Archive for November, 2014

Automating the Box Joint Jig Lead Screw

I constructed an Arduino based controller to automate the carriage on my lead screw Box Joint Jig which was originally inspired by Matthias Wandel at woodgears.ca. Interestingly, Matthias added automated operation by a laptop to his design at the beginning but later removed the function in favor of multiple wooden gear sets. My jig was manual at first and automated later after I kept losing count of the crank turns

See this WordPress Blog entry on construction of my Box Joint Jig and also this Blog entry on some of the applications.

A video of the development breadboard in action is at www.youtube.com/watch?v=6Zz1fGDO5jw.

A video of the controller installed on the jig and working is at www.youtube.com/watch?v=URk4qYnEWgI

I used an inexpensive DC motor driven with a Polou MD01B H bridge, and added position feedback to the lead screw. This gear drive motor from All Electronics (DCM-697), was intended for actuating automotive power seats.  I sawed the shroud off the connector housing so I could use standard push on terminals.  The mounting base is a bit of hardwood flooring rounded out to fit the motor and hose clamped on. I can loosen the clamps and slide the motor to align the sprocket and adjust the chain.

Modified Power Window Motor

Modified Power Seat Motor

 

This shot shows how the lead screw shaft has been cut and ground down to fit the "D" shaped hole in the drive sprocket.

Window Motor Shaft

Seat Motor Shaft Ground Down

 

Two 24 tooth sprockets from All Electronics (GR-100).  They don’t come with a cap for the shaft collar so I made some from a piece of aluminium. Normally they have a “D” shaped hole. The sprocket on the left has it’s D intact – it will go on the motor shaft. The sprocket on the right has it’s D filed out round so it can clamp on the 3/8 threaded rod that drives the Box Joint Jig.  I have since replaced the motor side sprocket with a 42 tooth part to speed up the carriage motion.

24 Tooth Sprockets

24 Tooth Sprockets

 

Photo of the first test bed.  Power seat motor on left, Pololu motor driver (MD01B) above that, protoboard in the center and Arduino on the right.  Two buttons on the protoboard run the motor either CW or CCW.  The amazing little Pololu board has a VNH3SP30 H bridge chip which is less than 3/4 inch square but can switch 30 amps!

Bare Test Bed

Bare Test Bed

 

Since the motor is a simple series type, I need a way to inform the Arduino how far the shaft has rotated.  An optical sensor could be used but then there would be sawdust issues. Instead I use a Hall Effect sensor and permanent magnets.

This is the prototype position disc. It will go on the jig’s lead screw.  Quarter inch button magnets are coupled to six penny nails to focus the magnetic field and pressed into slots sawn in the disc.

Prototype Feedback Disc

Prototype Feedback Disc

 

Here the magnets and nails have been epoxyed and a coat of varnish applied.

This was intended to be a prototype but performs well enough that it probably will be the final.  The disc is 3 inches in diameter and will be taped directly to the motor sprocket for software development purposes.

Trimmed Magnet Disc

Trimmed Magnet Disc

 

Detail of the disc edge showing one of the six penny nails sawn off and filed flush.

The Hall Effect sensor (SS441A from Jameco) gives a clean transition when placed about a quarter inch from the edge of the disc. NO bounce observed (Yay!) so I can easily code an interrupt driven counter. Eight steps per rotation on the 16 TPI shaft will give a resolution of  0.0078125 inch at the carriage. One – One Hundred Twenty Eighth of an inch.

One of the Magnetic Poles

One of the Magnetic Poles

 

Since this is the Breadboard phase of development, I thought it appropriate to mount the parts on a real board.  At this point the motor software is done but the menus are not. A video of the development breadboard in action is at www.youtube.com/watch?v=6Zz1fGDO5jw.

Clockwise from the top:
– Chain and sprocket for the lead screw
– Sensor disk temporarily on motor
– Motor and mount screwed down now
– Hall Effect sensor glued to a stick
– Stick clipped to mount so its adjustable
– Arduino clone board
– 16×2 LCD display
– PWM pot (not used, will be removed)
– Proto board with LEDs and buttons
– MD01B motor driver

Final Development Breadboard

Final Development Breadboard

 

Here is the box I selected to hold the completed controller.  It is a standard electrical box from Lowes, but it has a bump out on one side that forms a nice surface on which to mount button switches. The lid of the bump out is molded as part of the box. You fold it over and it snaps on. You can do this about 3 times before the plastic hinge breaks off so plan the layout carefully beforehand. 30 Cubic Inches sounds like a lot until you start stuffing cables in there.

I amputated the 8 penny nails and mounting ears.  LCD and LED indicators mount flush on the top where the AC receptacle would normally be.

Electrical Box

Electrical Box

 

I think the box has enough holes now….  Putting the controller hardware into the box is more complicated than it seems. Just the box itself needs wires from two buttons, power switch, 12 volt feed, motor feed, two limit switches, and the Hall Effect sensor.

Outside, a blue Euro style block is glued on for the Hall and limit wiring, Two pin Molex connectors added for the 12 volt leads.  The box material is soft enough that it cuts easily with a utility knife.

Box With Wiring

Box With Wiring

 

Here is the Pololu MD01B motor driver in it’s new home. Have to use plastic screws because the plating around the mounting holes is electrically hot (why??).  This small sheet of aluminum fastens inside the box via the two countersunk holes visible just above the buttons in the previous photo.

Pololu MD01B Mounting

Pololu MD01B Mounting

 

The Arduino clone processor is mounted on the opposite side of the aluminum plate.  Four analog inputs and 12 digitals are cabled out.

Arduino on Mounting Plate

Arduino on Mounting Plate

 

Four LEDs and the 2×16 Liquid Crystal display are mounted on a piece of plexiglass cut to fit the top opening of the box.

Leds are:
slewing left
power on
hall sensor (added for coolness factor)
slewing right

Display Panel Front

Display Panel Front

 

This is the display panel seen from the bottom.  Four 2 wire connectors for the LEDs and a 10 wire cable for the LCD display.

The small connectors are salvaged from PC front panel displays, the multi wire connector is sawn off an IDE hard drive cable.

Display Panel Rear

Display Panel Rear

 

I used a Radio Shack PC board to make a central interconnect for all the buttons, limit switches, LEDs, Hall sensor, LCD display, and processor.  There is a 5 volt regulator for the logic side, pullup resistors and LED dropping resistors.  This cries out for a printed circuit board but since I’m only building one of these, it will do as is. I would have to work through this stage to design a PC board anyway.

Interconnect Board

Interconnect Board

 

Made a drawing of the interconnect board so I could remember where things plug in.

Interconnect Board

Interconnect Board

 

Final mock up to test wiring. All this has to go into the blue electrical box. Found two LEDs functionally reversed. One of the cool things about the Arduino is the pins are software defined so that took maybe a minute to fix in software. The 5 volt regulator got too hot for comfort so in a last minute change, I moved the regulator chip over onto the aluminum sheet – even more wires!

Final test Before Assembly

Final test Before Assembly

 

Well it does all fit, though it’s a PITA to find a place for all those wires.  This shows the completed controller connected to the breadboard motor mount having just made a 128 step (1 inch) simulated slew, sixteen revolutions of the sensor wheel.  Those two microswitches will be limit switches on the jig, and I will use an inline fuse in the 12 volt feed, couldn’t find room inside.

Testing Controller on the Breadboard

Testing Controller on the
Breadboard

 

This shows the motor screwed to the end of the jig, two sprockets, and #25 chain. These parts came from All Electronics.

It sticks out more than I hoped.  Maybe need some kind of guard to keep fingers out of the chain.

Motor as Mounted

Motor as Mounted

 

I made a small L shaped plywood structure for mounting the controller on the box joint jig.  The mounting is tall enough to protect the sensor wheel assembly and the right limit switch.

Controller Mounted on Box Joint Jig

Controller Mounted on Box Joint Jig

 

Mounted the left hand limit switch horizontally. It is very exposed so I cut off most of the actuating lever and made a guard out of aluminum.

Left Limit Switch

Left Limit Switch

 

This photo shows the sensor wheel mounted on the lead screw shaft. The Hall Effect sensor is epoxied into the small wood block just right of the wheel.  It gave me grief, it didn’t work!  After a lot of experimenting, I determined the Hall sensor is only sensitive on one side. I had glued it into the block upside down.  Turned it over and success!  You can also see the right limit switch mounted vertically.

Sensor Wheel

Position Sensor Wheel

 

I set the controller to slew sixteen inches. Ran it up and back about ten times, it always came back to the exact same spot.  Takes more than a minute to go 16 inches.  I will look for different sprockets to speed it up. The motor has plenty of torque, I put most of my weight on the carriage and it didn’t slow down a bit. I’m using an XBox power pack to supply 12 volts, it’s easily up to the job, but wish I could figure out how to get it up to 15 volts.

A video of the controller installed on the jig and working is at www.youtube.com/watch?v=URk4qYnEWgI.

Sixteen Inch Setting

Sixteen Inch Setting

 


Completed Box Joint Projects


 

A Roy Underhill Memorial Tool Tote.  About 30″ long, 9″ wide.  The yellow pine does not seem to take an oil finish well.

The box (finger) joints all cut on the automated lead screw jig.

Yellow Pine Tool Tote

Yellow Pine Tool Tote

 

Another smaller tool tote done on the automated jig. This example in Cherry.

Tool Tray in Cherry

Tool Tray in Cherry

 

These boxes made for my two Stanley 45 Combination Planes.

House for Homeless Stanleys

House for Homeless Stanleys

 

I made this to hold a small Variac transformer. Keeps my soldering iron at just the right temperature.

Variac Box

Variac Box

 

This Walnut, Butternut, and Oak box was made for my Brother-in-Law.

A Box for Johann

A Box for Johann

 

 

Compound Angle Box Joints

This is a practice piece for a larger project.  I wanted to make a tool tote like the one Roy Underhill carries in the introduction to “The Woodwright’s Shop”.  There is a description of the tray in Roy’s book “The Woodwright’s Apprentice”. His example is butt jointed and nailed together, but I thought it would be nice to do the tray with box joints and glue.  Thus started a journey into trigonometric hell.

Practice Piece

Practice Piece

 

The sides of this piece are 15 degrees from vertical (75 degrees from horizontal) which is close to Roy’s slope of 1 1/2″ rise over 5 1/2″ run.

The only other reference I had for compound joinery was a section in Tage Frid’s book “Tage Frid Teaches Woodworking, Book 1: Joinery” on hand cutting dovetails in a similar situation. Not for the amateur woodworker and difficult to follow.

Other references may be available – Google is your friend.

Strange things happen when you slope the sides of a box.  All the angles change and the side edges are no longer parallel.  People who install crown moulding are familiar with this.  I used the Butt Joint calculator at www.pdxtex.com/canoe/compound.htm.

To get the side and bevel angles needed for the project. It is easier for me to think of these angles as offset from vertical (90 degrees) so I entered 75 degrees as the side slope.

Compound Angle Calculator

Compound Angle Calculator

 

The table saw has it’s blade tilted to the calculated bevel angle (3.84 degrees) and the miter gauge tilted to the calculated side end angle (14.51 degrees from 90 or 75.5 degrees).

Cut the first edge with the miter gauge in the left hand gauge slot. It helps to label the faces as the small bevel angle is small and not obvious. The narrower face goes towards OUTSIDE of the pyramid. For my right tilt saw, the piece being cut off in this photo has it’s INSIDE face up in this photo. The next piece, on the left of the blade, has it’s OUTSIDE face up in the picture.

Compound Cut

Compound Cut

 

Now rotate the miter gauge 180 degrees and put it in the right hand slot. Flip the board over and make the second cut. The piece being cut off now has it’s INSIDE face up.

This method does not waste any wood, but every other piece has it’s face side reversed which may be a concern if you’re matching grain.

After all the pieces were cut out I ran them through the saw a second time with a stop block clamped to the miter gauge to ensure they were all the same width.

The final step in fabricating the four sides is to tilt the saw blade to the slope angle (15 degrees in this case) and bevel the top and bottom of each piece. I used the table saw fence to guide this, but watch out for kickback.

Second Compound Cut

Second Compound Cut

 

If the butt joint angles are cut correctly on the table saw, a straight edge held parallel to the top or bottom will show no gaps across the junction of two sides.

Joint Alignment

Joint Alignment

 

To dado angled box joints exactly parallel to the slanted top and bottom edges, the work pieces have to be held in the jig in the position they will occupy in the finished assembly.

I made two complimentary spacer blocks, one for the right edge of the work piece, and another for the left.  I first glued up a 3 inch thick blank from four pieces of 1×6 pine. This was trimmed and planed square.  Then I laid out the lines for the necessary slopes all the way around the block.

Angle Block Layout

Angle Block Layout

 

The next corner of the block.

I found it was easier and more accurate to lay out the lines by calculating and measuring rise over run rather than use a protractor.

Second Side of Angle Block

Second Side of Angle Block

 

This is the opposite corner of the block.  The layout lines go all the way around.

I made several of these blocks before I got the angles dialed in right.

Third Side of Angle Block

Third Side of Angle Block

 

The fourth corner of the prepared block. The next step is to slice the block along the layout line.

Fourth Side of Angle Block

Fourth Side of Angle Block

 

A Sketchup model of the jig spacer block.  Angles for this 15 degree project are 3.8 degrees on the long side, 14.5 degrees on the short edge.

The dimensions shown are approximate due to Sketchup limitations.

Sketchup Screenshot

Sketchup Screenshot

 

This shows me and Henry Disston dividing the block along the layout line. It’s easier than it looks.

For a good example of how to do this see www.pbs.org/woodwrightsshop/video/2800/2810.html where they slice veneer off a walnut block by hand sawing.

Splitting the Angle Block

Splitting the Angle Block

 

Here the two halves of the block have been smoothed, and pegs added so they will plug into my box joint jig.

Note the orientation. The block on the left will go against the jig on it’s square face. The block on the right plugs into the jig on it’s sloping face.

Two Setup Blocks

Two Setup Blocks

 

A view showing how the sloping faces of the spacers lay against the jig. One spacer tilts out 3.8 degrees and slopes 14.5 degrees left, the other tilts in 3.8 degrees and slopes 14.5 degrees right.

Side View of Spacer Blocks

Side View of Spacer Blocks

 

The dado stack has to be tilted to match the side angle. This aligns the slot with the top and bottom surface of the work piece. For this 15 degree side slope project, the angle is 14 1/2 degrees off vertical.

An additional complication is, now that the dado is angled, the slot will be slightly wider than the stack width. Box joints depend on the slot being exactly the same width as the pin, so the pin size has to be increased to match. For this 15 degree project, I added 0.012 shims to the dado stack and increased the pin cycle by 1/16 inch. It came out pretty close.

Wixey out the Angle

Wixey out the Angle

 

Finally the jig with spacer is ready for duty. Here one of he blocks is plugged into the lead screw jig carriage, the work piece and a backer board are clamped to the spacer and I am pushing through the dado.

Note the masking tape throat plate. The jig itself provides a throat for the Dado set, the tape just keeps down the sawdust.

Clamping the work piece at the necessary angle is difficult. I used tapered shims to get a straighter purchase for the clamps.

Clamping the Workpiece

Clamping the Workpiece

 

Since the stacked Dado set cuts a square bottomed slot, but the edge parallel fingers require a trapezoidal hole, there is a small triangle of material that must be removed from each of the slots by hand.

Here I am knifing the edge of the triangular area.

Knifing the Slots

Knifing the Slots

 

The small side of the triangular areas can be sawn.

Sawing

Sawing

 

One of (many) practice pieces showing the small triangular area at the top of each slot that must be removed. Here I have defined the triangle using a straight edge and utility knife, also the small side has been cut with the dovetail saw.

DSCF0324

 

Now to remove the waste from the triangular area with a paring chisel.

It might be possible, if thinner stock is used, to build a fixture and do the clean out with a 14 degree dovetail router bit. If I had to do a lot of these I would investigate but it doesn’t take long with a sharp chisel.

Paring the Slots

Paring the Slots

 

Not a bad dry fit.  The material is cupped a bit which left some spaces but I think it will pull together with sufficient glue clamps.

The sloped sides are going to be a problem on the glue up.  I will make some 15 degree cauls to keep the clamps from sliding off, also will use strap clamps.

Practice Piece

Dry Fit Practice Piece

 


Finished Compound Angle Projects


 

This is the finished Roy Underhill Memorial Tool Tote created with the compound angle box joint jig.

First Tool Tray

First Tool Tray

 

Close up of the compound miter box joints on one end of the tool tote.  I don’t have all the cool hand tools Roy has so this project was built with machines.

Corner View

Corner View

 

Detail showing how the handle is mortised into the end pieces. Just like Roy’s.

Handle Detail

Handle Detail

 

This is a smaller tray in Cherry.

Tool Tray in Cherry

Tool Tray in Cherry

 

This was the last one I made, in Yellow Pine from Home Depot stair treads. The bottom is nailed on the sides, I covered up the finishing nails with copper carpet tacks.

Yellow Pine Tool Tote

Yellow Pine Tool Tote

Lead Screw Box Joint Jig


Jig Construction


There is an excellent woodworking site at woodgears.ca.  Matthais Wandel documents projects beautifully.  I was inspired by his box joint jigs, in particular the video at the end of woodgears.ca/box_joint/jig.html though I thought the gear part was overkill.  The premise is to use a lead screw to position the board while cutting the slots.  The usual technique for finger joints is to use an indexing pin on a sliding sled.  The problem with that method is any error in spacing between the pin and the blade will be cumulative, if you  cut 10 pins and they are each off  by 2 thousanths, the last one will be off by 20 thousandths.  The lead screw should be more accurate, it’s easy to cut multiple pieces at once, and quite large stock can be handled. This fixture will easily handle four inches of material stacked up.

This is the jig mounted on the table saw. It is 11 x 40 inches, will be able to handle 18″ stock in a single pass. Material for the miter slot rails is plastic coated MDF.

Box joint jig and table saw.

BoxJjoint Jig and Table Saw.

The lead screw is 3/8″, 16 Threads Per Inch so one turn of the crank advances the carriage exactly 1/16 inch. In the photo, the block on the right end is fixed to the carriage and has a T-nut to engage the rod. The doubled block also has a T-Nut but is floating (not attached to the carriage). Springs between the fixed block and the floating block take up any backlash in the lead screw. The rest of the blocks support the carriage face and also protect the threaded rod.

Lead Screw

Lead Screw Nut Anti Backlash Springs

At the crank end, a soft rubber washer provides tension on the rod to eliminate backlash at that point. The rod protrudes an extra inch so I can use a 9/16 socket in a drill to rapidly slew the carriage back to the end. 18 inches times 16 TPI is a lot of cranking.

Lead Screw Crank

Lead Screw Crank

This shot shows how the carriage is mounted on two full extension drawer slides, one on top, one on the rear. Each has a maximum travel of 18 inches, and since they are mounted at opposite ends, when one is at maximum extension the other is at minimum extension.

I was surprised at how rigid this was.

Lead Screw Extended

Lead Screw Extended

This is the other end of the fixture. You can see the rear mounted drawer slide. I will be cutting a port for the shop vac in the end piece as soon as I figure out how to couple in the hose.

Keeping sawdust out of the ball bearing drawer slides may be a problem. I have an Aluminum extrusion modified to slip over the rear slide for protection.  In practice, sawdust has not been a problem after adding the shop vacuum coupling.

Left End of Box Joint Jig

Left End of Box Joint Jig

This is the face of the carriage. Also shows the board added across the front of the sled for stiffness, and you can see the two runners fitted in the saw’s miter gauge slots.

Front View of Box Joint Jig

Front View of Box Joint Jig

You can cut all four sides of a box and stack the pieces in the fixture. There’s two clamped up in this photo. If you do all four at once you need to offset two of them by the width of the slot. See the video on Woodgears.ca.

Normally you need a sacrificial backer board between the carriage and the stock because the slot in the jig gets too big.

Box Sides Set Up for Cutting

Box Sides Set Up for Cutting

These were cut on the jigs maiden voyage. Actually the second try, I screwed up the first set. The material is half inch MDF left over from another project.

Part of planning a box joint or dovetail project is figuring out the pin width that leaves a good half pin on the ends. Clearly that didn’t happen here, but it works OK just looks odd.

Four Box Sides Ready for Assembly

Four Box Sides Ready for Assembly

The box joints fit well though a hair loose. These are half inch pins, two 1/8 chippers in the Freud Dado set. A perfect fit would require narrowing the dado set a few thousandths but it’s good enough as is.

Dry Fit

Dry Fit


Completed Box Joint Projects


Toy Box for the Granddaughter

This is wood salvaged from an old Pine table, had a nice patina even after planing off the epoxy paint.  About 24″x15″x12″.

Toy Box

Toy Box

Toy box opened. Spring loaded holder upper gadget from Menards.

Toy Box Open

Toy Box Open

Box joints are half inch pins, one inch pitch. The banding top and bottom was fitted, then cut with one eighth inch box joints. Biscuits reinforce the banding.

It was quite an effort to glue this up. I did all four corners at once with slow setting Titebond which gave just enough time to get every clamp I own on the box.

Toy Box Detail

Toy Box Detail

 

 

Garden Planter Frame

The previous owner of this house had made a planter box from treated 2x12s around a back yard tree. The tree grew and pushed the box apart so I replaced the planter with a larger box made of Cedar.

I used box joints with half inch pins to assemble the new planter. The new box was more than four feet on two sides, I had to move the table saw to the driveway because the boards clamped to the carriage hit the roof trusses in the garage.

Cutting Fingers for Planter Box

Cutting Fingers for Planter Box

Each side was formed from two 2×6 Cedar boards. Two opposite sides had one 2×6 ripped in half so adjacent board seams don’t line up when assembled.

One Completed Edge

One Completed Edge

I assembled each pair of sides and bored a 3/8 hole all the way down through the pins. Then I inserted a 12 inch long galvanized nail to hold the joint together at each corner. There is no glue.

Corner Detail

Corner Detail

The final assembled planter. Under the dirt I put 4 inches of gravel inside hoping it will drain better and last longer.

Planter Installed

Planter Installed