:smack::smack:I cannot screw the stair treads together to make a 4’ square garden bed. I tried predrilling the sides and ends but I cannot get the screws from one side to go into the other side. I am using a Ryobi battery operated drill/screwdriver tool. Tried every torque from4-16. Should I have simply nailed them together? I am soo frustrated, and cannot get them together or brace these treads. Can anyone help me? 
Can you explain the plan a little more extensively? Because I’m not sure I understand what you’re trying to do or what the problem is. You have oak stair treads you’re trying to put together to make a raised bed border, right? And you’re trying to screw them together at the corners of the bed or trying to screw multiple treads inline to make the sides of the bed? Is this just plain oak? Or is it treated? Because if it’s not treated wood, it’s going to rot fairly quickly where it touches damp soil. Anything else from pretty much anyone else is going to have to wait until you explain the design on this and what you’re trying to do that you’re having trouble doing.
Try using some metal brackets to hold them together.
If I understand correctly, you can’t get the screws to go into the end grain despite pre-drilling.
You probably want to pre-drill again using a slightly larger bit.
As previously mentioned, oak will tend to rot in the application you are attempting. You might try to set your oak box on top of a “foundation” of landscaping timbers. Landscaping timbers are relatively inexpensive at any home improvement store.
But don’t use treated lumber if you’re planting vegetables for eating. That’s some nasty stuff they use to keep the damp from affecting the wood.
Rotting issues aside, when you pre-drill for a hard wood like oak, you need to use a drill bit that is just about the same width as the screw’s shaft, only the threads should be outside of the drilled hole. The hole should also be as long as the screw. You should also use a countersink so that the screw sits flush.
I would not worry much about treated lumber, at least new treated lumber. They’ve stopped using arsenic in the treatment years ago.
Modern pressure-treated lumber is perfectly fine for use in a raised-bed garden.
Thank you both. I was not aware of that.
Yeah, they changed the chemicals that they use back around 2003. I’ll try to post more info when I get in front of a real PC.