drilling steel?

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
Reply to
Dave
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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
Reply to
BAH
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
Reply to
Bob Minchin
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.
Reply to
Dave Plowman
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.
Reply to
Andy Dingley
...
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
Reply to
<nightjar>
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
Reply to
Paul Hewish
This may assist you in your quest...
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Jesse L Zufall Silt Colo
---- ****---- If at first you don't succeed, skydiving is not for you.
Reply to
Jesse L Zufall
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?
Reply to
Dave
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.
Reply to
Andy Dingley
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.
Reply to
Nick Finnigan
Just to say thanks for all the help.....
I got a new drill with variable speed, a Champion 750W from Focus, a new B&D Bullet drill and used some cheap engine oil i had laying around as lub. Decided that although in theory the drill had a 2 speed range setting that the slowest was still too fast for the 12mm drill bit, so I held the trigger, pushed the drill down fairly hard and drilled pretty slow, while my helper sqirted oil on the work. What a difference! It was amazing...... cut though the steel easy :)
Thanks again
Dave PS The work was clamped in a vice under a wolfcraft drill stand, which was clamped to a B&D workmate. All seemed pretty solid and safe'ish!
Reply to
Dave
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
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Reply to
Bruce Simpson
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.
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Reply to
Bruce Simpson
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
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Reply to
Bruce Simpson
Actually, a TV ad for a really crappy brand of TiN-coated drill bits here in NZ was dumb enough to do a "conventional drill-bit versus *our* titanium drill bit" comparison. Of course the titanium drill went straight through the piece of 1" square-section -- whereas the conventional bit just spun, hardly making a mark.
It didn't take a rocket scientist to spot however, that the conventional drill bit was spinning the wrong way!
I checked out a set of these "titanium" drills and they were crap. Not only was the titanium coating already starting to rub off while they were still in tbe box, but the angles were uneven and there were actually coarse grinding marks visible. I swear they look as if they were ground by hand on some old foot-operated grinding stone.
I heard from someone else who actually bought a set that they *bent* two of the bits through about 70 degrees simply by applying a normal amount of pressure.
Fortunately these drills have a 30 day money-back/replacement guarantee but I suspect that most of those stupid enough to buy them are only drilling stuff like softwood where they must last at least 30 days of occasional use ;-)
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Reply to
Bruce Simpson
I've got the tee shirt for that, but it was a long time ago :-) I've drilled many metals since then and have learned a lot about the subject.
I'm not sure about the quality of that drill, but see later.
The maximum speed you quote is for best conditions. 1000 RPM is a bit fast for the average home user.
Some one else has said that you should pilot hole the metal by using a smaller drill, followed by a larger one. Good advice. When you come to drill the hole to the size you want, you will need a much slower drill rotation speed. The only way to do this, is to start and then stop the power to the drill, thus keeping the rotation speed down. This will be hard on the power tool, but kind on the twist drill. If the power tool heats up, take a break till it cools down.
By keeping a heavy pressure all the time, on the drill, (very important you keep lots of pressure while cutting the hole) on the power drill, to ensure that you continue cutting, you will be better off starting and stopping the drill by flicking the switch on every few moments. This keeps the rotational speed down and will prevent the cutting edge of the drill from blunting through heat.
HTH
And I hope you understand what I am saying :-)
Dave
Dave
Reply to
Dave
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
Reply to
Gary Coffman
I agree that this is the best way, provided your drill motor has enough power to do it. The problem comes when you don't have enough power to let you push hard enough to get a sufficient bite. Then the bit just spins and dulls. A clue you aren't pushing hard enough is when you don't get nice curls coming off the bit as you drill. If you're just getting piddly little shavings, you aren't feeding aggressively enough, and the bit dulls prematurely. If the motor stalls when you push hard enough, you don't have enough motor (or it's geared too high) to let you drill that hole.
Gary
Reply to
Gary Coffman
Good grief. You could have had a drum of the stuff couriered around for the cost of that stuff. ;-) Talk about black gold.
Reply to
Dave Plowman

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