Partially or Fully Threaded Screw?

[Ben_Heda]

You are building a wooden ladder. You are attaching/securing the rungs to the rails using screws only (two 1/8 steel screws on each side). I know this is a design for failure, but my question has more of a technical nature than practical. Also assume the rungs are made of hardwood such as oak, and the rails are made of a softer wood.

In this hypothetical project, should one use a partially or fully threaded screw? And why? (Or maybe it won't make any significant difference?) Also any recommended screw head type?

 

[Cabinetman]

So just to be clear, you aren’t going to make a ladder that way. Just don’t please, ask on here.
The reason there is an unthreaded portion on screws is so that the first piece of wood you screw through will be pulled down tight against the wood underneath without having to drill a clearance hole.
With a fully threaded screw if the two pieces of wood aren’t tight together when you screw, they never will be, unless you have a clearance hole in the top bit of course.
Ian

 

[Jameshow]

I built a short ladder for my van a few years back out of 4x2 CLS,
Notched the steps into the CLS by 1/4" and screwed through with 4" coach screws worked really well.

 

[Orraloon]

First welcome to the forum. I would not trust a ladder that is just screwed together. Normally the rungs are round and fit into holes in the side of the rails. A more basic ladder can have rectangular rungs that fit in notches on the front of the rails then screwed. The screws just hold the rung the weight is on the notch.
Regards
John

 

[ChaiLatte]

The reason there is an unthreaded portion on screws is so that the first piece of wood you screw through will be pulled down tight against the wood underneath without having to drill a clearance hole.

To expand on this, some of the more advanced screw designs, especially decking screws, have a small portion of the shank near the head with a reverse (left hand) thread on it. On these, the pull down action is enhanced over that of a plain shank.

Many ladders on mass produced pine bunk beds are made with the steps just screwed into the stiles. These are items that have to meet some kind of safety standards, so the technique is perhaps less loathsome as some here might suggest.

 

[TheUnicorn]

To expand on this, some of the more advanced screw designs, especially decking screws, have a small portion of the shank near the head with a reverse (left hand) thread on it. On these, the pull down action is enhanced over that of a plain shank.

I had to remove a load of these a couple of weeks ago, they'd been used for a temporary structure and I presume driven in quite aggessivelly with impact drivers, the main effect seemed to be they were a pipper to remove and the head was buried so deep that there were huge splinters around every hole when I did get them out. If anyone is using these I advise extra caution, as having to remove one could ruin the look of a project

I assume these are a quick and effective fastener for rough construction, and of course the design is to go in and not to go out