Drilling Stainless Steel

[SAMYL]

The problem with these threads is someone can advise the complete opposite to another, and still be right. My advice is NOT to use a pilot unless you can find one about 1.5 mm.. Holding the job secure, and keeping vibration down is the key (IMO)

+1 to that.

Drilling a pilot hole just work hardens the edges of the hole causing problems later. Use the size of drill for the size of hole you need and, as others have said, go very slowly with lots of pressure and lots of lub.

 

[vyv_cox]

In answer to the difference in drilling the flat bar would have been slightly more tempered/work hardened during its forging as opposed to your sheet plate - the heat affected zone in this case in the flat bar is more spread over a small area i.e a piece of flat bar 40mm wide is more affected than a sheet 1200 wide. even though the grade of them both is the same i.e 316 or 304.

300 series stainless steels cannot be 'tempered' or have their strength/hardness modified by heat treatment. They are hardened by work, which means plastic deformation, e.g cold rolling during manufacture.

 

[Daydream believer]

#14 would have been my suggestion- ie milling cutter - but I would have added clamp work well in pillar drill & use a 2 flute cutters plus cutting fluid if available

 

[sailorman]

#14 would have been my suggestion- ie milling cutter - but I would have added clamp work well in pillar drill & use a 2 flute cutters plus cutting fluid if available

Well "Anchored " down is a good suggestion

 

[Graham_Wright]

I would use a spotting drill.

A spot drill is preferable to a centre drill because of the point geometry; 90° v 60°.

 

[PaulRainbow]

Blimey, lot of posts for drilling a hole :eek-new:

I just enlarged two holes in the cheeks of my bow roller to 12mm with a HSS drill bit, lubed with some WD40, in a £50 cordless drill.

But i do agree, there are several correct ways of drilling stainless, depending on circumstances.

 

[sailorman]

Blimey, lot of posts for drilling a hole :eek-new:

I just enlarged two holes in the cheeks of my bow roller to 12mm with a HSS drill bit, lubed with some WD40, in a £50 cordless drill.

But i do agree, there are several correct ways of drilling stainless, depending on circumstances.

Did you manage to anchor it down securely

 

[PaulRainbow]

Did you manage to anchor it down securely

I made sure the anchor was mounted securely on it.

 

[Ian_Edwards]

Some feedback

I've just drilled 10 @ 6.9mm holes (tapping size for a 8mm x 1.25mm tap) in the 6mm flat bar, without first using a pilot hole. Didn't have problem with the jobbing drill I bought. Having drilled 6.9mm holes with and without a pilot hole, I don't see much difference. It's marginally easier to line up the pilot drill on the indent from the centre punch and then the line-up the 6.9mm drill on the pilot hole, but using 2 drills takes longer.

 

[Daydream believer]

Personally for stainless I would have drilled 7mm holes & if the stainless was a bit hard or the holes a bit deep then even 7.1

 

[jon and michie]

300 series stainless steels cannot be 'tempered' or have their strength/hardness modified by heat treatment. They are hardened by work, which means plastic deformation, e.g cold rolling during manufacture.

I don't think you read my post quite well -"the flat bar would have been slightly more tempered/work hardened during its forging" - meaning during its manufacture and yes stainless 300 series can get harder - especially when you push harder on a blunt drill bit you would then see the bit get cherry red blunting the bit then the stainless starts to hot with a brown/blue appearance around the heat affected zone - easily more identifiable when grinding plate that has been cut/gouged with a plasma.

jon



the flat bar would have been slightly more tempered/work hardened during its forging

 

[wotayottie]

What are these values (TT) please?

tonnes tensile - I'm old fashioned and couldnt remember the hardness numbers. But there is a correlation. and when drawing wire or rolling sheet i was tensile strength that we worked to most of the time.

I predate things like Newtons and moist other modern named units.

 

[d4dunmor]

Have to concur with this post
A full thread in some types of stainless is
Very difficult especially when tapping by hand
Chamfer hole . I sometimes start the thread straight after drilling the hole using the drill chuck by hand
No drunken threads even load on tap
And again bit of lube in the form of tapping fluid

 

[d4dunmor]

Personally for stainless I would have drilled 7mm holes & if the stainless was a bit hard or the holes a bit deep then even 7.1

Have to agree with this !

 

[myquest]

Last year at the local agri show there was a stand with a drill bit outfit from Plymouth. They were selling drill sets that claimed to be capable of drilling anything! One of the demos was drilling holes in large drill bits with a cordless drill. They were called 1 drill drills all or something similar. They were a bit expensive but has anybody tried one on stainless?

 

[Ian_Edwards]

Personally for stainless I would have drilled 7mm holes & if the stainless was a bit hard or the holes a bit deep then even 7.1

I've just tapped 28 @ 8mm x 1.25 holes by hand in the 6mm SS flat bar, using a 6.9mm hole, using standard carbon steel taps. Because the flat bar is only 6mm thick I found that I only needed to use the #1 tapered tap, by the time the torque required had reduced to the point that I could, more or less, spin the tap, I didn't need the #2 tapered tap, but I did run the plug tap down just to make sure.

I ran a countersink into the hole before starting the tap, just to clear the burr, and carefully lined up to tap and applied an even vertical pressure by hand. I had very little problem starting the thread and after checking the thread with a long bolt, they all seem to be square enough for what I need.

 

[Daydream believer]

I've just tapped 28 @ 8mm x 1.25 holes by hand in the 6mm SS flat bar, using a 6.9mm hole, using standard carbon steel taps. Because the flat bar is only 6mm thick I found that I only needed to use the #1 tapered tap, by the time the torque required had reduced to the point that I could, more or less, spin the tap, I didn't need the #2 tapered tap, but I did run the plug tap down just to make sure.

I ran a countersink into the hole before starting the tap, just to clear the burr, and carefully lined up to tap and applied an even vertical pressure by hand. I had very little problem starting the thread and after checking the thread with a long bolt, they all seem to be square enough for what I need.

It may be that if you had trouble drilling the holes you actually drilled bigger holes than 6.9mm which is not unusual
I have just checked my tapping chart as I have to tap some steel parts on a model traction engine I am building & I see that the recommended hole size for stainless is in fact 7-7.2 mm for an 8mm * 1.5 tap . It varies from 6.75mm for softer steels.
But if you have done it OK then there is no problem & you did not need the comment from the forum. Apologies for interfering

 

[Ian_Edwards]

No problem with comments ... in any form, I'm trying to learn, I haven't done much metal work since school day, and that was a frightening 55+ years ago.

And you may be correct, I could well have been drilling a larger hole than the size of the drill bit would suggest.

Drilling SS seems to come up regularly on the forum, so I thought I'd add some feedback. I did have big problems when I first started drilling the 6mm flat bar, but it all seems to be down to getting the right drill bit for the job and clamping the work very securely.

I still have 20+ 8mm holes to drill in the plate, the bits I have in my box of bits won't touch it, I've struggled to drill 4 holes so far, and have given up for now, until some cobalt drill bits I've ordered arrive in the post. I hope they are as good as the 6.9mm bits I used to drill the holes prior to tapping the threads.

 

[rogerthebodger]

No problem with comments ... in any form, I'm trying to learn, I haven't done much metal work since school day, and that was a frightening 55+ years ago.

And you may be correct, I could well have been drilling a larger hole than the size of the drill bit would suggest.

Drilling SS seems to come up regularly on the forum, so I thought I'd add some feedback. I did have big problems when I first started drilling the 6mm flat bar, but it all seems to be down to getting the right drill bit for the job and clamping the work very securely.

I still have 20+ 8mm holes to drill in the plate, the bits I have in my box of bits won't touch it, I've struggled to drill 4 holes so far, and have given up for now, until some cobalt drill bits I've ordered arrive in the post. I hope they are as good as the 6.9mm bits I used to drill the holes prior to tapping the threads.

I do wonder sometimes why people seem to have so much trouble drilling and tapping stainless steel.

When I a drilling tapping holes for M8 I use a 6.5 dia HSS drill in my 13mm bench pillar drill and tap with a HSS second tap with some tapping grease/soap.

This is just one of the jobs in 316 flat bar 6 mm thk. Each frame has 24 holes 2 are all tapped M8 the mating 2 have 8.5 clearance holes. Each frame pair were drilled 6.5 together to ensure matching the 8.5 clearance then drilled opening up the previous drilled 6.5.

 

[sailorman]

I do wonder sometimes why people seem to have so much trouble drilling and tapping stainless steel.

When I a drilling tapping holes for M8 I use a 6.5 dia HSS drill in my 13mm bench pillar drill and tap with a HSS second tap with some tapping grease/soap.

This is just one of the jobs in 316 flat bar 6 mm thk. Each frame has 24 holes 2 are all tapped M8 the mating 2 have 8.5 clearance holes. Each frame pair were drilled 6.5 together to ensure matching the 8.5 clearance then drilled opening up the previous drilled 6.5.

You must be very lucky not to have all the troubles that most here seem to experience.