Cobalt drill speed to remove broken tap

[John CoatesParticipant @johncoates48577]

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

[John CoatesParticipant @johncoates48577]

[JasonBModerator @jasonb]

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

[IVATTLMSParticipant @ivattlms]

I agree solid carbide slotdrill no problem

[John CoatesParticipant @johncoates48577]

Oh arse!

[John CoatesParticipant @johncoates48577]

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

[Clive FosterParticipant @clivefoster55965]

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

[John CoatesParticipant @johncoates48577]

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

[David LittlewoodParticipant @davidlittlewood51847]

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

[John CoatesParticipant @johncoates48577]

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

[Ian AbbottParticipant @ianabbott31222]

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

[Ian S CParticipant @iansc]

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

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