Thursday, March 17, 2011

LOG: Notes and Comments


1) Today I received the parts to finish the fences on my router and drill press tables. Also, I have been in the market for a router designed for a router table, i.e., hight adjustment above the plate, and today Sears online had a sale on routers.  I purchased a 917542 for $60. Good price.

2) I have been exploring USB GCode interpreters. There are two open source versions available for the Arduino and a proprietary one by using the PIC 18F4550. One of the Arduino versions can be found at the REPRAP site and the other here,

  Grbl:  3-axis interpreter
         Pros: It's free. To use it download code into Arduino with the IDE and then connect to it with a terminal emulator. Use the terminal to send GCode files to the Arduino. Three Arduino bits are assigned to limit switches.

        Con: There are no jogging switches. As yet there is not a PC GUI to operate Grbl.

 Planet-cnc:  4 axis interpreter
        Pros: Cost is $200. Includes assembled PCB and GUI. There are jogging and limit switches, as well as, other neat features. The firmware for the 18F4550 is not open source, but it appears to be free to use. You are even free to layout your own pcb. The license for the PC software is 69euro. You can run your CNC from a laptop, not a parallel port.

       Cons: ? Time will tell.

3) Though the CNC router base build is not finished, I will start Part 4, The Gantry Base, which will show how the adjustable linear bearings are made.


I added the BOM and a drawing to the Part3: Router Base. Sorry about the hand drawing, but it was quicker.


I have spent some time looking at the CNC USB Motion Controller of Planet-cnc to the extent that I decided to layout my own version of the PCB. The Planet-cnc site provides a DIY section with complete info for building your own hardware. There interest is in selling the PC software, ($100.). There are a number of people who have built the hardware with success. The unlicensed software will run 25 GCode statements which should be enough the get it tested.

The pcb, I have laid out, is slightly larger than theirs, I added a few features, but I did keep connector compatibility. Though I still have small changes to make to the pcb, I sent a trial run to Batchpcb. It passed with a single price of $27. for which you usually get two boards. The 18F4550 is $5.36 from Mouser and you will need a programmer such as PicKit2. I have the parts to build a prototype and should receive the pcb's in about 3 weeks. Batchpcb is cheap but slow.

I started out by thinking how I would mount the electronics in a case and connect all the parts to the front and back panels. I will make some rough drawings and put them online here. Briefly, the front panel will have 8 jogging push buttons and a USB connector. The rear panel will have connectors for the motors, limit switches, emergency stop, master fuse, USB connector and power cord. It might be interesting to put LED's for the limit switches. Inside there will be two power supplies, one for the motors and the other a 5V for the controller. The motor drivers, I have designed, have opto isolation on the input and onboard 5V regulators for driver electronics. This should protect the controller and the PC.


The pcb has been submitted to Batchpcb and, hopefully, should be here in three weeks. In the mean time I will program a 18F4550 with the bootloader and test it.

I am in the process of assembling the cnc router base, as well as, making the gantry base.


When I started work on the CNC Router, I first designed two modular bipolar step motor drivers: one using the L297/298 (Stepit 1) and TB6560 (Stepit 2). Rather than a single pcb with multiple drivers, the design is modular, that is, a single driver per pcb. These drivers are connected to the parallel port breakout board using PMinMO, s defacto 10 pin IDC connector standard. This turned out to be a good choice, since the CNC USB Motion Controller from Planet-CNC uses the same standard. I have now added two more drivers two my stable of drivers, in this case, unipolar drivers: the first, using the SLA7062/67M (Stepit 3) and the other using the SLA7078MPR (Stepit 4).

 Stepit 3 uses a SLA7062 or SLA7067 unipolar drivers by Sanken which is not the easiest chip to find, but find some I did. After examining the Sanken data sheets, I have designed two versions of the driver: one, with opto isolation (Stepit 3) and the other without (Stepit 3A). The pcb's have been laid out and in a few days will go to Batchpcb.
    Non opto version
    1. Enable pin can provide half or full power to motors when in disable mode, pin high.
    2. 3.3k network for pull-ups, other resistors are discrete.
    3. An optional trimmer added for changing sense level.
    4. Trigger voltage chosen so that .5 ohm 1 watt resistor will set current to 1 amp
    5. Ground plane
    Opto Isolated version
    1. As above
    2. True opto isolation
    3. On board 5V regulator
    4. Motors fused
    5. Ground plane
    6. Disable mode can be jumpered for motor half power or power off.


    I started driver designs using the SLA7078MPR. As with the SLA7062M there are both opto and non-opto versions, but in both a new half power delay feature has been added. If at anytime, step signals stop for 10 seconds, the motors will switch to half power. These features are jumper selectable.


    Started the construction of a table for the CNC Router.


    The basic table is completed except for the leg leveler which are on order from McMaster Carr. In the meantime I will begin to assemble the CNC Router on the table.


    The CNC Router table section is up with pictures. Also Stepit 4 and 4A (SLA7078MPR) schematics and BOM's are now posted.


    Ordered a emergency stop switch from Ebay for $8.00.

    This switch is also available from Amazon for $6.10 with free shipping. Switch is SPDT and will work with CUMC. When ON will set all drivers enabled, i.e., low signal. If pressed, all motor will be disabled, enable high.

    I have added to the CUMC post.


    We have motor driver pcb's from Batchpcb for L297/298 and TB6560 driver chips which have the same form factor as the drivers already shown here. In the next few days we will post schematics and BOM's for these drivers.

    The CUMC post has been updated, again.


    Sorry that I have not added anything in the last 6 weeks, but I have had other commitments. I hope to get back to the work in the next 2 weeks.


    New project: Filter blower to deal with the MDF and other dust  generated in the shop.


    No, I have not forgotten about the CNC router. I found that I have a number of housekeeping projects that need to be completed for my shop. There are parts and tools piled everywhere which has been added to with CNC Router project, so I have made the decision to clean up. For the shop to work well I need unencumbered bench and floor space. Presently I am using my Kreg jig to build a number of wall cabinets which I will add as projects.


    I have completed the prototype wall cabinet. I have chosen to make two cabinet sizes: 32"x 29" x 11" and 32"x32"x16". The smaller cabinets will be mounted between the front windows of the shop and the larger along the back and side walls.


    I am still here and intend to complete this project. I am working on my last shop project in my attempt to organize my shop. At present I am building a router table which can be found in my workshop blog.

      Wednesday, March 2, 2011

      CNC Router Part 3: Building the Base

      First step is to cut and drill the front and back of the base from MDF.

      1. From a 2' by 4' sheet of MDF cut off 24 1/2" piece.
      2. Adjust the table saw to exactly cut a 4 1/2" width. Cut and check with scrap wood. Now cut two pieces 4-1/2" by 24-1/2".
      3. Take one piece and set it face up. This surface will be designate as the rear of the back base plate. Using the drawing below, mark the vertical position of each hole. Start by finding the vertical center and mark that. Remember the piece is 24-1/2" wide so the center should be 12-1/4" from one end. Now position all the holes from the center line and mark each hole position from the bottom edge. Also mark the ends of the piece, 24", and the 45 degree cuts. Note: I used a center finding ruler, Utrecht 36 inch, Item No: 56746.
      4. Dimple each hole position lightly with a small center punch.
      5. Now, sandwich the two pieces together and place on the drill press table with the marked side face up and the bottom edge against the fence. Using a center bit or a center finder adjust the fence for hole number one. Making sure the ends are squared up then clamp the pieces to the table. Drill hole number 1 with a 1/8 inch bit through both pieces and insert a spare 1/8 bit in the hole as a pin. Notes: (1) Drill slowly or else the bit may bind or overheat. (2) Use a good quality bit for drilling and cheap bits for pinning.
      6. Drill hole 2 as you did hole one.and leave it pinned.
      7. Now reposition fence for hole numbers 3 and 4. Hole 3 which is on the center line will be drilled through both pieces with a 5/8" Forstner bit.
      8. Place a 3/4" Forstner bit and set to a drill depth 1/4" above the table surface. Re-position the pieces for hole number 4 and drill both pieces. This hole will not be drilled through the front pieces because of the stop.
      9. Re-position fence for hole 5 and drill with the Forstner bit.
      10. Leaving the pieces pinned, use the cut off saw to cut the pieces to length and cut 45 degree ends.
      11. The pieces are now ready for the next step.Remove the pins. Because of the symmetry, mark each piece: front of front, rear of front, etc.

        The next step is to cut the 1/8" circular groove for the PVC pipe into the back of front and front of back plate.
        1. You will need a Dremel rotary tool, a Dremel 678-01 circular cutter and 1/4" straight router bit (654).
        2. Following the Dremel instructions set the cut depth to 1/8" and outer diameter to 1.9". Using a piece of scrap MDF cut a circular groove and check the pipe fit, 1-1/2" schedule 40 PVC.
        3. Now cut the grooves in the rear of the front plate and front of the back plate, 4 places total. See picture.
        Next is to drill the motor mount holes. The following pictures show the centering of the motor template over the bearing hole. First, the 1/2" by 5/8" sleeve bearing was inserted into the hole and second, a 1/2" drill with a quarter inch shank was inserted into the bearing. This shank was then used to position the template. After aligning with a square, spring clamps were used to hold the template in place and the 3/16' holes were drilled. These holes were later drill out from the rear to 5/16" and a depth of 1/2". The later step was for the 10-32 EZ Lock threaded inserts.

          Next step, enlarge the four 1/8" holes to 23/64". Center the hole on the drill press table and clamp the piece. First, drill out the hole with a bullet nosed 5/16" bit, then enlarge to 23/64" with a regular drill. I found that the bullet nose drills do not chatter. These holes are now the right size for the 1/4" cap nuts.

          Next step, mount the 3/4" aluminum angle. First, cut two pieces of angle to 18". I did this on a cutoff saw with an aluminum cutting blade.

          BOM: CNC Router Base
          1. 1          MDF 3/4", 2ft by 4ft
          2. 6ft        1 1/2" schedule 40 PVC pipe
          3. 4ft        3/4" by 3/4 by 1/8" Aluminum angle
          4. 8ft        3/4" sq aluminum tube
          5. 2          1/2" bronze bearings flanged, MC 1677K9
          6. 2          1/2" thrust bearings, MC 6655K17
          7. 2          1/2" collar aluminum, MC6157K14
          8. 4          2" #10 unthreaded standoffs, MC92511A032
          9. 4          3", 10-32 PH PHIL screw, MC90272A842
          10. 1          Lovejoy coupling 1/2" by 1/4", Amazon
          11. 4          1/4-20 threaded rod 3ft
          12. 8          1/4-20 cap nut, MC90835A310
          13. 3ft         Acme precision threaded rod, MC99030A005
          14. 2           3/4" 1045 precision steel rod ground/polished, Speedy Metals
          15. 2           1"OD Aluminum round tubing, 3ft, Speedy Metals
          MC =