# Downcut vs compression bits for mortising



## Mike_C (Jul 11, 2020)

Am I correct to think Downcut spiral bits cannot be used for plunge mortising? Only for full length slots or dados...

Can I force plunge them like I do with straight bit by dragging them along as I plunge?

Price difference between them and compression "mortise style" bits is quite high and the compression bits are not good for shallow dados so that means buying both 

Thoughts?
Mike


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## kp91 (Sep 10, 2004)

Down cut spiral will work for mortise cuts, just make multiple passes increasing the depth as you go. It doesn't Clear chips as well as an uncut, but the shallower passes will help with that


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## Mike_C (Jul 11, 2020)

Thanks @Doug

I thought pure Downcut spirals cannot plunge well....

M


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## difalkner (Jan 3, 2012)

Are you wanting to know for handheld or CNC work, Mike? I use downcut spiral all the time on the CNC although I do my best to ramp rather than plunge (plunging is hard on the equipment). My ramps are steep, though, and typically 45° to 75°, so they're almost like a plunge but not quite as abrupt.

David


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## Mike_C (Jul 11, 2020)

@David

Yeah - I meant handheld...

M


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