The tricky part about Knife Hinges is that each blade of the hinge must be precisely mortised into the top and bottom rails and the top and bottom edge of the doors and there is no adjustment for positioning (unless you make the mortise oversized).  The blade is flush with the wood surface and the only part that is exposed is the pivot.  Each pivot has a spacer which precisely defines the top and bottom gaps for the inset door.  For appearances sake, the right and left gap of each door should match the top and bottom gaps.  Therefore, the door is sized to fit the opening with this small gap at each edge of the door.

With the hinges I’ve purchased (5/16″ Brusso hinges) the spacer is 0.048″, halfway between 1/32″ and 1/16″.   This means that the hinge positions for the right and left hinges must be precisely 0.048″ from the right and left legs, respectively AND, even more tricky, the center two hinges must be positioned 0.024″ from the center of the rail AND must precisely line up with the corresponding mortise on the opposite rail.

WHEW!

As I thought about what technique to use to make these mortises in the quarter sawn oak rails I realized that each mortise is identical to each other.  Some are mirrored, but the dimensions are identical.  Further, trying to chop out a mortise with a 0.048″ end wall or a pair of mortises with a 0.048″ wall between them, I knew that chopping with a chisel wasn’t an option.  That meant the best way was probably routing.

My first thought was to use my CNC Router to make a jig for a hand held router, but then, after a flash of light! I knew how to make these mortises!

The rails are 40 1/2″ long so I couldn’t cut all mortises in one pass (the CNC router is limited to 24″ of travel).  However, since the mortises on the top and bottom are identical but mirrored, it would be easy to design the pattern to cut TWO mortises at once with the two rails clamped together face to face!

Further, with the two rails perfectly aligned, the top and bottom mortises would be perfectly aligned.  AND if I took shallow passes on the cutting, then there was a good chance that the thin end and center wall could be maintained.  Finally, the FOUR center mortises could all be cut in one pass so the hardest alignment should be easy.

So, here ya go…

Here is the prototype, just to make sure the pattern and technique would work.

You can see the center mortises precise cut in the two rails.  Here is the fitting of the hinges to the mortises:

To fit the rectangular hinge, I needed to trim the 1/32″ radius corners.

Here are the two hinges mounted back to back. The spacing is exactly 0.048″!!!

Now it was time to do the REAL rails!  Here are the oak rails (with first coat of tinted oil) with all the mortises cut.

All eight mortises have been cut. Unfortunately, I messed up cutting the center mortises!!!

When I set up the rails to cut the center mortises, I reloaded the CNC program and forgot to tell the CNC software that the cutting bit was already mounted.  When I began the alignment to the center of the rails, the software tried to move the router lower than the bit would allow and I needed to realign the bit after it got pushed in slightly.  Unfortunately, I didn’t tighten the collet well enough and, while routing the first set of center mortises, the bit slipped and cut the mortise about 0.088″ deeper than it should have!  Pooh (this is what I said at the time, I’m sure of it…)

Ok, the secret to ‘fine’ woodworking is knowing how to cover your mistakes…

The two center mortises, one deeper than the other. In the foreground you can see a piece of oak that I machined to exactly 0.088″ thick…

Here are the two mortises repaired with the fillers. All mortises are back to the same depth and, after the glue dries, the excess will be trimmed off and stained. No one will ever know ;-)

To make the hinge mortises in the doors, the CNC router would be difficult since the mortise is cut into the ends of the 18 3/4″ stiles and I’d have to jury rig some kind of reliable mount with most of the door hanging under the modified CNC base plate – Yuck!

Instead, I used the CNC router to make a routing template that could be clamped to the door and hand routed with the trim router.  Here is the jig I made.

The CNC router cut the 1/4″ MDF sheet with mirrored openings for the top and bottoms of the doors.  The extra holes were used to temporarily screw 1/4″ bolts used as guide pins to align the center clamping block.  This gave me a reference edge for the face of the door and allowed the guide to be perfectly aligned when clamped.

Here are some underside views of the Jig.

Under side of the jig with slot for clamp.

Here is the jig clamped to a door.

Finally, here is the result of mortising the door with hinge inserted into mortise.

Finished Mortise with hinge inserted.

The “Good News Is”^[1] that I learned how to take care of this kind of problem a few years ago at a woodworking school in Hertford, NC.^[2]

The trick is to ‘refill’ the compressed wood cells (AKA ‘Dent’) with steam and they’ll inflate back to original size (more or less) and goodbye dent.  The photos below show the Before and After using the technique.

As you can see in the first photo, the dent is very pronounced and easily seen if not corrected.  My choices were:

1. Sand the leg until the dent disappears – not a pretty choice as the whole leg would have an obviously large depression.
2. Fill the dent with some kind of wood filler – this might work, but, over time, the filler would separate from the wood and fall off leaving an even worse appearance.
3. Drill out the dent and plug it – this could work, especially since I’m painting the vanity and don’t care about grain matching.  Unfortunately, being at the LHV, I didn’t have any plug cutters with which to make a plug.  Still a possibility, but only if nothing else works.
4. Steam the dent away…   What the heck?  It’s easy enough to try and I can always go back to choice #3 if it didn’t work.

Only problem was, to steam out the dent, I needed a clothes Iron.   Once again, our neighbors, Phil and Mary, came to my rescue and loaned me one.  Phil, being a curious guy and always ready to learn a new trick, decided to observe the process.

To steam out a dent:

1. Lay out the dented piece on a stable surface – one that won’t care too much if it gets wet.
2. Place a thin cotton cloth or, in this case, I used a folded over piece of Scott’s Rags in a Box, over the dented area.
3. Dribble a bit of water onto the cloth, making sure the surface of the wood is wetted.
4. Place an Iron, set to its highest heat setting, onto the wetted cloth and press down until the steam stops rising (no longer than this or you risk charring the wood).
5. Lift the Iron and the cloth and see how much of the dent remains.
6. Repeat steps 2-5 until the dent is sufficiently gone or no further progress is made.

After the wood dries, you may find that the dent has shrunk even more.  However, if you’ve wetted too much of the wood or repeated too many times, you may find that the area around the dent has swollen a bit.   If this happens, try to resist the urge to sand the swollen region flat.  If you do sand it, you may find that the area develops a depression after the wood dries completely.

That’s it!  Vanity Leg salvaged!

Installing these are actually pretty easy, if you make the right jigs.

Here is an example of a board that is bowed length-wise (over 3″ of bow) and width-wise (by about 1/4″).

Warped Floorboard

The first step is to flatten the board enough to get its groove positioned into the floor’s tongue.  To do this, align the end closest to the last installed board and use a small tie down block to hold the end in place.

One end held down with block.

Once that end is held down, you can step on the far end and tap the board into the floor’s tongue.  If the board isn’t bowed in any other way, then you can tap it home and staple it down, starting at the end furthest from the block.  However, in this case, there was a slight bow width-wise so I had to install a jig I made to press the bow against the existing floor.

Warped Floorboard showing gap

Jig to press bowed floor board into alignment.

In this case, since the bow was fairly small, it only took a couple of taps to wedge the board into position.  You can see that the jig has three pieces.  One is just a hunk of flooring to anchor to the subfloor.  The other two pieces are cut from a single scrap of flooring.  The cut is along the length of the scrap at a very slight angle (basically a 1/2″ taper from side to side).  With this taper you can compensate for up to 1″ of bow (I had some that were even worse than this – a crowbar comes in handy for these).   Normally I would make this kind of cut on a table saw since you want the edge of the cut to be straight and smooth.  Since my table saw is in storage until the Workshop is done (Classic Chicken and Egg problem) I used a jig saw and then a block plane to straighten and smooth the edges.

With the jig in place and the wedges shifted to press the bow against the existing flooring, it was a simple matter of tapping the board into position horizontally and stapling in place.

Perfect!

Warped Floorboard after installation.