Replies

1. 
   hammer1 | May 11, 2007 09:51am | #1

   If you are drilling out a 1" mortice, you should use a 1" bit. Forstner bits are designed to drill overlapping holes but a 1/4" one will likely run off. With any bit, you should clear the waste often. Bits can heat up pretty quickly and loose their edge. It's not unusual for bits and even morticing chisels to run towards less resistance. To avoid this, you do the two ends first, then remove the center.

   Beat it to fit / Paint it to match

1. 
   Hendo | May 11, 2007 10:16am | #2

   Thanks Hammer.

   I didn't make the mortise dimensions clear -- it is one quarter inch wide, by an inch long and an inch deep.  So the quarter-inch bit was the full width.

   I did do the ends first.  But in hindsight I screwed up when I then did a hole in the middle;  which didn't leave enough meat between the holes for the bit to bite.  Had I done one less hole I think it would have worked out much better.

   Live and learn!

   Thanks for your comments.

   -Tom Henderson, Ventura, CA

1. 
   philip | May 11, 2007 12:58pm | #3

   You are now on the right track- the spacing is the thing, but as long as that centre prong has sufficient material to support it you should be able to get away with quite a lot of overlap. I suggest you experiment with different woods also, and different drilling speeds.If you gauge a centre line with a cutting gauge this helps, even if the work is against a fence.
   Somebody mentioned forstner bits losing temper from overheating- this may only happen to cheap imitations- the real thing is made from high speed steel and is immune to woodworking "heat". (Quality pays).Philip Marcou

2. 
   mwenz | May 11, 2007 04:37pm | #4

   The Forstner is fine. But as you found out, dimensions of the mortise and bit can make it easier or harder for the bit to follow.

   Perhaps one each defining the ends and one just in-board enough on each end to have little overlap would have made that easier.

   However, if the lines are scribed and not mearly drawn on the surface to define the mortise, and I desired to waste the mortise material first with a bit, I would have opted to simply drill the ends and the center as you did and chisel/pare out the remainder to the scribed lines. Faster and to me an easier method.

   Sounds like you did a good job, though--so simply keep experimenting on how much overlap you can get away with for a given bit size. Larger ones can handle greater overlap.

   Take care, Mike

2. 
   SARGEgrinder47 | May 12, 2007 03:26pm | #5

   Morning Hendo...

   It would be hard to find fault in any advice given to you. But I will join Mike on drilling the ends.. center and paring the rest. I have found when you have to significantly over-lap, there is always an outside chance that the bit will wander to the side and the paring will avoid that.

   Even though a slight rupture of a straight line would be hidden by the shoulder of the tenon after assembly in most cases, if I set out to cut a rectangular hole anything short of a rectangular hole is un-acceptable. Nobody would see that mis-cue, but I know it's there and that just bugs me for whatever silly reason. On the other hand... life is short and "roses have thorns"as someone once said. ha.. ha...  ha..ha..ha...

   Regards...

   Sarge.. jt

   
   

   ---

   Edited 5/12/2007 8:27 am ET by SARGEgrinder47

3. 
   ScottNewsom | May 12, 2007 04:08pm | #6

   Hendo,

   If you are going to be doing lots of mortises (or even just a few), a mortise attachment is a worthwile addition to the shop. The hollow chisel mortising bit makes short work of mortises. I was doing a big project a few years ago that called for several mortises and decided to get a dedicated mortising machine. I don't know that I use it enough to justify having it versus the drill press attachment, but it is a sweet tool as well. Got the Jet model.

    

   Scott

4. 
   Dave45 | May 12, 2007 04:12pm | #7

   A brad point bit would probably work better - and the longer the brad, the better it should work. 

   A Forstener bit is designed to cut a flat bottomed hole with very clean sides.  The center "spur" really only aligns the bit until the rim begins cutting.  It's the rim of a forstener that keeps the bit aligned and it works fine until you do overlapping (or open sided) holes.  Then, the part of the rim that isn't buried in the workpiece sees less resistance and the bit will want to "skate" in that direction.  You can minimize the skating by tightly clamping your workpiece and feeding the bit very slowly, but it's still going to want to move on you.

5. 
   ClarkCustoms | May 13, 2007 01:57am | #8

   Tom,

    I started making mortise and tenon joints traditionally with a brace and bit and with a hammer and chisel (No I'm not real old I've always tried to do things with hand tools first then move on to "POWERTOOLS" ) A few years ago I purchased a dedicated mortiser. I have to say I wish that I would have started with the power mortiser first. Mines just a Delta bench top mortiser but it does an excellent job doing what it's supposed to do. If you have any intentions of creating projects that require mortise and tenon joints then before you purchase one go to a local high school or college and ask if you can try theirs before you buy one of your own that's what I did when I was trying to decide if I was going to put out the $$$$$ for a tool that only did one function but once I used the schools the rest was history.

    Good Luck,

   Sincerely,

   Jim at Clark Customs 

    

1. 
   Hendo | May 16, 2007 09:00am | #9

   I would like to thank everyone for taking the time to post your thoughtful replies. 

   Reducing the hole "overlap" fixed the big problems.  The second try fits a LOT better than the first, although there is a loooooooong way to go before things really fit properly.

   So thanks again for taking the time to help educate me.  I really appreciate it!

   -Tom H. Ventura, CA

1. 
   TomT226 | May 16, 2007 02:17pm | #10

   Lots of good advice here.  I do it a little diffently.

   I just draw a centerline and end lines of the mortise, and wrap the end lines around the workpiece.  Chuck up a 1/4" BP bit, and set the depth, and drill out most waste.  Chuck up a 5/16" straight bit in the router table with a tall fence with edge lines of the bit scribed on it.  Set the fence +/- to the center line of the stock, and run it into the bit. Pull it out, and run it in the other way.  For mid piece mortises, plunge the workpiece down, back and forth, flip and do the same. Perfectly centered mortise. Cut the tenon to fit the mortise.

   Goes pretty fast, and no centering errors as you may have with decicated mortisers.

   BTW, DO NOT use a spiral bit because it may get away from you. 

6. 
   Rich14 | May 16, 2007 07:06pm | #11

   Tom,

   I believe you have a slight misunderstanding of the role of drill bits in "helping" cut mortises. I'm sure you're aware that a mortise cut completely by hand is done with a mortise chisel and a bench chisel. The heavier mortise chisel removes most of the material, forms the sides and (as the last few cuts) chops the ends exactly to the layout lines. Then the bench chisel is used to clean up the cheeks and corners as needed. The mortise width is ALWAYS defined by the width of the mortise chisel.

   It's a lot of work to remove all the wood tissue with the mortise chisel and a "shortcut" is to first "waste" (rough out) most of that material with a drill, then come back with the mortise chisel and bench chisel. But the drill bit is NEVER the full width of the mortise and is not meant to establish that dimension. It's just meant to remove most of the material, without regard to exact placement of the bit side to side or hole to hole. Material must be left on the cheeeks and at the ends for final (exact) paring by the chisel(s). The operation is most frequently done using a dowel drilling jig, but it certainly can be done on the drill press.

   The only time a mortise is cut to it's desired width (and length) using a rotating bit, is when you do it with a mortising bit/chisel combination in the drill press, or use a router in a jig with a router bit or end mill.

   Rich

1. 
   TomT226 | May 16, 2007 07:54pm | #12

   IMHO, I think people make mortise and tenon joinery much more difficult that it really is.  I build a lot of face frames, and I never use a mortising chisel, I fit the tenon to the mortise.  I leave the ends rounded from the router bit and round off the tenons.

   Through mortises are another aspect.  They need to be sharp and square for appearance.

   As long as there is good glue distribution and a snug fit, do it the easy way.... 

1. 
   Rich14 | May 16, 2007 08:34pm | #14

   Tom,

   I agree. I cut my tenons to fit my routed mortises. I also cut my tenons to fit my mortise chisel's width when I "hand cut," which isn't that often anymore. To make it even more simple, I think "loose" tenons are as strong as "real" mortise and tenon construction in just about anything short of a heavy entrance door.

   Rich

2. 
   joinerswork | May 16, 2007 08:17pm | #13

   Rich,

   FYI, it is a viable way to cut accurate mortises, to drill a row of holes the exact size you want the mortise to be, using a drill press, then to pare the sides and square the ends til they are just tangent to the edges of the holes just drilled.  I've done it many times.  If you have a reasonably sharp bit that doesn't want to wander, and a reasonably sharp chisel, it's easier to pare to the edges of the perfectly plumb holes than to pare an oversized mortise perfectly plumb somewhere slightly beyond the holes' perimeter.  For me anyway.  If I'm not gonna rely on the accuracy inherent in a drill-pressed hole, I'd rather just chop the thing altogether and be done with it.

   Ray