Drilling holes in-situ in my stainless panelling and chassis is proving a problem.

I've no problem drilling 3.3mm holes in stainless sheet or box section, using a pillar drill, however, trying to drill them in-situ is a nightmare, they will barely touch the stainless, I've broken 3 HSS drills in as many holes....

Pre punching the holes isn't an option... I have to drill them in-situ (the chassis is stainless too)

Are there specially sharp/hard drills for stainless. The ones I'm using are "rolled" High Speed Steel. I know that ground HSS drills are more expensive, but would they be any better.

Thanks

John

Use a cutting fluid/ general oil will do, never let the bit get too hot little pulses at a time it is a bastard to machine!

if your still stuck next week, send me an email. I might be able to nab a couple of cobalt tipped drill bits (not titanium - i'm a nob), will cut through almost anything - if you use them right

chris



[Edited on 20/2/04 by flyingkiwi]

cobalt tipped cutting tools and drills are avalable and use a good cutting compound/oil and they'll last a lifetime

Screwfix do a really good aerosol cutting oil, try sharpening the drill every hole, you can do this on an angle grinder with a bit of practice, if you sharpen a 1/8 drill off centre, you will end up with the hole size you need. The offcentring will put more pressure on one flank of the drill and make it easier to drill. try a really slow cut to cut down on the heat.

Cobalts will last loads longer though!

Hi John

This is going to be difficult to explain.
If you look at the point of a drill it's two flat surfaces. The centre of drill where these two surfaces meet dosn't cut, it wears its way though. So the trick is to grind off the trailing edge on the corner of the grind stone to reduce the length of the junction of the original surfaces.
I bet that's clear as mud.
If you don't get what I mean U2U me and I'll grind up a big drill and post a photo.

Go's without saying, use a slow drill (500rpm) and coolant. I use soluable oil / candle wax, heated & mixed 50/50 . It should just set. Use as a dip.

Paul G

As a general rule of thumb - cutting St.St it is imperative to thin down the web (centre) of the drill (to 25% it's diameter)to reduce force otherwise it heats up the St.St. and hardens it - making it even more difficult to drill. Using an 8% cobalt (5% if no option) HSS drill is the best option as it is physically harder than standard HSS. If you can also get Titanium Cobalt Nitride (TiCN) Coating as this helps reduce friction when cutting and therefore reduces heat further. Use a general purpose water based/oil emulsion cutting fluid to keep the material cool. The speed at which you cut the St.St is also important: to work out the recommended speed use the formulae:










Surface Speed for Stainless: V=80metres/min

RPM = (V/drill diameter)*318

eg RPM = (80/3mm) * 318
8480

If you can always try to hit the speed - if you can't always go slower.

This will give you the optimum cutting speed for St.St.

For mild steel use V=230

Any information regarding cutting materials from Automotive to Aerospace get in touch.

[Edited on 20-2-04 by Hellfire]

The trouble with some stainless is that it work-hardens if your technique is not right.

Basically, use cutting fluid (as mentioned above) and don't go light on the drill bit - as soon as the drill rubs it will work-harden and then you may as well go and drill somewhere else! You have to keep the drill bit cutting.

David

and on a similar tack, you can stop the bit wandering by clamping a piece of wood to the 'target', with a pilot hole to aim it.

As above, take it slowly and use a good lub (to stop the tip from melting of course)

I found out earlier today as I was making the front wishbone compounts out of stainless steel bar which needed drilling out to min 16mm, found a slow speed and lots of RTD cutting compound worked best as it sticks to the drill tip. Admitedly I was on a lathe thou. Have fun

Wow what a wealth of information !!!

Just drilled some more holes using 3 in 1 oil as a lubricant (funny, I used it on the piller drill, but never thought to use it when hand drilling) Results much better.

I can associate with the "keep it cutting" comment, it will definately quickly drill the hole, if I can keep it cutting once it starts.

Trouble is, drilling a vertical surface, I need 3 hands!

I'll also try the clamped piece of wood idea, as it will also help set out the holes, rather than scribing and punching.

Now then let me look for some cobalt HSS drills, for when I (inevitably) get through the remaining 5 drills.

Type 907, we corresponded before about stainless tapping etc, I'm using the 3.3mm drill for 4mm metric tapping, though at the moment I'm actually pop rivetting the transmission tunnel using 3.2mm stainless pop rivets.

I guess with such a small drill, it'll be difficult to minimise the size of the drill centre by grinding the flanks - but I'll have a go

Thanks everybody for the info and help

John

If its slippy and looks like youve tried writing your name (or looks like that magazine ad with a woman and powertool - im not the one with the sexist jokes, just setting you lot up for em!) then use some cloth tape/gaffer tape. Dont use it for any long than you have to otherwise the sticky goes glumpy.

quote:

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the sticky goes glumpy.

---

or if your still struggling, just drill pilot holes first 3/32 or 1/16" even. makes a big difference and your full size hole will be a more accurate size.

IMHO I would not normally recommend pre-drilling as the material you just drilled is then work hardened.

A trick I was oncetold about, that worked well for me on a very hard rifle receiver was to take a carbide tipped masonry bit & regrind it to a normal shaped tip as you`re currently using. Gives a very hard & sharp edge & I can`t see that it wouldn`t work on stainless. Cheaper than cobalt bits as well . Usual provisos re cutting lube & try at own risk etc. Cheers, Steve

Hi

Right, I'v found my "anorak" so if I may I'd like to clarify the point made about "work hardening".

Stainless is a very low carbon steel.
Grade 304L : The L stands for low carbon.

HSS drills are high carbon steel.

When drilling, if you get the stainless hot and "round off" the drill tip, the carbon from the drill will go "into solution" with the chromium in the stainless forming chromium carbide. This compound is extremely hard and brittle, and as David says, "you might as well go and drill somewhere else".

So the moral of the story is, as soon as a drill ceases to cut well, and before it gets blunt, stop and sharpen it.

Also, in a pistol drill I prefer to use "jobber" drills. They are shorter so less likely to break.
For tapping, bike chain lube is very good.

Good luck John

Paul G

Jobber drills are good too, the ones we use have a diferent angle on the tip, dont know if theyre all like this but it might make them bite better.