End to End Joint - puzzle kerf?

[bwente]

I am trying to join two pieces end to end. First I was going to make them flush, then decided to make it at an angle. Then realized it would be easier to glue if it "locked in place like a jigsaw puzzle piece. It was too loose and I added kerf and got a satisfying fit. The problem is that it is longer than what I measured. Is it the kerf making it longer or the glue?

[wesleyjames]

Did you add the full kerf to both sides or only half to each side?

You should only be adjusting for half the kerf on each piece.

1/2 kerf + 1/2 kerf = full kerf

This may be good enough but if you wish to get fully clever, cut one of the parts mirrored. Then when you flip the mirrored part into the correct position, the shape of the cut(a slight angle due to beam focal point and defocusing past the optimal point) will match up to the other part.

[bwente]

I added the full kerf to one end. ( I was lazy ) )

You might be right about the angle. The wood was thick, 5mm and used .5mm kerf (which seemed like a lot).

[dehne1]

I use this technique in Illustrator quite often and have developed a process for it that I just follow by habit. I do the design drawing of the parts at full dimension, completely ignoring kerf compensation. Then when I’m ready to do the cutting, I make a copy of all the pieces on a new layer, make the “outside” paths red strokes with no fill and the “inside” (hole) paths blue strokes with no fill. I then use path offset to turn these into kerf-compensated cut paths. When I iterate on the design, I always recreate the cut paths for all the parts from the full-dimension part drawings. It just takes a few seconds and ensures that the set of cut paths all match the current state of the part drawings.

For example, in the drawing below, the black lines are the full-dimension drawings of the parts. I then offset the paths (in AI, its Object/Path/Offset path) to create the kerf-compensated cut paths. For “outside” paths, shown in red, the offset is positive. For “inside” paths, shown in blue, the offset is negative.

Here, the kerf compensation is greatly exaggerated, of course. For 3mm Baltic birch plywood, an offset of 0.12mm gives me a “press fit.”