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Old 28-08-2018, 22:46   #1
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Drilling through stainless steel

My transom swim ladder is made of hardy stainless steel tubing. It does not have wooden steps or rungs. So, it is difficult to climb out of the water.



I purchased some teak steps but when I tried drilling the holes for the machine screws the steel burned out two drill bits, a normal steel bit and a cobalt bit. I then bought a titanium one but it fared no better.

Anyone have a suggestion on what type of bit will work with this sturdy tubing?
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Old 28-08-2018, 22:51   #2
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Re: Drilling through stainless steel

Go very, very slowly and keep filling the screw hole with wd-40 as you drill.

It may take 10-30 minutes per hole.

You can use even a low end bit if you keep it cool by going slow and keeping it well lubricated.
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Old 28-08-2018, 22:57   #3
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Re: Drilling through stainless steel

Drill with low RPMs and with as much pressure as you can apply. Stainless steel has a low coefficient of conduction for heat and air quench hardens if you heat it up whilst drilling. If this has already occurred you may have to drill a small pilot hole and open the hole out with a couple of smaller drills.
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Old 28-08-2018, 23:29   #4
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Re: Drilling through stainless steel

Yes, as others state, very low drill rpm, very high pressure and lube. You can use fancy cutting oils etc but I get good results with dish washing liquid.

If using a battery powered drill, it is difficult to get the rpm lower enough and the pressure high enough.

Oh and use a sharp drill and don't stop cutting. It the drill stops cutting, STOP, otherwise the SS heats up very fast and work hardens the SS super fast.
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Old 28-08-2018, 23:51   #5
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Re: Drilling through stainless steel

You can buy bits for drilling stainless on ebay or a good home store. Not that expensive if a small size. HSS (titanium aluminum nitride) gold color. Package should say titanium aluminum nitride. Cheap ones are painted gold. Should last many holes if used wisely. You have to keep the bit cool. Use some oil thicker than WD-40. Motor oil if noting else. You need lots of oil to keep the bit cool. Make a cup out of tape surrounding the drill area to control the oil. You need to use less pressure and medium speed to avoid over heating the bit. You don't want either the bit or ss to change color. It ruins the bit and hardens the stainless. If you're getting yellow/gold chips, it's too hot.
Use a center punch to keep the drill from wandering when starting. If you've already created a hard spot, use a smaller bit (correctly, with oil and lower pressure, lower speed) for a starter hole. I assume you're just drilling a hole for a screw?
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Old 29-08-2018, 02:26   #6
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Re: Drilling through stainless steel

Geez, didn't know that trick with dishwashing liquid, thanks Wotname!

I use one of the fancy cutting oils, and it's greatest advantage in this situation is that it sticks like glue to the job, so working on a vertical surface is much easier. And it makes a huge difference to drilling speed, like literally 10 or 20 times faster.

Other than that, as the others have said, low rpm, lots of pressure, but, not sure if it has been said already... lots of patience too. Back off and let things STAY cool (by the time you are letting things cool down it is too late, the damage has been done.)

Also, good quality drill bits are a must. Over here in Oz we have a couple of brands, one of the traditionally good ones has recently gone downhill badly. I was getting poor results, blaming myself, but thankfully mentioned it in passing to a REAL tool shop and they hinted that I might find better results from another brand and they were dead right.

I recently fabricated four engine mounts (mild steel) for a bus engine conversion. In total I drilled through 1200 mm (yes, that's 1.2 METERS) of steel with just the one drill bit (Bordo) and it was still cutting like new at the end.

YMMV.
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Old 29-08-2018, 04:12   #7
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Re: Drilling through stainless steel

^^ and the dish washing liquid keeps your hands clean as a bonus

Give us the low down on the dodgy drill bits - by pm if you prefer.

I recently was drilling though 3/4" 316; 8mm and 30mm holes and you gotta keep your eye on the ball with that thickness - Wotie shamelessly big noting himself
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Old 29-08-2018, 04:25   #8
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Re: Drilling through stainless steel

You have lots of good advice (low rpm, use lube, lots of pressure, stop if the bit stops cutting, etc). I didn't notice anyone else saying, but I have had good success with 135 degree drill bits. No need to buy expensive cobalt or other bits. Just a good quality sharp jobber bit works for me. Buy a few from a reputable company and stop using it if it gets dull and cuts slow.
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Old 29-08-2018, 04:29   #9
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Re: Drilling through stainless steel

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Originally Posted by slowneasy View Post
You have lots of good advice (low rpm, use lube, lots of pressure, stop if the bit stops cutting, etc). I didn't notice anyone else saying, but I have had good success with 135 degree drill bits. No need to buy expensive cobalt or other bits. Just a good quality sharp jobber bit works for me. Buy a few from a reputable company and stop using it if it gets dull and cuts slow.
Good advice

Plus learn to sharpen drill bits. While there is a short learning curve, once mastered, your HSS bits last a long time.
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Old 29-08-2018, 04:52   #10
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Drilling through stainless steel

Quote:
Originally Posted by Chotu View Post
Go very, very slowly and keep filling the screw hole with wd-40 as you drill.

It may take 10-30 minutes per hole.

You can use even a low end bit if you keep it cool by going slow and keeping it well lubricated.


As others have said, lube/coolant helps. But it’s not necessary if you go slow enough.

Pressure is key. It should not take more than a minute or two to drill a hole in even thick walled SS tubing. I drilled and tapped 8 holes in some recently to replace set screws with machine screws on my bimini. The whole job took about 30 minutes.

If the drill bit is turning faster than @ 1-2 revs per second, you’re going too fast. Slow, as much pressure as you can apply, and regular drill bits should work.
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Old 29-08-2018, 05:58   #11
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Re: Drilling through stainless steel

Press hard, use lube and drill in steps. I recently drilled 2 holes of 10mm diameter deep into my solid rudder stock using only a cordless 10.8v drill and standard hss drill bits. Started at 3 mm diameter and stepped up 1 to 2 mm in drill diameter with each pass. Job was done in no time.

I've drilled hundreds of holes in various grades of stainless with rarely an issue using the above technique. The trick is not to allow the steel to work harden by deforming it. You simply need to get a clean cutting action going. I think the choice of cutting fluid is probably the most critical element to success.
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Old 29-08-2018, 06:06   #12
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Re: Drilling through stainless steel

If your scarf is coming off the bit in two nice spirals, you have the right combination of speed and pressure. If you can maintain the two spirals of swarf, nothing else matters!
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Old 29-08-2018, 06:32   #13
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Re: Drilling through stainless steel

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Originally Posted by Wotname View Post
If your scarf is coming off the bit in two nice spirals, you have the right combination of speed and pressure. If you can maintain the two spirals of swarf, nothing else matters!

The above is the key. And it is true for any material.

As previously stated, low thermal conductivity (applies to Titanium also) and work hardening are major contributors for SS



The optimum cut will result in only 2 shavings for the entire cut. Once you start you are committed.


When drilling or milling on a cnc machine you have control over both the tool rpm (mil or drill) and the feed rate x,y or z in case of drilling. You want a continuous chip load of around 0.003-0.005 in per tooth. By doing a simple calculation, SS drills no different than aluminum on a CNC machine. You should end up with a chip thats 0.003 inches thick.


That being said, on a hand drill or a drill press your only controllable variable is force. Once you start trying for the continuous chip you'll notice how fast a hole can be drilled.


Also, your drills and mills will last longer since their life is proportional to linear inches of cut material. Ie you can make twice as many thick chips as thin chips.
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Old 29-08-2018, 06:58   #14
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Re: Drilling through stainless steel

Also it is easier to start the hole in a flat spot. So I just touch the angle grinder to the spot to grind a tiny flat, then centerpunch. Tiny pilot hole. If the pilot hole is too big, the final bit will grab really bad.
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Old 29-08-2018, 07:06   #15
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Re: Drilling through stainless steel

I am surprised that no one has recommended carbide drills over cheap cobalt and titanium oxide drills. They are much harder and will stand up to hard usage much longer.
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