Boxford 190VMC conversion with Mesa 7i96S

Hello

I'm starting a project to convert a Boxford 190VMC to LinuxCNC. I'm hoping this thread will log my progress (although I expect it to be slow).

I've ordered a Mesa 7i96S and 7i84 (I'd have preferred a 7i76E but Mesa told me that new stock of these was still a long way off).

Any tips or hints would be great.

I have what is hopefully a quick question...

If I install the Mesa cards in the machine is it possible to wire it up and program it in such a way that the machine can still be operated in manual mode, even when the PC running LinuxCNC is disconnected?

I.e. The machine control panel has manual jog buttons for each axis and FWD and REV buttons for the spindle. Could these be connected to digital inputs on the Mesa board and the FPGA programmed to execute the appropriate actions? Another digital input could perhaps be used to toggle between manual and cnc modes?

Best regards,
Matt

The 7i76e has two MPG inputs which is perfect for a lathe. With the right firmware the 7i96s should be able to do the same at the expense of some inputs. But being a lathe, you will have some spare stepgens that can be repurposed, so maybe PCW will have a solution.

No need to go after Boxford... it is indeed a small 3 axis milling machine, inside an enclosure.

@andypugh,

I guess that makes sense if you are fluent in gcode. (I only have a vague and limited knowledge of it so far).

Still, it is probably a good idea to just concentrate on getting the Mesa card wired up to the steppers and spindle first and get them moving under LinuxCNC. Then worry about manual button controls later if still wanted.

...About the "in theory possible" part... So does LinuxCNC provide a way of programming rules onto the FPGA for stand alone operation? Or would this be something I'd have to tackle by customising the Mesa firmware?

I'm trying to gather information about all of the components at the moment, will be easier when I can actually open the machine (need to set it up in a better place first).

...About the "in theory possible" part... So does LinuxCNC provide a way of programming rules onto the FPGA for stand alone operation? Or would this be something I'd have to tackle by customising the Mesa firmware?

This is most easily done using LinuxCNC, The 7I96S has 4 MPG inputs (plus the 7I84 has 2 more)
so having either a manual mode or a complete LinuxCNC configuration devoted to manual mode
is possible. A manual mode configuration could also incorporate straight line moves at any angle
None of this requires any firmware changes.

A bit of an update...

The XYZ steppers are working well (using the original drivers).

There are homing switches for each axis - also now working.

The spindle is working (including stop, variable speed and direction changes).

I've connected up the lamp relay and made a custom pyvcp control for it.

This has been enough to do a couple of little milling/engraving tests under linuxcnc control. (The original manual buttons are currently disabled).

The next thing to tackle is probably the spindle encoder. The machine currently has a single slotted switch (TT OPB866T55) but has a wheel with both holes and an index slot. I guess it was intended to function only as a tachometer in this version but the manufacturer offered upgrade options.

The existing slotted switch plugs into the original main control board (which is going to be removed). So this means that the encoder will lose whatever circuit it currently has to work. I'm not sure if this switch can function directly with the Mesa card or what circuit it would need.

I'm considering replacing that single slotted switch with 3 of the TT OPB900 series as I think these can give TTL level outputs that might have a better chance of working with the Mesa card. Two would be for the quadrature signals, the third for index. I might need to make a little bracket to mount them (although it looks like the existing bracket could already mount 2 slotted switches).

Obviously it would be nice if the mill could tap holes but the spindle control seems fairly basic. It has a relay to switch the direction polarity, an enable/brake relay and a 0-10v analogue signal for speed. It probably won't ever be able to change direction quickly - it has to be stopped before it can engage the other direction.

What do you guys recommend?

I'm leaning towards slotted switches over a stand alone encoder as that will allow me to use the existing drilled wheel. Are there particular models recommended here? Also, are there any ready made pcb's that I can use to wire the slotted switches to and get a more standard encoder output?

If you use opto-interrupters on that disk you will probably need to make them adjustable
to get decent quadrature, so a pre-built PCB is unlikely unless you make it yourself for
the specific pitch of that disk.

if you are trying to achieve rigid tapping then forget it, the spindle does not have enough torque at the speed that you would use for tapping.
This is the reason that the VMC190 only had the index signal on the spindle so it would know spindle speed.
The ring that as the slot and holes is a common Boxford part hence it is fitted to the VMC190
I have one of these also converted to Linuxcnc, runs very well and the tool change is so convenient it almost does away with the need for an auto tool changer