Drilling stainless steel.

Allan

Allan

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I need to drill some stainless steel tubes and fittings in the near future. I've had problems buying good quality drills recently. Can anyone recommend a good reliable supplier? While I'm asking, are there any good lubricants/cutting liquids?
Allan
 
Toolstation sell decent drill bits and lubricant.

HSS are good enough, especially if it allows you to buy more bits and use really sharp ones. Then go slow and steady.
 
Motor_Sailor said:
HSS are good enough, especially if it allows you to buy more bits and use really sharp ones. Then go slow and steady.
Click to expand...

+1 No need for expensive bits. Sharp HSS is fine.

Slow speed, steady pressure are key, but patience even more so -- unless you have a hefty drill press on which you can just bash through the job. (Not a recommended approach for thin-walled tube.) The biggest peril is overheating the piece, which will work-harden the steel and then you're in trouble. The 'lubricant' is actually more of a coolant. Light oil will do: pause when it smokes.

There's a thread on this every three months or so, but they'll all tell you much the same.
 
I had to drill holes in my pedestal tubing for cables etc and was advised on here to use cobalt drills. I purchased a set from Toolstation of Cobalt Pro Drills being 2,3,4,5,6
and 8mm drills , current price £11.92 and they did the job perfectly without any cooling liquid.

If you have a lot of holes to drill of one size you can buy the drill bits separately.
 
My experience is that a heavy duty drill which will go slow is more important than the drill spec but I also use cobolt drills. I have failed completely when using a small power drill that would not slow and gear down enough and just work hardened the stainless. Then I had to grind the area and start again with a big power drill and the same drill bit. Success then.
 
Sometimes the stainless bits that boat bodgers like myself end up drilling have been work hardened by previous work or use.
I have found cobalt drills a great help when HSS struggles.
Particularly when you can't use a bench drill.

When somebody has already failed to get through with a Black'n'Decker and a blunt bit, carbide is the thing.
I often use water as a coolant.
 
Allan said:
I need to drill some stainless steel tubes and fittings in the near future. I've had problems buying good quality drills recently. Can anyone recommend a good reliable supplier? While I'm asking, are there any good lubricants/cutting liquids?
Allan
Click to expand...

A good quality HSS bit will do the job but if you have many holes to drill consider a cobalt bit/ bits


Drill steadily, without any pauses which can cause work hardening. Be aware that centre punching will also cause work hardening!
 
C08 said:
My experience is that a heavy duty drill which will go slow is more important than the drill spec but I also use cobolt drills. I have failed completely when using a small power drill that would not slow and gear down enough and just work hardened the stainless. Then I had to grind the area and start again with a big power drill and the same drill bit. Success then.
Click to expand...

Definitely. The critical factor for all machining of metal is the cutting speed - expressed in feet per minute (or some metric equivalent if you've crossed over to the dark side). According to my cutting tables, you should not try to drill stainless at more than about 55 feet per minute - mild steels can go up to more than 100 feet per minute - aluminium can go up to 400 feet per minute. This is the maximum speed of the end of the fluke of the drill - if you know the diameter of the drill, you can work out the maximum rotational speed by dividing the cutting speed by the circumference of the drill. For a quarter inch drill in stainless steel, this translates to a speed of about 750rpm.

Do a quick web search for something like "cutting speeds for metals" - you will find several web sites with cutting speed tables and a few really helpful ones that do the arithmetic for you if you input a drill diameter.
 
VicS said:
Drill steadily, without any pauses which can cause work hardening. Be aware that centre punching will also cause work hardening!
Click to expand...

I don't believe pausing itself is the usual cause of work hardening, Vic. Heat's the main culprit...typically when drilling without cutting (i.e. creating no swarf). Yes, a continuous steady cut is ideal, but often elusive in the conditions applying on a boat, rather than in a workshop. I've always found that if the job isn't allowed to get too hot (indicated by the cutting fluid), resuming the cut is no problem.
 
Allan said:
I need to drill some stainless steel tubes and fittings in the near future. I've had problems buying good quality drills recently. Can anyone recommend a good reliable supplier? While I'm asking, are there any good lubricants/cutting liquids?
Allan
Click to expand...
I bought dormer drills off eBay, specifically designed for ss with shallow angle cutting edges. Superb. Plenty of oil and slow with heavy pressure, knife through butter!
Like these https://www.ebay.co.uk/itm/HEAVY-DU...633885?hash=item2852f7599d:g:dDgAAOSw6GJaAgs3
Stu
 
Last edited:
^this 100%

I needed to make 8mm holes in my tabernacle. I actually used a big heavy SDS drill (hammer off obviously!). CT90 is good fluid, but even engine oil will make a massive, massive difference.
 
Back-in-the-day when drilling stainless in ultra clean room conditions where oil was a no-no, we used Iso propyl alcohol as a cutting lubricant at slow speed with considerable success - doesn't do to break a drill in a $3m machine!! These days, I keep old bottles of aftershave beside the drill and mill for cutting stainless. Certainly works!! So come Christmas when your Auntie gives you some dodgy aftershave as a pressy, you know what to do! Keeps for years - I think it's Pagan Man sitting beside the mill these days...
 
maby said:
Definitely. The critical factor for all machining of metal is the cutting speed - expressed in feet per minute (or some metric equivalent if you've crossed over to the dark side). According to my cutting tables, you should not try to drill stainless at more than about 55 feet per minute - mild steels can go up to more than 100 feet per minute - aluminium can go up to 400 feet per minute. This is the maximum speed of the end of the fluke of the drill - if you know the diameter of the drill, you can work out the maximum rotational speed by dividing the cutting speed by the circumference of the drill. For a quarter inch drill in stainless steel, this translates to a speed of about 750rpm.

Do a quick web search for something like "cutting speeds for metals" - you will find several web sites with cutting speed tables and a few really helpful ones that do the arithmetic for you if you input a drill diameter.
Click to expand...

Do not drill 7075 alloy at high speed - its an expensive product and you will destroy the temper - treat like stainless, go slow, and use lots of coolant.

Jonathan
 
ditchcrawler said:
I had to drill holes in my pedestal tubing for cables etc and was advised on here to use cobalt drills. I purchased a set from Toolstation of Cobalt Pro Drills being 2,3,4,5,6
and 8mm drills , current price £11.92 and they did the job perfectly without any cooling liquid.

If you have a lot of holes to drill of one size you can buy the drill bits separately.
Click to expand...

I purchased Toolstation cobalt drills and their cutting fluid. Made drilling stainless steel very easy.
 
macd said:
I don't believe pausing itself is the usual cause of work hardening, Vic. Heat's the main culprit...typically when drilling without cutting (i.e. creating no swarf). Yes, a continuous steady cut is ideal, but often elusive in the conditions applying on a boat, rather than in a workshop. I've always found that if the job isn't allowed to get too hot (indicated by the cutting fluid), resuming the cut is no problem.
Click to expand...

You're mixing up symptoms with causes. Heat doesnt harden austenitic stainless steel and neither does pausing. Indeed heat softens it but heat in that case is about 1050C - thats the temperature at which we annealed stainless wire after drawing it. What work hardens it is work, so if you put work into it without achieving cutting or just limited cutting then it gets harder and ever more difficult to cut. To put it another way, you need sharp drills, decent steady pressure and a lubricant to avoid the flukes of the drills getting to tempering temperature and softening. At all costs avoid anything remotely like rubbing or skidding across the surface that would come from a blunt drill.
 
I would recommend you look at a drill press for drilling. These used to be relatively cheap from China etc. With variable gear ratio by moving a belt on pulleys you can get slow powerful speed. But most important you can get a lot of pressure on the drill bit. Go slow and if you are not cutting out swarf you will just harden the metal. (as said). I like to use engine oil or even WD40 the beauty of these is that they smoke terribly if you get the job too hot. The heat damages the drill bit. So sharp drill bit. It is easy to sharpen a large bit. I put bit vertical in a vice and use an oil stone to carefully sharpen the cutting edges. good luck olewill
 
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