Archive for the 'Digital Fabrication' Category

Bus Servo Draw Bot

I wanted to complete a start to finish project with the LX-16A bus servos to do a complete review of their viability for the type of mechatronics projects I do. The low price of the LewanSoul bus servos make them a competitive option over digital servos. I chose to do a remake of the Line-Us clone drawing machine because I would not need to spend too much design time and it would be a good 1:1 comparison with digital servos. Since the bus servos are quite a bit larger, I decided to scale up the machine by 1.5x.

Made My Own Brackets.

I started by buying one servo and it came with brackets. When I went to get more, I noticed the price was lower. I did not realize I was getting these without brackets. These are the brackets you get with the more complete kit.

I requested some 3D models from LewanSoul. They were only able to provide 2D DXF files, but they were easy to convert in Fusion 360. This allowed me to 3D print some brackets. It actually worked out quite well because I was able to thicken up the brackets and integrate some captive square nuts.

They mounted easily to the servos and were plenty strong for this project.

Servo Arms

I made two arms and one short cam for the Z. They were about 4mm thick and had a little pocket that slid over the standard round actuator. They screwed on with the screws that come with the servos. Before mounting anything I turned on the servos and moved them to the center of the range. This put the arms at a known angle.

Support Bracket and Base

The support bracket holds all three servos and there are 2 pockets on the bottom for some shaft bushings.

The base has two shafts pressed into it.

The shafts slide into the bushings and there is a spring to hold the parts together.  The spring prevents the pieces from separating and also provides a little extra pull down force in case the shafts bind a little. The cam provides about 6mm of lift.

Final Assembly

The servos are mounted to the support bracket.

The wires are connected to the servos. They just daisy chain from one servo to the next.

The remaining links are then connected.

Testing

Here is a video of the first run.

Results

I think these are a good alternative to digital servos. They are very strong, easy to mount and accurate. Depending on the design of the controller, using a simple UART might be easier than having multiple PWM signals or extra hardware. The servo’s size might be larger than some machines need but that comes with the higher power.

 

LewanSoul Lobot LX-16A Serial Servo Review

I stumbled upon these LewanSoul LX-16A Servos the other day on Amazon while searching for standard digital servos. These servos are digital serial bus servos. That means they use a serial protocol on a bus rather than a PWM signal. I have used bus servos before, but the $12 price got my attention. That competes well with plain old PWM servos.

Serial bus servos have some real advantages over standard PWM servos.

  • Wiring: The wiring can be a lot simpler because you can put all your servos on a single 3 wire bus. Each servo has 2 connectors to make daisy chaining easier.
  • Higher resolution: The resolution is typically higher. It depends on the way they sense position. These use a high accuracy potentiometer and list 0.24° as the resolution.
  • You can set the speed: You can set a destination and speed for each move.
  • Set the range: You can limit the range of the servo. This is great if the using the full range would crash a joint on your machine.
  • Continuous turn mode: There is a speed adjustable continuous rotation mode on these, but absolute distance moves cannot be done.
  • Motor On/Off: Turn the motor off for manual movement.
  • Feedback: The communication is bi-directional so you can query a servo for…
    • Position: If you manually move a servo, you get its position. This is great for recording “poses” or setting range limits.
    • Temperature: You can read the current temperature of the motors.

Compared to Robotis

I have used the Robotis Dynamixel XL320 servos before but these are a lot stronger and the XL-320 has a weird, plastic rivet, mounting systems that I am not fond of.

Here is a size comparison with a XL-320.

Specs

Spec LX-16A XL-320
Max. Torque 17 kg-cm 4 kg-cm
Resolution 0.24° 0.29°
Range 240° and Continuous Rotation 300° and Continuous Rotation
Speed 62 RPM 114 RPM
Weight 52g 16.7g

Usage

To use the servos you need to use one of their controllers. The most basic controller just converts a USB or TTL serial signal to their protocol. The controller is small and low cost ($10). You can send commands via a USB (Com Port) or via the TTL pins.

Setup Program.

They have a setup program.  The program is Windows only and I had to run it in Administrator mode to get it to work. This makes setting up the servos easy, but you could write your own program if you don’t want to use theirs.

TTL Control

They also provide some Arduino Sketches. They worked fine and are a good place to grab some code if you are writing your own program.  The sketches use the Arduino hardware TX and RX pins. That conflicts with uploading, so you need to disconnect the controller every time you upload. I edited the sketch to use SoftwareSerial on some other pins and that made playing with the code a lot easier.

First Impressions

I found the servos very easy to use and they appear to be strong and responsive. I think they will be a good option for my on my machines.

Next Steps

I want to test these in a real machine. I thought I might try to make a slightly larger version of my Line-Us clone. That would be a good comparison of accuracy. I might try one day build on it tomorrow.  I can probably get a machine designed and built in a day, but the controller programming would need more time.

 

The Polar Coaster – A Drink Coaster Drawing Machine

I designed this machine to draw custom, round drink coasters. I already have a laser cutter for square coasters and I wanted to try something unique for round coaster.

The Base

The base of the machine has two stacked 5mm bearings in the center for the bed to rotate on. There are (3) 3mm bearings on the bed perimeter that provide support and keep it level. They have little shafts that snap into the base.

The Bed

The bed is  a 156 tooth GT2 pulley. It has little springy fingers that grip the coaster when it is on the bed. The bed connects to the motor pulley with a closed loop belt.

The Radial Arm.

This is a belt driven, cantilevered arm that uses 6mm shafts and linear bearings. The belt is a cut pieces with the ends clamped at the carriage. It has a slotted mounting hole that lets the arm rotate. The pen must be adjustable to get to the exact center of the coaster or the drawing will be distorted. There is a limit switch on the top.  This is the only axis that needs to be homed. To setup the machine you home it and jog the pen until it is exactly over the center of the bed. You then set the work zero for X (Gcode: “G10 L20 P0 X0”). This only needs to be done once. If you use different types of pens, the center should be rechecked.

The Z Axis

The Z axis uses a micro servo and a cam to control the height of the pen. The firmware is setup to only have (2) Z positions, pen up and pen down. It uses 3mm rods and tiny little 3mm linear bearings.  There is a compression spring on one of the rods that applies a little pressure to the pen, and allows the pen to float a little on uneven coasters.

The Controller

I used my Grbl HAT controller. It is a bit overkill for this project but works perfectly.  It is attached to a Raspberry Pi in this photo, but I have not been using the Pi in this project yet. I just connect directly via USB.

Kinematics and Pre-Processin

See this blog post on how it was done. The pre-processor is written in C#, but it is rather simple and you could probably read the source file and convert if you cannot deal with C# on Windows.

Firmware

I use a modified version of Grbl 1.1f.  Grbl does not support servos, so I needed to hack that in.  I used the PWM that is normally used for the spindle speed to control the servo. I turned off the variable speed spindle option and streamlined the spindle functions to the bare minimum I thought Grbl needed.  I adjusted the PWM parameters for use with a servo and added pen_up() and pen_down() functions. I tried to put as much of the custom code into one file spindle_control.c. I had to add a few lines in stepper.c to look at the current machine Z height and apply the correct pen up/down function.

CAM

You can use anything to generate the gcode that works with Grbl. The pen will go up when the Z is above zero and down when it is below zero. Therefore, you want the Z movement as short as possible to speed up the drawing and not have the pen dwell on the material and bleed.  I make the depth of cut 1mm and the z clearance 3mm.

CAD Files.

The design was done using PTC CREO 3.0.  A STEP version of the design is linked at the end of the post.

Performance

It does a great job. Here a recent coaster. This was done from a rasterized bitmap image found online (searched: circular Celtic braid).

Here is a Fat Tire beer themed coaster.

Coasters are made to be super absorbent, so larger tipped felt pens tend to bleed a little too much. I like to sketch with Micron pens and the thinner ones really work well on this machine.

Build You Own?

The build is not difficult, but covers a lot of areas. You should know how to work with STEP files and compile firmware.

The design is open source with no commercial restrictions, so feel free to use any part of my work. I found most of the parts on Amazon and eBay. I bought the belt from Stock Drive Products. The polar motor pulley is 36 tooth and the arm pulley is 20 tooth.  Cutting the shafts requires an abrasive cutoff wheel.

Please post any questions in the comments section and I will try to address them.

Links

 

 
I sell on Tindie

 

 

 

Polar Pen Machine Kinematics

When you have a round work piece like a drink coaster, it makes sense to have a round work area.  A round work area works best with a polar coordinate system. A polar coordinate system uses an angle and a distance from a center point to define a point in 2D.

The problem is that most drawing and CAM programs work in Cartesian (X,Y,Z) coordinate systems. My machine controller firmware, Grbl, also works in normal linear X,Y, and Z. The process of converting one system to another uses Kinematics.

 

The Firmware

The firmware is side is actually quite easy. I defined the X axis as the distance in mm from the center (the radius). The Y axis will control the angle. The Y axis is setup so that millimeters will equal degrees. If I tell the Y to move 360mm, it will actually rotate the work area by 360°.  I could have used radians, but my brain works a lot slower in radians.

The machine will only need to home on the X axis. It needs to know where the exact center of the work area is. The starting angle does not matter because the coaster is a circle.

The conversion from X, Y to polar is probably won’t fit in into the firmware, so the X, Y conversion is done in a preprocessor software program. The X,Y gcode is output from normal CAM programs, then run through a conversion program.

The Conversion Program

The program reads the X,Y gcode, converts any X or Y coordinates into polar coordinates and outputs a new gcode file. The sender simply sends the new files.  The math is actually quite simple.

Typical Gcode sends line data by giving the end points of lines. You simply draw from one point to the next, unfortunately this creates a few problems with a non linear machine.

The basic non-linearity problem

If we were trying to draw the green square centered on the work area, the generated gcode would basically send the corner points. Each corner point has an equal radius to the center. Therefore, the pen will never change radius when going to the next point. This will result in a circle. We want the green square, but we get the red circle.

We need to calculate each point along the way to stay on the desired path. The preprocessor divides the line into tiny segments. Each segment has the same problem, but at a scale you won’t be able to see.

The Spiral Problem

If we are drawing a shape that crosses the 0° angle we don’t want the angle to spin the wrong way. If a point is at 350° and the next point is 10° (crosses over 0) we don’t want it to spin backwards from 350° to 10°. We want it to go to 370°.  It happens anywhere the angle difference between 2 points is greater than 180°. The program will choose the shortest direction even if that means going above 360° or below 0° degrees.

The Feed Rate Problem

Feed rate, in CNC terms, is the speed of the tool across the material. The CAM software is setting the feed rate as if this were a Cartesian machine. On this machine, if you were drawing a circle, you would simply move 360 units in Y. Without compensating feed rate, the pen would move across the work piece faster for larger diameter circles. I want to do some sort of compensation to help with this. The coasters are very absorbent, so the  lines look thicker if the speed is slower. A consistent speed will help the quality of the work.

Since the lines are all very short, the easiest way to compensate for feed rate is to use the current radius. With a simple circle, Grbl thinks the machine moved 360mm. The real distance is easy to to calculate from the perimeter of that circle.

We can compare it to the 360mm (full circle) and apply the ratio to the desired feed rate from the CAM program.

polarFeedrate = cartesianFeedrate * 360 / (2 * pi * radius)

 

Video

Here is a video of it. The machine is rerunning a file to see the repeatability.

Next Steps.

I would like to automate the preprocessor.  I think a Raspberry pi, might be an easy way to do this.  It would sit between the sender and the controller.

 

 

 

Coasty Update

Here is a quick update on Coasty. Several people have asked if I am releasing the source files or selling a kit. I am adjusting the design to make that more viable.  The original version was made with parts I had laying about and not necessarily the best design choices for an open source project.

X Axis.

Originally I used an TR8-8 ACME thread lead screw. It was mounted to the motor by drilling a hole in the lead screw and epoxying it to the motor shaft. This worked well, but you needed a lathe to drill the hole and a special low backlash nut. The axis was also a little loud with and all metal design.

I changed to use a GT2 open belt cut to length.  Belts and pulley are really easy to get and don’t cost too much.

Electronics

Need to shorten some wires after testing.

There were some issues with the EleksMaker electronics that I did not like. The laser circuit did not appear to have a pull down on the signal and it tended to fire if the Arduino was not pulling it low. This would happen during reboot and other scary times. The wiring was also quite a pain. There were no connectors for the limit switches so you had to directly solder to the Arduino Nano.

I changed to use a custom PCB that is the entire rear panel. This contains all of the circuits including the limit switches. Building a Coasty was a little like building a ship in a bottle. Now the bottle has no bottom and there are less parts inside.

Front Door.

The front door now has a window. This makes the machine more fun to watch and no glasses are required.

Next Steps.

I have one build and am testing it for a while. If all goes well, I will release the source files and consider a kit.

 

Line-us Clone Controlled by Easel and Grbl

Last week I made a Line-us drawing robot clone.  Unfortunately I had no good way to make it draw easily.  I thought I would give the CNC toolpath a shot.  My goal is to have a super portable thing to generate conversation at meetups. If I used Easel it would allow anyone with a web connection to easily make something.

2dbenchy

Grbl

Grbl Logo 250px

The most compact machine controller is Grbl and I have a lot of experience with it.  Grbl is designed to send step and direction signals to stepper motors.  The draw ‘bot uses hobby servos.  The nice thing about hobby servos is they don’t need to be homed.  They have feedback to tell them where they are. They also don’t care about speed, acceleration or steps/mm.  They just go wherever you tell them as fast as they can go. It occurred to me, the easiest way to hack this into Grbl was to not modify the Grbl code at all.  I would let Grbl think it is using stepper motors.  I would just add some extra code that runs on regular interval to tell the hobby servos where the stepper motors are in 3D space and they would be told to go there.  I played around with some intervals and 8 times per second (8Hz) seemed to work pretty well.  The ‘bot uses machine coordinates. The work coordinates are offset to the left because the ‘bot cannot draw at 0,0.  The pen would crash into the frame.

PSoC

I recently port Grbl to PSoC. I used (3) 16bit PWM components to control the hobby servos.  See this blog post on how I did that.  I then attached a 8Hz clock signal to an interrupt.  The interrupt sets a flag when it is time to update the servos.  When the main code sees this flag it does the calculations and and sets the PWM values.  Keeping the code out of the interrupts gets Grbl happier.

servospwms

Easel

Easel is already setup to use Grbl.  You can either import gcode or create a design right in Easel.  I started out with importing gcode because the Benchy design was not in a format I could import. I created a template that shows the allowable work area. This will allow anyone to quickly create a drawing.

easel_template

2D Benchy

I wanted to have a little fun with the first print.  “Hello World” was not good enough.  3D printers use benchmark prints, so I thought I would do a 2D version of the classic 3DBenchy.  To get a 2D drawing of 3DBenchy, I traced over an image with the line tool in CorelDRAW.  I then exported a DXF of that.

trace

A Line-us Clone

image1

I have been going to the monthly Amp Hour, Hardware Happy Hour meetup.  A lot of people bring something to show.  My projects are too big.  Also, you need to bring your own power.  The meetup standard seems to be running off a USB cord. I was brainstorming ideas, when I saw the Line-us project on Kickstarter. It looked like the perfect size and power. I also love the challenge of non linear kinematics.

8d65c4576042e58c834aa36d1098ceb6_original

I decided to make a clone of it.  I started by importing one if their drawings into CorelDRAW and scaling it up to 1:1.  I then added some measurements.  I rounded them up to 80mm for the pen arm and 30mm and 50mm for the linkages.

measurements

I looked into hobby servos and found that the “mini” size looked about right.  I ordered 4 of them from Amazon.  I made sure to get metal output shafts because I thought I might have to press them into the 3D printed arms.

mini_servo

 

Design

I created a basic design in PTC CREO.  I added a lot of construction sketches for the linkages to help me with the kinematics later.  I downloaded a model of the servo from GrabCAD  to use while I waited the delivery.

design2

I used 3mm bearings for all the joints.  These are pressed into the linkages.  This would allow me to firmly tighten the joints and not have to worry about slop in the joints.

Assembly

When the servos arrived, there were slight differences in from the model.  The mounting holes we much smaller at about 2mm.  I had to reprint with some changes.

My concept was to press the arms onto the servo shafts.  This sort of worked, but after a few crashes, they loosened up.  I ended up using a drop of thick super glue to secure them.  They were able to stall the motor without slipping.  It is important to mount the arms at the precise angle.  I made an Arduino sketch to hold the servo in the precise position while attaching the arms at the angle I wanted.  Each servo has a 180° travel.  The upper arm travels from 135° to negative 45°.  The lower arm travels from 45° to 225°.

Kinematics

In order make the pen go where you want it to go, you have to figure out what angle to set the arms. This is not a simple linear equation. You have to solve a multi-step geometry problem for each new location. I’ll walk you through the basic process. I placed the axis of the two servos at XY 0,0 to simplify things. You know the desired Pen Tip location, so start working back towards the cranks.

  • Step1: Find the Pen A point. You know the lengths of the linkages between the 0,0 point and the pen tip. They are both 50mm. Each arm end has a set of points where it can exist that scribes a circle. If the desired pen point is within reach of the machine, the circles (green ones) will cross at two points. The solution is a well documented process. I used the C code from this page. So far, I found that using the location, of the two, with a higher Y value is the one to use.
  • Step 2: Find the Pen B point. Pen B is easy to find because you now know the slope of the Pen Arm. Multiply the X distance from the pen tip to the Pen A point by the ratio of the length of the pen arm (80mm) over the length of the arm from Pen Tip to Pen A (50mm) and add it to the pen tip. Do the same for the Y axis.
  • Step 3: Now that you know the Pen B location, you can do the intersecting circles (red ones) trick again. This time I used the left most point of the two.
  • Step 4: Find the angles. Use the X and Y distances of the crank tips and the atan function to get the angles. ( angle = atan(deltaY / deltaX) )

Another problem with non linear machines is that moving between two points will not be a straight line. The points will typically be connected with a slightly curved line. You need to constantly recalculate points along the way to keep it straight. If you break a line into smaller segments, the connecting curves also get smaller to the point where they are not notices.

 

 

kin2

Electronics.

Everything I chose was for prototyping ease and probably not the final solution. I used an Arduino UNO as the controller. I used a PCA9685 based servo motor controller for the servo. The Arduino could probably handle it on its own, but the wiring is so clean and simple with this. I used a breadboard power supply to power the servos. It had a handy switch to kill the power to the servos without killing the Arduino.

pca9685-16-channel-12-bit-pwm-servo-driver_1

PowerMBV21

 

The Results

Here is a video of the machine running. The rectangle is hard coded via some for loops recalculating at 1mm increments. The results are shaky, but consistent with the Line-us results. The machine is quite rigid. Most of the shakiness comes from the servo motion. I also do not have the machine held down. If I get some magnets like Line-us, it might help.

image2

Open Source (sorry)

I don’t think it is fair to the Line-us folks to release any files at this time. I think there are plenty of resources in this blog post if you want to clone it yourself. So far I only have about 5-6 hours into the project, so it is pretty a pretty easy project.

The real Line-us looks very polished and they are selling it at a good price. I am sure a lot of the work they did was on the UI, which I did not replicate at all.

Next Steps

I need a way to stream drawing data to the machine. I would like to use g-code. It also needs a UI and I thought Easel might be best. For the gcode I might try hacking Grbl. I would just add a timer that reads the current location at about 5hz, send it through the math and set the servos. Any value above Z 0 would be pen up.

For Easel, I could create a template that shows the usable work area. You would then just click Carve.

 

Firmware

Here is the firmware I used.  It is a quick and dirty port of my PSoC port of Grbl. I cannot give support for this. Only experienced PSoC programmers will be able to install and use this.

Grbl Line-us PSoC Firmware

CAD File

Here is my STEP file of the design. This contains all of the printed parts and some of the hardware.  You will need to figure out a few things on your own.

Line-us Clone STEP File

 

 

 

 

 

 

The Bipolar ORD Bot

bipolar_ord_bot

 

It’s ORD Camp time again this weekend.  Every year I have done a gonzo build of some type of CNC machine.  This year I only had a few hours to spare, so I wanted something simple.  These are never meant to be practical machines, just conversation starters.

This was hacked together and programmed in about two evenings with stuff I had laying around, but working at Inventables means there is a lot of cool stuff “laying around”.  It was inspired by the RepRap Wally 3D printer, but vastly simpler in construction.  This only uses a couple of fabricated parts.  There are (2) sets of indentical actuator arms.  The inner arms are hard mounted to small NEMA 14 stepper motors.  The other end is attached  to a wood base, but free to rotate on a bearing.  The outer arms are mounted to the stepper motor shafts using Actobotics hubs.  The other ends have 1/4″ I.D. flange bearings.  These are bolted together, but free to rotate using a screw with a holed drilled for the pen.  That is basically it for the mechanics.

The stepper motors are driven with some high resolution stepper drivers.  These are driven by stock grbl 0.9 firmware running on an Arduino UNO.  The UNO does not know what the heck it is driving though.  The resolution is done in degrees.  I wrote a quick conversion tool that converts Cartesian gcode to bipolar gcode using these formula.

  • L = 150mm
  • A = 90mm

penbotkins

I have my CAM software output circles as multiple lines, so circles don’t need to be dealt with.  It has an odd, shield, shaped work area that you need to stay within.  Before powering on the steppers, you place the pen at the top middle of the work area.  You then tell grbl that both angles are at 51 degrees with G92 X51 Y51.

workarea

 

Here are a few more pictures taken at this weeks Beer and Making session at Inventables.

0121151912 0121151912b 0121151912c

 

The shield has a solenoid driver that I was going to use for pen up, but I never got around to that.  I kind of like how it runs so silently.

Here is a video of it running.  It is rerunning over an old plot to show the repeatability.   I think if I used true inverse kinematics the plots would look even better.  Maybe Machine Kit on a Beagle Bone is in its future.

UPDATE:

A few people have asked if the motors could be moved to different locations.  Yes, I think you could put the (2) motors on any (2) joints and still have a controllable machine.  Not all work areas would be the same size and some might have issues with much higher torque requirements.  I believe separating the the motors by one linkage, like this one, yields the best results.

Skate-oko-asaurus: The self replicating skateboard

We build a lot of skateboards for fun at Inventables.  Some of the guys even sell them at local craft fairs.  They thought it would be cool to have a CNC router optimized for skateboards that was easily portable.  I first thought about putting wheels at one end, then realized the machine itself could be a skateboard.  We thought it would make a perfect Gonzo Build.

2014-10-26 11.00.15

A Gonzo Build is something we came up with at Pumping Station One CNC Build club.  The concept is that we try to build an original, “one off”, CNC machine in one evening.  They also tend to have a whimsical aspect to them, so we don’t take ourselves too seriously.  We usually get about 8-12 people to help build.  If parts need to be fabricated, they must be done that night on -site.

2014-10-26 11.00.50

Building a stock Shapeoko 2 in one night is a challenge in itself, but we decided to up the challenge by totally tricking this out with every feature we could think of.  We did have a few master CNC building ringers in the group, like Tait Leswing and David Ditzler.

Here are the stats of the machine.

  • 1200mm x  250mm work area
  • Skateboard specific wasteboard supported by additional extrusions.  It is narrower than a stock Shapeoko 2 and about 3 times as long.
  • Drag Chain
  • gRAMPS Controller running grbl 0.9.
  • Quiet DC spindle with full speed control.
  • Feed hold / Resume / Reset buttons
  • Homing switches on all axes
  • Auto Z zero with Z probe
  • Trucks and wheels
  • NEMA 17 motors with dual Y stepper drivers.
  • Portable dual 24V/48V power supplies with master power switch.

2014-10-26 11.18.20

 

soa_controller

Most of the Shapeoko parts came from reject area at Inventables, so there are a few dings and scratches.

The wasteboard was cut from 5/8″ particle board on the PS1 Shobot.  It has a grid v carved into the work area.  There are threaded inserts for clamps, primarily around the perimeter, but there is a truck bolt pattern strategically placed so a cut out board can be flipped or remounted accurately . It is supported below by 2 additional MakerSlide pieces and tied to the MakerSlide rails above.  It is the bed turned out very rigid.  It does deflect a little with heavy rider but pops right back.  After the build, I added several coats of spar varnish to ward off the dusty footprints.  Biggest guy to ride it so far tips in at about 230lbs.

soa_bottom

We set our selves a goal of completing before midnight.  Done or not, I was going to ride it at midnight.  We thought we were finished about 20 minutes early.  Everything worked fine except the Z axis was not moving correctly.  It had the classic stutter and random motion of one coil wire not connected.  We tried to find the problem, but over 2 meters of drag chain slowed us down.  Midnight came some we dropped it to the floor and I rode it across the shop.

2014-10-26 11.03.30

As a skateboard, it is pretty much a joke.  On the first ride, we didn’t even have long board trucks, so the turning radius was huge and you can easily scrap an edge.  The front has a handle cut into the nose of the bed.  The ideal way to move it around is to lift the front and drag it on the back wheels.

 

 

 

Bridgie – A new look for a CNC router

Bridgie CNC Router

When our Hackerspace, Pumping Station One, had it’s mini router repossessed by a member who was leaving, I decided to design a replacement.   As always, I wanted to try out some new ideas on the build.  I also wanted a project made primarily in metal to force me to get up to speed on using my CNC Bridgeport.  The result is Bridgie.

bridgie_01

Bridgie?

Bridgie was inspired by the Bridgeport’s sliding X axis, so the working name became Bridgie.  The other inspiration came from a sliding chop saw.  This was used on the Y axis.  The Y axis is remarkably stiff and makes the Z far stiffer than many other routers I have used..  All rods except for the Z are 20mm hardened steel and the 12mm ball screws add strength.  The X is even stronger and the bearings always stay directly under the spindle.  The entire machine weighs about 45 lbs..

Bridgeport  Bosch_10_Sliding_Miter_Saw_Large

 

Clean Design

I wanted a very clean design, so I designed it so it is totally self contained.  The power supply, controller, limit switches and motors are totally contained inside the body of the machine.  The only external interfaces are power and USB on the back.  There is also a fan on the back that blows directly on the motor drivers and flushes any hot air out of the interior.

Spinning Ball Nuts

It uses 12mm ball screws on the X and Y axes.  In order to bring the motors inside, I decided to use spinning nuts and stationary lead screws.  This actually simplifies things because you don’t need to put expensive bearings on the lead screw, you just firmly attach it to the end plates.  The lead screw becomes a structural member in the machine.  The bearing on the nut is important for reducing backlash, so I used a large dual angular contact bearing.  These were about $10 each from VXB.  I did not take too many pictures during assembly, so here are some screenshots and renderings of the design.

Spinning Lead Screw Nut

Exploded view of the nut assembly.

Top view of X axis nut area

Top view of X axis nut area

 

http://www.buildlog.net/blog/wp-content/uploads/2014/06/Untitled-Project-30.jpg

Bottom view of X axis

 

Controller and Firmware

The controller is an Azteeg X3 with a Viki LCD.  I have used the X3 on a lot of projects.  It worked really well on this project because it has the on board SD card and works well with the Viki LCD.  The firmware is a highly hacked version of Marlin.  Here is what I changed.

  • Totally altered the LCD menu system to be right for a router.
  • Tore out all the temperature stuff.
  • Left in the extruder features in case I want to add a rotary axis.  I have used the extruder as a 4th axis successfully on other projects.
  • Added a Z zero touch plate feature.
  • Added a G54 machine offset like feature in EEPROM.  You you set a 0,0,0 for your workpiece, you can recall this later if there was a power failure or other crash.
  • The arrow keys on the Viki jog the machine.  In jog mode the up and down keys jog in XY.  The rotary encoder is still active and sets the rate of the jog, so you can jog XY in fast, slow and micro mode all from one screen.  Z can be jogged as well on it’s own screen.
  • There is a feedrate override feature on the main screen to speed up or slow down the feedrate.
  • All features are accessible via gcode, so pendant use is not required.

Homing and Work Offsets

The machine can be homed at any time.  The Z homes first at the top of travel before homing the X and Y so this is less likely a chance to hit a clamp.  Homing at the top of Z is not too useful for setting up your job, but the machine will now know the limits of travel and will never crash into the ends of travel.

The machine then homes at minimum X and Y.  There are also two other configured locations called “park” and “access bit”.  Park moves to center X, zero Y and top of Z.  The head is out of the way in this spot so it is easy to clamp the work piece in this location.  It is also has the minimum footprint in this mode for easy transport.  It also has an access bit location that moves the spindle to the front for easy access to change the bit.

You can jog and set a work 0,0,0 anywhere you want.  The machine resets it’s soft limits so jogging or G Code cannot crash at either end of any axis.  If you restart the machine, you can recall the last work 0,0,0 so a previous job can be completed accurately.

Feature List

  • Work area 12″ x 8″ x 3.5″
  • T Slot table (larger on all sides than the work area for clamping).
  • Sliding X table – Like a Bridgeport.
  • Spinning lead screw nuts.
  • Jogging with the pendant arrow keys
  • Z touch plate.  You can manual set the Z zero on the top of the workpiece or it can be done automatically with a touchplate.
  • X,Y,Z limit switches.
  • Park feature that moves the machine into it’s smallest size for transport.
  • Weight: heavy…about 45lbs
  • Soft limits.  If you set a new work zero, the machine still knows the new limits of travel.
  • Does not need a PC.  It can run completely off the SD card with control via the pendant.
  • No exposed wiring.
  • Super quiet DC spindle.
  • Cooling Fan directed on drivers, but flushes the whole interior.
  • “Park” command shrinks the size to smallest footprint to help with transport.
  • Freaking heavy at over 45lbs

Videos


To Do

  • It would be nice to have easy access the the SD card.  It is buried inside the unit now and you need to upload files to it via USB.
  • Add a real feed hold (immediate deceleration like grbl does now)

Changes.

  • There a few thing I would do to make it a little easier to fabricate.  A few holes were difficult to drill and tap and some simple changes would make that a lot easier.
  • I added an e-stop button since taking these pictures that cuts the DC power.