Hard spots in mild steel

Can you get hard spots in mild steel that can't be drilled?

I need to drill a 8mm hole in some mild steel. I centre popped the point where I want to drill and using a 3mm drill and cutting oil proceeded to drill a pilot hole.

No way would the drill cut the mild steel, it was if I was trying to drill some really hard steel. I tried this three times, each time without success and also blunting three brand new unused Dorma drills. At a different place on the steel I tried again without using a centre punch to give me a guide. This time it worked, just as it should. I then increased the hole size ready to finish with an 8mm drill and this was ok too.

This is not the first time this has happened to me, but I put it down to not being able to sharpen drills properly, until I made a drill sharpening jig.

I wonder if anyone has the answer to this problem, as the only thing I did different was to NOT pop the steel with a centre punch. which isn't the best way to go.

I turned a piece of mild steel plate to make a 6" backing plate for something and across the middle was a seam that was very hard and blunted the tool a few times, it was possibly a weld but there was no indication that it was and I made sure the holes were well away from the hard bit.

That's a symptom of work-hardening - are you sure it isn't stainless? No true mild steel would blunt a new Dormer drill.

Neil

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Neil,

I don't want toappear excessively pedantic, but Alan mentioned using Dorma drills

It may be a typo, but they are [apparently] available here

... Perhaps Alan could confirm ...

MichaelG.

Edited By Michael Gilligan on 14/08/2015 21:48:35

Hi, I agree with Neil, if it is truly mild steel then it will not have any hard spots anywhere and the fact that Alan says he centre popped the place where he wanted to drill the hole would mean that there were no hard spots. I would be suspicious about the quality of the drills if it happened to me.

Regards Nick.

I've had hard spots in Gauge plate and some unknown steels but not mild steel from a known source before.

Guessing it must be your drill bits?

I'd hazard a guess that the problem is a combination of a low quality drill bit and metal of unknown parentage? If bought from a proper steel stockholder then there shouldn't be any hard spots in mild steel. However, acquire from elsewhere and it is entirely possible that what is sold as mild steel will have hard spots - it probably has got the park railings in it.

Andrew

Is it possible that it is a peice of alloy steel of the work hardening type , the stuff they make jail cells out of comes to mind.

Try a new drill bit on some aluminium , it should drill easily with two nice even swarf curls coming off the drill.

I have a few sets of cheapie drills and most are ok but some have had the ends ground by a blind monkey and i have one where the outside of the flutes has not been relieved ( if you look at a drill bit the outside diameter is relieved along the flute to minimise contact area) you should try drilling a hole with that drill !

Make sure the drill is turning in the right direction , you won't be the first or last person to run a drill in reverse or have a left hand drill bit in the chuck !

Ian

Try drilling the same spot with your 8mm drill and see how it goes.

Like others, I've not come across hard spots in mild steel before, except welded pipe etc. I'd be suss of the drill bits.

My boss of the time borrowed a drill and drill bits from me once to drill holes in his house wall, he kept coming back with the drill bits burnt out. He was adamant that the wall was sandstone? Eventually I got him to bring the dril back as well. Turned out he was running the drill back wards!!!😢

If if you bought the drill bits off the market, bin them. I bought some once, tuned out I had harder nails. The bits bent when any weight was put on them. 😰

Edited By Boiler Bri on 15/08/2015 07:10:20

I used to machine rifle sights many years ago and the steel used to have ball bearings in which wore the cutter away. Although probably a special spec it looked like mild steel.

As far as the drill bits are concerned, they are Dormer Drills, bought from a reputable company in boxes with the Dormer info on them. The steel had originally been bought from a steel stock holder, by the firm my son works for and he gets me some off-cuts from time to time.

.

Thanks for the clarification, Alan ... Your original post said Dorma [which is what gave me cause for concern] ... Looks like you must have some 'not-so-mild' steel.

MichaelG.

Hi Michael, What I can't understand is that the same drills will drill the steel in different parts of the same piece of steel. Could pop marking a point where I want to drill my giving the centre pop tool more than one clout of the hammer, work harden that small area?

Hi Alan, mild steel will work harden to a degree that it will fracture, but it will need very much more work than pop marking it, even if you clouted it half a dozen times, work harden-able steel may harden enough through pop making repeatedly, but I would have thought you would still be able to drill it.

Regards Nick.

Edited By Nicholas Farr on 15/08/2015 10:14:13

Try drilling without centre punching. At first my thought was, he's using a hand held electric drill, and it's running in reverse.

Ian S C

May just be rubbish steel, some does not seem to be even remelted scrap- just rolled up. You can get allsorts wrapped up in it, some delaminates on machining. Usually sold as" best commercial quality" or even EN3. I think this has been covered before.

.

Alan,

It certainly seems, from that experience, that the drills are O.K. and are rotating in the correct direction.

On that basis, it *must* either be a work-hardening material, or something with nasty inclusions.

It may be worth bending a strip of the steel, to see just how 'mild' it is ... if you can actually break it, you may learn something from the nature of the fractured surface.

MichaelG.

> The steel had originally been bought from a steel stock holder, by the firm my son works for and he gets me some off-cuts from time to time.

So could be almost anything then...

When I start din this hobby I went to a bootsale and was sold a job lot of 'silver steel' that was actually stainless.

Aside from the managing to turn the stuff. imagine the fun I had when all my attempts at hardening it made it softer.

Neil

HI all, I reckon most of the steel we buy had a previous life, Cadillac bumper comes to mind......

most suppliers will buy in the cheapest steel they can get....mostly from China - India that's unless it a special grade..

then who know's.........

when it's sitting on a dock side it could be anything from anywhere...u can't trust the paper work.....

I have to drill angle iron all the time for my regular work and this problem happens all the time.....

the odd hole I just use reg quality drill bit's but if it's series of the same size holes I use a good ol Meddings drill press with De-Walt Extreme drill bit's...I only use a pilot hole for anything over 10mm in a hand drill....these Extreme bits are self starting and hardly ever go blunt...well worth the £50 squids.....

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