Just a Prototype

Often I sit with a sketchbook iterating little drawings of table designs.  A table after all is just a horizontal plane held above the floor with a structure. The structure's only purpose is to support the top and whatever it might be used for securely and reliably. Something to span the gap between floor and top and resist gravity. This can range anywhere from a solid block to a spindly center post with spindly feet. 

Iterate.

Occasionally I come to a design that appeals to me more than usual. If it looks even better a day later  I'll do a digital drawing of it. If the digital design is still appealing I often make a prototype. 

This little table is one outcome from such a process. The prototype leg shape is CNC cut from 3/4" thick MDF.  

MDF

The top is solid walnut.  The leg design I envisioned to be made from walnut pieces joined together.  No need in a prototype to use expensive material and labor though.   

Walnut Wood

I painted the MDF legs with red primer with the intent to then paint them with a final color.  The primer color looks good with the walnut top.  This is just an aesthetic prototype and once walnut legs are made the MDF versions will be discarded. Good enough it is. 

Underside

Overside

The legs dovetail into a triangular center post. Screws through the top hold tight to the post and legs.  Screws are counterbored  and covered with walnut plugs.

Comments welcomed.

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Elliptable. A Table Composed of Ellipses.

Ellipses are simple to draw using most CAD software.  They are also fairly simple to cut out using a CNC.  I designed and made this table before I had a CNC I could use though. It evolved from an idea I had to invert a simple ellipse drawing jig.  To test the jig out I used it to swing the wood panels through a router bit on my router table in elliptical paths. Every ellipse in the design was cut with the same jig.   The legs have a slight rounded edge that echos the ellipse shape of the top above. 

Cherry hardwood

The top came from the center.

Ellipse Jig

The legs join together with dovetails. This design is a good example of detail continuity.

An Ellipse Drawing Jig

Comments welcomed and appreciated.

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A Simple Finger Joint Jig for the Router Table

This simple jig makes cutting finger joints on box corners fairly simple to set up on a router table.  Variations can be made quickly for fingers of different sizes. 

It uses a piece of 3/8" x 3/8" x 12" long steel key stock, embedded 1/8" deep in a piece of 12mm birch plywood. This provides a guide rail for making the repeated stepped cuts for finger joints.  

Backboard Sled

The backboard sled has a slot cut in the bottom which sets over and slides on the key stock rail.  The center flange of this sled helps keep the sled square and face vertical. Join it to the bottom and face with French dovetails.  It can have a hand hold cut in it and the shape rounded for a more comfortable hold. 

Center Flange with Handle

A 3/8" spiral end mill peeks through a hole in the base which is slightly larger and 3/8" away from the rail.  Clamp the base down to the router table top on two opposite corners. Adjust the bit height to match the thickness of the boards above the base.  To adjust bit spacing from key stock loosen one clamp and bump the base slightly. 

Base with Key Stock Rail. 

To help the jig work smoothly apply some paste wax to the sliding surfaces.

Jigs for smaller or larger fingers can be made using key stock to match the router bit diameter. 1/4" key stock for 1/4" fingers.  1/2" key stock for 1/2" fingers. 

Amazon.com: 3/8" x 3/8" x 12" keystock.

CNC Frame Bridges as an Alternative to T-Track rows or Vacuum Beds.

I previously made a couple of frame bridges to support an assembled student project for some CNC joinery cuts: Here

Lately I've been using the bridges more often to support flat work. They have proven their worth in every case and these are the advantages they offer:

1. They are stiff and flat and remain level to each other and plane-parallel with the CNC's X/Y travel.

2. They have horizontal edges to provide clamping surface for c-clamps to hold the work down.

3. They have aligned holes for pins to set the project board against for perfect alignment with the CNC Y axis. 

4. They attach quickly into the side frame rails with one screw (or cam lever) on each end into a t-nut. 

5. They can be positioned anywhere along the side rails. 

6. With a little modification, two bridges and some all-thread turn into a bed vise that can clamp parts vertically for joinery cuts on their ends.  Link:  Bridge Vise

7. Since the bridges can slide anywhere up and down the side frame members, only three strips of 30" long t-track are needed to cover the entire X/Y cutting range of the CNC. This compares to six strips of 60" long track needed before. 

Waiting for cam levers

With cam levers to permit quick positioning

So far two have been enough, but a 3rd will be useful for long boards that may have a bow in them. The 3rd bridge could also be used to clamp a stop block on for repeated identical cuts using the same Y origin. Small C-clamps have been enough to hold work to them, but with a t-slot track embedded in their top any other t-track clamp can be used. 

My Probotix Meteor CNC has one design flaw.  The backplate that the router bracket attaches to comes down with the router.  This can collide with clamps behind where the router is at. Switching from t-track that runs up and down the bed to bridges that run side to side keeps me from clamping down anything from the front or back. Since changing to bridges I have yet to see the router bracket collide with a clamp. 

  

MDF slats between t-track on another MDF panel that span the CNC frame tend to sag in the middle over time. Plywood bridges in an L or T configuration remain stiff and straight with no deflection under the weight of projects boards or flexing when clamped to warped wood. 

So far I haven't come across any flat work I couldn't clamp securely down to these bridges.   

My strategy so far for clamping down flat cuts is to use the center of the board as the Home (start/end) point.  Then I make sure the bit won't try and pass though a clamp during cuts. I can offset the start point to the center even if zeroing the bit on the board edges.

I have some thin cork sheets I bought that might be useful as shims to protect the bridges from through-cuts. A 1.5" square to put under boards where each c-clamp ends up should be enough lift to account for router bit penetration. I'll pre-cut a stack of them and keep them stored close to the CNC.  1/8" Baltic Birch plywood scraps can also be used as shims.

I used a self-centering punch to make sure the screws for the t-track would be centered in the screw holes. Their screws go through the top plate and into the top edge of the vertical rib.  
Locking the bridges down doesn't take much time, but does require getting the Philips screwdriver out and putting it away when done. The cam levers are the magic bullet that makes the bridges easy and quick as possible to set in place and use.

Now I'm contemplating how best to accommodate thick/tall work that I could cut if I could sink it down into the frame.  The bridges could be bolted into the bottom slots of the frame to gain 78mm save for the Y-axis limit switches that protrude into the 30mm width of the rails.

The day the cam levers arrived I cut a notch in the top end of the side rails to slip t-track nuts into for them. The levers came with a stud too long but none were available the size I needed. I cut the threaded studs down to the the length needed using my metal cutting chop saw. 

So far I'm happy with this design.  The cam levers make a huge difference in the time it takes to set up for a cut. When I can't use the t-track clamps small C-clamps do a great job of holding down the work. I just have to take care when setting up a job to not run into a clamp.

The black t-track came from Amazon.com:

The cam levers came from Zoro

Comments and questions welcome.
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A Rare Book Display Stand.

I was asked by our college librarian if I could design and build an original stand she could use to display large rare books on. Once she provided overall dimensions for the stand I set about sketching out a few alternative ideas. 

Initially I wanted to use Northern Hard Ash, but after finding a couple rough Ash boards in the college wood storeroom and planing them flat and clean I discovered they were riddled with bug tracks. My local source for hardwoods would also not sell any Ash for the same reason. 

While I don't usually care for white oak thanks to its busy face grain and color, I bought 26 board feet of it for this project. I ripped it into 1" wide strips and turned them 90 degrees to glue them into quarter grain panels for most of the stand parts. After the glue dried I scraped one side flat before running them through the planer. The resulting planks look beautiful showing medullary rays and far more interesting color variation than the original face grain ever did. 

The Probotix.com CNCs I oversee in the college shop were used to cut the edge and joinery details needed to create the parts and assemble the stand.

The top of this stand is 25" deep by 45" wide. Most parts are made from layered quarter sawn white oak. It is held up by two 3" x 2" posts connected with 4 bowtie tenons through-cut in their top end grain. The tenons are slim waisted which increases the contact area between mortise and tenon, and also resists racking of the joint which can lead to loosening. As this is a stand for books I added a couple of famous quotes about books/reading on the visible faces of the two stretchers. The librarian also requested that the stand would have a shelf to keep a box of cotton gloves on. The triangle sides of the shelf slip into dovetail slots, and help keep the top from bowing. 

Glove Storage

I could find no better words than these about the value of reading.

You can see the varied grain patterns in the top.

The design is a result of my pursuit for simplicity in structure. 

The 2 columns of 4 bowtie tenons are end grain of the posts peeking through the top.

Photos above were taken in the finish room of the fabrication lab where I taught. They were taken right before I delivered the stand to the college library.

Installed in the college library rare book room.

The stand is displaying rare drawings created by Frank Lloyd Wright. It is

standing in the college library rare books room entrance window. Seaton Hall, KSU.
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A Simple Box, with Four Different Corner Joints.

This is an assignment sample I made for our beginning Workshop One class.  I designed it to show the students different ways to connect wood at a right angle.  All the joints on this example were cut using my CNC.  Simpler versions of each corner joint can be done using more conventional tools in a woodworking shop.  To show them what a CNC can do if they think out-of-the-box each corner has a feature that would be very difficult to do with conventional tools. To see the actual assignment look HERE.

Miter.  The conventional way to reinforce a miter joint would be to use a spline or biscuits to cross between the two halves.  Using my CNC I've made a hidden alternating mortise and tenon row that disappears inside when the joint is closed. Much easier to glue up as this joint won't slide in any direction when clamped.

Tongue and Groove.  Normally a simple tongue in a simple groove is enough to make a good corner joint.   Using the CNC I've added a row of 5 small through-tenons that center the joint and add some aesthetic detail to this corner.

Box Joint. The CNC enhancement for this row of fingers was to make them each a different progressively larger width.  Tough to do using any other jig or tool, but fairly easy to draw up for the CNC to cut them.

Shallow Rabbet.  Conventionally we would reinforced this with screws covered by wood plugs.  Using the CNC I simply cut 3 round tenons from the end grain of the short side to replace the screws and plugs.   The end look is the same. The tenons align the joint.

The bottom is 1/4" (6mm) Baltic Birch plywood.  Rather than install it near one edge of the box, I'11 put it 1/3 of the way up from one end.  This will divide the box into two compartments with one twice as deep as the other.   Flip the box to access each.  The lids won't open unless they are on top. Twisting latches slide into the lid to keep it in place when it is on the bottom. A shallow perimeter rabbet on each lid aligns it to the box. When on top just twist the latches then the top can be lifted out.

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Dowel Splice Joint

I've got a closet in my spare bedroom (storage room) that I wanted to add another clothes hanger rod to.  Among my scrap pieces I had two 1.25" diameter closet rod sections that together would be long enough, but neither was long enough on their own.  The distance to span was roughly 22". 

This is a CNC-cut splice joint I came up with to solve the problem.   My test cut done on smaller scraps is shown in the photos.  I'm calling it my radial finger joint.

The finished spliced rod is now loaded with clothes and is handling the weight with no complaint.

To hold the dowels on my CNC I used my adjustable angle clamping jig set to vertical with a vertical scrap of plywood clamped to it.  The dowels were trapped/clamped against the jig and edge.

One application of this joint was for a student of mine's project.  Walnut dowel extensions to oak dowels.  A coat rack with key tray and umbrella hook, By Ellie Williams:

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