Cobalt drill speed to remove broken tap

Right the cobalt drills have arrived so I can drill the broken tap out

Original hole = 5mm

Tap size = M6 x 1.0mm

What size cobalt drill should I use and what RPM should I run it at?

Thanks folks. The sooner you answer the sooner I can get at it.

Oh and will I need coolant? (I don't have a pumped coolant supply btw)

John

I would have thought you wanted solid carbide not Cobalt as thay are not much harder than the HSS the cobalt is added to.

J

I agree solid carbide slotdrill no problem

Oh arse!

What size please for the carbide slot drill? And is ball nose OK?

A three flute carbide centre cutting endmill did the deed for me in a similar situation. Either M2 or M2.5 size and cutting dry in a Bridgeport varispeed running flat out. Somewhat below book speed, which is approximately supersonic, but it shifted 3 dead taps for me. Found the cutter on E-Bay, can't recall the brand but I think it began with N. Not a job I care to remember. Too many holes, hard spotted material, and rapidly blunting taps.

Clive

Thanks Clive

Bought a 3 flute 5mm bottom cutting carbide end mill from ebay. Ran it at 1800 rpm and it cut the broken tap out

So now I've got a 5mm hole I just need to see if my tap can cut a thread in it as I don't know if using the carbide end mill will have hardened the walls. If not I can cut the thread from a 6mm bolt and silver solder it in place as there will be three other bolts securing the workpiece to the trolley

John

John,

You didn't mention - here at least - the material you were tapping, which would affect the answer to your question. Both stainless steel and titanium alloys are notorious for workhardening, other metals mostly less so.

Another though - have you seen the Helicoil system for replacing drilled-out tapped holes. Never used it myself but I have seen people say very good things about it.

David

Edited By David Littlewood on 29/02/2012 15:05:02

David

Material is a 15mm thick piece of MS plate

Yes have seen Helicoils used on motorbikes, my "models" as I don't do trains or tractions (yet) but full sized motorbikes!

Will try tapping later on. Just chuffed that the end mill got it out. I did break one of the new cobalt drills though before the end mill arrived, just seeing if it would work

John

Shouldn't think that ms will work harden.

Helicoils have worked a treat for me. A drop of Loctite helps them to stay put.

Ian

John, I think I would tend to either make a bolt to fit the enlarged hole with a head to match the other bolts, or if its a stud, make a stepped stud, save you hunting around for Heli-coils, and a tap for them. Or you can do as I think you may be doing, and plug and redrill and tap. Ian S C