Screw length & wood thickness

[Ken Cobbing]

Hi all,

I am building a kitchen island. The island is made out of top is 3/4" baltic birch plywood (laminated) and probably weighs about 40lbs and will hold loads of perhaps 100 lbs on occasion.

One side will be attached to the wall (studs). The other side will be supported by a welded steel leg that I had custom made. My question is about how to properly attach the steel leg.

The steel leg is attached to the top by a T-shaped bracket with screw holes. The leg is a modern angled design (photo below) so I think it will exert some pullout force that would not occur if it were a conventional leg design.

I'd like to hear opinions on how long the screws should be in order to be prevent pulling out. Since the top is only 3/4" plywood, I will need to use screws shorter than 3/4" - which intuitively seems too short - unless I add additional wood under the T-bracket. Opinions?

[Frederick Skelly]

I agree that the angled leg seems likely to leverage the screws loose over time. If it were me, I would add wood under the T-bracket as you suggest. But I'd cheat a little. Id buy some T-nuts and insert them upside down (so they cant pull out) in the wood part you are going to add on. Here's a crude sketch of what I am thinking.
Hope it helps.
20181019_175834.jpg

[Wayne Lomman]

Increase the quantity of the screws and also the gauge. 3/4 x 10's will be good. The thickness of the steel will stop them breaking through. The dimensions of your T plate for fixing are generous enough to for this to work. Add a piece of timber for packing and you increase the height of the top. Not good over time. Cheers

[Ken Cobbing]

Thanks a lot for the replies so far

Add a piece of timber for packing and you increase the height of the top. Not good over time. Cheers

Wayne, can you explain why this would be a problem over time? If I added even a thin piece of wood - say, 1/4" - then I would be able to use a 1" screw instead of 3/4". That's a 25% increase in depth, and virtually the same table height.

A related question I have is: how close can you drive a screw from the underside of a table top without stressing the top? As mentioned, my top is plastic laminate. Is it safe to drive a screw almost through the plywood, i.e., about 1/8" away from the laminate? If not, how far away should screws stay away from piercing the top?

[Wayne Lomman]

4mm is my rule for being sure you won't see a pimple on the face of the laminate. It was the rule we always worked to when doing laminate kitchens.

My reference to height being a problem over time goes back to the reasons why there are standard height for furniture and cabinets. These standards suit the most people for most of the time without causing back aches or general discomfort. 1/4" won't matter but 1/2" will. As an example, our kitchen (which needs replacing when I win lotto or something) is about a half inch too low and we all get a crook back doing the dishes. Not so when at the son's place.

If you haven't laid the laminate yet, use Fred's bolt idea and just bog the counterbores before you lay the laminate. It solves all the problems. Cheers

[Ken Cobbing]

Unfortunately I have already laid the laminate top.

We are all quite a bit taller than "standard" height at my home, and I thought about increasing the height of the island anyway because of the aching back issue you mentioned. I think I'll just add some plywood under the T-bracket and have a slightly higher island vs. the kitchen cabinets.

I'll be sure to stay 4mm away from the face of the laminate. Great tip!