Dealing with rivets that won’t be drilled!

[Not_Anumber]

David. The problem here is that you are drilling stainless steel, a material which is very widely used but has extremely different properties to normal steel. It takes people by surprise when they try to drill it with standard methods.

During industrial manufacturing processes stainless steel is treated very differently. It is worked with especially sharp tools and drills and the area is continually sprayed with a cooling agent.

Attacking stainless steel the wrong way will create heat to the extent that it will readily burn away drill bits without creating any depth of hole. The hotter the metal gets the more work hardened it becomes making the problem rather worse.

Start again but buy only drill bits which are specified for stainless steel. Then drill it slowly and steadily and you will get there.

[Statler]

An HSS drill bit is designed to work at a particular speed. Running them below or above their optimum speed means they won't work properly or will blunt more easily.

The Bosch HSS-Co bits are designed for mild and stainless steel.
Their optimum speeds are printed on the back of the retail pack. From the ones I have it looks like that optimum speed reduces as the drill size increases. My 5mm bit suggests 800rpm for SS and the 3mm is 1000rpm.

[Bourne]

Chris - thanks. That was the missing piece of the puzzle. The rivets on the lower hinge mechanism must have been a different metal - hence the drill bits worked.

Stephen - very useful to have the RPM number (most advice online just says slow). For information (in case anyone else ever reads this thread), the correct drill bit size for these particular MGB quarter light hinge rivets is reportedly 3.2mm

[ChargedAutoGT]

If you drill stainless too fast it 'case hardens' and you will be very lucky if you manage to drill it out after that. It just goes so hard it will blunt a drill quite easily.

The way to drill stainless is *slowly*, and by that I mean in a pillar drill - at about 200rpm for what you are drilling sizewise.

But now, tbest thing to do is to buy a new drill, as stated before, Wd40 to lube and drill very slowly. Not even 200rpm, just as slow as you can. If you see some shards created you are lucky. Just keep going real slow. It takes a long time but that's how you need to do it now.

You could use something like an electric file (a manual might not have the guts now but give it a got if it's all you have) to try to reduce some of the height and skim the surface of the rivet but you obviously have to be careful. Mask with several thicknesses of tape.

[Adrian Oliver]

Remove the glass by carefully cutting into the retaining rubber and gently ease the glass out, WD40 will help.
When you see the rivet tails centre punch them.
If the rivets are 1/8" drill from the inside out with a 1/16" cobalt drill.
Finally, drill into the 1/16" hole with a 1/8" cobalt drill.