 2009, 07:50 PM
[QUOTE=Barry_White;256388]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 <SNIP> because you only need one hand to centre punch.
<SNIP>

Barry.
I have what looks like the same type of Centre Punch. It is identified as: Eclipse No. 171. The problem is that while it still operates and the end cap is adjusting the spring tension I can no longer get the punch to do light marks. It is obviously softer than the full setting but not like it used to be when I can remember being able to make light 'witness' punches with one hand.
Do you know how it operates and what may be wrong and need repairing? Having taken it apart several times I am thinking that the top pin (connected to the adjusting cap) may be worn short and so it needs further spring compression to 'trigger' the punch.
If you or anyone else can supply any information I would be very grateful.

TIA Cheers, Peter.
***************

Woodlee
3rd Mar 2009, 10:23 PM
Trefolex is for use with hand tools such as taps and dies ,not meant for power driven tools .
I don't know if it the same formula as it was years ago , but a warning was issued many years ago about using this lube on powered tools .The smoke that is generated from the heat is proven as carcinogenic.
We were stopped form using it in the toolroom where I worked for this reason.

Kev.

Kody
3rd Mar 2009, 10:57 PM
Ok, If I may squash everybodys toes, here's my answer to the original question. You're up on a ladder, right? Use what you can to center punch the position of the holes, be it an automatic C/punch or a two handed job. marking the holes is the easy part. You have to hang on with one hand and use the other for drilling. You need a pilot hole of no bigger than 4mm and no smaller than 3mm. Forget what was said about what sizes to use being a percentage of the diameter and do what I would do. The 3 or 4mm drill is easy to put pressure on it with one hand and drilling the pilot hole will be easy. As someone described earlier, the pilot hole is to take away the force (pressure) required to make the 8mm drill penetrate. Run the drill at maximum speed for the 3mm or 4mm hole. Any slower and you are bound to break the drill. The cutting speed for HSS drilling mild steel is 100 feet per minute (about 30 meters per minute). You do the maths for the correct RPM.
Grind the 8mm drill with the minimum amount of lip clearance. If it wont cut, increase the clearance gently untill it cuts cleanly without grabbing. With the correct lip clearance, the drill will be very easy to use with one hand. The speed for running the drill with the 8mm HSS drill is 1100 to 1200 RPM. The RPM for the 3mm drill is 3000 and for the 4mm drill is 2400. You can drop these RPM's to (8mm drill)1000, 4mm drill, 2000 rpm but no slower. Use a good lubricant and go for it. You will not burn the HSS drills at these RPM's and if you use a good quality HSS with Cobalt the drill will last for all the holes. Do not force the 8mm drill thru the steel. Let it cut at its own rate.
If the 8mm drill is shaped carefully with the correct clearance angles, it should not grab and be out of control when the drill breaks thru the 3mm steel. However, be very careful and dont hurt yourself.

Kody

Barry_White
3rd Mar 2009, 11:38 PM
Hi Kody

This thread is over three years old and I gather by now Stinky has drilled his holes and moved on. He never said how he got on anyway.

I gather from a lot of the replies to this thread that most have never seen a step drill let alone used one because to drill a large hole in thin metal with a normal drill will usually produce a hole the shape of a triangle with curved sides even by drilling a small pilot hole first.

I have been using step drills for forty years and had to get them specially made by a engineer long before you could buy them off the shelf.

Peter

My punch still works fine so I couldn't really say what is wrong with yours. They are really cheap enough to buy a new one.

Gavin Newman
4th Mar 2009, 03:46 PM
We use to use stuff called " treferlex" I think is the spelling a green compound with a most distinctive odour a must for tapping steel espically with small taps but also for good for turning and drilling

Woodlee is correct, the Trefolex paste (as opposed to the liquid) that you refer to is not meant for use in drilling. If you look at the label on the container it goes to great pains to warn against using with power tools or in a situation where its use would generate fumes (ie drilling, turning etc). It is only meant for use with hand tools.

But surprisingly enough given the above I have seen it used in TAFE workshops with no safety warnings whatsoever - go figure!

Sir Stinkalot
4th Mar 2009, 08:33 PM
Good news .... I finishes the holes last weekend :2tsup:

Nahh just kidding. Can't remember what I did but most likely used a centre punch and then just the 8mm drill. It was to mount some eye bolts for the shade sail and was drilling through recycled fire sprinkler pipes.

Sorry that I didn't previously post a thank you and follow up .... quite unlike me I like to think!