20MM Dog Hole question

I am making a spoil board to use with my existing 20mm dogs. I have a spoil board file I paid for that is made for 3/4in dogs, but the hole is oversized by about .020in. I am adjusting the holes in my software to use the metric dogs, but am questioning the .020in oversize. It seems a little loose?

Should I oversize the 20mm holes or just cut them exactly to 20mm ?

For my 3/4" Kreg bench dogs, I made the holes 0.765" — or 0.015" oversized — and they are perfect. But I didn’t get this number from the internet. I created a test file with a number of different size holes and checked to see which worked best before cutting into the spoil board. I would highly recommend you do the same if you want the best results.


I use the 20mm Bench Dogs. Mine have threaded centers, so I have a little 8mm threaded knob that helps pull them out of my MDF wasteboard.

Like Matticustard, I did a test piece making holes, varying the diameter by a couple of thou, until I found the best snug fit.

You don’t want them super tight as MDF will vary a little with changes in humidity.


Be cautious of your bit selection, both programming and physically. 6mm versus 1/4", etc.

As already mentioned, test holes will get you the right answer. Be sure and use the same bit when you cut the Waste Board.