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SmartJointer: fully automatic SmartMini-based box jointer by trusley_mike in woodworking



Picture of SmartJointer: fully automatic SmartMini-based box jointer

This is part two of two parts about SmartJointer – an easy-to-assemble CNC box (“finger”) jointer controlled by SmartMini.

Please click here for part one.

This Instructable converts SmartJointer for fully automatic operation.

SmartJointer is a an easy-to-assemble CNC box (“finger”) jointer controlled by SmartMini. No PC or mains power supply is required to operate SmartJointer in the workshop.

Part one showed how to make the version of SmartJointer which is manually pushed/pulled over the saw blade to make each cut.

The video shows the automatic version which is the subject of this Instructable – it cuts box joints while you have a cup of tea and a biscuit.

Some statistics and advice

Maximum timber width: 200mm (8″) – but easy to scale up SmartJointer for more.

Maximum timber thickness: 18mm – but easy to scale up the softwood support pieces for more.

Time to cut one set of pins/tails: multiply timber width by 0.75. E.g. 60mm width = 45 seconds per set.

Number of pieces cut in one pass: up to 4 – depends on timber thickness.

Always use a backer. I hate tear-out!

Step 1: Tools required

Picture of Tools required

To assemble SmartJointer pusher you will need:

  • Pozi No 2 screwdriver
  • Pozi No 1 screwdriver
  • Revolving hole punch or means of making small holes
  • Precision screwdriver set (Try ebay)
  • A digital volt meter. (Try ebay)
  • The Micro switch requires a short length of two wire cable so you will probably need a soldering iron

I invented SmartJointer because I am lazy – I don’t see why I should do things that a machine can do better – that’s why I use a Bosch IXO cordless screwdriver.

To program the control system you will need:


Step 2: Parts

Picture of Parts

SmartJointer pusher is built from good quality 9mm birch plywood.

  • 1 off base: 400mm x 200mm x 9mm plywood
  • 1 off pusher bar: 340mm x 100mm x 9mm plywood
  • 4 off rail supports: 33mm x 100mm x 9mm plywood. These will be glued together to form two pairs.
  • 3 off motor support blocks: 60mm x 100mm x 9mm plywood (The photo shows only two of them.)
  • 1 off drive belt fixing block: 34mm x 34mm x 9mm plywood
  • 2 off fixing clamps cut to fit your saw bench

I am based in England and I get my plywood from Farmwood Timber Suppliesnear West Hallam, Derbyshire.

You can download a .DXF file for all the plywood parts.

You will also need the following kit of hardware parts (more details on the SmartJointer Instructable):

  • 1 off Nema 17 stepper motor
  • 1 off acrylic mounting plate for motor. .DXF file available on web site.
  • 1 off 2.5T 16 teeth pulley to fit to motor spindle
  • 2 off 10mm housed linear bearings
  • 2 off 300mm x 10mm guide rails
  • 1 off 710mm x 2.5T drive belt with wooden mounting block: 34mm x 34mm x 9mm plywood
  • 1 off free running 2.5T 16 teeth pulley
  • 1 off 5mm dowel to act as a spindle for the free running pulley (A cut-down 5mm bolt will do.)
  • 1 off micro switch and cable (Try ebay.)
  • 4 off 5mm x 12mm bolts to secure linear bearings
  • 4 off 3mm x 12mm pozi countersunk screws to secure stepper motor to mounting plate.
  • 4 off 3mm x 50mm pozi countersunk screws and nuits (I used wing nuts) to secure stepper motor mounting
  • 4 off 3mm x 20mm pozi countersunk screws and nuts to secure SmartMini-UMP to the base
  • 4 off 3mm spacers (3mm nuts will do) to secure SmartMini-UMP to the base
  • 5 off 3.5mm x 25mm wood screws
  • 2 off 3.5mm x 10mm wood screws for drive belt fixing block

Step 3: Control system

Picture of Control system

I used:

You can use a 12V power supply (a “wall wart”) if you wish – but you will be back to trailing wires again.

Step 4: Cutting wood and making holes

Picture of Cutting wood and making holes

The wood dimensions are shown in the parts list.

The key locations are:

  • The holes in the guide rail supports for the 10mm guide rails
  • The holes in pusher bar for the linear bearing screws
  • The holes in the stepper motor mounting plate
  • The holes in the base and mounting blocks to receive the stepper motor mounting plate

CNC systems tend to “bind up” (i.e. go solid and refuse to move!) if things are not aligned correctly.

I have created a .DXF file showing the locations of all holes.

Location of clamp holes

The two holes at the front/bottom of the base are located for bolts going into clamp blocks cut to fit the slot in your saw bench. I use short 5mm bolts going into captive nuts

Step 5: Assembly: guide rails and bearings

Picture of Assembly: guide rails and bearings

Building the pusher is almost exactly the same as building SmartJointer itself so apologies for this text being almost identical.

Each guide rail support is a pair of 9mm plywood parts – one of each pair has holes for the rails. Glue the pairs together making sure you have a left-hand pair and a right-hand pair.

Slide one bearing on to each guide rail.

Insert the ends of the guide rails into the holes in the guide rail supports.

Look carefully at the photo, align the ends of the guide rail supports to the top of the back and centre them on the vertical fixing holes. The opening should align with the motor cutout.

Check, check and check again before carrying on.

Clamp in position when you are happy with alignment.

Drill 3mm pilot holes into the guide rails supports using the pre-drilled mounting holes as a guide.

Screw the guide rail supports to the back using 3.5mm wood screws.

Step 6: Assembly: motor and micro switch

Picture of Assembly: motor and micro switch

The motor is fitted upside down.

Fit a pulley to the spindle of the stepper motor.

Screw the motor to the acrylic mounting plate.

Insert four 3mm x 50mm pozi countersunk screws through from the back of the base at the motor end and place the three mounting blocks on top of them.

Drop the motor mounting plate on top and hold everything in place with nuts. I used wing nuts but that’s probably OTT.

The slots in the mounting plate allow the plate, with motor, to slide left and right to tension the drive belt when fitted.

Fit the micro switch to the guide rail support closest to the motor.

Step 7: Assembly: fitting the drive belt

Picture of Assembly: fitting the drive belt

Overlap the two ends of the drive belt by by about 30 mm, punch holes about 20m apart through both ends. (A leather punch is excellent for this.)

Drill two pilot holes 20mm apart through the drive belt fixing block.

Drill another pilot hole through from the front of the drive belt fixing block – this will take a screw that will pass through the pusher bar.

Screw the drive belt to the drive belt fixing block.using short 3.5mm wood screws.

Pass one end of the belt through the right hand rail support and loop it round the motor pulley. You may need to turn everything upside down to do this.

Put the free pulley into the other end of the belt, locate it in the gap in the left hand rail support and secure in place with the 5mm dowel or 5mm bolt cut-off.

The dowel or bolt must not protrude above the surface of the rail support or it will foul the pusher bar during use.

Loosen the screw on the acrylic motor mounting plate and slide the plate to adjust the tension – not too tight and not too slack!

Re-tighten the screws.

Step 8: Assembly: fitting the pusher bar

Picture of Assembly: fitting the pusher bar

Place the belt drive fixing block between the two linear bearings with the screw hole upwards.

Insert a 3.5mm wood screw through the pusher and screw in place. Look carefully at the back of the pusher bar and ensure that the drive belt fixing block is aligned vertically – adjust if necessary.

Use the 5mm screws to fit the pusher bar to the linear bearings. You will see the bearing holes through the fitting holes – slide the bearings left or right to locate them before fitting the screws.

Step 9: Assembly: adjusting the stepper drivers

Picture of Assembly: adjusting the stepper drivers

The photo shows SmartMini-SA (Single Axis) with one A4988 stepper motor driver. For the automatic version of SmartJointer you will be using SmartMini-MA (Multi Axis) which supports up to three driver modules.

Very important warning

Never connect anything to anything with power connected. Always physically disconnect the power source before connecting any electronics components. The 12V line on SmartMini is always live when a power source is connected. Accidentally connecting 12V to a 5V line, even for a fraction of a second, will destroy the Arduino Pro Mini.

You, like me, will ignore this advice. You, like me, will destroy things (many things in my case). You,like me, will learn a salutary lesson!


Mount SmartMini-PS and SmartMini-MA together on a SmartMini-UMP plate and fit the EPort Link – make sure it is the right way up and that all pins are connected

You will be using two A4988 stepper driver modules (X and Y) and I reproduce below the instructions from the original SmartJointer Instructable.

Setting the step resolution

  • Make sure no power supply is connected to the board.
  • Carefully remove the A4988 driver modules from the board.
  • Between the female headers you will see three jumpers – blue in the first photo.
  • Using a jumper to connect the two pins makes a line high, leaving it off makes the line low.
  • The A4988 has three lines to control step resolution: MS1, MS2 and MS3. (S1, S2 and S3 on SmartMini.)
  • On the SmartMini-SA board S1 is closest to the motor terminal and S3 is closest to the Pro Mini.
  • By default the SmartJointer software is set to use half stepping – 400 steps per revolution.
  • The microstepping table shows that MS1 should be high while MS2 and MS3 are low.
  • Ensure that the jumpers are set correctly.
  • Replace the A4988 modules – make sure they ares the correct way round and all pins are inserted correctly.

Setting the drive current

  • Make sure no power supply is connected the the board.
  • You are going to adjust the small pot on the A4988 board so you need a slim screwdriver.
  • Connect the meter ground lead (black) to 0V on the SmartMini board.
  • Connect the meter plus lead (red) to the shaft of the screwdriver. You can purchase hook connectors suitable for most meters – try ebay.
  • Switch on the meter and select a suitable voltage range (you will be measuring up to 2V).
  • Apply power and switch on.
  • Carefully insert the tip of the screwdriver into the pot.
  • Turn clockwise until you get the maximum reading.
  • If you go too far the reading will drop back to zero – so back off and creep up to the maximum again.
  • Different modules will show different maximums – the one in the photo shows 1.6V.
  • Switch off, remove power and disconnect your meter.

Step 10: Assembly: wiring up and programming

Picture of Assembly: wiring up and programming

Connect up the four motor wires and the two micro switch wires for motor X (the one on the original SmartJointer) and motor Y (the one on the pusher).

See step 16 of the original SmartJointer Instructable for details.

The Arduino Pro Mini in SmartMini-SA is programmed using the Arduino IDE.

I am assuming you know what to do and you have a suitable USB to serial module (with DTR!) that will allow you to program the Pro Mini.


The software is provided “as is”, free of charge and with no warranty as to suitability for any particular purpose.. You are free to replace it, change it or tweak it.


  • Do NOT connect battery power.
  • Do NOT switch on.
  • Connect the Remote Controller to the MultiPort socket.
  • Connect your USB to serial module to the Pro Mini – including the 5V power line.
  • Connect the other end to a serial port on your PC. (I use a USB extender cable to make life easy.)
  • Download my Arduino code for the automatic version of SmartJointer and store it in a suitable place on your PC.
  • Load the Arduino IDE and load my source code.
  • Compile and download it to the Pro Mini.

If everything is OK you should see the startup message on your Remote Controller.

Common reasons why programming fails

  • Almost always a loose wire or wires in the wrong order.
  • No power to the Pro Mini. Check the Pro Mini LED is on before you attempt to program. Check the VCC and GND wires are connected at both ends.
  • Programming wires in the wrong order. Check that DTR is connected to DTR, TXD to RXD, RXD to TXD.
  • No driver. Make sure you have installed the driver for your programming module/cable.
  • Wrong port. Check that the Arduino IDE is connected to the correct COM port.

Don’t go any further yet.

Step 11: Linking to SmartJointer

Picture of Linking to SmartJointer

A 6mm hole is drilled into the end of the pusher bar and this is used to insert a short 6mm bolt through into a hole drilled into the back base support of SmartJointer.

The location of the hole in SmartJointer should be as close as possible to the line of the saw blade so the pusher will be pushing directly against the resistance of the blade.

The pusher will be clamped to your saw bench so the location of the linking bolt will determine where you fit your clamps

Safety warning 1

Don’t use too long a bolt because, if you push SmartJointer too far, the tip of the bolt may contact with the blade., You may wish to slightly offset the holes just in case.

Safety warning 2

The pusher makes SmartJointer fully automatic – you won’t be holding anything. My bench saw has a T slot and the runner I made for SmartJointer is an inverted T shape. This prevents the front of SmartJointer rising up against the saw blade. You will need to take similar precautions with your own installation.

Never leave SmartJointer unattended – even when it is running automatically. Always have a hand close to the Emergency Stop on your saw.

Step 12: Testing

Picture of Testing

If you’ve got this far at least you know the control system is working.

  • Disconnect the USB to serial module.
  • Do NOT connect battery power yet! Do NOT switch on!
  • Check the belt drive tension – you should be able to move the pusher bar slowly and carefully – you will feel resistance from the stepper motor but the spindle should rotate.
  • Don’t fit everything to your saw bench yet but place SmartJointer and the pusher on your bench/desk without connecting them together. Both motors and micro switches should be connected to SmartAngle-MA. We are going to test the movement of the two parts.
  • Position the work holder and pusher in the middle of their travels – if they go the wrong way you want to be able to switch off before they hit the end!
  • Connect the battery and switch on.
  • The startup message should appear on your Remote Controller asking you to press “#” to start.
  • With one finger hovering over the off switch, press “#” on the keypad.
  • On SmartJointer the work holder should move slightly away from the motor then move back towards it until the bottom linear bearing contacts the micro switch before the work holder stops and backs off a little.
  • On the pusher the pusher bar should move slightly away from the motor then move back towards it until the wide end of the bar contacts the micro switch before the bar stops and backs off a little.
  • Switch off immediately if either goes the wrong way and continues heading for the other end!
  • If it went the wrong way, physically disconnect the battery and swap the motor wires for any pair. So, swap 1A and 1B or 2A and 2B. Now, reconnect power, switch on and try again.

Now fit both SmartJointer and the pusher to your work bench – see step 19 onwards of the original SmartJointer Instructable for details.

You are ready to cut joints!