Festool Domino Machine Instruction Manual - page 7

into the sides of the 

mortise slot, but the 

slot is longer than the 

width of the tenon al-

lowing some assembly 

adjustment room side 

to side.  The third width 

setting increases the 

oscillation to 23.2mm 

resulting in a 28.2mm 

mortise slot which pro-

vides close to 10mm 

side to side adjustment 

room.

The ability to vary the 

slot width is key to 

many of the Domino 

machine attributes.  As 

indicated, at the narrow 

setting the domino tenon fits tightly into 

the slot.  At the wider settings the thick-

ness of the domino tenon fits tightly into 

the mortise slot front to back, but the 

domino tenon is free to shift side to side.

When you cut a tight mortise (width knob 

at the narrowest setting) at the same lo-

cation on two different boards, that one 

M&T joint will keep the two boards 

aligned as desired.  Placing wider mortise 

slots along the same face of one of the  

two boards means the remaining domino 

mortise slots can be cut with some mar-

gin for positional error while still allowing 

the joint to close properly, a great advan-

tage over dowel joints where the posi-

tional accuracy must be dead on or the 

joint simply will not close up at all.

Since the majority of the strength of a 

loose tenon joint is derived from the fit 

and glue surface on the faces of the mor-

tise slot and the faces of the tenon, little 

strength is lost when the width of the mor-

tise is greater than the width of the tenon.

We will see numerous examples of when 

and where you want to use tight fitting or 

over-width mortise slots as we progress 

through the manual and show actual pro-

jects in process.