[harrysin]

Some time ago I carried out a lot of research concerning insertion depth of router bits. During this research I contacted all major router manufacturers and examined as many routers as I could get my hands on and the definitive answer "beyond 1" serves no purpose at all" 1" was the length of all the collets that I examined. The armature shaft of the Makita 3612/C has a VERY deep hole and so a plastic rod is supplied so the bits don't get lost inside!
This simple jig makes it easy to fit "O" rings on each bit so no guesswork is involved.

 

[harrysin]

As a point of reference, I just checked a Musclechuck collet and it is 1 5/16” from the top rim to the bottom of the collet. Assume then that the shank should be inserted accordingly. To follow Stick’s suggestion that would be at least 1 3/8”.

Not at all, study the photograph and you will see that only approx. the top 3/8" grips the bit close to 360° but to avoid run-out insert the bit 1".

 

[harrysin]

I don't think I've ever installed a bit that I didn't bottom out and then just slightly raise before tightening. If you have a straight bit that won't cut deep enough this way I've always felt you have the wrong bit. At the speeds these bits are turning you really want a firm grip on them. I've never had an uissue using this method.

Even two of the manufacturers, one who's instructions stated to FULLY insert the bit and the other that stated to fully insert then withdraw slightly agreed with me when I pointed out that below the depth of the collet, nothing was achieved.