Tips on drilling steel

[carrot]

I'm pretty new to fabricating. I've been trying to drill some 12mm holes in 6mm plate and my chassis, to make my bullbar mounts, but I keep making the drill blunt!

Longer story: I have an el chepo pack of HSS drills from Big W (the are half copper-coloured), and I use them to drill the holes up to 10mm in about 3 steps, without too much trouble. I bought a 12mm drill bit from bunnings (HSS, silver coloured) for about $8 which lasted a few holes, then I got another from an engineering supplies place for about $18 (HSS, dull grey, same brand as the bunnings one but I can't remember what brand) and that only lasted a few holes as well.

Any suggestions? (And is it worth getting someone to sharpen my 12mm bits?)

[bogged]

are you keepign the drill bit lubed while drilling? also cools it??
Pilot holes? or straight into the 12mm?

[Emo]

Start with smaller holes and then increase the size.

[Gwagensteve]

Controlling heat and pressure is important.

Many hand drills won't really run slow enough for a 12mm hole. You'll need to run the drill as slow as you can, use lots of cutting oil, and take your time.

Don't use excessive pressure- the drill should cut smoothly.

If you rush the job, and drill fast and dry, you will stuff the drill pretty quick. Also, wathc your alignment - wiggling the drill around will make it worse. That's why drills last much longer in drill presses rather than ahdn drills.

Personally, I don't bother with sharpeneing drills, I throw them once they are useless.

Also, I wouldn't step up in so many stages. you shoudl be able to go from about a 5-6mm pilot hole to 12 in one step. opening up a 10mm hole to 12mm is hard on the outside edges of the cutting face of the drill and that's what determines the sharpness of the drill.

If you're rough, you can break the edge of from that last little bit of the cutting face quite easily and the drill is ruined. I did this with a brand new 10mm drill the other day... opening a laser cut 8mm hole to 10mm.

Steve.

[GRPABT1]

Drill pilot holes first and get some cutting compound. I have found Drill bits containing cobalt to be the best.

[carrot]

Thanks for all the advice! Yes, I have been stepping the hole sizes up, something like 5, 8, 10, 12mm. So... less steps (maybe 6mm, 12mm), low speed (I think I was revving the drill too fast) and some sort of cutting compound.

PS: I re-checked, both bits are SUTTON and cost about $20ea! Eh, more wasted money!

[carrot]

Oh, btw... are there any good alternatives to cutting compound that I might find around the house? Grease? Oil? Water? It'll save me another trip out to the shops, and I probably won't use it much at all.

[80's_delirious]

generally the pilot hole should be 1/4 the diameter of the finished hole size. if your pilot hole is too big the edges of the drill bit will bite too deep and tend to jam the drill or break the corners off the drill bit.

the bigger the drill bit the slower you want to spin it. you need a drill with plenty of torque (grunt) but still needs to be able to spin slowly. if you are spinning the drill bit too fast it will squeal and the tip will end up changing colour from overheating, once overheated they lose their edge very quickly

lube, lube and more lube. you can get a spray can of Trefolex from bunnings for about $11 works a treat, just dont be shy with it

titanium or cobalt stay sharp much longer if looked after
If you use a titanium or cobalt bit make sure you use the procedure above or you'll end up farking drill bits worth $$$

if not too badly damaged a drill bit can be resharpened on a bench grinder, there is a bit of a nack to it, and probably not worth paying to have it done.
if you think you need to buy a few of them it is cheaper to buy them from engineering supplies in packs rather than individually.

[Shadow]

Personally, I don't bother with sharpeneing drills, I throw them once they are useless.

O_O

[phippsy]

At work for a chassis, if we're not using a mag base drill, we'll do one 6mm or so pilot hole then drill the larger one. Otherwise you're trying to drill with only the last bit of outside edge of the drill bit, and they don't really like that...

[v6hilux]

HSS 12mm is not the same speed as HSS 2mm.

As others have said, slow it down and use something to cool the bit and the cut, like a squirt bottle with kero in it.

The drill pitch is important too, not too sharp or flatter is better for bigger holes.

In the past, for difficult big holes, I had my angle grinder ready to re-sharpen every 30 seconds. This has worked the best for me before I knew what I was doing.

[Shadow]

any sort of lube will do

i use 55-6 or wd40 when its at arms length.

[GRPABT1]

You can use WD40 just to lube the drill bit but it wont work as good as trefolex or the like to aid in cutting.

[Nuckingfuts]

as said above drill a pilot hole about 5 or 6mm ish wouldnit go any bigger.
drill does not need to spin ridiculously slow but at high speed u will not go anywhere and melt/soften/break your drill and make a mess of your hole. If you cant get through with a HSS drill dont waste money on a cobalt/carbide drill,these will snap much easier, the drill bit is not the problem.nothing wrong with Sutton.You should be able to do many holes on a brand new drill without sharpening it. The more rigid your setup the better. as for an alternative to cutting fluid, CRC, WD-40, Thin oil, undiluted engine coolant something like that you will need lots of it if you want to keep it cool and lubricated(CRC and WD-40 wont really keep it cool but it definately helps) to give you an idea the coolant we use at work when drilling etc comes out with more pressure than a garden hose(you shouldt need anywhere near that much lol).
cheers

[carrot]

Now it makes a lot of sense why I killed two bits: Too fast, pilot hole too big, too hot... This stuff should be taught in school!!

I think I'll go and get the cutting compound stuff, I need to get a new drill bit anyway!

[Shadow]

Now it makes a lot of sense why I killed two bits: Too fast, pilot hole too big, too hot... This stuff should be taught in school!!

I think I'll go and get the cutting compound stuff, I need to get a new drill bit anyway!

its relaly not necessary unless your drilling through very thick or very hard material.

I can drill 4 holes in a beam in quick succession with nothing as a lubricant, just make sure youve got a slow speed and a good amount of pressure.

[spazbot]

carrot where bouts in sydney are ya mate, i can give those blunt drills a sharpen for ya and you can have a bit of cutting lube aswell if ya want ?
send me a pm

[dazzah]

300V/D

so 300 X velocity divided by the diameter of drill

Mild steel velocity is around 30 mts per min

your drill speed should be 300 X 30 divided by 12 = 750

That's easier to accurately change speeds on pedestal drill with belts or gears, it's more of a visual thing on a hand drill, i guess maybe around a medium speed depending on drill.

As has been said before drill bits can be resharpened, but it requires practise to get angles right, I would be more concerned about heating drill up and hardening work piece, if you harden your metal from overheating you will never be able to re-drill that hole.

[Slunnie]

Now it makes a lot of sense why I killed two bits: Too fast, pilot hole too big, too hot... This stuff should be taught in school!!

Ahhhh. It is taught at school.

Also, particularly with the big drill, back the pressure right off when you feel it start to break through...

[awill4x4]

300V/D
If you harden your metal from overheating you will never be able to re-drill that hole.

I suspect dazzah has it right. You have overheated the drill bit and the hole you are drilling in the chassis. The steel plates wont be the problem as they are a low carbon steel, the chassis however will probably have a higher carbon content which will harden with the heat generated by too fast a drill speed/ lack of cutting compound/coolant.
You have essentially surface hardened the area you are trying to drill but it should only be the surface area though. Get a sharp drill preferably Cobalt and use a good cutting compound ( Trefolex is good) slow speed and use a stop/start procedure to get below the hardened surface. Use firm pressure but don't allow the heat to build up just turn it on and off repeatedly using cutting compound as you go.
You'll know once your through the hardened surface it will go much better then. Just be glad your not doing this on stainless steel as you generally have to use reground carbide tipped masonry bits to get through an overheated drill hole in stainless.
Regards Andrew.

[Thylacine]

300V/D

so 300 X velocity divided by the diameter of drill

Mild steel velocity is around 30 mts per min

your drill speed should be 300 X 30 divided by 12 = 750

That's easier to accurately change speeds on pedestal drill with belts or gears, it's more of a visual thing on a hand drill, i guess maybe around a medium speed depending on drill.

As has been said before drill bits can be resharpened, but it requires practise to get angles right, I would be more concerned about heating drill up and hardening work piece, if you harden your metal from overheating you will never be able to re-drill that hole.

Circumference, not diameter.


ed

[KiwiBacon]

Find someone locally who can sharpen drill bits well. No sense throwing away perfectly good drill bits.

25 m/s tip speed was the number I work to for drilling with HSS bits, for 12mm that's about 650 RPM.

[Harb]

What sort of metal are you drilling....
Sounds like it may be high tensile......

[crispy]

For lubrication get a small tin of tap magic, its a tapping fluid but is bloody awesome for drilling!!

[ISUZUROVER]

Personally, I don't bother with sharpeneing drills, I throw them once they are useless.

O_O

My sentiments as well - you must be rolling in money if you can afford to do that (or don't drill many holes).

I have sharpened countless drill bits on a bench grinder. Not perfect, but with a bit of practice you can do a good job that stays as sharp as a new drill.

[RUFF]

opening a laser cut 8mm hole to 10mm.

Steve.

This is very hard on drill bits. As the hole is surface hardened all the way through.

[RUFF]

This stuff should be taught in school!!

Was when i was at school. Maybe you just didnt listen.

[RUFF]

carrot where bouts in sydney are ya mate, i can give those blunt drills a sharpen for ya and you can have a bit of cutting lube aswell if ya want ?
send me a pm

If you can Take Spazbot up on his offer do so. Knowing how to sharpen drill bits correctly is a very handy skill. It could save you thousands of dollars over a life time. Especially if you keep going the way you are Sharpening drills is an art but its a very easy art to pick up once shown. Its very hard to explain via the internet though. And those drill sharpeners you can buy suck.

Otherwise i think you have all the advise you need here now.

[dazzah]

300V/D

so 300 X velocity divided by the diameter of drill

Mild steel velocity is around 30 mts per min

your drill speed should be 300 X 30 divided by 12 = 750

That's easier to accurately change speeds on pedestal drill with belts or gears, it's more of a visual thing on a hand drill, i guess maybe around a medium speed depending on drill.

As has been said before drill bits can be resharpened, but it requires practise to get angles right, I would be more concerned about heating drill up and hardening work piece, if you harden your metal from overheating you will never be able to re-drill that hole.

Circumference, not diameter.


ed

The circumference is used for lathe work and it's the circumference of work piece.

[carrot]

Yep, I've PM'ed spazbot. And maybe I didn't listen at school... but y'know, until I got to those 12mm holes I thought I knew how to use a drill!!

Yes, I think I have all the advice I need to do a better job next time. Thanks!