Screws in oak

[Steve_Scott]

The iron / steel in oak thing is interesting though. I was unaware of the silicon bronze screws. Will check that out.

Re steel in oak. The oldest part of my house is about 400 years old -timber frame. It it has some seriously big iron reinforcing brackets in places. These will be a good deal less than 400 years old but well over 100 years as will the large number of metal nails. In an indoor environment these have survived perfectly well and have not materially discoloured the oak (which is rather dark now). I wonder if the tannin action diminishes as the oak ages.

Proper wrought iron (not modern mild steel bashed by a blacksmith, but the stuff that was puddled before Bessemer and BOS furnaces started to produce clean steel) can actually exhibit some remarkable resistance to corrosion. The mechanism is not well understood but its thought to be a combination of the lamella structure that results from forging and critically the remnants of slag left in the iron that get trapped between the layers.

 

[MikeG.]

Undo the fixings, though, on those old blacksmith made items, and they'll be seriously corroded, particularly at the point where they emerge from the wood. I don't think they survive for so long because of any inherent resistance to the tanins, but because of their size. I'll happily use mild steel coach screws in oak, but they're 18mm or so in diameter, with huge threads. They are rusty in no time, but the damage only penetrates so far, and with a big fitting that's not far enough to critically undermine the hold it has. With a small item like a normal screw, the same amount of corrosion spells the end of it. I've removed literally hundredweights of old iron and steel fixings from both ancient oak and new oak over the years, and particularly in the last 5 years, so I am pretty confident in what I recommend with regard to modern fixings in oak. Screws, nails......stainless, brass, copper, or very big cut nails. Visible bolts etc, ditto (not copper, obviously). Hidden bolts, carriage bolts, coach bolts/ screws....galvanised MS is fine, so is bright shiny steel. They'll corrode, but they'll hold.

 

[MikeG.]

Can anyone remember the last time they saw a nice table and thought hold on a mo, I'd better crawl under it........

Everyone does that, don't they? Don't they? It's not just me, is it? :lol:

 

[Phil Pascoe]

I think I might draw the line at coffee tables.
I know it's easy to ascertain whether someone is a turner - watch a turner pick up a piece of turnery and within seconds it'll be turned over and the bottom inspected.

 

[woodbloke66]

Depends on your preferences; for me it's always brass screws and as others have said, cut the thread first with a steel screw with an identical thread and make sure there's a smear of lube in the hole; I always use Vaseline and keep a tub specifically for that purpose.

Two additional things to do with brass countersink screws where they're on show is to firstly use a bit of worn 320p paper to mirror polish the screw head. Secondly, you must, must, must use a screwdriver where the tip is an exact fit in the screw slot. Even the slightest bit of 'wiggle' will mangle the slot; done properly, brass screws are really the only acceptable ones to use with good quality brassware (though not applicable in this case) - Rob

 

[woodbloke66]

Can anyone remember the last time they saw a nice table and thought hold on a mo, I'd better crawl under it........

Everyone does that, don't they? Don't they? It's not just me, is it? :lol:

True tale. When I was making for Linely some years ago, my then boss made a trial piece for 'Linners' which was then inspected by one of his team, who examined the underside with a torch and spotted some Pozidrive screws buried deeply in counterbored holes. Without averting his beady eyes from the offending screws he casually mentioned to Richard...."you will use proper brass countersunk screws in any of our pieces, won't you?"
Much sucking of the teeth and embarrassed foot shuffling followed by an affirmative.

As I say, a true story - Rob

 

[Blackswanwood]

Thanks guys ... I am using brass. Out of interest I have also put a passivated and normal steel wood screw in an oak off cut just to see how they fare.

 

[Keith 66]

In reply to Steve Scott, It is true that A2 (304) & A4 (316) are austenitic, but there is a world of difference in performance, A2 is the cheaper & is commonly used in industrial kitchen manufacture, A friend scraps the stuff regularly from a large kitchen manufacturer & A4 is definately not used as much due to cost!
A2 (304) can vary considerably depending on where it comes from, It is often faintly magnetic, often if buying stuff from the far east there is no real guarantee what grade it is. I have seen some stainless screws & machine screws rust as quick as mild steel.

 

[That would work]

Also... I don't think anyone has mentioned that the screws slots MUST all be in line? You may laugh but...

 

[Doug71]

Also... I don't think anyone has mentioned that the screws slots MUST all be in line? You may laugh but...

Sounds easy but that is when the screws break

Always a dilemma, the slots are in line but the screw is not quite tight or seated properly, will another half turn be too much, SNAP, yes it was

 

[MikeG.]

.....Always a dilemma, the slots are in line but the screw is not quite tight or seated properly, will another half turn be too much, SNAP, yes it was

You just back them off to the previous half turn, then. Simple. If the head falls out, then just put a dab of silicon under it.

Yep, I've seen that done.

 

[Steve_Scott]

In reply to Steve Scott, It is true that A2 (304) & A4 (316) are austenitic, but there is a world of difference in performance, A2 is the cheaper & is commonly used in industrial kitchen manufacture, A friend scraps the stuff regularly from a large kitchen manufacturer & A4 is definately not used as much due to cost!
A2 (304) can vary considerably depending on where it comes from, It is often faintly magnetic, often if buying stuff from the far east there is no real guarantee what grade it is. I have seen some stainless screws & machine screws rust as quick as mild steel.

Again I will highlight that I do not know where the A2 and A4 designation comes from... I'm looking into this, but it appears to be specific to fasteners. You wouldn't specify A2 sheet or bar stock. Who is governing what composition and microstructure is required for these grades?

AISI 304, or to be technically correct in Europe, 1.4301 according to BS EN 10088-1:2014 (its a whole lot easier to say 304 so the Americans got something right for once!) are well defined compositions.

There is no reason for a 304 to be more magnetic that 316, both grades have plenty of nickel present to allow an austenitic microstructure. If your real world experience is that A2 fittings are frequently magnetic, its because the A2 fittings are poor quality, and you have alluded to the fact that any old rubbish get sent out of the factories in the Far East and A2 is made in large quantities.

The driving force is cost, and nickel (the austenite stabilising addition) is the expensive part of a stainless steel. this has driven manufacturers to sit at the lower end of the allowable nickel content, often drop below it, and even develop 200 series stainless steels which vary from almost ok in some applications to utter dog poo! Worryingly, a lot of this is finding its way into products that are specified as 304.

To reiterate my point... 316 only offers improved corrosion resistance to chloride pitting and crevice corrosion. Its general corrosion resistance is comparable to 304. That being said... when does a fastener not create a crevice?

 

[Keith 66]

I too dont know where the A2 & A4 designation comes from, doesnt seem to be a lot about it on google. It has been used for at least twenty years to my knowledge probably a lot longer.
It boils down to buying from good suppliers.
As for crevices, i had a hall of horrors on the wall of my boatshed, there were some wonderful examples of failed stainless steel in that lot!

 

[Doug71]

If the head falls out, then just put a dab of silicon under it.

Yep, I've seen that done.

Seen it too many times!

It's a favourite on door handles, the brass screws supplied are generally useless but the joiner uses them anyway (doesn't help that he uses his cordless driver to put them in #-o), snaps the head clean off, sticks it in with silicone (or whatever he has with him) and leaves it as a problem for whoever takes the handle off next.