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-Y TABLE Part.3: Building The Z Axis WITH STEPPER MOTOR CONTROL OK; you thought that the XY table was heading in the right direction but wouldn’t really do the job you wanted it to. Well, you’re right. You can’t really do much with it without the third axis control. Mechanical Design & Construction by Ken Ferguson Electronics by Rick Walters 72  Silicon Chip T HE Z AXIS IS constructed as an additional frame to which the XY table is bolted. It is capable of supporting a pen, a small electric drill or some other tool you may deem useful. We used a Dremel drill and stand, mainly because we already had it to hand and we made up a pen holder which will be de­scribed in a future article. A third stepper motor was used to drive the Z axis but instead of the threaded lead-screw system used for the X and Y axes, we used a crank system to move the tool. While there is nothing essentially wrong with using another threaded lead screw, it is not cheap and we didn’t really feel that it was necessary. The Z axis stepper motor is driven by the single stepper motor driver board which was featured in SILICON CHIP in August 1997. The board should have the modification detailed in the May 1999 issue. If you don’t already have these, we have now modified the stepper motor drive boards and these will be fea­tured as part of this series of articles on the XY Table. For convenience, and also to keep them safe from harm, we mounted both the stepper motor boards in a small plastic case with a 12-way terminal strip on the back. The terminal strip provides a convenient termination point for the leads from the three motors. An additional 4-way connector terminates the wires from the power supply. We brought the LEDs, which were originally mounted on the PC board, to the front panel so we could monitor each board’s operation. If you don’t fit the modification featured in May 1999, you MUST turn the 5V supply on first then load and run the software, turning on the other supplies at the opening screen. As we ex­plained last month, it is possible for the ICs to turn on in a manner which can cause some of the output transistors to fail if this procedure is not followed; not a nice sight or smell! With the modified PC boards, this procedure will not be necessary. We set the jumper to select board 2 for the dual stepper driver and board 3 for the single stepper. If you plan to use the relay interface board, which was described in the July 1997 issue of SILICON CHIP, with this setup (or even if you don’t) we sug­gest that you Fig.13: the Z axis frame is made from 20mm x 20mm steel tubing which is welded into a frame measuring 830mm x 240mm. (Drawing scale 1:5). Stepper motor driver JULY 1999  73 Fig.14: details of the top motor mounting bar. This is made by cutting two pieces of 10mm x 10mm bar 280mm long. One piece of 27mm x 10mm x 10mm is then welded at each end to make a slotted bar with a ¼” Whit­worth slot running almost the full length. (Drawing scale 1:2). Fig.15: details of the motor mounting bracket. It is folded from a piece of 3mm plate and has an outrigger bracket 50mm x 25mm x 5mm welded to one side to mount a terminal strip. (Drawing scale 1:1). bypass IC4c as this makes that board compatible with the current software. Z axis frame The Z axis frame is made from 74  Silicon Chip 20mm x 20mm steel tubing which is welded into a frame measuring 830mm x 240mm. The details are shown in Fig.13. The bottom left and right ends protrude about 50mm at the front and back to form the supports for adjust­able feet. A 20mm x 20mm plate 5mm thick is welded at each end, then drilled and tapped to support the 1¼” Whitworth bolt which is used to level Parts List 4 790mm 20 x 20mm tube 4 470mm 20 x 20mm tube 2 340mm 20 x 20mm tube 2 240mm 20 x 20mm tube 1 50 x 50 x 5mm plate 4 20 x 20 x 5mm plate 2 260mm 25 x 25mm angle 1 13mm 20mm rod 1 15mm 15mm rod 1 12mm 15mm rod 2 125mm 50 x 5 bar 2 270mm 25 x 5 bar 4 50mm 25 x 5 bar 2 130mm 12 x 5 bar 1 70mm 12 x 5 bar 2 280mm 10 x 10 bar 2 27mm 10 x 10 bar 14 1¼” x ¼” Whitworth bolts 16 1½” x ¼” Whitworth bolts 22 flat washers 22 ¼” Whitworth nuts 4 plastic inserts 2 4mm grub screw Fig.16: the motor crank is made from a circular piece of 5mm plate 50mm in diameter. A ¼” clearance hole was drilled at 20mm radius. A piece of 15mm diameter rod 15mm long was cut and slotted at one end to fit over the motor pin. It was then welded to the crank to form a boss. (Drawing scale 1:1). the frame. Fit a nut to the bolt before screwing it in and use the nut to lock the adjustment. Four plastic in­serts are fitted into the open ends of the tubing to finish off the stand. Drill stand support The drill stand was mounted upside down and its baseplate was supported by two pairs of brackets made from 270mm lengths of 25mm x 5mm steel bar. Clearance holes were drilled 10mm and 50mm from each end and the brackets were mounted either side of the top rails and clamped together with 1½” bolts. Obviously you will have to drill mounting holes in the bars to suit your particular base. Fig.17: this diagram shows the details of the crank pushbar. This attaches to the motor crank and moves the drill up and down. (Drawing scale 1:2). Motor mounting The top motor mounting bar (Fig.14) is made by cutting two pieces of 10mm x 10mm bar 280mm long. One piece of 27mm x 10mm x 10mm is welded at each end to make a slotted bar with a ¼” Whit­worth slot running almost the full length. Cut two pieces of 25mm x 5mm bar each 50mm long and drill clearance holes 10mm from each end of both bars. Four 1½” Whitworth bolts and nuts are used to clamp these to the top bar. The details of the motor mounting bracket are shown in Fig.15. It is fold- Fig.18: the stand actuator lever is made from a piece of 25mm x 5mm bar 60mm long and has a 20mm-diameter x 15mm long boss welded to one end. (Drawing scale 1:1). JULY 1999  75 Fig.19: the fixed XY table clamp is made by cutting a piece of 25mm x 25mm angle 260mm long. This is welded in position and needs two slots centred 107.5mm either side of the centreline in the vertical face. (Drawing scale 1:2). Fig.20: the adjustable XY table clamp is slotted in both directions so that it can be pushed close to the XY table before the bolts are tightened. (Drawing scale 1:2). ed from a piece of 3mm plate. Two clearance holes were drilled on the centre­line 20mm and 40mm in from one end. The other end had four holes drilled to mount the stepper motor. An outrigger bracket 50mm x 25mm x 5mm was welded on one side to mount a terminal strip. Motor crank Fig.16 shows how the motor crank was made from a circular piece of 5mm plate 50mm in diameter. A ¼” clearance hole was drilled at 20mm radius. A piece of 15mm diameter rod 15mm long was cut and slotted at one end to fit over the motor pin. It was then welded to the crank to form a boss. The centre of the crank (and boss) was then drilled to neatly 76  Silicon Chip fit over the motor shaft. The boss was tapped for a 4mm grub screw to allow it to be locked onto the motor shaft. Crank pushbar The details of the crank pushbar are shown in Fig.17. A piece of 15mm rod 12mm long was welded to a bar 12mm x 5mm, 70mm long. The rod was then drilled for ¼” Whitworth clearance. Two pieces of 12mm x 5mm bar 130mm long were cut, then eight holes were drilled in each bar, the first 10mm from one end then every 10mm. These were then welded to each side of the 70mm bar as shown in Fig.17. Stand actuator lever The stand actuator lever is shown in Fig.18. It was made from a piece of 25mm x 5mm bar 60mm long. A boss 20mm in diameter 15mm long was cut and welded to one end of the bar. The centre was drilled out to fit the shaft of the drill stand and the boss was tapped for a 4mm grubscrew. The other end was drilled ¼” clearance 10mm from the end. XY table base clamps These were made by cutting two pieces of 25mm x 25mm angle 260mm long. The fixed one is welded in position and needs two slots centred 107.5mm either side of the centreline in the vertical face. These should be made around 8-9mm wide to allow a little clearance, as shown in Fig.19. Fig.20 shows the adjustable clamp. It is slotted in both directions to al- Table 1: Example Files LCOSW.TOL ­­ PROTEL TRAXPLOT Version 1.61 NCDrill Tool Loading Specification PCB File : C:\PROTEL\PCB\LCOSW.PCB Date : 10/03/1999 Time : 15:41:41 T01 31 T02 51 T03 39 This shows that all the holes under the T01 header should be drilled with a #31 Imperial drill. The Windows versions of Protel give a Metric drill size as well. Those under T02 should be drilled with a #51 drill and the T03 (nothing to do with a T03 transistor) group of pads should have a #39 hole. This close-up view shows how the drill stand is clamped to the top of the Z-frame. It also shows how the push bar is attached to the drill and to the circular crank attached to the stepper motor. low the XY table to be bolted to the fixed clamp, then this one is pushed close and tightened both to the base and to the table. The bolt heads for this bracket which pass through the base bar should have their heads tack-welded. Software The software we have supplied for this stage allows you to drill a PC board which has been laid out with Protel Autotrax V1.61 or Easytrax V2.06. As Easytrax (and Easyplot) was a free layout package you should, with a little effort, be able to get your hands on a copy (try www.cia.com.au/rcsradio). Using Traxplot or Easyplot, load the board you plan to drill then select NC drill from the menu. Three files will be generated: FILENAME.TOL, FILENAME.DRL and FILENAME.TXT. With Traxplot, the drill sizes for the different pads are listed in the FILENAME.TOL; with Easyplot the TOL file is empty. This is not a problem as you will normally drill all holes with an 0.8mm or 0.9mm drill, then redrill those that need to be larger. FILENAME.TXT contains a list of the X and Y co-ordinates for each hole. Thus by locating the XY table at 0,0 it can then be moved to each pad centre. If the Z axis drill is then moved down, a hole will be drilled. The software will read the next pad centre from the list then move the table to that location. Once LCOSW.TXT M48 T01F00S00 T02F00S00 TO3F00S00 % T01 X00825Y008 X00575 X00825Y0065    |    |    | Y00375 Y00275 T02 X004Y0085 Y003 X02525Y008 Y004 X03175Y00775 T03 X01275Y008 etc to last entry M30 There were actually 38 holes to be drilled T01 (#31) size, only five T02 (#51) size and 18 for the T03 drill size. If you don’t select the redrill option the software only reads through the file once, drilling each hole in turn. As we have already said, use an 0.8 or 0.9mm drill for all holes, then manually redrill those holes that need enlarging. If the redrill option is selected, the software will finish drilling that size hole, home the table, advise the next drill to be fitted then drill those holes, repeating the sequence until all the holes are the correct size. JULY 1999  77 The XY table sits on the base of the Z frame and is secured using a fixed clamp and an adjustable clamp. The completed unit can be used to automatically drill PC boards, or can be used for other tasks. The drill stand is clamped to the top of the Z frame using two pairs of flat metal brackets made from 270mm lengths of 25mm x 5mm steel bar. Clearance holes were drilled 10mm and 50mm from each end and the brackets were mounted either side of the top rails and clamped together with 1½” x ¼” Whitworth bolts. 78  Silicon Chip the PC board is drilled, the table will return to 0,0. Just in case you experience problems while drilling, you only have to press any key and the program will abort, homing the table (to 0,0). The software consists of the following seven files: PCBDRILL.BAS, PCBDRILL.EXE, DRLSETUP.BAS, DRLSETUP.EXE, DRLSETUP.FIL, DRLTEST.BAS and DRLTEST.EXE. These are available free from our web site, or on a floppy disk (price is $7.00 including packaging and postage from SILICON CHIP). The first two files are self explanatory; they drill a PC board. The BAS file has been provided to allow you to modify the software if you wish. The setup files let you key in the maximum X and Y values for the table position and the table stepping speed. They also allow you to allocate the addresses of the XY and Z stepper driver boards, select an Imperial or metric display and select which Above & bottom right: these two views clearly show the drill stand set-up in relation to the XY table. parallel printer port you plan to use to drive the stepper boards. The software which drives the Z axis moves the drill down close to the PC board surface (assuming we plan to drill a PC board) as soon as the program begins, then moves it the shorter distance through the board each time a hole is drilled. This reduces the time taken to drill the board. Both these adjust­ ments can be set or changed in the setup programs. The last setup option either allows the program to go through the drill cycle once, as would be the case with Easyplot, or home the tool. It will then ask for the next drill size and redrill these holes, until the board is completed, with each hole the size that you specified when you were laying out the board. The DRLTEST programs allow you to move the drill up and down to fine tune the initial drill down position and then the fully down position. Obviously, you should move the PC board out of the way of the drill until your adjustments are correct. You can use the XYTABLE program, which we talked about in a previous article, to do this. The Protel TOL (TOOL) file and an extract from the same PC board TXT file is shown in Table 1 SC on page 77. JULY 1999  79