How deep do you cut mortises for dominos?

[Toller]

I actually did search on this before asking.

How deep should I set the machine for a 10x50 domino?
Is 25 adequate, or should I add some slop on one or both sides?

In a related question...  If I am setting two dominoes and make the second wider to protect against error, should it be wider on both pieces, or is one enough?

 

[Brice Burrell]

  Toller the 25mm depth is the setting you want for the 50mm dominos. Try your tape on a 50mm domino and you'll it is a little short, around 49mm or so. And both ways will help align the work, I tend to use a wider mortise in both pieces.

 

[Eli]

I pretty much always use the medium width for both pieces. Makes it so much easier to put stuff together. I don't have any long term reports on whether it affects the strength, but everything seems to be fine so far.

 

[Tim Sproul]

I've not had problems setting depth to 1/2 the length of the Domino.

You want both mortises wide if you're doing a string of them.  Otherwise you can't use those registration pins.

 

[Rocker]

If I am using twin mortises in a joint, I use the narrow width for three of the four mortises, and the medium width for the last one. I see no need to make two of the four medium-width.

I have a gripe about the index pins, which I believe that most Domino owners share - that they are too far apart. The inner edge of the pins is 37 mm from the mortise center; so, if the index pin is used to locate the second mortise, the outer ends of the mortises will be 70 mm apart for an 8 mm cutter and 73 mm apart for a 10 mm cutter. This means that the workpiece needs to be a minimum of about 95 mm wide before the index pins can be used. It would seem to be quite feasible for the index pins to be located 27 mm from the mortise center, so enabling the workpiece to be 10 mm narrower.

I find that in practice I rarely use the index pins, except when I am milling the mortises for back slats in the back rails of a chair. For table-top glue-ups I just mark the domino positions with a pencil as for biscuits.

Rocker