Hand drilling stainless steel 3mm thick

I am in the process of trying to drill the rear buffer beam of my new Kingscale BR4 standard loco to fit a clevis fitting instead of the BR hook.

To my astonishment I discovered when trying to drill 4mm holes with an electric hand drill that the beam was stainless steel of an unknown grade. A brand new SKF/Dormer HSS drill bit made little impression of the stainless as after 2 minutes drilling the bit only cut a depression the width of the drill bit.

Can any kind member of the forum offer any suggestions as I do not want to comtemplate removing the buffer beam. Will a cutting oil do much good as it is difficult to apply to a vertical surface in this case? I have ordered some 5% cobalt drills in the hope they may be successful. Reading about carbide tipped drills they seem to shatter easily, perhaps a member can reccomend a good carbide tipped drill not solid carbide, as I fear they will shatter instantly being hand held and using the clevis fitting holes to position the drill bit.

Cutting fluid will certainly help. the trouble witl most stainless steel of unknown grade; & known grades too is it work hardens very quickly as most of us have found out at some time or other. Using cobalt drills do help & carbide drills will help too but you've got sharpen those to a proper cutting angle as per normal drills..118*.. using a 'green wheel'. I've tried a similar process with stainless frames for my latest project with 3mm drills.. not a cat in hells chance! I reverted to making them out of aluminium!

You've also got to keep a constant pressure on the drill, preferably using drill/mill machine as you rarely can keep up the pressure with a hand drill, you could well end up breaking the drill trying to keep alignment square, I have a few times & as said as soon as you start to drill.. boom! the job work hardens if you don't get under the 'skin'. I have purchased a set of three fluted cobalt drills from 'Banggood' usual disclaimer, which claim to be specifically for stainless & other hard alloys.. yet to be tried & proven!. It may be a case of having to remove your beam & setting it up securely to maintain constant pressure. I'm sure other members will offer their advice , as I type. good luck.

George.

Yes, as Mechman says you've got into the work hardening problem, where the tip of the drill skates on the surface of the hole and no amount of rotation will progress the drill forward. Pressure is your friend, by which I mean drilling a smaller hole. But then the drill is (disproportionately) more fragile. If it cuts through the hardened area (which is a big if) it's likely to snatch and break, and that's if you can avoid putting side forces on the drill, which will also break it.

Having drilled a pilot hole it's not guaranteed you can drill it out to size, that material is going to grab the drill and snatch again, always supposing you can get under the hard skin.

Cutting oil or coolant would have helped, but are now irrelevant. You needed pressure on the cutting edge to keep it cutting. Once it skates you're lost.

I wonder if you would be better off going abrasive. Having got the hole area work hardened I'd rather have a go with a carbide bur in a Dremel kind of tool. Keep the area wet to keep the tool from burning out, but you should be able to make progress, if slowly. Once you've got a hole open it out - if need be with a stone point (they sell grinding burs for sharpening chainsaws - they have all sorts of other uses).

Carbide drills or carbide tipped drills both need lots of pressure, so you're fighting the inevitable trying to use them in a hand drill. And, as you say they are very brittle so sideways pressure will shatter them.

Good luck

Simon

Bryan

Try to obtain stub length drills not jobber length, much less chance of breakage especially if using a hand held drill.

Emgee

If you are using a hand drill you could try using a 'tipped ' masonry drill, sharpened up as many times as necessary until you are through.

At work we use cobalt drills for removing titanium screw heads - one drill will not last more than for a hand full of screws. What I found works best are Dormer stub drills A123 meant for sheet metal use. As long as you do not drill deep you will be ok and the hole you get is a very good finish and round.

From Cromwell tools: **LINK**

Hand sharpened masonery carbide drills will do it but if the stainless is like the stainless on the jaws of your cheap hand held verniers then you need a heck of a lot of pressure to get through

I needed to use my drummond M on the backgear to drill those stainless jaws which are about 3mm thick

HSS doesn't fare well against work-hardening stainless steel, though if cutting starts and can be maintained, it will do the job. The trick is to not let the drill rub, because doing so converts many stainless steels into a harder metal than HSS. Persisting with a blunt drill just deepens the hard area and makes progress all but impossible. The technique is to hit the metal hard and fast - high RPM with plenty of pressure. Don't expect the drill to stay sharp!

Once hardened, the safest answer is a twist drill made from something harder than HSS. TiN coated HSS are a possibility, masonry are often recommended but have to be reshaped, so I would go for a drill sold specifically for stainless (usually Chrome hardened), Carbide tipped or solid Carbide. But I've succeeded in penetrating the hard layer with an ordinary HSS drill, newly sharp, forced hard into the failed dimple.

Just a thought, but this is the sort of tool-damaging job where drills might be considered disposable. Spending lots cash on premium brands 'because they last' could be poor tactics. Why waste decent drills on a difficult material? Instead buy cheaper drills, expect them to go blunt, and throw them away. Different logic in manufacturing, making lots of 4mm holes in stainless is a job for an expensive coated solid carbide drill rotated at high rpm.

I hate stainless. Every so often a job super-hardens and ruins my day.

Dave

We had to drill stainless steel for a pop rivet to lock parts of a springbox used in the tail of the Hawk trainer jet. The best method was slow speed and high pressure with a sharp drill. It was done dry, as oil would contaminate the assembly and make the drill swarf difficult to remove.

Can't you change the problem by making a clevis which will fit in place of the hook without drilling?

Many thanks everybody for all the suggestions to date. I have 5% cobalt drills on order also a carbide tipped drill bit. I had a stock of new SKF/dormer drills in 4.1mm so can continue to try using these the first of which shows no sign of any wear at all so continuing with a cutting compound is an option.

I have gone too far to change the clevis design and started one hole so will persevere.

I said high-speed, but I think Old Mart is right - slow and hard so it cuts. Pretty sure he's correct.

Dave

For austenitic steels a sharp drill is vital. A cheapie is going to lose its edge quickly and that's where the rubbing and the trouble starts.

My elderly Dormer booklet recomends stub length drills with a point angle of 135-140 deg.

Slow speed and heavy feed-rate.

Just remembered

Someone who had a tuff job in here used a copper pipe with carbide grinding paste to burrow through

Something like that

The pipe wore down about an inch befpre the job drilled through

I've seen that method suggested for drilling glass.

hi, definitely slow and constant pressure, a little cutting oil will always help, just keep dipping the end of the drill every now and again.

Regards Nick.

I have had similar problem when drilling stainless, it work hardens and the drill just skids, I tried cobalt drills without any success, I did have success with diamond core drills, slow but eventually successful. Arc Eurotrade sell a limited range of sizes, depends what size you can manage with, maybe adjust size of your fitting to suitable core drill size.

Dave W

A sharp centre drill works quite well sometimes in stainless.
The small diameter centre point helps it start cutting, as it allows high pressure on the cutting edge, but the smaller diametaer part is very short, so well reinforced by the rest of the drill behind it.
Use a stainless grade tapping lubricant, and a conventional shaped drill, rather than one of the modern bell shaped ones..

Bill

Electric drill is going to be way too fast for this job.

If things could be held stable enough (big if) an old style "belly braced" hand drill would probably do the trick. Lean on it hard and turn steadily in high gear. I keep a nice one, with enclosed gears too, on the shelf for such emergencies when its the only way. Perhaps twice a decade! Apart from holding things steady the main issue will be chuck grip on the small drill. The old style hand tightened chucks were never known for being really tight holding.

Same principle as the Cole "clamp on the job" ratchet drill **LINK** trick of drilling through a bearing race with a sharp masonry drill. The Cole has screw feed and can generate up to 500 lb or so pressure on the drill. Somethings going to move.

Ideally need a different drill point grind shape for slow speed high pressure drilling. Razor sharp but more clearance to ensure the edge lasts. The conventional point puts a bit more emphasis on plenty of metal close to the edge to take heat away at high speed. The aboslute razor edge coming straight off a good sharpener is normally soon lost. Still very sharp but ....

Clive

I've drill a bearing race with a carbide locksmith drill, it wasn't difficult.