Drilling in stainless steel & tapping mild steel

[Guest User]

Could anyone tell me please; how easy (or not) is it to drill 3mm thick stainless steel(5.5mm and 6.5mm diam holes) ? Would I be getting through a lot of cobalt bits ?

 

Also, what would be the correct size hole in mild steel prior to tapping to M5 and M6 ?

 

Many thanks in advance

[RLWP]

Tapping drill sizes

 

You shouldn't need special drills to drill Stainless, but don't go too quick. It's nasty to drill when it's work hardened

 

Richard

[landroversforever]

Just go slowly with the drill, and use plenty of coolant type stuff, or even a drop of oil.

 

Tapping size for M5 is 4.2mm, and for M6 its 5mm

 

Hope this helps

[Justme]

If you have a lot of holes to drill in the SS then hire a Mag drill if it will fit where you need the holes. Or if its on loose parts use a pillar drill.

 

Slow, lots of coolant & lots of pressure (which is why a Mag & pillar drills are good).

[Sir Nibble]

Tip for metric drilling sizes. To find the correct tapping drill, subtract pitch from diameter. For instance 5mm screw would normally have a 0.8mm thread pitch so 5-0.8=4.2mm; 6mm screw has 1mm pitch so 6-1=5mm.

[RLWP]

Tip for metric drilling sizes. To find the correct tapping drill, subtract pitch from diameter. For instance 5mm screw would normally have a 0.8mm thread pitch so 5-0.8=4.2mm; 6mm screw has 1mm pitch so 6-1=5mm.

 

That's clever

 

Richard

 

Clearly you're more than just a peachy arse...

[WotEver]

Tip for metric drilling sizes. To find the correct tapping drill, subtract pitch from diameter. For instance 5mm screw would normally have a 0.8mm thread pitch so 5-0.8=4.2mm; 6mm screw has 1mm pitch so 6-1=5mm.

Hey Snib, that would be a great tip if only I was an engineer

[Timleech]

If you have a lot of holes to drill in the SS then hire a Mag drill if it will fit where you need the holes. Or if its on loose parts use a pillar drill.

 

Slow, lots of coolant & lots of pressure (which is why a Mag & pillar drills are good).

 

Surely a mag drill won't hold very well to stainless (if at all, depending on grade)?

 

As others have said, good quality sharp drill (yes cobalt drills are recommended for stainless but not essential), moderate speed, lots of lubricant and enough pressure to keep it cutting. Don't let it rub without cutting, it'll work harden the surface and you'll have trouble getting the cut going again.

No harm in going a little over the recommended tapping drill size if the job isn't super-critical, it'll make the job easier and loss of strength will be minimal. I wrote that thinking you were going to be tapping the stainless, realised you're not but it's still true.

 

Tim

Edited May 9, 2011 by Timleech

[Justme]

Surely a mag drill won't hold very well to stainless (if at all, depending on grade)?

 

 

 

 

Doh, your right.

[Guest User]

Many thanks for the useful info and advice .... I shall set about perforating my boat

[RLWP]

It might be best to practice drilling and threading your boat first in some inconspicuous place. Perhaps the bottom of the engine room?

 

Richard

[Guest User]

It might be best to practice drilling and threading your boat first in some inconspicuous place. Perhaps the bottom of the engine room?

 

Richard

 

 

Good point, it's nice and dark too, no-one will notice if I make a mistake drilling holes down there

[Guest]

Good point, it's nice and dark too, no-one will notice if I make a mistake drilling holes down there

One bloke here reckons to use masonry bits for S/S:

 

http://www.pistonheads.com/gassing/topic.asp?h=0&f=23&t=807739&mid=0

 

I assume an HSS drill would be ground differently for S/S?

Edited May 9, 2011 by Guest

[RLWP]

One bloke here reckons to use masonry bits for S/S:

 

<snip>

 

Hideous

 

Richard

[Timleech]

Hideous

 

Richard

 

Masonry drills can be useful in difficult situations, but as supplied for masonry they are deliberately blunt so they need regrinding to an edge.

There are 'all purpose' drills on the DIY market which are exactly that - sharp masonry drills

 

Tim

[RLWP]

Masonry drills can be useful in difficult situations, but as supplied for masonry they are deliberately blunt so they need regrinding to an edge.

There are 'all purpose' drills on the DIY market which are exactly that - sharp masonry drills

 

Tim

 

Touch and go with a cheap DIY grinder to know if you'd sharpen the drill or reprofile the grinding wheel

 

Richard

[Timleech]

Touch and go with a cheap DIY grinder to know if you'd sharpen the drill or reprofile the grinding wheel

 

Richard

 

You need a green grit or diamond wheel for carbide.

 

Tim

[RLWP]

Zackly

 

Richard

[Guest User]

Masonry drills can be useful in difficult situations, but as supplied for masonry they are deliberately blunt so they need regrinding to an edge.

There are 'all purpose' drills on the DIY market which are exactly that - sharp masonry drills

 

Tim

 

Ahhh .. so I could drill through the wooden floor, the concrete ballast and the steel bottom plate all in one go ?

[Timleech]

Ahhh .. so I could drill through the wooden floor, the concrete ballast and the steel bottom plate all in one go ?

 

Yup, but it'll be slower than using the proper drill for each material

 

Tim

[WotEver]

Ahhh .. so I could drill through the wooden floor, the concrete ballast and the steel bottom plate all in one go ?

You've taken Richard's advice to heart, I see

[Sir Nibble]

Ahhh .. so I could drill through the wooden floor, the concrete ballast and the steel bottom plate all in one go ?

Yes, but you would need to countersink the hole

[Grace and Favour]

Ahhh .. so I could drill through the wooden floor, the concrete ballast and the steel bottom plate all in one go ?

 

You may prefer it if you counter-bored the wooden floor, then fit a finishing plug into it - then you'd have a beautiful final finish - and no-one could tell that you've perforated the hull

[Deano]

You may prefer it if you counter-bored the wooden floor, then fit a finishing plug into it - then you'd have a beautiful final finish - and no-one could tell that you've perforated the hull

 

I understand you may get a drop of water in if you do that, so best practice says you need to drill another hole next to it so the water will have somewhere to run out as well.

Edited May 12, 2011 by Deano

[smileypete]

Could anyone tell me please; how easy (or not) is it to drill 3mm thick stainless steel(5.5mm and 6.5mm diam holes) ? Would I be getting through a lot of cobalt bits ?

 

Also, what would be the correct size hole in mild steel prior to tapping to M5 and M6 ?

 

Many thanks in advance

How did it go? Some good advice here.

 

(I've got some experience drilling thin stainless sheet but don't want to risk getting shouted down by the 'experts' )

 

cheers,

Pete.