drilling steel?

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Hiya
I have just tried drilling some 3mm thick mild steel with a 13mm hole......... hell of a lot of noise, loads of vibration and now the drill seems to do anything but drill!
Ok, please stop laughing, I'm a beginer!! ;)
The drill bit was a Piranna 'Bullet' that it said was for drilling metal, but what I have only just realsied is that the max recomended rpm for 10mm was about 1000. The drill was the cheapest Clarkes one speed drill (i'm on a budget and this might be a '1 of' project) so I guess this is much faster.
So my questions are: Is the drill running too fast? What speed should i drill 12mm holes at? Does anyone know where I can the cheapest drill to drill at the recommended speed?
Thanks for any help given
Dave
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a
Does
May I answer two questions you haven't asked? 1. Use a lubricant, old engine oil will do, and it will save your drill bit 2. Fix (clamp) the sheet of steel and be prepared for a 'snatch' when you break through. BAH
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Dave wrote:

I'd aim to use lkess than 1000rpm for 12mm but you are where you are and have only one drill speed. Clamp the work firmly onto a sacrificial piece of wood. the workmust not deflect away fromthe drill bit. This is possibly where your noise is coming from. For mild steel, a quality brand drillbit (dormer etc) is all you should need. Use a pilot drill say about 4mm followed ideally by something around 8mm. As a minimum, the pilot drill should allow the chisel portion of the next drill to pass into the pilot hole. Often helps to put some oil when drilling.
Good luck
Bob
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IIRC, most single speed drills run at about 2400 off load - but you should be able to slow it down quite a bit on load.
--
*Starfishes have no brains *

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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wrote:

It doesn't slow down enough. I've spent a while blunting bits with a single speed B and D before borrowing bu FiL's Lidl special offer with a gearbox which was much easier. Even a cheap Argos with a lockable trigger is better.
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wrote:

I've found that the judicious application of some off/on/off/on trigger work can provide what amounts to a lower spindle speed even on a cheap single-speed electric hand-drill.
-- you can contact me via http://aardvark.co.nz/contact /
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On Thu, 28 Aug 2003 20:21:50 +0000 (UTC), "Dave"

You're pretty lucky it didn't decide to spin the metal, rip a hole in your leg and leave you bleeding to death from a femoral artery ! 8-)
13mm isn't a small hole in thin steel. Now I'm a cowboy, but even I don't like to drill that with a handheld drill. If I have to, I do make sure it's clamped down pretty well. If I don't have a slow power drill, I'll do it by hand. I am _not_ going to over-speed a big drill bit into something that's likely to fly up and tear chunks out of me - Sorry, done that one far too many times already.
Use lubricant. Something oily is good. Buy some RTD if you want (it's gooey enough not to run away from a hole in a wall), but old engine oil is a lot better than nothing.
Drill a pilot hole. You should be able to fit the centre chisel edge of the bigger drill into the existing pilot hole.
Use a backer - bit of scrap wood clamped on the back, or something. If you don't do this, then it's going to go completely random when you break through,
Go slow. For 13mm, go damned slow.
Use decent drills. The shed sets are garbage. Go to a real engineer and get some black ones (you're in the UK - buy some Presto), not the Chinese gold-coloured TiN ones.
Don't drill 13mm holes in thin sheet with a handheld twist drill. Get a Conecut or something if you're going to make a habit of it. A two-flute drill that isn't held rigidly gives you a lousy hole that's probably more pentagonal than round.
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...

The colour is not really a guide. The TiN coating reduces friction and can be applied to any quality of drill. I would, however, agree that you don't want to buy any drills made in the Far East.

For a two-flute drill it will be triangular, rather than pentagonal - that would require four flutes. Polygonal holes are always drilled using one less flute than the number of sides you want to end up with.
Colin Bignell
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On Fri, 29 Aug 2003 02:03:14 +0100, <nightjar> wrote:

I used to like TiN coatings. I have some old ones here (German, AFAIR) that are still in excellent condition after much use.
But the common TiN sets around now aren't worth a damn. As a general rule of shopping, I'd avoid the colour entirely unless you're absolutely sure of the quality. A TiN coating (even a good one) adds little for most DIY users, until you're into production work on tough metal. How many drills do any of us really _wear_ out, compared to loss or breakage ?
The cobalt drills are even worse ! The "coated" sets with the blue rainbow finish (mine came form Northern Tools) are absolute rubbish. OTOH, a real set (from Axminster) of silver-coloured M42 steel were a great addition to the workshop.

My Japanese stuff is good. I'm sure that both the Chinese sources could do better too, if there was a call for it - but "cheap sets for DIY sheds" are always going to be intended to be cheap, not high quality.

I'd agree that large holes in sheet tend to the triangular, or more likely torn and oval during breakthrough.
But I've definitely had chatter in a drillpress, probably caused by drilling a pilot hole larger with a blunt drill, used too fast, and these have been pentagonal.
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On Fri, 29 Aug 2003 02:03:14 +0100, <nightjar> wrote:

Correct -- and the black ones you buy here are made of pewter I swear (well I swear at them anyway).
One brand sold here seem to use black oxide on their really poor quality (ie: either soft as butter or brittle as ice) drill bits. I steer well clear and just stick to a known brand of good quality HSS (for most metals) or cobalt (for stainless). -- you can contact me via http://aardvark.co.nz/contact /
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can
don't
Yep. I had one unspiral itself when I tried to drill with it. Thinking it was an isolated fault, I returned it to the supplier and the same thing happened with the replacement and with the replacement for the replacement, even though the supplier, a respected specialist supplier of drills to the engineering trade, assured me that they were all from different batches.

As I mostly use automatic machinery, I prefer solid carbide for stainless.
Colin Bignell
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On Fri, 29 Aug 2003 01:39:45 +0100, Andy Dingley

Is it?
When I was out of cutting lube I trued using a squirt of Mobil 1 once.
It was really bad. The drill would not "bite", despite the application of significant pressure -- and then when it did bite -- well fortunately the work was clamped really well (as it always is in my shop ;-) so the drill-press stalled (only 3/4HP and a 12mm drill bit).
It would appear that the film-strength of a good motor oil (a synthetic anyway) is too high for it to function as a good cutting oil. I would assume that cutting oil should be designed to have a relatively low film strength so as to allow the cutting edge to reach the work and actually do some cutting -- rather than skating around in a thin film of oil.
But, given that I'm not an industrial chemist, I might be completely wrong.
However, if you've got some synthetic motor oil in your shop, try using some as cutting oil and see what happens.
-- you can contact me via http://aardvark.co.nz/contact /
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wrote:

You aren't wrong. Motor oil is formulated to *prevent* metal to metal contact. When drilling, you *must have* metal to metal contact in order for the bit to cut. The main purpose of cutting oil is to *cool* the bit to prevent it getting so hot it loses its temper. The high sulphur content also tends to promote shearing action. It is not intended to *lubricate*.
Gary
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Good grief. You could have had a drum of the stuff couriered around for the cost of that stuff. ;-) Talk about black gold.
--
*Eat well, stay fit, die anyway

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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On Sat, 30 Aug 2003 01:58:17 +0100, Dave Plowman

Actually, I spend probably about US$9 a year on the stuff for the workshop. I use it as way-oil, general lube and rust protectant. It's clean, doesn't smell, works *very* well and a little goes a long way.
I once made the mistake of using regular mineral motor oil instead -- what a stink -- it took days to come out of my hands.
-- you can contact me via http://aardvark.co.nz/contact /
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On Sat, 30 Aug 2003 08:35:44 +1200, Bruce Simpson

Yes, it works fine. Note the qualifier "old"
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Not really -- use WD40 instead or, failing that, water applied from a hand spray. Even if the water doesn't lubricate the drill bit, it will at least help to keep it tolerably cool.
I must admit that, whilst I've not tried it as a drilling coolant or lubricant, I have used "I Can't Believe It's Not Butter" [1] when turning stainless steel; it seemed to work reasonably well, though the workshop stank like a chip shop for days afterwards.
[1] I'd bought two tubs in a B.O.G.O.F. supermarket promotion and, on tasting it, I soon decided I'd been overcharged on both. There again, I'd doubt that anyone could pay me enough to *eat* the stuff...
--
< Paul >

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Dave
1000rpm is way too fast. You should be running at 750 (ish)rpm in mild steel if using high speed steel (HSS) twist drill but slower, say, 220 (ish) rpm if using carbon steel twist drill (yes, they're still around). Other posted advice is good about pilot holes, clamping and coolant, but don't use water as this can cause small checks or cracks which may result in the twist drill tip chipping out. You may have knackered your 13mm twist drill so a re-grind may be necessary - check for dullness of the tip and wear to the extreme outer corners of the cutting edges (a sure sign/confirmation of too high a speed).
Speeds and feeds for any type of metal cutting is a complex business. Factors such as type of material to be cut, the type of drill, the kind of steel in the drill, the design & condition of the drilling machine, the shape & sharpness of the drill point and the coolant used.
The 'economy' drilling machines affordable by DIYers mostly have limited speed ranges (& usually excluding slows!), acceptable for lots of jobs in timber, plastic, most non-ferrous, & 'light' steel work. They're clearly not designed for heavy duty work. But if you follow earlier advice about pilot holes (lots of them getting bigger in stages 'till you reach 13mm) you should get away with this job.
Best of luck
Paul
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IIRC, those "Piranha" drills are impossible to regrind to the same profile and may have too thick a web for a conventional re-grind.

http://snurl.com/278c or, to download (18Mb), http://snurl.com/278d

Except that, by then, the final hole may have wandered a little from where you'd like it to be.
The cutting point of a twist drill is meant to be the "chisel edge"; by drilling a pilot hole, you're making the drill cut on the flutes rather than the chisel edge and therefore the drill will faithfully follow the pilot hole. However, as the smaller drill is thinner, it is also more flexible and may have deformed or deflected as it was fed into the work- piece. Yes, it's a lot easier to drill one or more pilot holes, but it may not be as accurate as drilling with the "right" size of drill.
But then, if one really wanted accuracy, one would drill slightly undersize and then ream out the hole to the final diameter...
--
< Paul >

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Thanks for the help people :)
BTW
Didnt rip my leg open as the hand drill is in a stand with the work clamped ;) I'm a beginer but i can remember back to my metal work days at school!
cheers dave
PS wont a power drill that allows screwdriving, or a variable speed drill be able to run at slow speed?

a
Does
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