Drilling stainless steel

[davel]

I've just returned from the boat after failing to drill a hole through the stainless steel tube of my wheel pedestal.
Blunted two HSS drills and left only a tiny dent in the tube.

Ideas and suggestions welcomed.

Dave L.
Location: 50 51.0 N 1 18.6 W

 

[Guest]

Your drilling machine is operating to fast for stainless it has to be drilled at a very slow speed cos it work hardens the surface and pre heats your drill bit.
Try a slower machine also if you can get a cobalt twist drill it will cut through like it was cheese.
Hope I have helped
Bluebeard

 

[Strathglass]

Slow speed, cobalt drill helps and cutting compound Also centre punch the position.
Iain

 

[Craigt]

Strong downward pressure on the drill may also help.

 

[Andy]

Slow speed with cobalt, wear goggles as they can shatter (not often) but be aware. I know someone who lost part of their sight due to it (used allot on aircraft) if you know anybody in the trade!!

 

[Guest]

The trick with drilling stainless is very slow drill speed and "dig in" ie. pressure. You don't give the drill size so I'm guessing. I drill 6mm. holes at about 125 rpm, if this helps. Bigger/much slower, smaller/bit faster. 1/8" dia and smaller is a pain because it's too easy to bend the drill due to the pressure applied. Most power drills are far too fast! Black and Decker used to make a step-down box. Drill swarf should come off in long spirals, not small chips.
You must centre punch a start dimple first, especially in tube stock. If you haven't got a good punch, find an old thread tap with a pointy end.
Last, but most important of all, lubricant for the drill and plenty of it. Keep pouring it on all the while you are cutting. If pushed 3 in 1 will do as long as there is enough of it. If it stinks it's doing it's job.
Hope this helps, Rod.

 

[AndrewB]

Work hardened. Once it gets like that, you're stuffed, though you might get it started again with a different sized bit. A lubricant may also work.

I find it helpful to use a water-bath if possible when drilling stainless, to disperse the heat.

 

[mtb]

Re: what grade of stainless

I would suggest you first find out the grade of stainless used, then go to a real engineer supply company tell them what you are doing ,they will if you went to a good place look it up in a book then supply you with the correct , pilot drill then depending on size of hole end drill .
Properly as already suggested a cobalt drill .
Apart from a good quality centre punch ( not cheap crap like draper or do it all )
I always use a quality tools because it actually works out cheaper in the long run and dose not wast time .
Dont know where you from but places like Tunes Engineering in Slough or RS Components who have depot's all over and then there are Rotogrip ltd who do it mail order for light machining tools and so on 01215511566 very handy if your into model making .

One thing though surely the grade of stainless for your pedestal wont be that hard and a good sharp drill with the right speed should be fine ,when I use a hand electric that I know is to high a speed for drill size I pump the switch to keep the drill from going to fast and biting in especialy when breaking through through.
Cheers
Mick

http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v/cheep or swap for tug

 

[LORDNELSON]

I find cobalt drills work well, slowish speed and some lubricant. I buy my cobalt drills from Axminster Power Tool Centre. Sales orders 0800 371822, Technical Advice 01297 33656. Their cobalt drills have always worked well

 

[davel]

Many thanks to everyone for the advice !

Dave L.
Location: 50 51.0 N 1 18.6 W

 

[Avocet]

I agree with everyone else - modern electric hand drills are MUCH too fast. Using a masonry bit can sometimes help - their tips are extremely hard. DON'T use the hammer action though!

Also, if you can press harder (maybe by pulling a webbing strap round the back of the thing you're drilling and round the back of the drill to pull them together) - otherwise, the bit will just polish the surface and (as others have said) work-harden it.

 

[Juggler7823]

You must avoid the tip of the drill getting too hot as it blunts quickly. Avoid pressure. Use a low speed. Any HSS drill will do. Using a cutting/lubrication fluid is ESSENTIAL. Buy from a engineering shop

Roy

 

[Guest]

Dave
We happily (well almost) machine stainless all day. a CARBIDE drill is best, even those "gold" coated ones you seen in DIY shops are better than the normal high speed steel. Dearer but worth it as they stand much more heat.
Don't use LUBRICATING oil on it, you need some form of cutting oil, similar to the milky stuff you see in pictures of machine shops.
I'll send you some if it helps.

Keep plenty of pressure on the drill, start with a smallish one say 2mm which will be quite OK at the speed of your pistol drill.

Regards
Bernard

 

[billskip]

Hex1e are you sure you dont want to edit your post..seen some of those pics in mchine shops!!

Bill
www.aegeansailing.co.uk

 

[Guest]

Only boat pics allowed in here but I get my share of exciting pics watching the forum replies!

 

[mtb]

Tell im to op it
du speilling dunt count
Mick


http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v/cheep or swap for tug

 

[Guest]

Used to work in the stainless steel industry.

The steel used for your pedastle will be austenitic (ie 300 series) and within that group it doesnt really make much difference which grade for your purposes. The problem is, that the tube is likely to have been cold drawn and hence work hardened even before you started. It will now be worse, because the skating of a blunt drill on the surface will have hardened further. As a last resort, it can be softened by heating to red heat and cooling in air - but only advised if the surface is to be painted.

The technique for machining stailess is to take big cuts slowly. Since it is difficult to get real force on a hand electric drill on a boat , always start with a small drill bit. Thereafter the combination of the parallel hole and angled point of the drill helps avoid skidding and hardening.

In your situation, I would now remove the pedastle and take it to somewhere where there was a proper drilling machine. The danger is that if you try by hand again, you make the problem worse.

 

[LeonF]

I once spent four hours with the sailing club know it all insisting that he could drill through my pulpit when i had failed miserably. He ruined an entire set of drills. The next day another member went through it like butter using a new drill and a very slow speed. Nothing fancy!

L.A.R.Ferguson

 

[gus]

The real secret to drilling stainless, is the same as working with teak and similar hardwoods. Sharp tools! Your drills have to be freshly sharpened with a slightly steeper cutting edge than normal. A steady slow speed, a steady pressure so that the drill is cutting all the time for if it slips at all it will blunt, heat and harden the stainless steel. Any squealing at all and it is time to change your drill for a sharper one. I have done a lot of drilling in stainless with ordinary HS drills with no more trouble than drilling ordinary steel. If your set-up is correct you should cut through it like you were drilling hard butter.