Rocking Balans Chair

Mechanically Rocking Balans Chair

In the late 70s a new seating idea arrived.  As personal PCs started to show up in the early 80s a new set of ergonomic posture concepts also showed up.  

As part of my personal academic research I designed a progressive sequence of balans type chairs in search of a version that would fit better in an office environment.  The original rocking Balans chair had a dynamic quality to it. The rocker base allowed easy transition from perched forward to sitting level. It allowed fidgeting to keep from getting stiff while in the chair.  Many versions that followed copied the perch forward position but had no dynamic nature. 

Of all my prototypes this mechanically rocking version came closest to duplicating the qualities of that original rocking version. The X geometry allows the occupant to rock forward to the perch position or rock back to a level seat. The knee rests pivot to meet your shins at any angle. They pivot out of the way when rocked back and feet are flat on the floor.  

The Bubinga wood version above with blue seat and knee pads was my original prototype. The Maple wood version shown below was #1 of a series I made and sold to different campus offices that were just starting to use computers. 

Maple Production Version

Final Destinations Unknown

I don't know what happened to these chairs.  The owner of a local auction company told me he once had a group of some unusual chairs with orange seats to auction off, but he couldn't remember where they came from.  It wouldn't surprise me if the university sold them off as a group.  Modern office chairs with ergonomic adjustments have taken over. 

Questions and Comments welcome and encouraged. 

4D

25" x 48" Hobby Workbench Design

A Simple Workbench

Many home stores carry butcherblock slabs in different sizes. 

4x4 Cedar posts are also readily available in most areas. 

This bench design is made from a 25" x 48" x 1.5" thick slab of Birch butcherblock. Home Depot, Menards, Lowes etc. also carry 6' and 8' and 10' long slabs. The legs are  4x4 (3.5" x 3.5") cedar.  The legs attach to the top with a CNC cut tenon array. An example is shown here: Simple Desk. Stretchers are solid Birch and tenon into the sides of the legs. In assembly belt clamps around the legs helped pull the stretchers tight until the glue dried. 

Solid and Sturdy

The legs flare out a few degrees for a more stable stance. A shelf could be added atop the stretchers if desired. 

While not the 3" or thicker slab of 2x4s that makers often glue up for a bench top, this hardwood top is solid and stiff.  A bench vise would be a good addition.  Hang a drawer or two on the underside of the top for storage.  Apply 3 coats of finish on top and bottom of the top to stabilize it against bowing or splitting. 

The photos here are of a scale model I made.  The college I taught at was remodeling their workshop and needed more student workbenches. I made this model to present one option for them to consider.   Same construction and materials used as intended for full sized versions. Small details such as the mortises and tenons were cut using my CNC.  

Some stores carry wider butcherblock slabs.  A  36" x 72" slab would make a larger bench for those who need room to spread out their work. The same simple base would work with slightly longer stretchers in both directions. 

Questions and comments encouraged and welcome. 

4D.

CNC cut Radiused Corners for Furniture Projects

I would occasionally have students design a cabinet box with radiused corners.  Before we had CNCs to use we might run the corner board across the table saw blade at an angle to cut the inside cove. Optionally we might use a cove bit or large ball end bit on the router table. Follow with a few angled table saw slices to remove much of the outside surface.  Then plane/scrape/sand away to smooth out the outer surface of the corner. 

Using a 3-axis CNC and Aspire software, and the job set up as a 2-sided job, both the inside and outside faces of the corner curve can be cut. 

The goal is to remove the red shaded areas from the rectangular starting block. 

Top and Bottom cut Areas

As the whole top area of both sides is being cut, an extra inch was added on both ends for a place to clamp it down.  The moulding toolpath in Aspire software using vector drawings of the section views makes easy work of removing the waste areas to leave a perfect curved corner. The 1" ends can then be trimmed off. 

Inside Surface

Outside Surface

Care must be taken to align the board when flipping to do the second side. The material used and grain direction of the board should also be considered when cutting the adjoining flat side of the cabinet box. Plywood could be used with corners with grain running as shown in the renders above.  The grain direction of hardwood sides must match the grain direction of the corners. Front to back for the examples shown, Use Biscuits or Dominos to join the curved corners to the flat sides. Cutting a slot for a spline between adjacent parts could also work. 

This same strategy can be used to make corner sections that aren't 90 degree. I had a student from another class request how to make radiused corners to attach angled wings for a chair seat.   With the potential load on the wings of the chair seat being fairly great he eventually attached them with metal brackets.  Wood corners might split in such cases. 

A hexagon box with radiused corner would be a great application for CNC cut corners. Just draw up the inside and outside vectors of a 120 degree corner section. A few other drafting tricks might be needed.  :)

4D

Comments or Questions welcomed and appreciated!

  

Single Side Cantilevering Shelves

One Sided Shelf

These shelves were more about testing an idea than needing more shelf space. Still, they've become a home for a few of my foxes. Yes, I have a collection of foxes.

The challenge was to find a secure way to connect and support cantilevering shelves from one end. 

The shelves vary in length, with the shortest at the top and the longest at the bottom. 18mm thick plywood brackets, all identical, are used to keep all but the bottom shelf square to the vertical side.  They slide into dovetail slots in the supported end of each shelf. Each bracket also has an embedded threaded nut at the bottom for a bolt that will hold them tight to the vertical side.  Brackets are closer to the back side of each shelf to minimize their interference with whatever is displayed on each shelf.  

Support Bracket with Slot for a Nut Carrier

The embedded nuts are typical hex nuts held in a 3D printed carrier.   A simple slot is all that is needed to slip the carrier with nut into. Slots parallel to an edge are easy to cut on a router table or with a CNC while the perimeter is also being cut.  A hole for the intersecting bolt can be  drilled with a clamp on self-centering drilling jig. 

Drilling Jig @ Amazon.com

Typical Shelf Underside

The shelves also have two embedded threaded nuts for bolts piercing the end that connects to the vertical panel. The tightly held shelf traps the bracket.  The bracket holds the shelf level and keeps it from being lifted up. Shelves progress from 6.5" long to 23.25" long. They are 9" deep and spaced 13.25" center to center.  Some ash wood trim covers the exposed sides of the plywood shelves. Corners have a radius that matches the rounded over sides of the vertical panel. 

The bottom 23.25" long shelf is also the supporting foot for the whole system.  It has a bracket below that extends from the vertical panel to a short vertical foot. The bracket dovetails into the bottom of the bottom shelf. It also has an embedded nut for a bolt through the vertical panel. 

Bottom Bracket

The foot includes threaded adjustable feet to keep the vertical side perfectly plum. The adjustable feet screw into embedded nuts. A dado slot receives the bottom bracket end which is held with wood glue and two wood screws.  Trapped in the dado the plywood bracket can't split. Perforations in these parts allow air to flow from a floor vent below the shelves. 

Bottom Foot

This prototype uses a spare ash wood 9" wide x 6' tall vertical section from my much larger and more versatile shelf  system.  It can still be attached to that system if need be, and add its cantilevering display shelves to that system.

9" x 6' solid vertical panel

The notch in the bottom is so cables can pass through.  When used in the shelf system power cables run through to power a radio/music player and lights in the top cap of the shelves. 

All components of this shelf can come apart and stack flat for easy packaging or moving or shipping. The shelves/bracket unbolt from the panel.  The brackets slide out of the shelves.

In use this cantilevering shelf makes a good display space for my foxes. Needed is a light to illuminate the normally dark corner where it resides. There is an outlet on the wall behind the shelves where a light could be plugged in.  I'm in search for just the right clamp on light to do the job.  

4D.

Comments or questions welcomed and appreciated.

Coffee Tables with a Glass Top

These table designs are the outcome from an iterative sketching session.  The construction details are simple and style independent.  I've made 3 different styles of this system with different legs and wood choices that all are put together the same way.  The variations were inspired by a former student's research project. Her hypothesis was that age, gender, socio-economic status, and a few other factors would influence style-based buying choices.

I call this one Chéri.

Cherry Legs. Wax Finish

Simple Construction

Cherry Top.  Oil Finish

The legs of Chéri were also an outcome of their own iterative sketching session. The height of the foot is the same as the gap between the glass top and the wood top. The upper curve (a French curve) if continued down would end at the inside corner of the legs. I've made copies of this design out of hard maple with a birds eye center strip and red oak with a curly oak center strip. Both have found their own homes.  This cherry version was the original prototype.  The finish on the legs was an experiment which I don't care for. Plywood templates of both the front and side curves of the legs make it rather easy to duplicate the legs.  The two that I sold had a nicer glass top with an ogee edge to compliment the French ogee edge profile on the wood top.  Having a transparent top encourages featuring more interesting wood grain on the shelf below. The shelf is also a good place for seasonal or thematic décor. 

This one is Savanna.  Where Zebras roam.

Zebra Legs

Simple Construction

Zebrawood Center

I used a photo of Zebras to help inspire the shape of the legs. Zebra wood is rather busy when used in wide panels, so the top is a center strip of Zebrawood with quarter sawn white oak strips on both sides that the legs appear to run through. 

The third design was simpler with square post legs and made from red oak. "Country" might best describe the style. Red oak with a cherry stain. My parents chose it out of the three designs and it was handed down to my oldest sister. She enjoys it. I don't have a photo of this one but below is a rendered image of what it looks like without a glass top.

All versions normally have silicon pads atop the legs which both keeps the glass from being bumped out of position, and covers the top of the bolts that keep the top and bottom sections of the legs attached to the wood top.  

So which design do you prefer?  I'd love to know and if you don't mind sharing your age and gender that data would add to the data the student collected.  

4D

Comments and questions welcomed and encourage.  

Cam Levers vs Twist Knobs

The longer I use a jig or a fixture, the more likely it is that I'll find a subtle flaw or a feature that could be improved.   The Angle Clamping Fixture I have on my CNC works fine, but is a little finicky to lock in place to set the angle. I used two twist knobs to tighten the fixture position.   They worked, but would occasionally bump the fixture angle as they rotated to get tight. 

My Compound Angle Clamping Fixture

When I made the Bridges I now use for spanning my CNC bed area I chose cam levers to lock down the ends quickly.  I am extremely happy with how quickly I can loosen, reposition, then tighten down the bridges using the cam levers. 

My Bed Bridges

It took me awhile to realize again the value of cam levers.  When a jig or fixture works OK it doesn't beg for small improvements.  An email add from the company I bought the cam lever for the Bridges from provoked me to wonder if anyone sold a size I could use with the existing 5/16-18 bolts on my clamping fixture. Apparently yes. 

Cam Levers at Amazon.com

When these cam levers arrived they included 5/16-18 T-bolts that were too long. The hex bolts I'd used were too short for the cam levers.  The fix required CNC cutting a pocket for the oval head of the t-bolts, and cutting down those bolts with a hacksaw.

Improved cam locking

What used to take several turns of twist knobs to unlock then relock this fixture now takes flipping two cam levers to loosen or tighten.  

Router Fence

The fence I have on my bench mounted router is another place where cam levers make adjusting it quicker and easier.  I had some cam levers on hand that would work with the 1/4-20 T-bolts.  The bolts were too long though and had to be cut shorter with a hacksaw.  

Cam Release

Cam levers are available in many sizes. As I revisit many of my shop fixtures/jigs/tool fences that use twist knobs it is apparent that cam levers would improve the simplicity of using them all.  As I look back on the furniture projects I've done over the last several decades I realize that cam levers have been the ideal solution many times.  One example was a chair design with an adjustable seat that would slide forward or back for the user. Back then was before there was an internet and I made my own cam lever from an aluminum block using a milling machine as well as a few other shop tools. 

4D

Comments and questions are welcomed and appreciated.

 

Scraps. A Window Table made from Assorted Workshop Scraps.

Scraps

This table came to be from my desire to use up some assorted material scraps I had in my shop.  A vinyl wrapped particle board 18" wide shelf scrap became the table top.  A scrap of hickory that used to be one side of a wall mounted shelf became the drawer front. The angled ends of the drawer front inspire angling the ends of the back stop above for some detail continuity. The knobs on the drawer front are located where there were two screw holes to cover. Some old growth pine was used to cover the edges of the base which was made from 3 pieces of cheap plywood. The cheap plywood was painted black to diminish it's visual impact. 

Smooth running drawer.

The drawer hardware rollers were salvaged from old cassette tapes.  A Teflon spring loaded guide t-pin was embedded into the back edge of the drawer to run in a t-slot and keep it from racking when pulled out or pushed in. 

The top of the base sides slide into dovetail slots in the bottom of the table top. The center panel slides into dovetail slots on the inside faces of the two sides. This table can be quickly disassembled for relatively flat storage or moving/shipping. 

The construction is simple.  The details make it look more interesting.  A nicer version could be made from solid wood rather than MDF and cheap plywood, but wouldn't be any more useful.  I had this table on display in a gallery show of my work and was surprised how much interest it attracted. 

Without all the detail the 4-plane assembly (2 sides, a center plane, and a top) is a quick and simple way to make a table (of nearly any size) from sheet goods. The center slips down dovetail slots in the sides. The sides slide into dovetail slots on the underside of the top. 

24" x 24" x 24" four plane table

With some thoughtful reflection even a pile of scraps can become a nice looking useful little table. 

4D

Comments and Questions welcomed and encouraged!