Drilling stainless steel

[Weyalan]

So, on saturday I am going to be fitting the new rope clutches and deck organisers.

The clutches are no big deal - I have pre-made backing plates that will go inside the cabin under the clutches.

The deck organisers are a little more tricky: They have a different spacing on the bolts from the old ones, so I have to drill new holes. This, in itself is not difficult, except that I have to drill through not only the cabin top, but also through a stainless steel plate underneath the cabin top. This plate runs transversely right across the cabin top i.e. on the roof of the saloon and is, for the purpose of this exercise not removable (I could probably remove it but that would just open up a whole new pandora's box; one that I am not ready for just yet).

So, the problem is drilling down through the roof and stainless plate in-situ. The required size is about 8mm (5/16"). My plan is:

High-speed steel drill bit(s)
Very Low drill speed
Maximum drill pressure
Regular rests to keep heat generation low
Coolant? Not sure what is best

Drill 3mm (1/8") pilot hole
Then drill 8mm (5/16") hole

Any thoughts? Tips? Recommendations?

[cat man do]

I have used Trefolex for many years with great success for a lubricant.

Trefolex from CRC

If tapping into the SS it is good for that as well.

I have also used water and metho mix for cooling when I dont have the trefolex around with reasonable success.

[Alan Wheeler]

The better bit to use is Cobalt. But HSS will do the job.
Don't allow the drill to vibrate. Keep a constant pressure. Not too much pressure, but certainly not to little. And a good cutting oil.

[cooper]

As above , if the drill bit becomes at all blunt it will heat the SS and harden it. If this happens your stuffed.....well nearly....

I try to use a new bit or at the very least one that has been just sharpened (and not by me) Standard metal working liquid...(machining and drilling) works fine..If you can get a nice spiral of swarf coming off the parent steel its probably going well...It gets easier with practice because one stuff up teaches you to get good quick !!

[Evan]

Buy a set of cobalt drills (or just a 5/16" one if you must). They go through s.s. like butter.

- moderate pressure
- center punch first
- slow speed for 5/16" (might think about using a smaller drill like 3/16" or so as a pilot drill too)
- coolant yes. Water in a pinch
- don't slow the drill to a stop gradually. Just lift it off quickly from the surface while you're drilling.

Stainless steel will work harden if you let the drill bit just lightly scrape the surface. Be somewhat forceful.

[delmarrey]

Now from a Machinist...................

Drill the cabin top first. Lay the plates under the existing holes just you drilled. stick a pencil down the hole and mark the spots. Take the SS plates, center punch them, center drill them and then drill thru them the next size up drill from the bolts. Use Colbalt if you can! If not go as slow as you can appling good pressure. And use a squirt bottle with water or very light oil and keep the thing cool for God's sake.

What ever you do don't try drilling thru SS from the top side of a deck.

Besides you'll want to seal the decks core so water won't seep in after the sealant fails. And it will too, some day!

Enjoy..........................._/)

[Stevem]

Hi Wayhlan as Cat man says Trefolex is A#1 but maybe only available here in Aus. I fabricated in SS for many years and all the above info is good. slow speed as possible & plenty of pressure and the drill I found the best is a split point cobolt with a flatter drill face angle in fact you can do this in your grinder but search out the split point bit.
lead with an 1/8" for a 5/16" hole I found I could drill many, maybe 100 or more through 1/8" and not need reshapening

[Stevem]

Hey Weylan just noticed your in Tassi so youll get trefolex alright I think its a bit toxic if fumes come off from heat and that may be the reason I coulnt get it in US (had to take tins back there while I was working SS)Its in a green and black tin (about 1L size)
Its also superb on a hacK saw or a jig saw for cutting SS plate just go real slow and steady to keep heat down

[GordMay]

Trefolex, apparently available in Canada & USA from:

Newman Tools Inc.
185 Iber Road
Stittsville, Ottawa, Ontario, Canada K2S 1E7
Phone: 1-613-836- 6776 or 1-800-465-1384
Fax: 1-613 -836 -9070 or 1-800-605-2442

Newman Tools Inc.
151 New Park Avenue
Hartford, CT 06106, USA
Phone: 1-800-465-1384
Fax: 1-800-605-2442

Email: info@newmantools.com
Web: Trefolex cutting compound

[Stevem]

Hi GordMay Id tried in Seattle tool places when I was there then in Ventura with no result so Just assumed it was on the 2 toxic list I also uesed it on holesawas when doing fish mouth joints in SS tube and the cutters just lasted and lasted Its one of those products that just changes the way you can do things with regular tools
Steve M I

[noelex 77]

I have just drilled 8mm holes throgh 5mm thick stainless steel with some cobalt drill bits (3 then 5 then 8). I got the drill bits at Bunnings in Australia.
No problem as easy as drilling timber. I used a very slow speed lots of pressure and no lubricant (I couldn't find anything suitable).
If you get the details correct its easy.If you work harden it, then its a nightmare. Before I discovered cobalt drill bits I spent an hour drilling a 2mm hole in 2mm stainless with a dull drill bit.
Cheers John
see my blog at “Amzer Zo” Yacht Blog

[GordMay]

Drilling Stainless Steel requires lubrication at the drill's tip, and flushing to eject chip s from the hole. Without fluids, chips can bind in the hole, and average roughness of the machined surface can be twice as high as what is possible with a wet operation. Lubricating the point of contact between the drill's margin and the hole's wall can also reduce the torque required from the machine.

A split-point cobalt steel bit is often used for drilling S/S. The bit’s split point reduces the tendency of a spinning bit to rotate away from the point at which you want to drill (walking). The split point also causes the bit to penetrate the metal more quickly, and with less force than is needed with other bits. In many cases, using a split point eliminates the need to mark the hole with a centerpunch (which may work harden the metal).

Regardless of the type of metal you are drilling or the type of bit you are using, reduce pressure on the bit as it exits the work. This prevents the bit from grabbing the surrounding metal and violently twisting the drill and perhaps your wrist.

If your final hole size is more than about 1/4", start with a small-than-required bit size (pilot hole), and use a slower* speed, and a lot of pressure. As the hole begins to break through, lighten up on the pressure, and speed up the drill slightly. Then switch to the larger bit size and drill again, using plenty of cutting oil.

Pilot holes should be the same diameter or a tiny bit larger than the web (the centre or area that joins the two cutting flutes of the drill bit) again to ensure that the drill does not wander or chatter. E.g. a 1/2" bit should have a pilot hole of about 1/8".

Use Cobalt bits. Tungsten carbide will last approximately 3 times longer, titanium will last approximately 6 times longer, and cobalt should last 10 times longer than HSS bits.

* The RPM setting for drilling depends on the cutting speed of the material**, and the size of the drill bit. The RPM setting will change with the size of the bit. Therefore, to maintain the recommended cutting speed, larger drills must be run at slower speeds than smaller drills.

Rule of Thumb:

RPM = (Cutting speed X 4) ÷ Diameter of Bit

** Generally, the harder the material, the slower the speed of the edge needs to be.
APPROXIMATE Recommended cutting speeds:
Stainless Steel: 30 - 50 fpm
Carbon Steel: 70 - 90 fpm
Brass/Bronze: 100 - 120 fpm
Aluminum alloys: 250 - 300 fpm


HSS Bit on Left - Split-Point Cobalt Bit on Right (pic "7" below)

[Weyalan]

Thanks for all the info folks; I appreciate it.

I will get hold of a 5/16" cobalt bit, or maybe 2, just to be safe. Incidentally, my local Bunnings sells cobalt bits in Imperial sizes but not metric; how wierd is that?

I will also try to get some Trefolex

To answer Delmarrey's point about (not) drilling plates in situ:

The backing plates for the clutches were drilled (& tapped) at a local machine shop (but I did polish them myself), so I will just be drilling through the cabin top to mount the clutches. However, for the rope organisers, there are no backing plates, per se. What there is is a stainless steel strap that is about 6" wide by 1/4" thick by about 7'(yes; 7 feet) long (curved) that runs transversely across the roof of the saloon (i.e. underside of the cabin top). This plate is, for the sake of this exercise, fixed i.e. I could probably remove it, but it would be a bigger exercise than I want to do at this time (we are racing in the local pennant on Sunday), so I pretty much have to drill in-situ.

[delmarrey]

Originally Posted by Weyalan

To answer Delmarrey's point about (not) drilling plates in situ:

The backing plates for the clutches were drilled (& tapped) at a local machine shop (but I did polish them myself), so I will just be drilling through the cabin top to mount the clutches. However, for the rope organisers, there are no backing plates, per se. What there is is a stainless steel strap that is about 6" wide by 1/4" thick by about 7'(yes; 7 feet) long (curved) that runs transversely across the roof of the saloon (i.e. underside of the cabin top). This plate is, for the sake of this exercise, fixed i.e. I could probably remove it, but it would be a bigger exercise than I want to do at this time (we are racing in the local pennant on Sunday), so I pretty much have to drill in-situ.

Then I suggest hitting the plate first with the full size drill leaving a on center divet, then a smaller pilot drill thru first as stated above. And back to the full size drill. There's less chance of it getting too hot and most of the chips will come out rather then logging in the core.

enjoy........................_/)

[Weyalan]

Thanks delmarrey.

None of the local tool-warehouses sold trefolex, and the cutting oil that they stocked was like $15 for a egg-cup full, so I went along to the local machine-shop and one of their fitters/machinists gave me half a pint of cutting oil for free

I have picked upa 1/8" and a 5/16" cobalt bit (again, not cheap), so I am good to go. Fingers crossed!