Screwing wood plank to steel support

[unionworkeruk]

I am making a stair case with wood planks supported on two steel stringers There are two holes already drilled in the steel support. I need to be able to line up the plank and know where to drill the holes for the bolts to exactly meet the holes in the steel support.

The problem is two sides of the plank are wany edge so no straight edge to measure from and the stairs are free standing so not resting against the wall to give a measuring point. They are 35mm thick by approx 230 wide by 74mm length

The only suggested way is to mark the rings of the holes from underneath the plank then mark the centre of those holes and drill tnrough the wood from the underside.

Is there a simpler or more reliable way of lining the plank to holes for drilling. Could it be done easier in a joinery shop if I can find one ?

 

[Deleted member 174758]

Wouldn't be an issue if the nose of the tread were straight or at least consistently shaped (as it legally should be) - you could simply make-up a jig from plywood or MDF and use that to marl-out your drilling points

 

[unionworkeruk]

The front of the treads only vary by a few mil but even that stops me measuring accurately for drilling a hole from the top As I said I could mark the drill point from the bottom and use a drill pillar or press to make sure the hole is straight for fitting the bolt from the top Or I could use screws to fix the tread from underneath. Each tread is 350mm so I could use 4 300mm screws and if necessary glue them in for final stability.

I dont see any problem with using screws as they would be easy to fit from underneath, would not show on the surface of the tread and as I said could be glued in to make sure they do not become loose over time . They would just be there to hold the tread in place as all the weight will be on the steel supports and each tread being hard wood is far heavier than a "normal" one so takes a lot to move them even without any fixings .

But I am sure there are objections. I just need to hear and deal with them

 

[foxhole]

If your tread timbers vary in species then stainless steel screws would prevent reaction with timber or the screw could be compromised and snap.

 

[unionworkeruk]

So are you saying I could use stainless steel screws it would work ?

Others say the screws would work loose but surely that applies to all screws and I dont have shelves, doors etc falling down every week thro normal use. The stair are in a private house and mainly only in use morning and evening as I have both down and upstairs bathrooms.

Do you think they need gluing in because I prefer to be able to remove all fixings if necessary. I use screws on all replacement floorboards for example. I dont glue them. I dont see the difference between them and stair tread except the boards get far more use.

 

[Chud]

OK so maybe do the marking out the Japanese way - set a centre reference line and work from that rather than an edge?

Also if the variance of the front edges is only a few mm then I would be inclined to plane them even - if the boards are at all waney you could just plane the top 10-15mm to give you an even tread but still have shape when looking (see pic)?

A drop of pva wood glue in the screw holes would act as a threadlock I would think, you could also use a pan head or coach bolt type screw with a lock washer between the head of the screw/bolt and the steel tread support.

 

[Chud]

Just to clarify are you talking about screwing into the end grain (through the stringer) or from the underside of the treads through a support welded to the stringer?

 

[unionworkeruk]

Screwing from under the tread through the support which as you say is welded to the stringer There are 8 screws for each tread, four each side I am using 8m 30mm coach screws for each 35mm tread. It seems as though that should be secure as the weigh of the hardwood itself should stop them moving. I have removed all the bark and the wood will only be 30 -40mm over the end of the support with 150 - 200mm screwed into the supports