TCT (carbide) Drills

[ngt]

Hello there i am trying to drill some holes on stainless (10mm thick). With an electric drill.
I made a pilot hole of 2mm with a cobalt drill kidna easy but in needs way much pressure so i snapped one at the base, and medium to high rpm (managed to make a continuous swarf once) didnt dull before it snaps though :P

But i find out later that my tct drills (8mm) do not bite the metal too good, tried high-low speeds, much or little pressure. But all i end up is thick or dust like chips. And the drill edge broke at the edges of the pilot hole.
So what do you suggest ? Titanium or cobalt are any better ? Or is it a matter of technique mostly? Does hardened stainless is that all mighty ?

 

[pedrobedro]

That looks like a masonry drill, I use ordinary high speed steel drills for stainless although I don't do much of it. Stainless needs lubrication and constant pressure and not too much speed for your 8mm drill. Once it goes blue and work hardens you've overdone it. Titanium or cobalt would both be better than what you are trying to use there.

 

[ngt]

Here is the drill and was advertised as a suitable replacement for drilling stainless.
Didnt let anything go blue at all, i was able to touch he drill and the swarfs seconds after each try. I stopped cause i saw the chipped edge of my drill.
It doesn't look like masonry though...

 

[hotrodder]

It's mostly technique but decent quality drills are a must- once the drill loses it's edge it will rub rather than cut which = work hardened stainless and a hole that's harder to finish making. Correct speed and a positive feed also important to avoid overheating and/or workhardening

Hand drill or drill press?
Drill rpm? To convert surface speed in metres per minute to rpm... RPM = (1000 x m/min) / (3.142 x Diameter)

Decent quality HSS should be fine, cobalt HSS tougher (and can take slightly higher rpm) and the best choice imo, TCT relatively brittle. Good quality HSS better than cheap cobalt etc.

 

[brightspark]

just a pilot hole 1st with good quality hss twist drill slowish speed with cutting compound on it and a good pressure. rechargeables arent realy up to it. u can get about 25 holes out of one drill. best are dormer presto sherwood and guhring. without the compound u are wasting your time

 

[Pete.]

Keep the pilot hole small and then peck-drill with a normal HSS bit with lower then average speed, medium heavy pressure and coolant. If you let the drill skid you'll instantly work-harden the piece and blunt the drill.

 

[ngt]

Ok i found a stationary vertical drill, i dont know the rpm, but i set the pulleys at the lowest setting.
My first chipped TCT drill, managed to make one very good pass with two continuous swarf (video in 3 hours) But some abrupt stops cracked the carbide

I used a second new drill but it didnt make any good pass just chips.
I used simple motor oil as lubricant.

 

[brightspark]

Ok i found a stationary vertical drill, i dont know the rpm, but i set the pulleys at the lowest setting.
My first chipped TCT drill, managed to make one very good pass with two continuous swarf (video in 3 hours) But some abrupt stops cracked the carbide

I used a second new drill but it didnt make any good pass just chips.
I used simple motor oil as lubricant.

tct are no good they bite in and chip motor oils better than nothing but cutting compounds the answer with hss drill

 

[hotrodder]

Milk or water would be a better choice than motor oil (too thick with too high of a film strength)- you want the drill to cut, coolant to keep the drill cool. Shox Dr posted a link to some vids a couple weeks ago (might be in the links forum too), one of which goes into some detail regarding drilling demonstrating the telltails of incorrect speeds and/or feeds

Carbide tooling needs very rigid tool set ups and higher speeds to work properly

 

[ngt]

tct are no good they bite in and chip

Yup thats what they do to me

Here is the best pass
I just saw that it squeels at the begining before the oil gets thinner from the heat, and bites when there is no more oil.

 

[Welderpaul]

Your chuck looks to be running out of true which won't help things, we use Cobalt drill bits on stainless, but HSS bits will be fine. A decent cutting fluid keeps the heat down, allows you to apply the pressure required in order to get the bit to cut, and prevents work hardening.

You frighten me drilling things like that without it being clamped to the table Cause for instant dismisal doing that in a lot of machine shops (the ones that are left anyway)

 

[Hitch]

I always thought carbide tipped drills were for cnc machining centres, where everything is fixed down nice, and constant pressure/speed is applied.