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Topics - MachinistSF

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1
Show"N"Tell ( Your Machines) / EMCO VMC-100 upgrade ready
« on: March 13, 2014, 07:40:23 PM »
I have replaced a 80s EMCO TM-02 controller with MACH3 PC based control system including new electronics for a VMC-100 CNC mill.

There is a servo controller, stepper controllers, programmable logic controller (PLC) and some power supplies and minor things. Interface to PC is via parallel port, using a VSDEPI break-out-board (BOB) from Granite devices, and another Chinese BOB. The original EMCO mill connectors are cut away and cables are connected to new electronics located in a metal cabinet bolted to the left side of the mill. There is also a large transformer for changing 230Vac voltage to 110Vac for the Vexta stepper controllers - this voltage is also handy for the servo powersupply, and offers isolation from mains.

Servo controller is Granite Devices VSD-E 160. It has a simple 150Vdc high-voltage powersupply based on a rectifier bridge and storage capasitor. PLC controls a relay that short-circuits a current inrush limiting resistor at the DC powersupply circuit. There is a bleeder resistor to bleed the charge from capasitor when power is switched off - the energy stored in the capasitor is easily enough to kill a person. Spindle control is with step-direction -control from PC. The tool changer rotation is based on spindle servo, so spindle had to be a true servo spindle instead of a more simple RPM control. In the servo controller there is scaling of the input pulses so that the full speed of spindle can be reached with the limited pulse rate of PC parallel port. This limits angular accuracy of spindle, but is a necessary compromise.

Stepper controllers are Vexta (Oriental motor) UDK5128. They can drive the 5-phase penta-connected original Berger-Lahr steppers of the mill. The control is with step-direction -control. I have also added X and Y axis limit switches, as EMCO design relied on software limits only. The overheat output signal goes to PLC from stepper controllers, and PLC controls enable input of stepper controllers. The stepper input/output signals are optically isolated so interfacing is simple.

2
General Mach Discussion / Spindle vs A-axis motor tuning, steps per unit?
« on: January 18, 2014, 04:10:18 PM »
Hello,

I have a servo spindle (using step+dir for Granite devices VSD-E) which I have configured both as spindle and as A-axis, so they have both the same LPT port pins in Mach config. My A-axis is in general config not angular (no checkmark there). I use the A-axis during tool change to rotate spindle which also rotates tool carousel in Emco VMC-100 when carousel is in top position. The step input in servo drive has electronic reduction even though servo encoder is 500ppr. This keeps steps per second reasonable at 4000rpm maximum speed.

It works.

Now, the strange thing is that I have to set the "steps per unit" for spindle to 200 (steps per rev) and to A-axis to 20 (steps per rev).
With these settings I get ok results: "G01 A1" does one full turn of spindle, spindle speed "60" does 1 full turn of spindle per second (also
measured from spindle index pulse by mach).

I'm propably missing something. I did read the fine manual, but couldn't find a difference there between spindle and a-axis tuning..
Why is the steps per unit different?

Thanks!

3
This is the new version of my plasmacutter.

The mechanics is the same as before. You can see them in another thread with chinese HF-start plasmacutter. That was the previous version. Stepmotors running X, Y and Z with chain drive.

There is a waterbed for catching dust. The water level is a few mm above plate to be cut. It keeps even 1mm sheet totally without heat warping and thick plate cool to touch after cutting. The water is only about 6cm below the plate to be cut, that is enough to stop the plasma stream. I have added some citric acid to water to prevent rusting. The water container is made from stainless steel and coated inside with polymer to prevent galvanic corrosion of stainless steel.

At the top of the enclosure is a modified (cut the bottom open and connected to enclosure top hole) industrial vacuum cleaner that is sucking air from the enclosure through filters. It practically eliminates dust escaping the cutter. The enclosure has polycarbonate walls and door so it catches also splashes of water and sparks.

The plasma cutter is Everlast Powerplasma 60. The torch is a heavily modified WSD-60P from ebay. I actually sawed off most of the plastic handle etc. so I could mount it to Z axle conveniently, and bent the copper air tube of the torch. I also run separately pressurized air, plasma current and pilot arc. The connection to plasma cutter is a euro connector that has all in one connector. The plasma cutter is mounted under the waterbed.  

The electronics is in electronics enclosure mounted under waterbed. Next to electronics cabinet is PC. All the signals are either optoisolated or relay-isolated. For the plasma cutter there is 3phase 400V 16A supply with RFI filtering. There is separate filters for PC and TFT display. PC works ok with PS/2 connected mouse and keyboard. For some reason USB mouse/keyboard sometimes caused problems (had to unplug and plug again), so I replaced with the PS2 connected ones. PS2 has much lower data speed so I think it is more noise immune than USB.

I think the use of a vented cabinet around the plasma cutting is a novel innovation. I have not seen it anywhere else. I am now plasmacutting inside my shop next to lathe and mill. Also the placement of keyboard, mouse and display on top of the enclosure is a novel innovation, making the floor space required minimal. The device is on wheels so I can move it.

(C) KU 2013

4
Show"N"Tell ( Your Machines) / China HF-start plasma CNC design!
« on: November 17, 2011, 06:25:04 PM »

Hi,

I just cut the first pieces with my new DIY CNC plasma today!!

It uses 3 steppers with chain drive for all axis. Z is a floating design with limit switch
for detecting zero at plate surface with G28.1 Z. Movement is 70cm x 70cm.
Torch is a PT-31 machine torch. Steppers are controlled with chinese 3-axis
TB6560 card - replaced 12V fan with 24V one and removed the "current
reduction when not moving" feature.

I initially had problems with RF interference from the Chinese CUT-40 HF-start
plasma, but I managed to solve the problem cheaply. I added a ground wire to
the copper electrode sticking out from the plasma torch - this way it creates always
a "pilot arc" (at full current) and initiates the cutting reliably without HF interference.
Without this it would not ignite reliably and would emit HF interference, causing
limit switches to trip, USB mouse at PC to stop working etc.. None of that now,
the immediate arc to groundwire will shunt the RFI, I'd say.. Based on some test
cuts, it works very nicely. I figured out that the electrode is touching ground through
the workpiece anyway, so it won't hurt connecting ground to the electrode always - and
this way it ignites reliably. It will also send a nice plasma flame to air if it is far away from plate!

I'll send some photos later. Now the main point is that this way one can use the
cheapest of the cheap Chinese CUT-XX plasmas for CNC, to save amateur costs!!
I haven't seen this anywhere else so I might have invented a new thing here!


5
General Mach Discussion / EMCO VMC-100 conversion
« on: November 13, 2011, 03:43:22 PM »

Hello,

Anyone out there who has converted their VMC-100 to mach3, including tool changer?

I'm thinking of doing that - using original 5-phase stepper drivers (accepting step&dir directly).
I'm not certain about spindle servo drive - especially controlling it for driving tool change gear.
I'd really prefer interfacing to the existing electronics, so I could use the original electronics too
if necessary.

I'd really prefer not to invent the wheel again if someone has done this!

Thanks!

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