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.

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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

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?

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

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

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

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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.

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…..

clogs

Alan made no mention of the steel type,was it black or bright,? mild steel does not work harden,so rule that out,its probably some hard material possibly slag rolled into the metal during manufacture. in recent times i have come across en1 a bright bar with internal laminations due to poor rolling,centrifugally cast,cast iron with internal cracks,all from good suppliers, and the wrong material delivered, No mention was made of the material thickness,it would be interesting to try drilling in the exact spot on the other side of the material to see if the hardness was right through the material or just under the skin on one side.

Dorma drills and Dormer drills are not the same thing. I would suggest that 3.3mm drills at GBP 0.15 may only be suitable for drilling holes in plasticene.

cheers

Bill