Enlarging a hole in stainless steel

[pcatterall]

I recently fitted a bracket for my new inner forestay. I foolishly had the hole for the stay drilled at 10mm and now find it needs to be slightly bigger for the turnbuckle pin.I don't want to remove it from the deck and will appreciate advice on the best way to enlarge it. Its 4mm stainless. In the past I have managed with a round file but also wonder about those drill like bits with file like edges, would they be quicker.Thanks.

 

[Lon nan Gruagach]

I recently fitted a bracket for my new inner forestay. I foolishly had the hole for the stay drilled at 10mm and now find it needs to be slightly bigger for the turnbuckle pin.I don't want to remove it from the deck and will appreciate advice on the best way to enlarge it. Its 4mm stainless. In the past I have managed with a round file but also wonder about those drill like bits with file like edges, would they be quicker.Thanks.

If you can get the drill to it then a bit the right size is best for the job, Just think of the existing hole as a pilot.
Filing or reaming out is never going to be as round (as good) as drilling. 1/2mm sized bits are available, or you could make one with a larger bit and a grind stone.

 

[rogerthebodger]

Sorry drilling stainless with a drill 1/2 mm bigger will not do the job easy as the drill will just bite into the edge of the existing hole and stall the drill.

The beat way is to use a tapered reamer to enlarge the hole a little . The next best is with a die grinder and either a rotary burr of a mounted grind wheel. The other option is with a round of half round file depending on the size of the existing hole.

 

[pcatterall]

Thanks guys. Yes I have tried in the past to just use a larger drill and as Roger says it just chews up the edge of the bit and stalls the drill. It seems ok when going from a small hole to something quite a bit bigger. I will get a good quality tapered reamer for my next visit.

 

[Kelpie]

What about a step drill?

 

[vyv_cox]

Throughout my life I have been drilling stainless steel with hand held drills by starting with 4 or 5 mm and gradually increasing drill sizes up to 12 mm. There are undoubtedly better methods but for most of my purposes this method has been adequate.

 

[lw395]

Depends how much you've work-hardened it already?
One option is a spade shaped carbide drill as sold for glass and tiles.
Or a diamond burr, these can be quite cheap.
How much material do you need to remove?
TBH, I'd probably just file it if it only needs to be 11mm.
You want a good file though, not a poundshop job!

Maybe use the spade drill or a carbide drill to countersink the hole from both sides first, this gives you a guide to work when filing?

 

[LadyInBed]

Throughout my life I have been drilling stainless steel with hand held drills by starting with 4 or 5 mm and gradually increasing drill sizes up to 12 mm. There are undoubtedly better methods but for most of my purposes this method has been adequate.

Vyv, could you expand on this a bit.
hand held - electric?
if electric hi or low revs?
How much do you increase by each time?
what type of bit for ss?

 

[Seajet]

The most important thing is to keep the hole round, avoid ' square corners ' via flat or triangle etc files at all costs as they propogate stress cracks.

That's assuming ( most dangerous word in the English language ) there's sufficient meat of material in the fitting around the hole.

 

[Norman_E]

Trying to enlarge the hole in situ may well result in a poor job, especially if the hole is horizontal and close to the deck. It might be better to remove it and take it to someone with a decent bench drill, because stainless needs good drills, high and steady pressure to ensure that the drill cuts and does not rub, and slow speed. A taper reamer will make a tapered hole even if put in from both sides, do you really want that?

 

[lw395]

One might be tempted to work out if a 10mm pin was strong enough?

 

[vyv_cox]

Vyv, could you expand on this a bit.
hand held - electric?
if electric hi or low revs?
How much do you increase by each time?
what type of bit for ss?

Hand held electric drills, slow speed. I have a De Walt battery powered right angle drill on board, excellent tool. At a guess, 5 mm - 10 mm - 12 mm, depends a bit on the thickness of the metal, maybe add an 8 mm if thicker. Important to keep bits sharp and load heavily. I usually lubricate with gear oil from a small dispenser (unpleasant smell!). I reserve cobalt ones for stainless steel in Greece but HSS ones are fine if sharp enough (no sharpening facility on board)

 

[rogerthebodger]

If doing this by hand I also use a battery drill as the speed is much lower than most mains. I also tend to use increments of about 5mm but on holes much bigger than 12mm the only way is reamer /die grinder or file if not to big an increase.

This is the kind of reamers I generally use. Expanding/adjustable for a parallel hole in thicker material. Tapered in thin sheet material.

http://www.ebay.co.uk/bhp/adjustable-reamer

 

[drew silverwitch]

http://www.screwfix.com/search?search=stepped+drill
any of these will sort you out

 

[KellysEye]

>Thanks guys. Yes I have tried in the past to just use a larger drill and as Roger says it just chews up the edge of the bit and stalls the drill.

I used Cobalt drills and machine oil as recommended by a marine fabricator in the Caribbean.

 

[macd]

I used Cobalt drills...

Cobalt or HSS makes little difference. The main quality they need is sharpness.
If the piece has work-hardened, it'll be a struggle to get any conventional bit to work in situ: the force you can apply in a drill press makes a heap of difference. A step-bit might be the best bet if the piece is difficult to remove.

 

[Daydream believer]

The problem may be that the drill wants to bite into the metal too much. When cutting brass for instance one puts a back chamfer on the cutting edge of the bit.I would suggest grinding the cutting edge of the bit so it is square to the face so it does not cut so quickly. If the SS is work hardened by earlier drilling it will just knock the corners off an HSS drill bit so be prepared to keep sharpening it - possibly with a grinding wheel in an angle grinder if at a marina.

I am told- but have never had occasion to try- that carbide masonry bits are successful.
Grind a masonry bit so that the slight reverse taper on the very tip is removed & left square - rather like a lathe tool- & try that.

 

[pcatterall]

Thanks again to you all. I suppose that the question is of general interest as we may all need to do this at sometime.
While I do believe that a 10mm pin would be strong enough it would then be a loose fit in the turnbuckle fork so not really an option.
Looking at the suggestions I am now considering that a step bit may be the best option. I looked at the ones being advertised and realised that some did not have a long enough 'step' to accommodate the 4mm steel. Another issue was quality, there seems to be a massive difference in the price range, I recognise that I will need a good quality item but would appreciate a steer on getting a good tool at a reasonable price.
I have only a mains drill on board and cannot get it run at low enough revs, is there a device I can obtain that will 'externally' control the drill?
Thanks once again

 

[earlybird]

I recently fitted a bracket for my new inner forestay. I foolishly had the hole for the stay drilled at 10mm and now find it needs to be slightly bigger for the turnbuckle pin.I don't want to remove it from the deck and will appreciate advice on the best way to enlarge it. Its 4mm stainless. In the past I have managed with a round file but also wonder about those drill like bits with file like edges, would they be quicker.Thanks.

You don't say how much you need to enlarge the hole. If it's not much more than say ~1 mm. on diameter, and access is OK, I'd go for a good quality 2nd. cut rat-tail file, near as big as you can get in the existing hole, say 10 or 12 inch, with a handle.
It'll probably finish up rounder than bodging a drill through it as well!

 

[reeac]

The tip that I was given by a man who did a lot of s/s work was always to make sure that swarf was being produced I.e. No skimming of the drill tip over the metal surface. Low speed and plenty of pressure. CPersonally, though, I'd go the rat tail file route.