And then the drill would no longer cut....

[Dog Star]

I had been drilling 0.45mm holes in circa 0.25mm nickel silver (half-etch holes in 0.45mm sheet), happily going along the sheet and had done about ten holes when the drill refused to cut any more metal. I looked at the drill bit using a magnifying glass and good illumination expecting to find either a blunt or a chipped tip to the drill. In silhouette the drill looked complete... and then I noticed that the flutes were mis-shapen, as in:-



Aplogies for clarity of image.

No kidding, the flutes about 1mm behind the tip of the drill had "unwound".... as if the tip had snagged in the hole and the remainder of the drill continued turning. However, under a magnifying glass the tip was still as formed with the cutting edges no longer able to contact the metal surface. Not just once, not just twice... this behaviour happened with four more drills. I bought what was described as HSS bits from an UK based supplier of repute.. a supplier used by, I suggest, modellers without a second thought.

The next time that I need to buy sub-1mm drills I shall be asking about supplier, material spec. (ie. HSS) and country of manufacture.

regards, Graham

 

[garethashenden]

Twist drills do untwist sometimes. Are you lubricating the drill? Oil works well but can be messy, beeswax works too.

 

[michael080]

That's weird! If you are using a decent drill press and if you can fix the part rigidly, try carbide PCB drill bits. Their performance and durability is so much better. The only problem is that they brake if bend. Search for resharpened PCB-drills, they are very cheap and their only disadvantage is that their length is undetermined.

edit: sorry, this makes two disadvantages in total.

Michael

 

[simond]

I bought a miscellaneous selection of Carbide PCB drills at an ME exhibition many years ago, they are very hard and very sharp and cut really well, but they’re brittle like glass and they go ping...

I’ll be boring & say “safety glasses” and reiterate what Michael said, drill press and rigidly located workpiece.

Despite the fact that they are flat bottomed (like a slot drill) the little ones don’t like being used to mill, though repeated plunging works.

I have successfully “free cut” & milled with 3mm ones.

Atb
Simon

 

[Eastsidepilot]

For a cutting compound I can recommend 'Trefolex' Cromwell Tools - Experts in Hand Tools, Power Tools and PPE

It's more like a grease than an oil so is easier to clean up, good on hacksaw blades as well.

You don't need lots of it and a tin lasts for ever.

As for drills straightening the flutes out I've only expect that from Chinese crap.
I use these people 1000's of Drill Bits, & Many Power Tool Accessories | Drill Service Horley I've never had a problem with twist drills so I hope you didn't buy them from here. !

Col.

 

[3 LINK]

The fact that the drill has not distorted along its length but the flutes are no longer in touch with the cutting face looks to me like there wasn’t any lubrication used or not enough.

 

[Eastsidepilot]

The fact that the drill has not distorted along its length but the flutes are no longer in touch with the cutting face looks to me like there wasn’t any lubrication used or not enough.

Thing is I've often drilled multiple holes in .25 mm nickel etches before with out lubrication and never had this problem, well maybe the odd cuppa or beer

Col.