Messages

4561

Mach4 General Discussion / Re: Mach4 Printer Port Discussions

« on: June 17, 2014, 12:05:29 PM »

Hi Art,

I have been searching my PC but cannot find the link to it - The Synrad UC2000 controller data sheet gives a lot more information on Duty Cycle and Pulse Repetition Frequencies and how they should be managed - perhaps may be worth looking for it if it is still available on the Synrad site.

I have no practical experience of mounting a tube vertically I am just going on the manufacturer's advice trusting that they are correct.

Tweakie.

4562

Mach4 General Discussion / Re: Mach4 Printer Port Discussions

« on: June 17, 2014, 11:32:37 AM »

@ Craig,

I understand what you say, however, the logic gates invert the signal - connecting another gate in series restores the state. As there are 4 'and gates' in a package it makes sense to use one of them this way rather than use a separate inverter chip.
The output shown from the tickle pulse generator is signal 1 and GND. Signal 2 is fed from the Mach PWM or a stand alone PWM generator then the output goes to the laser control circuitry. Hope this makes sense. 

@ Art,

I think the Synrad CW operation may only apply to the relatively new models of their RF lasers. I don’t know for sure but I suspect that externally we can apply 100% duty cycle while internally the electronics is still pulsing at a reduced duty cycle and I would be concerned that older models do not have this safeguard. Perhaps we need to contact Synrad for more information.

As far as I am aware the grey scaling was not incorporated into the version of the plugin that you released.
If it’s any help this is typical of the shades of grey that can be achieved from the plugin as it stands http://openbuilds.com/attachments/a1-jpg.1862/

Tweakie.

4563

Mach4 General Discussion / Re: Mach4 Printer Port Discussions

« on: June 17, 2014, 08:20:34 AM »

Hi Art,

For the Synrad I use an external tickle pulse generator. It is a very simple circuit and has approx 10% of adjustment for both the frequency and pulse width – this enables it to be set to just below the point of lase. The Mach PWM and the tickle pulse are then switched in or out by a separate trigger circuit (diagrams attached).

In order to get the best laser versatility (never know what we will want to do tomorrow) I think you need as many different individual levels of power as you can achieve (I believe Synrad use 5% step variation of the duty cycle between 0% and 95%).

You will have to be careful if operating the Synrad above the recommended 5kHz PRF – for example at 20kHz then a 95% duty cycle will exceed the maximum recommended internal photon density for the tube (overheating the output coupler and / or the rear mirror). The Synrad controllers software limit the maximum available duty cycle as PRF is increased thereby negating the problem.

I am no expert here but it is my understanding that the Mach3 engraving plugin allocates a set number of ‘dots’ per each individual pixel value and because for high pixel values the dots overlap each other many times during one X axis scan it produces ‘dot-gain’ and thus a shade of burn in accordance with actual pixel value. In my opinion this process works extremely well and I think I am able to get results that are up there with the professional laser systems. Overall the engraving plugin is going to take a lot to better but you are the expert and I am really looking forward to trying the Mk II.

On the other side of the coin those using diode lasers have found that DC variation in actual laser output power level in accordance with pixel value is the way to go.
I can actually do this with my DC excited laser but I still prefer to vary the output power level by varying the PWM in the same way as the Synrad is controlled.

Tweakie.

4564

Mach4 General Discussion / Re: Mach4 Printer Port Discussions

« on: June 17, 2014, 06:04:25 AM »

My first laser test with Mach4 and Darwin (using a well trusted GCode toolpath that has been run many times before). Although this is not a method I would prefer to use the laser switching was done by using the A axis direction pin (A1=on and A0=off) and everything ran exactly as expected with no errors.

The problem mentioned in my earlier post regarding the final G00 X0,Y0 home move has now been identified as being the M30 command which, on my old and perhaps rather slow PC causes, both motors to stall during the GCode rewind. Removing the M30 cures this problem.

The ‘run today and not tomorrow’ problem I was experiencing has also been cured so it’s onwards and upwards with perhaps some more adventurous testing. 

You need to get that Synrad hooked up and running Art. 

Tweakie.

4565

VB and the development of wizards / Re: RSLinx DDE/OPC

« on: June 17, 2014, 03:37:46 AM »

Hi Roboticist,

No worries about filling space here - thank you for posting the information.

Tweakie.

4566

Mach4 General Discussion / Re: Mach4 Printer Port Discussions

« on: June 16, 2014, 07:09:45 AM »

My congratulations go out to the Mach4 team and Art for his excellent work with the parallel port driver.

This engraving was my first test run using Mach4 ver.1767 with the Darwin driver and it behaved faultlessly (except for the final blended G00 X0 Y0 home move which stalled both motors but that was my fault for having my Velocity / Acceleration settings optimistically set way too high). The 4 holes and the profile cutting require a tool change and as I don’t have Auto Tool Zero set-up decided to give this part of the toolpath a miss. The actual engraving is not the finest – I used an old (retired) engraving bit mainly because I just wanted to get some confidence in the software without damaging a good engraving bit if anything went wrong during the run.
It is hard to describe the sound but the motion is just so smooth my machine sounds entirely different – the steppers make a much higher pitch whine as opposed to the hum they make when running Mach3.

Setting the spindle to respond to the M3 / M5 commands defies my understanding and seems to be just a matter of luck. Although I finally succeeded I don’t know how I did it or if I will ever be able to do it again. I still have no idea how I will be able to switch my laser on / off  from Mach4 but that will have to wait until another day.

I don’t know if it is just me or if others will encounter a similar issue but once everything has been set-up and is working OK – shutting down the PC then restarting the following day nothing works and the only cure has been to re-install Mach4 then enter all the settings again from scratch. This could just be a WinXP problem in the way it saves settings on shutdown but I need to investigate this further.

One major problem I encountered initially was that the graphics card fitted to my machine PC was not up to the task of handling Mach4 and this card had to be swapped out for a higher spec. gaming graphics card before I achieved anything like smooth motion from the steppers.

Overall I am very impressed with the performance of Mach4 but the initial setting-up is very different to Mach3 and takes quite a bit of learning (without a manual) but I am getting there slowly.

Tweakie.

4567

General Mach Discussion / Re: Engraving Spindle.

« on: June 14, 2014, 03:29:13 AM »

Hi Gary,

I think you would be able to do quite successful MILLING with a 5kW BLDC motor (although gear reduction may be necessary to reduce the speed). 

Quite obviously, a much smaller motor is required for engraving work (which is exactly what this thread relates to) although I quite like the idea of a 'combined engraving spindle and spot welder'. 

Tweakie.

4568

General Mach Discussion / Re: Engraving Spindle.

« on: June 13, 2014, 06:14:22 AM »

Hi Ozymax,

Thank you for your excellent suggestion - I will investigate the possibility of using a 'gov/esc' (I did not even know they existed for BLDC motors) but it sounds like a brilliant idea to me and would be a very easy solution to maintaining constant RPM.

Tweakie.

4569

Show"N"Tell ( What you have made with your CNC machine.) / Re: Marines Emblem 1st Carve

« on: June 13, 2014, 05:13:21 AM »

Nice work Artcarver - thanks for posting the GCode file for others to try.

Tweakie.

4570

General Mach Discussion / Engraving Spindle.

« on: June 13, 2014, 05:01:01 AM »

Just as a heads up…

Tests have shown that small brushless dc motors (BLDC), more usually used with RC models, (mainly because of their high power to weight / size ratio) can make ideal engraving spindles.
The construction of just one such spindle is detailed here; http://openbuilds.com/builds/890kv-ox-rc-spindle.411/
To facilitate BLDC motor speed control and operation from Mach3 I have now made a simple interface circuit which takes the Mach3 generated PWM signal and converts it to the necessary pulse stream for operation the motor’s ESC and this is detailed here; http://openbuilds.com/builds/software-speed-control-of-a-brushless-dc-bldc-motor-from-mach3.762/

Tweakie.