Plunge router mortise - straight bit?

[Tom DiBiasio]

I am following a FWW plan and video series to build a floating top hall table. The legs are joined to the aprons and stretchers with mortise and tenons. In the video series the author uses a plunge router to cut the mortises, and uses a spiral upcut bit. I don't have a bit like this and with the cost of the cherry wood and a few other bits and guide I already had to buy, I am stretching beyond the project budget. I got to thinking today that these spiral bits are relatively new and was wondering if in the past these types of cuts were done with a standard two flute straight bit? I know chip ejection is one of the primary benefits, along with the ability to plunge directly into the ends of the mortise. Can anyone offer guidance or experience with cutting mortises with a straight bit, or should I simple put the project on hold until I can afford to get a spiral bit? I have one extra "test" leg I could try it on but thought to ask here before just jumping into that and ruining my extra leg safety net.

TomD

[Mike Cutler]

Tim

Thousands and thousands of mortises have ben cut with a two flute bit with bottom cutters, and without.( You want the bottom cutters to plunge the initial bit start.) A spiral bit makes it nice for removing debris while you router the mortise, but it's not imperative that one be used.

If you only have a few mortise to do, you could use a standard two flute bit without bottom cutters , but you would want to start the bit out in a drilled hole, or make repetitive shallow passes, increasing the mortise depth.

You're good with what you have to work with. :D

PS
Have fun shoveling out this am. I'll get to my driveway in a little while. I'll let the neighbors wake up first. ;)

[Curt Harms]

What Mike said. Here's an example of a plunge cutting straight bit.
http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_plung.html?zoom_highlight=plunge+straight+bit

Some people use TiN coated steel spiral mill cutters designed for cutting ferrous or non-ferrous metals, they're cheaper than carbide spiral upcut wood bits. I have no experience with those.

[glenn bradley]

I have used up, down and two-flute straight bits for mortising. Upcut pulls the spoil out better for larger mortises (mortisi?), downcut gives a cleaner entrance if the edge of the hole will be seen, straight bit does fine if sharp (like any other cutter) so I wouldn't hesitate. If the straight bit is old or worn I would look at the budget I am about to exceed and ask myself if all my time, effort and money to date are not worth a little more to avoid screwing it up.

[John TenEyck]

Take shallow passes and you'll be fine. By shallow, I mean 1/8" or less. Seriously. Even with a spiral bit you take very shallow passes. At least you do if you want the resultant mortises to have smooth walls.

John

[Charles Lent]

Spiral bits will produce a mortise that is closer to the dimension of the bit, but a standard 3 flute bit with a bottom cut feature will do the job. Just take it slow and keep the chips cleared. Make the cut in multiple passes at slightly increasing depths clearing the chips after each pass and you should do well. Compressed air blowing into the mortise while cutting it will help clear the chips and make it easier to cut deeper with each pass.

Charley

[pat warner]

A standard brazed on carbide (to HSS) bit will do it.
(Spirals are not silver bullets.)
You must sweep as you plunge; a little more skill.
But cheap & effective, nevertheless.
Even tho there are hundreds of the non-spiral contestants, I would not use one cutter width cutters. I'd choose something smaller than the prescribed mortise width.
If you do, you can plunge the cutter in the center of the mortise, (the most stressful part of this), let it bend and moan.
Then as you approach the perimeter you're only taking a modest amount of waste and the walls & ends of the mortise will be chatter free.