Drilling advice needed

[ChrisCar6]

Working on current project http://www.borderbogie.co.uk/

Trying to ream out M14 thread on bearing cups of BMX hub to fit on 14mm axle. Hard as fun! HSS bit doesn't touch it, nor does file. Any suggestions as to how to get rid of the thread? One shattered while drilling, so brittle too.

[Fingers]

Do you know anybody with a lathe? Might be a bit tricky if it is still laced up to the rim though, but that's easily fixed. That would be the best way I can think of, drilling may get it off centre, then you'll be in for a bumpy ride.

[AndyH]

Hi,
Masonry drills have a tungsten tip. If you can get hold of a 14mm Masonry drill and re-grind the tip from Chisel to HSS, this should cut through the hardened M14 threads.
The tungsten tip is only held in with some sort of solder, so don't let the drill tip overheat or the tip will come off.
Just a little bit at a time.

I've done this before (albeit on a smaller thread) and when traditional HSS won't touch it the tungsten tip worked a treat.

Good luck
Andrew

[ChrisCar6]

It's the removable outer cups I'm working on, so that's OK.
I'll try the masonry bit idea as I've got one already.

[ChrisCar6]

Hi,
Masonry drills have a tungsten tip. If you can get hold of a 14mm Masonry drill and re-grind the tip from Chisel to HSS,

What exactly do you mean by that Andrew? Is it the undercut edge on the HSS rather than the vertical face on the masonry?

[Stableblock]

....if that doesn't work three other suggestions.
1) find a 14 mm diameter carbide burr,
2) wrap emery cloth round a mandrel and use in a power drill - this will take ages but should get there in the end
3) I have seen special cobalt alloy tipped drills at car shows and these are demonstarted by brilling through files etc. These might be hard enough. Somthing like...http://www.toolstation.com/shop/Powe...its/d80/sd1230 - dont forget to use some coolant - even a little oil will help to keep temp down.

Peter

[Nigel]

You should be able to drill thru hardened steel with HSS drills if you keep the speed slow enough.(15 sfm or 5 Mm is only about 100rpm for 14mm) the problem with using a drill as a reamer is the tip is unsupported and will grab and chatter. Try screwing in a piece of soft bolt thread(allthread is even softer), put something underneath to stop it turning and then drill to the size you need, - this will support both cutting edges and stop the chatter.
Hope this helps
Nigel

[AndyH]

What exactly do you mean by that Andrew? Is it the undercut edge on the HSS rather than the vertical face on the masonry?

Hi,
I took a standard Masonry drill bit and sharpeneed the tip as you would a HSS drill bit. Cuts through hardened threads easily so long as you take it nice and easy.
The standard profile on the masonry is more of a point than an edge and the hammer action helps it to chisel through stone. No good for steel steel.
Andrew

[GrahamH]

spark erode, lots of places do it.

[Fingers]

A proper cobalt drill should work too, probably available from a good engineering supplier. We have them at work and they chew through titanium and hardened steel fasteners like they're butter if you keep the speed and feed rate slow.