Enlarging holes in PT wood

We have docks with wooden Walers. I need to enlarge the existing 3/4" holes to 1-3/8" to accommodate some new recessed nylon nuts. I figured I could use a step bit. I've used a spade bit in the past but it does produce a very nicely rounded and centered hole as it can jump around: I'm enlarging these holes as the boards are still attached to the dock so I'm leaning over the dock and drill horizontally.

Does anyone have any tips or recommendations or is a step bit the way to go? I need to get to a depth of about 1-1/2" so I'd prefer to only have the 1-3/8" width stop at that depth so I can not enlarge the inner Waler hole beyond the current 3/4" hole.

 

Take a piece of scrap wood and drill it to the new size that you want. fasten it to the wood that you want to drill and use the scrap as a drill guide to keep the spade bit from jumping around.

 

You don't use step bits in wood. You could use a hole saw with that method above... drill a hole in your guide block then clamp it over the hole. Drill to the appropriate depth, pull the hole saw out and use a chisel to clean out the waste left in the hole. Or better yet, use a forstner bit to clean out your bottoms perfectly.

1 3/8" forstner bits (35mm) are commonly used to drill perfect holes for cup hinges for cabinets.

 

Actually a step drill would might be a good choice, here is a 1/4 x 1 3/8 bit from McMaster that would get you through the wood thickness, a bit pricey but if you had many holes would get the job done!

https://www.mcmaster.com/5910N15/

 

Op wants to drill a 1 3/8 diameter hole 1 1/2" deep but doesn't want to enlarge the 3/4 hole. Not sure how a conical step bit won't enlarge the rest of the hole. ???

I would assume the op wants a flat bottom hole for a washer behind the nut. That's what a forstner bit does best.

 

Yeah. So currently there are two overlapping Walers made of various sizes: sometimes two 3x or a 3x and 2x, 4x and 3x. I just need to go from the outside to the 1-1/2" depth and leave as much of the remaining 3/4" diameter hole as I can as a 3/4" threaded rod runs through it to meet the newer nylon washer/nut combo that goes into the wood the 1-1/2" depth.

The concern was how the spade bit jumps around. The outer waler board already has a larger diameter recess to allow for the nut/washer to reside without protruding out from the dock. See image showing what I mean. So I'm not sure I can have a drill template work to hold the hole saw or forstner in place.

 

You should be able to clamp a drill guide to the walers if you make the guide the same width as the board.

BTW I had to look up waler. I don't think I had ever heard it before even though I've had a couple of docks, one of which had walers.

 

Looks like your template could be clamped from top to bottom.

Bud

 

I doubt it even needs to be clamped. If they are all the same distance from the top, your guide board (that you will drill through) just needs a stop on top so that it rests on the top of the deck as you drill. You could even make that top stop long (like a 2'x2' piece of of 3/4 plywood) so that you are laying on TOP of it as you drill. It won't go anywhere.

A spade bit would likely wobble around once its through the guide hole because it depends more on the center guide (which will be in a void) but a forstner bit would not.

Or fasten one of these onto the face of your guide board and your holes will all be perfect and the same depth thanks to the jig and the stop collar on the forstner bit.

But one question... will all the threaded rod and nuts in the photo be in there as you are doing the drilling? Or are you adding an additional layer on top of what is pictured? I don't completely understand what you're doing.