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  1. #1
    Hi All, I am helping my Father convert a Boxford VMC 190 to use with Mach3.

    I am wondering if anyone can help with a few questions I have about this as I am fairly new to the world of CNC.

    So far we have replaced most of the electronics with a Pokeys USB, CNC addon and their 2.5A driver boards. We have kept the standard power supply, spindle controller etc. We can now get all
    axis moving using the jog functions in mach3 etc. Spindle control is currently using a 10K pot but will convert this to mach control at some point.

    Does anyone know how we should be setting up the following?

    1 - Steps per mm? - Currently we have the default of 2000 but havent tried to measure this yet. Does anyone know the correct value for this mill based on the pitch of the leadscrews?

    2 - Microstepping? - The drivers support all kinds of microstepping but is there a recommended setting to start with?

    3 - Motor velocity - Some of the forums say you should hear when this is right but is there a good place to start when using this mill with the standard steppers?

    4 - Limit/Home switches - The Boxford has what appear to be inductive sensors on each axis. Are these suitable for use as home/limti sensors and does anyone have any experience with them?

    For info CNC control is done using the Pokeys56U with their CNC Addon and drivers. This has a plugin to work in mach3 but seems to work well.

    Any info or advice would be greatly appreciated.

  2. #2
    Hi Martin,

    I cannot help you or answer your questions as I am going to be in a similar position soon.

    I have basically bought a VMC190 m/c. All the drives run well in manual, it seems a shame to rip out all the insides and replace them with new boards. I have all the old software with the machine. I am assuming that I can add a RS232 serial socket to my PC so I can communicate with the mill. But what benefits does Mach3 have over the original software? Also, can you get other software that would allow people to run the machine in it's original configuration? I have a auto tool changer on my machine which requires air to run, it all runs at the moment in manual mode.

    How did you decide upon the CNC control boards that you bought? Was it through advice on the forum?

    I ask because if I have to go ahead with conversion I was looking at the HobbyCNC EZ or Pro chopper Driver board kit, I can see it works off a paralellel port but understand you can just buy a convertor (ie parallel to USB).



  3. #3
    Hi Steven,

    We didn't have the original software and Mach3 seemed to be the popular choice and has a large community to support it etc. I may also give LinuxCNC a try at some point but thought that Mach3 would be a good starting point. We were also reluctant to ripout all the boards but not being able to interface to them made them pretty much no use to us. Also I had read that modern drivers would be an improvement over the ST ones it used. We ripped out almost all the control boards and left the Spindle controller, main power transformer rectifier, cap etc and the Choke for the spindle. We then rewired everything to get a good understanding of what wire did what etc.

    Pokeys was chosen as I had a laptop spare that didn't have a parallel port and I had read all-sorts about timings being off with laptops and external converters. I started looking for external Pulse generators that would work with Mach3 and Pokeys was mentioned in a couple of posts. It was a bit of a gamble bit its been pretty easy to get that side of it setup. We use the USB version but there is an Ethernet version too. From what I understand the Pokeys plugin attaches to the Mach3 core so all the steps are counted in the pokeys itself when its running. You can use the pokeys direct with the drivers but we also opted for the CNC addon which adds a couple of relays and also expands the features of the pulse engine to allow more axis etc. It also makes connecting to their stepper drivers easier.

    So far we haven't interfaced with the spindle controller directly or with the existing home switches but I plan to take a look at that next. We setup the Stop button to trigger the E-Stop in Mach3. We have since had the machine cutting some parts in Ali which it does a treat although we did have a couple of issues with needing the swap the stepper wires for the Z axis to get the axis going in the right direction (0 at top).
    We also need to tune the steps/mm but we roughly did this by clamping a digital caliper in the vice and jogging the tool and adjusting the values. Its a bit crude but it got us to within a few points of a mm which is fine for testing etc.

    Would be interesting to see what you go with and how it fares.


  4. #4
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Current Activity: Viewing Has been a member for 8-9 years. Has a total post count of 1,303. Received thanks 125 times, giving thanks to others 3 times.
    1) This depends on 2) combined with pitch of screws, any gearing between motor and screw, and if you're setting up in metric or imperial.

    Essentially, most common stepper motors are 200 steps per revolution, so multiply that by your answer to 2) to get your steps per motor revolution. If there is gearing between the motor and screw, you then need to add that into your equation to get number of steps per turn of the screw. You then need to divide the steps per screw turn, by the pitch of your screw to get your steps per unit. Your unit will be either 1mm for metric, or 1 inch for imperial.
    i.e. 200 x 8 = 1600 steps per motor rev. I'm going to assume you're motors will be direct connected to the screws, so you still have 1600 steps per screw turn.
    Assuming metric and a 4mm pitch screw, you then divide the 1600 by 4mm to get 400 steps per unit.

    2) 8 is usually best the compromise. Any more doesn't gain you any accuracy with a stepper system, and less can make things a bit jerky at low speeds, although it may be needed if your step pulse isn't high enough to get reasonable speeds.

    3) How fast is your bit of string? Generic guidance is keep upping the figures until things start stalling, then back of a bit to provide some saftey margin.

    4) Depends on how many wires the sensors have. 3 or 4 wire, are easily useable provided thier voltage range is useable. 2 wire, bin them and buy new, as they'll be NAMUR output which interfaces will cost you more than new sensors.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  5. #5
    Thanks m_c,

    I am currently set to 16 on the drivers and it runs fine but will change this to 8 and see how it goes.

    The X and Y motors are directly connected but the Z has a toothed belt, It seems to be a 1:1 ration so should be fine. I think i need to measure the pitch of the screws then I can calculate the steps as you described.

    The sensors are the 3 wire type and are 10-36vdc so I will get one hooked up to some power and see what the output wire does when it reaches home.

  6. #6
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Current Activity: Viewing Has been a member for 8-9 years. Has a total post count of 1,303. Received thanks 125 times, giving thanks to others 3 times.
    If you get enough speed at 16 microsteps, then there's not really any need to change it. One thing to consider, is microsteps should never be relied on for accuracy, as the stepper position can only be guaranteed to the nearest step. While microstepping, both coils are proportionally energised, with the rotor essentially held between two magnetic fields, so can spring/float (there probably is a better word, but I'm tired!) depending on load.

    Sensers will most likely be NPN with an open collector. Are there any numbers on them?
    If there is, try googling it to see if there are any datasheets for them, which will confirm what they are.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

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  8. #7
    m100's Avatar
    Lives in Yorkshire, United Kingdom. Last Activity: 09-08-2015 Has been a member for 6-7 years. Has a total post count of 6.
    This post mentions a wiring diagram for the Boxford 190. No reponse to a PM and the user hasn't posted for quite a while.

    Interested if someone can supply a wiring diagram to aid conversion of my 190 (Lenze controller type)
    Last edited by m100; 18-08-2014 at 10:27 PM.

  9. #8
    Hi Martin,

    Sorry for delay in response. I have bought myself a smoothstepper board and just ordered a Breakout board. Looking at the insides of the machine I understand I can retain the steppers and the stepper drivers but need to disconnect the driver control boards. There is one driver control board for X & Y axis and one for the Z axis. I am assuming I can remove these boards and rewire back to my breakout board so I can connect upto my smoothstepper. Looking at the wiring for the auto tool changer it seems to be indenpendant from the rest of the machine so I am hoping to retain this but I shall see.

    I am assuming the photos below show the axis driver boards, photo on right is the 3rd axis or Z axis, photo on left shows the 1 & 2nd axis with the stepper drivers board above. If I am incorrect please correct me now.

    Click image for larger version. 

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  10. #9
    m100's Avatar
    Lives in Yorkshire, United Kingdom. Last Activity: 09-08-2015 Has been a member for 6-7 years. Has a total post count of 6.
    Comparing my 190 to the Boxford 160 lathe that uses a similar stepper driver board as the 190, and a similar MW Controls processor board underneath (in the case of the 160 the steppers are assigned to the x axis, the z axis, and the turret for the lathe toolpost toolchanger rather than X Y Z for the 190).

    The Bradford instruments board is possibly also a limit switch interface, the ribbon cable is labelled PL1 fast serial link at its connection to the main processor board and contains very similar components to the main processor board. Comparing the photos of my machine (without a toolchanger) to yours I have a total of 5 wires and a loop on the orange connector, you only appear to have two. Where you have two white wires I have an orange and purple connected to CL5 and CL6 respectively on CONN1 on the stepper board. Suspect these are the clock and direction for one axis.

    The additional wiring I have, a 3 core small diameter cable eventually goes through a conduit that leads, I think, to the motor head. That PCB also carries three LEDs L1,L2, L3 attention, limit plus and limit minus respectively.
    I suspect these are may be the Z limits, the wiring looks the same as the x and y limits and yours does not have a z limit switch or it does it is implemented in a different way.

    Below is a photo of the connector between the processor and the stepper board, at the stepper board end, with the two wires on the end that go to the standalone bradford instruments board

    The underside of the stepper board has a factory fitted 'bodge wire' to connect CL6 to pin 6 (step) on the GS-D200S stepper drive on the Z axis. Given that the stepper board is 'universal' there might be some confusion about the allocation of the pins and the silk screen.

    The terminal assignments for the 190 should, I think, be as follows:

    xd = x direction
    xc = x clock
    zd = y direction
    zc = y clock
    cl5 = z direction
    cl6 = z clock

    Click image for larger version. 

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    Last edited by m100; 20-08-2014 at 07:58 PM. Reason: added photo + pin assignments

  11. #10
    Quote Originally Posted by m100 View Post

    The Bradford instruments board is possibly also a limit switch interface, the ribbon cable is labelled PL1 fast serial link at its connection to the main processor board and contains very similar components to the main processor board.
    I have the original manual for both the 160 TCL and the 190 VMC, the manual for the VMC says the small board is the 3rd axis microprocessor board.

    Do you have yours running with original software?

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