Removing tiny drills in stainless

[Paul99]

Lead shot dripper by any chance? For the cost of a few new m8 SS bolts I don't think I'd bother trying to save them.

 

[langy]

Firstly I am a longer term member of this forum but was struggling with signing in issues so created a new account.

I have stainless M8x12 set screws with a 3mm hole down the length just stopping short of drilling thru the head. I then have a .9mm hole drilled into one of the flats to intersect this. I needed to open the hole up to 1mm so got some cheap HSS drill bits from screwfix but stainless being what it is they just grabbed and snapped off when a few mm into the original hole. I have tried heating them up, oil to try and loosen, and a compressor down the big hole to blow them out but they haven't shifted. Tried soaking them in vinegar hoping it would start a rusting process on the HSS whilst leaving the stainless untouched but it hasn't made any difference.

To be honest I can't see any of the ways of removing you mentioned working, drilling 1mm holes 12mm deep is gonna be a challenge even with good drills.
Did you drill the bolts originally yourself ???
I often drill 2mm holes in the heads of stainless bolts for wire locking and it's just a fact of life that at some point a drill will break.
As has been said pictures will help solve your problem.

 

[DanielW]

How are you drilling the SS are you using a bench drill or normal hand drill?
Never drilled SS but...try oiling the drill bit once or twice to keep the bit cool.
Its also worth cleaning of the bit as you drill in and retract,don't drill continuously.

 

[Maker]

Nitric acid will passivate stainless steel and dissolve steel but it would be easier, cheaper and safer to simply replace the bolt and get some quality drills.

 

[Fintray]

Why not start again and drill across the flats with a 3mm bit until you are a few mm from the opposite face then use the 1mm bit to make the hole and then a spot of weld over the opposite 3mm hole?

 

[Kent]

I have some special tiny drills donated to me by a big Aerospace firm a while back, never used them, never needed them but I was told "ver,ver spensive" I don't think they get them from screwfix.

 

[AndyP]

Lead shot dripper by any chance? For the cost of a few new m8 SS bolts I don't think I'd bother trying to save them.

Yes, lead shot drippers. if I can't get some nitric acid I'll just make some more as and when on my mill. I seem to recall brick acid is nitric acid, that being the case should be able to get a drop on site. Thanks for your thoughts everyone.

 

[graffian]

I have some special tiny drills donated to me by a big Aerospace firm a while back, never used them, never needed them but I was told "ver,ver spensive" I don't think they get them from screwfix.

When I buy small drills to drill bolts the bloke in drill service always says you want "something or other drills", it might be heavy duty cotter pin drills and they work better than normal jobber drills.

 

[hotrodder]

Brick acid is usually hydrochloric and/or phosphoric based, hydrochloric will pit most flavours of stainless and many flavours of brick cleaner are capable of at least staining it

 

[AndyP]

Brick acid is usually hydrochloric and/or phosphoric based, hydrochloric will pit most flavours of stainless and many flavours of brick cleaner are capable of at least staining it

Thanks for that, looks like I'll just be making some new ones after all

 

[mike os]

Far easier to just remake I think

I guess you really want to be drilling those in a decent mill

 

[DrDeAtH]

Cobalt drill bits are what you need.

 

[AndyP]

Cobalt drill bits are what you need.

You wont drill them out without damaging the existing hole.

 

[mike os]

cobalt for the new holes certainly... or solid carbide but existing is just not worth the effort

 

[AndyP]

cobalt for the new holes certainly... or solid carbide but existing is just not worth the effort

Yeh I've mad quite a few of these over time. Cobalt is definitely the way to go for sub mm holes, carbide is just too brittle in these sizes. I was just in a rush this time and trying to make do with what I could get quickly.

 

[DrDeAtH]

You wont drill them out without damaging the existing hole.

For a 20p bolt. I wouldn't bother opening up the hole. I would just start afresh.