Cutting a Through Slot
  Re: (...)
I applaud Page 23 of Woodsmith #226 for showing a method of cutting a through slot with a Forstner bit using multiple passes of course. They then recommend using a chisel to smooth out the sides of the slot. The chisel works, but it's tough to really get the sides smooth, especially when working with really hard wood. Your chisel's edge is usually going across the grain most of the time.

Lacking a mortising bit, I elected to try another technique on a 4" long slot that I needed. I used a fence and dropped the bit to the far right of the rough-drilled slot, lowering it about 1/4" down into the slot. Then I slid it all the the way around, right to left and then to left to right on the other side of the slot, cutting with the bit's lifters while moving the workpiece. You may get by with only a right-to-left pass. Then I stopped the motor, dropped the bit down another 1/4" and repeated until the sides of the whole groove were smooth. To drop the bit down, I raised the DP's table, being careful  not to swivel the table.

The rough sides will then be "routed" much smoother. This method also works to enlarge the slot a tad. Just nudge the fence back a little. You'll get the hang of it once you give it try.
Rip to width. Plane to thickness. Cut to length. Join.
  Re: Cutting a Through Slot by Edwin Hackleman (I applaud Page 23 of...)
If I am understanding this, you want a smooth sided mortise with parallel sides. You don't mention depth, so I am going on a limb it's not that thick. You do not have a traditional mortise bit for a DP, or mortising machine.

This has worked for me on through, and non through passes from 1/2" deep, to near 3". Easy Peasy. All that is at hand is centering your bit, and making the pins the same distance from center on both sides. You drop the bit into a drilled hole, and twist so both pins contact the sides of the work piece, at that point you are centered. All you lack is knowing when to quit routing.

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Video below

Worst thing they can do is cook ya and eat ya

Wink    Re: Cutting a Through Slot by Edwin Hackleman (I applaud Page 23 of...)
Align and clamp a guide block to edge of the slot and use a chisel to clean up sides.

Using a SHARP 2" chisel you'll already be done by the time you put your goggles, ear muffs and find the extension cord.

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OR, just buy a mortising bit and make a jig much better than drilling out.
  Re: Cutting a Through Slot by Edwin Hackleman (I applaud Page 23 of...)
it really depends on the size of your slot.  I made some 1/4" wide x 12" long x 3/8" slots in various ways. and chiseling worked the best for me. A cutting marking gauge and drilled just at the ends.  If the back was a show face, I'd mark that too.  Really annoying if the router can wander.
  Re: RE: Cutting a Through Slot by Steve N (If I am understandin...)
The grooves I cut were 1" deep in 1" thick walnut ( all the way through), 1/2" across, and x 4" long. I also have a bit for the DP that will soften the outer edges of the groove. Using a router for this operation tends to give me the creeps because it cuts so fast.

I like the idea of using the Forstner bit that Woodsmith published once again in #226. I've made quite a few mortises this way and dead smooth sides are really not that crucial most of the time. I just decided to take a shot at this to see if it could be done. I found out that it's possible and you don't need to pick up the wide chisel.

So, I thought I would pass it along, but only because I was successful and my drill press didn't seem to mind. If you would like to see Pics of the final grooves, please holler.
Rip to width. Plane to thickness. Cut to length. Join.

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