Routing Mortises: How Much Material Per Pass?

[Hans Braul]

When routing mortises on a router table, how much material can you remove in one pass of the router? I posted a problem with my new router earlier, where I couldn't get a smooth cut.

http://www.sawmillcreek.org/showthread.php?t=56277

I am now finding that if I take barely 1/16" per pass, I can get acceptably smooth results, except when I reach the end stops, where the bit occassionally grabs. I am using a router table with stops clamped to the fence to limit the length of the mortise. With my previous router I was removing over 1/2" in a single pass, with good results. I'm pretty convinced I have a defective router since I can measure 1/16 deflection in the bit when I flex the motor end with firm pressure.

SO .... my question to you: how much can you remove in one pass? Let's say the bit is 3/8" cutting diameter and the wood is cherry and you're cutting a mortise.

Thanks for your input!

Hans

[Mike Cutler]

Hans.

I'd go about an 1/4"-3/8". A 3/8" diameter bit isn't that big and won't take alot of side force before it deflects or breaks. I don't try to go real deep with straight cutters personally, so I may be a little conservative.
I'd also make sure the bit has bottom cutters on it.

[Cliff Rohrabacher]

I'll say that it all depends.

It depends on a variety of factors such as:
1.) the material
2.) the router bit it's quality number of cutter-blades and sharpness and grind.
3.) the length of the bit extending from the collett (deflection)
4.) the quality/condition of the router especially its bearings.
5.) how firmly the workpiece is being held.

[Doug Shepard]

Many years ago I read somewhere that you shouldn't try to go more than half the diameter of the bit in any one pass. I think that was being a tad conservative but I do know that most any time I've had problem issues is when I've tried pushing or exceeding that envelope.

[glenn bradley]

As Cliff says; it depends on a few variables. My rule of thumb is to remove about a 1/4" x 1/4" area. That is to say I would not generally cut deeper than 1/4" with a 1/4" bit. an 1/8" with a 1/2" bit or thereabouts. This changes with profile, material etc. I also reserve a very light pass as a final clean up on detailed profiles.

[David Dundas]

It is much easier to rout mortises if you use the proper bit for the job - that is a spiral bit rather than a straight bit. With a spiral bit 1/4" deep passes work well.

I would also suggest that it is much easier to achieve good results, and also much safer, to rout mortises using a jig on which a plunge router is used upright and cuts the mortise through a window, such as this one. With this jig, you use the router's edge guide as a fence, and clamp the stops in position using the built-in scales to ensure that the mortise is the right length.

David

[Mark Singer]

I do the full area and drop about 1/4" each pass using an upcut spiral...hand holding the router

[Hunter Wallace]

Darn it, Mark said it before I could...AGAIN:D