A4 stainless

[David AmbroseParticipant @davidambrose86182]

I’ve recently bought some Timco A4 grade stainless steel wood screws, 4mm by 60mm, for an exposed maritime application.  I was using an impact driver, and in quick succession I broke the head off one screw, then chewed up the head of another.  I had naively assumed stainless steel would be strong and hard, but this was not the case.  Is A4 stainless good for corrosion resistance, but poor for strength?

[JasonBModerator @jasonb]

Stainless woodscrews are nowhere near as resistant to overtightening as their modern steel versions. So set the torque of your driver low, use a good bit and keep the pressure on the driver and make sure you keep it lined up with the screw.

clearance drill the top piece of wood if joining two and even countersink particularly if a hardwood or you are going through a knot in softweed as they may not pull themselves in without the head coming off.

[noel shelleyParticipant @noelshelley55608]

I would use a new tip and be wary of using an impact driver, the more so on hard woods. Doing them by screw driver may be a pain but you know when to stop and open the hole some more. Stainless is good for marine use and its corrosion resistance takes precedence over it’s mechanical strength. Plan B would be bronze – at a price. See also Jasons comment. Noel.

[Richard SimpsonParticipant @richardsimpson88330]

I think mainly as a result of modern tools and things such as self drilling and self tapping wood screws we seem to have got out of the habit of drilling the wood appropriately.  I would still always advocate a clearance drill to clear the shank diameter and a pre-drilled hole of the same diameter of the root to ensure only the thread is cutting into the wood.

I think we sometimes fall into the trap of thinking that a screw is tight because it requires a lot of effort to screw it in.  In fact a wood screw should require little effort to fit it.  The quality of some wood screws nowadays is pretty appalling with a tendency for the head to snap off  if excessive torque is applied, so pre drilling is the best way to minimise the torque required.

[roy entwistleParticipant @royentwistle24699]

My dad used to say Use a hammer to put a screw in, use a screwdriver to take it out

[Mark EasingwoodParticipant @markeasingwood33578]

Yes stainless steel wood screws are not as strong as steel, some brands are better than others, and the ones supplied with fittings can be very poor. I find the Hafele ones are pretty good.

As said pilot holes and countersinking will help, and use of hand screwdriver for final tightening after using the impact driver/drill for the first 80/90%.

Running a similar size steel scew in first will cut a “thread” for the SS screw.

Dipping the SS screws in Vaseline before insertion also helps, but the Vaseline will bleed into the surrounding wood, paste wax is another option. Tallow is the traditional method for dunking screws in.

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