which drill bit for hardened steel?

[macafee2]

I am assuming the studs that are part of the exhaust elbow,
item 1 here, https://rimmerbros.com/Item--i-GRID001957
are hardened steel.

What drill bit would be best for drilling the stud assuming it is hardened?
Could you also advise on what RPM (a range will do) would suit the drill bit?
I require 4, 6 and 7.5mm.
I've searched Google and am confused but would cobalt be the ones?
What type of bit would be even more likely to drill the hardened stud?

Things were going so well until I went to drill. My bits don't seem to want to touch the stud. The guides I'd made to help drill centre I was very pleased with, thank you Youtube for the idea

macafee2

[kaiser]

Originally Posted by macafee2

I am assuming the studs that are part of the exhaust elbow,
item 1 here, https://rimmerbros.com/Item--i-GRID001957
are hardened steel.

What drill bit would be best for drilling the stud assuming it is hardened?
Could you also advise on what RPM (a range will do) would suit the drill bit?
I require 4, 6 and 7.5mm.
I've searched Google and am confused but would cobalt be the ones?
What type of bit would be even more likely to drill the hardened stud?

Things were going so well until I went to drill. My bits don't seem to want to touch the stud. The guides I'd made to help drill centre I was very pleased with, thank you Youtube for the idea

macafee2

Drills look most like each other. Chances are you have a set of Chinese drills. They are cheaper and not good. In this case absolutely useless for a job like this.
You go to an old fashioned hardware store and ask for a good quality drill, they could typically be Austrian, German or Japanese.
You most likely pay for one drill, half of what you paid for a whole set at the supermarket!.
This is a typical case where inferior tools will not even scratch the surface and your job is impossible to do with such tools.
As for speed, slow, and on and off also works. Punch a center before you drill.

[vitesse]

Not tried the 75 studs, but SD1 studs which were not especially hard to drill. I generally use consecutively larger drills - helps when you are bit off dead centre and I find bite better too. Lubricate, slow, lubricate again just a few mm at a time. Mind you just about all my drills are old imperial ex-Tracy tools Dartmouth which I sharpen every now and again.

Regards

[macafee2]

bit of an update.
tried heating and pressing stud out no joy, try taping stud out no joy.
I'm now getting desperate so I try a 6mm drill and low and behold it is drilling the stud. The 4mm would not do anything. Battery on cordless has gone flat and is now on charge but things are looking up. Once drilled with 6mm the next guide I have is 7.5mm so that will be next. I will look at 8mm, 8.5mm and 9mm but the drill bits but may hit the threads of the joining nut which forms part of my guide or will be the guide.

macafee2

[ceedy]

highly unlikely any studs are hardened, high tensile maybe.


Any decent drill should sort it


Only drill out to the thread core size max ..



And before that size try a smaller one and an easi out extractor as a last resort before going to the max then you will have to try to get out the thread portion or just re tap it .

[macafee2]

ha ha, stud drilled. The head wont separate from the elbow but I don't think that is a problem. I'm just relived its done.

macafee2

[Rich in Vancouver]

Something I learned in the aircraft industry is there is nothing worse than cheap drill bits. They break, and go dull quickly and can lead to frustration damage and even injury trying to make them do what they should do.
I buy common sizes in cobalt steel drills and use a good cutting lubricant to keep the bit cool as heat is what destroys drill bits. this helps your bits last, using one for many holes rather than a handful of cheap bits.
For the odd sizes I use quality high-speed steel bits and generally get as close as I can using the cobalt bits then take the hole to the final size with an HSS bit.

[COLVERT]

Originally Posted by macafee2

ha ha, stud drilled. The head wont separate from the elbow but I don't think that is a problem. I'm just relieved its done.

macafee2

I'm pleased to see you have got it drilled out.--

Many years ago when I was an apprenticed Tool Maker we had drills that would drill through the super hard blade of a file.

I tried it and it works.. But as it was such a long time ago I can't remember what it was called.

I do remember though that the file glowed red hot and the drill went through like a knife through butter.---

[macafee2]

I think in the end it was my 4mm drill bit that was not up to the job. Other drill bits were fine. I did use a cutting agent and it did seem to be beneficial.

It is just another thing I have met and mastered and now if anyone else has the problem I can offer words of advice.

The guides I made up were brilliant. So pleased with my lathe even though it is not top quality.

macafee2

[Rich in Vancouver]

Originally Posted by COLVERT

I'm pleased to see you have got it drilled out.--

Many years ago when I was an apprenticed Tool Maker we had drills that would drill through the super hard blade of a file.

I tried it and it works.. But as it was such a long time ago I can't remember what it was called.

I do remember though that the file glowed red hot and the drill went through like a knife through butter.---

"Cobalt" It is the bit of choice for titanium and hardened steels. A lubricant is a must to keep the temp down in order to prevent bit breakage and extend bit life. (The work should not be glowing red!) I use a cutting lubricant the consistency of honey as it tends to stay where you put it rather than flow away like lubricants designed for drilling/milling/CNC machines which are very thin.