Main Box Stops, Continued….

In the last post on the topic, I concluded it would be necessary to drill holes in the lower racks to accommodate the stop bolts. The thought of this makes me pause because while the current piece into which they are being fit is a prototype, the racks and gears are not. The thinking goes that once the prototype is properly operating, the mechanisms will be transferred to the final oak piece, and the poplar prototype will remain for pedagogical purposes. At some point though, you just have to cut metal…

The procedure:

  1. Drill & tap the hole in the lower rack.
  2. Once this is done, use this new hole to determine where to locate the hole in the side of the main box.
  3. Finally, install the bolt, and use it to mark the extents of the groove in the apron.

Simple. Right?

With the aprons modified, reassemble the carcass, reinstall the mechanisms, and test (anxiously holding breath…).

Oops! Lower guide contacts the main box stop bolt.

$#@!

Unfortunately, I neglected the thickness of the guides when locating the bolt hole. After a brief walk to consider options, it’ll probably be best to reduce the diameter of the stop bolts to clear the guides. This won’t necessitate drilling another hole in the lower rack, and the 1/4 x 20 bolts being used for this are readily obtainable. It is a bit tedious, however, to file them down and still get them to thread into the racks.

The solution. Modify the stop bolt by reducing its diameter.

A final point. A careful inspection of the lower racks on the Getty original reveals that drilling the stop bolt hole in the incorrect location is not a unique problem. Apparently, I am in good company.

Many thanks to George Hamilton for his assistance tapping the bolt holes.

2019 Class Schedule

I have two classes scheduled for early summer:

Tap on the links for descriptions and sign-up information.

In the marquetry course, we will explore various ways to embellish your projects using wood veneer. Intended for those with little or no experience, it begins with geometric patterns cut with knives, chisels, and a straight edge. By the end of the week, students will execute their own free form designs using a marquetry fretsaw.

I think the class at Campbell Folk School will challenge participants. Not only will we be making dovetail joints at angles less than 90º, we are going to do it without referring to the gradations on a ruler! It really is possible to construct furniture without measuring, and it is surprisingly accurate. To top things off, we will do all of this using only hand tools!

I will try to post more details as the times for these classes approach. Until then, feel free to contact me with questions.

Oeben book rest update

This weekend, I took a break from fiddling with the mechanisms to focus on a different aspect, namely the book rest. When originally created, it worked (somewhat) reliably, but was set aside so I could focus on the mechanisms. The main box, to which the book rest is attached, has been re-worked since then, most notably being disassembled for mechanism installation adjustments. It still worked after that, but required help to get beyond a certain point.

There are two tricks necessary for this to function properly.

  1. The leaf on the rest side of the hinge isn’t mortised into the wood like you would do for any normal hinge installation. This allows appropriate clearance between the back of the stand, and the bottom rest, and
  2. Radius the bottom corner of the rest with a plane. This ensures it will rotate when the lifting force is applied to the stand.

With things (once again) operating smoothly, the only step remaining was to chisel two notches in the stand’s back. This gives two angles at which the stand can be set.

…and before you comment, more than one person has already suggested using it as an iPad stand…

I want to thank Michael Koppy for working with me to fabricate the hinged support.

Main box stops

From previous posts, we have seen that there is a great deal happening within the aprons. Now, we need to make room for one last thing…

Proper right apron interior showing upper & lower racks with spring mechanism.

In this post, I described the process fitting the stop rods keeping the top from shooting off the back of the carcass when the works are set into motion. Something similar is needed to keep the main box from coming out the front. Two (fairly) sizable bolts, to minimize the force exerted on the stops, were used in the original. These need to be installed from within the side compartments of the main box such that:

  • they avoid contacting the lower racks,
  • the grooves in which they run must not protrude through the carcass front,
  • the main box is allowed to move to its fullest extent,
  • they avoid interfering with existing guides and drives located on the main box sides, and
  • they are installed above the main box floor.

Not too much to ask for, right?

Proper right compartment in the original main box. Circle shows stop bolt head (barely visible).

When Oeben created the original, he grooved the aprons just below the lower guides for the main box. This out-of-the-way location prevented anything else from interfering, allowing the bolts to slide unimpeded. So long as the bolts are installed behind the front legs, these channels won’t show through the carcass front. The other ends, naturally, aren’t a problem since the main box stops behind the rear apron.

Layout showing vertical alignment of main box and carcass.

This addresses the majority of the above criteria except for the “horizontal location”, or how far above the main box bottom are the bolts mounted? The challenge here lies in the limited available space between the lower racks, and the main box floor; less than 1/4 inch. Not much! Referring, once again, to the original, Oeben solved this by drilling a hole through the lower racks for the stop bolts to protrude. This has the added advantage of strengthening the bolts since overtime repeated collisions might loosen the bolts mounted in the wood alone.

Main box proper left side showing proposed stop bolt location.

As with the stop rods previously once these bolts are installed, they will be used to mark the location and extents of their grooves, and stop plates.

Postscript: having trouble visualizing things? Check out the first image in this post.