Wednesday, December 14, 2016

Envelope Table Mechanism


 A few years ago, I visited an antique store that had a small envelope table with four triangular leaves meeting at the center that opened up from the center to reveal a card table, or so I was told. The table was in the closed position and I kindly asked the salesperson if I could open the table to see the inside. Unfortunately, she said, "No." I stared at the table quizzically for a moment, both to figure out why the lady was so rude and to figure out how the leaves would open up since they were so tightly fitted in together. There were no opportunities for photos. Not understanding the construction too well, I hadn't really thought of building this table. I have never seen another table like this in person. 


Then, at our local woodworking club, I picked up a dog-eared copy of  the October 2010 issue of Woodworker's Journal in which Ralph Bagnall provides detailed instructions for the construction of the table. I used his plans to construct my table. There is an abbreviated version on the Rockler website and he also sells more detailed plans here. Unfortunately, he too was flummoxed on the mechanism of how to open the leaves. His solution was to place an elegant brass pull on one of the leaves.


Upon reviewing a few images of other antique tables online, there seemed to be a small hole in one of the fan-shaped corner blocks. (If you look at the linked image, the small hole is near the top of the image.) Somehow, this hole was probably related to popping up one of the leaves.



My version of the envelope table





Here is my version of the table leaf pop-up mechanism:






One leaf will pop up when the table is rotated a few degrees. This will allow you to open the table leaves.

Here is the base on which the table top rests and rotates. There is a hole in the center of the base (not pictured). The sloped metal plate will push up a metal plug when the table rotates, thereby popping up one table leaf just a bit to allow its opening.

This is the table top now placed on the base (with the felt central section removed).The table top consists of a central MDF section surrounded by a frame that is attached to the four triangular leaves with sewing machine hinges.All of this sits on the base pictured in the photo above this one. Note the bolt in the center of the table top which runs through the hole in the base. Table leaf lifting mechanism, bottom left.


Stepped hole  (ignore the mess up hole to the left) in the fan-shaped corner block.

Magnet, left, and steel rod, right, which are placed in the stepped hole.


Groove on the underside of the table frame to accommodate the sloped metal piece on the base when turning the table. The block on the upper right helps align the table to the home and 45 degree positions. To  locate the correct position of the groove, place the table top in position using the center bolt for alignment along with the sloped plate. Rotate the table top a few times back and forth to scribe a line. The groove can then be cut away using an oscillating saw or a mini saw blade using a couple of teeth placed on the end of a rod and rotated around an axis in the center of the table. The metal plug is seen intersecting the groove.



The sloped plate from an old saw blade was cut with a multi-directional hack saw

Final shape of sloped plate prior to insertion into its groove.
If you happen to have one of these tables, I would be curious to see if the mechanism is similar.

Monday, October 17, 2016

A Miter Jack Of All Trades


I am the eggman, 

They are the eggmen

 - I Am The Walrus, The Beatles



Modifications to a miter jack for accurately cutting both miters and tenons

Modified miter jack


Modified miter jack rear side.
The magnetized flat surface provides a reference for 90° cuts  such as tenon shoulders or removing the waste on the outer edges of the tails of a dovetail joint.

The Purpose of a Miter Jack

Suppose you are making a frame and panel door and would like to make a miter joint for a stuck moulding rail that has a tenon.

This rail contains not only the tenon, but a stuck moulding with a miter.
A stuck moulding is a moulding that is integral to the piece rather than applied or glued
A combination vise and shooting board, the miter jack is quite helpful for creating both the miter and the tenon shoulders of the rail. The miter jack is most commonly used along its 45° surface to make a miter by clamping the stock in place and removing the mitered material with a saw, chisel or  plane.

Uses  of a miter jack:

  • Shooting a wide miter that might be too wide for your shooting board.
  • Creating the miter for an integral or stuck moulding for a rail and stile frame.
  • Creating the miter for the upper and lower beaded strips for a cockbeaded drawer. (Since the upper and lower strips are wider than the side strips, a miter is present along only the front portion).
  • Creating or cleaning up the miter of a dovetail joint that has a mitered shoulder.
  • Paring the miter of a full blind or hidden dovetail.
And that is just for the angled side. There are more uses for the rear portion as noted below.


Miter jack
 


Behemoth miter jack.
Note that this miter jack has a vertical surface in the rear, unlike the smaller one above.
The vertical surface can be used for 90° cuts.


Each of the above miter jacks are useful, but have some limitations. The smaller one can only be used on its angled surface to make miters. The larger one is unwieldy and requires a massive chisel or slick.

People who have not used a miter jack often ask how the surfaces don't get marred when using planes, saws and chisels. To preserve the surface, you could:
  • Apply cardstock or wood to the angled surfaces and replace them when damaged. 
  • Use a saw with no set
  • Be careful and slow when using a plane or chisel
In general, the above works to prevent the surface from becoming damaged. But, every now and then, the surface becomes dinged despite my efforts. For the modified miter jack, I went about adding a couple of features:
  • Embedded magnets and steel plates on the rear 90° surface that grabs the saw for a flush.cut
  • A modified block plane with rails attached to the plane 
  • A surface protector made of ash for the mitered worksurface

Building the souped up miter jack

A 3/4" dowel is made using the Stanley 77 dowel maker

The end of the square stock needs to be tapered to pass through the dowel maker




Part of the stock is left intact to serve as the handle

Alternatively, a rounder plane or even a stail engine could be used to fashion the rod.

Screw box (die)





Tap


Base. The sliding central portion is trapped by the angled outer edges like a sliding dovetail. Screws were placed only temporarily to help with fitting and gluing of the outer boards.
Since I don't own a table saw, the angled edges were made using a shooting board
The tip of the threaded rod is made into a cylinder on the lathe.



Clevis pin inserted through a hole in end of rod
Copper pipe fitted to end



One screw on each side is placed from underneath the bottom board, through the outer board and into the fixed outer jaw

The dynamic jaw block on the right is screwed to the sliding beveled center board with the 2 screws coming from underneath the center board with countersunk holes. 
Note the thin piece of wood below the fixed left jaw protruding into the space of the center board. This provides a bearing surface when clamping smaller stock. To accommodate this, the sliding center section is not attached flush to the left edge of the right jaw. Instead, it is offset 1/4" to the right (not shown).
A pair of ash plates are secured to the faces.

Block plane modification

To ensure an  undamaged surface, I glued on thin metal strips to serve as runners on this old block plane. This prevents the plane from cutting into a flattened surface. The plane only cuts  material protruding out of the surface of the miter jack. These rails should not wear out since contact with the miter jack only occurs on the last passes. 
After using the block plane with add on rails. No need to worry about damaging this antique.

Perfect 90° cuts using magnetic plates

When The Beatles' Hello Goodbye single came out, it was a #1 hit. On the B side was I Am The Walrus, not as popular at first but it grew on us. 

When I first used a miter jack, I didn't pay attention to the rear side. But, side B of the miter jack, the rear end, has proven even more useful for me than side A after modifying it a bit.

I tried using the back side (vertical face) of the miter jack to cut tenon shoulders, but even the no set saw would occasionally dig into the surface. To correct this problem, 3/4" magnets were installed along with steel plates. The zero set flexible saw (from Lee Valley Tools) is then grabbed by these magnets and gives quite a clean cut.

Three quarter inch countersunk neodymium magnets 


Steel plates fashioned from old saw blades

Steel plates magnetically adhered to vertical surface

Cutting a tenon with mitered stuck moulding using the miter jack



The no set saw gets grabbed by the magnetized steel plates serves as a guide to position the stock
The saw blade can be positioned quite accurately to remove half of the scribed line..

Tenon shoulder cut. The saw stays true.


Cheeks removed with a moving fillester plane (one of several methods to remove the cheeks).

Another foolproof device. The magnetic Veritas right angle saw
guide assures a right angle cut of the ends off the tenon.





Moulding fashioned



A chisel is used to  miter the moulding.