Using a Stop Collar with a Forstner Bit

When you’re drilling multiple holes of the same depth — especially with a bit like a Forstner bit — the job becomes far easier when you add a stop device. While standard stop collars work fine on regular twist bits, they often won’t sit properly on the wider shank of a Forstner bit. A small tweak solves that problem and gives you accurate, repeatable depth without fuss.

Why this works

Forstner bits are prized for flat‑bottomed, precise holes. But when you use one for a batch of holes (say dowel holes, plug holes or pocket holes) you want each hole the same depth. The normal drill press depth stop works, but repositioning it frequently or losing settings between sizes becomes a workflow drag. By mounting a stop collar directly on the bit, you fix the depth once — then drill multiple holes at that exact depth with confidence.

The practical tweak

Here’s how to make it work:

• Choose a stop collar sized to your bit‑shank diameter. If the collar inner diameter is too small or too tight, it won’t sit right on the Forstner shank.
  

• Drill a washer or spacer out of thin plywood (6mm or so thick) whose bore fits your shank. Slide the spacer onto the shank so it sits between the collar and the bit’s cutting edge.
  

• Slide the collar and spacer assembly down to the height that corresponds to the depth you want, then tighten the collar.
  

• Now, when you drill, the collar/spacer will ride on the surface of your work‑piece (or the bed of your drill press) and prevent the bit from cutting deeper than the set depth.
  
  

How to use it in your workshop

In your Johannesburg weekend‑workshop this becomes a simple routine:

• Set the bit into the drill press or bench‑mounted device, clamp it securely.
  

• Slide on the plywood washer/spacer then the stop collar and lock it at the correct height.
  

• Test the setup on a scrap before drilling your actual piece to confirm that the collar stops the bit at the desired depth.
  

• Drill your holes. Every hole will stop at the same depth without having to reset anything between holes or between batches.
  

• Change bit size? Repeat the spacer plus collar setup for the new size.
  
  

Benefits you’ll see

• Consistent hole depths means less cleanup, less variation, and better fitting parts.
  

• Faster set‑up and fewer mistakes: you don’t waste time repositioning a depth stop on the press.
  

• A small inexpensive tweak — just a collar and leftover plywood — gives a big boost to accuracy.
  

• Works especially well in repeated tasks or production‑style work in a small workshop setting.
  

In your workshop, where you may not have an elaborate jig or high‑end drill press with micrometer stops, this trick brings precision into reach. Turning a standard stop collar into something that works with a Forstner bit is about smart adaptation rather than buying more gear.

Once you’ve tried it, you’ll find yourself reaching for the collar + spacer setup whenever depth matters. It becomes part of how you work — not just what you build.