Tuesday, 21 July 2009

Learning more and more

I've been building more nozzles and drilling some holes in metal. I tried drilling out a stainless steel bolt to make the extruder barrel, but it was hard work and didn't feel right. Usually when that happens, I'm doing something wrong...
So, I googled and read up on drilling into stainless steel.

Apparently, when the drill rubs over the metal in the hole, it starts to heat and work harden a thin layer of steel - making it harder and stronger - and more difficult to drill.

The advice is to drill at a slow to medium speed, apply lots of pressure, and drill few mm then pull right back to clear the swarf. This is pretty much the opposite of my original technique.

This works *really* well - you get lovely long spirals of swarf (razor sharp splinters) and the hole is much easier to drill. I found it much easier to drill out welding tips and have drilled a couple of stainless bolts using the afghan lathe technique.

Top Tip: Read instructions before using.


Erik de Bruijn said...

That's only intuitive in retrospect... I would also have taken the opposite approach, I guess.

Renoir said...

yeah, HSS (High Speed Steel) drills actually need to be used at low speeds? Who named them?

I was also a bit cautions about pressing too hard - trying to drill through hard metal.

It does work a lot better now!

hyperair said...

I just tried this yesterday, but kept either overheating my HSS-Cobalt bit or jamming my drill anyway. Could you offer some tips?

How much pressure is necessary, and how much is too much? What sort of coolant did you use?

David Reynolds said...

I used some standard kitchen vegetable oil. I've also used wax (from candles) and a stick form of drill cutting lubricant.
Slow and steady works better - even down to screwdriver speeds worked for me, and pressing down hard.
If the drill breaks, pressing too hard.
Make sure you have a nice solid vice and strong table - if you have confidence that is better.
If you have problems, try going to a proper hardware shop and buying a single drill bit of the right size. Lots of the 'sets' sold in DIY chains are cheap and fine for wood, but the steel is naff.
A decent drill might cost you a few pounds for a single size, but it's worth it - proper tool steel will hold the cutting edge and cut properly, especially with stainless.
p.s. I am no expert. YMMV :)